University of California Berkeley 
 
DEPARTMENT OF THE INTERIOR-U. S, GEOLOGICAL SURVEY 
 CHARLES 1). WALCOTT, JMIIKCTOU 
 
 THE 
 
 MINING DISTRICTS OF THE IDAHO BASIN AND THE 
 
 BOISE RIDGE, IDAHO 
 f 
 
 BY 
 
 WALDKMAR LINDG-RKTST 
 
 WITH A REPORT ON THE FOSSIL PLANTS OF THE 
 PAVETTE FORMATION 
 
 FRANK 
 
 , TCNOWLTON 
 
 EXTRACT FROM THE EKIHTEEXTII ANNUAL REPORT OF THE SURVEY, 1896-97 
 1'AIiT III ECONOMIC OEOLOOY 
 
 WASHINGTON 
 
 GOVERNMENT PRINTING OFFICE 
 1898 
 
THE MINING DISTRICTS OF THE IDAHO BASIN 
 AND THE BOISE RIDGE, IDAHO, 
 
 BY 
 
 WALDEMAR LIISTDGKREN; 
 
 if 
 
 WITH 
 
 A REPORT ON THE FOSSIL PLANTS OF THE PAYETTE FORMATION, 
 
 B'Y 
 
 617 
 

CONTENTS. 
 
 Page. 
 
 CHAPTER I. General topography and geology 625 
 
 Geographical position 625 
 
 Snake River Valley .. _ 625 
 
 Literature , 626 
 
 Topography 628 
 
 Geological history 630 
 
 Pre-Tertiary 630 
 
 The Payette formation 632 
 
 Early Neocene volcanic activity 634 
 
 Post-Payette erosion ... 635 
 
 Post-Payette orographic disturbances 635 
 
 Late Neocene basalts ... 636 
 
 Post-basaltic erosion.. ,. 636 
 
 Resume of geological events in the lower Snake River Basin 637 
 
 CHAPTER II. The ore deposits in general 638 
 
 General features 638 
 
 Alteration of the country rock _ ._. 638 
 
 Silicification ... 645 
 
 Structure of the veins. ... 647 
 
 Mineral deposits of post-Neocene age . _ _ 648 
 
 CHAPTER III. The Idaho Basin 651 
 
 Geographical position ... 651 
 
 Discovery and history ,-. 651 
 
 Production . 652 
 
 Topography.. 656 
 
 Grades of the water courses . .' 657 
 
 Tertiary and Pleistocene formations 657 
 
 Lower Moore Creek Valley .... . 657 
 
 Configuration of valley . 657 
 
 The basalt flow 658 
 
 The present stream gravels .... 658 
 
 The gravels below the basalt 658 
 
 High gravels . 659 
 
 Upper Moore Creek Valley. . 659 
 
 Configuration of valley ... 659 
 
 The present stream gravels 660 
 
 Bench gravels _. . 660 
 
 High gravels 662 
 
 Lake beds 665 
 
 Gold in the lake beds 668 
 
 Olivine basalt (dolerite) _. - 669 
 
 The valley of Grimes Creek 669 
 
 Configuration 669 
 
 619 
 
620 CONTENTS. 
 
 CHAPTER III Continued. Page. 
 Tertiary and Pleistocene formations Continued. 
 The valley of Grimes Creek Continued. 
 
 Present stream gravels.. 670 
 
 Bench gravels -- 670 
 
 Older gravels 671 
 
 Lake beds 671 
 
 Volcanic rocks - 672 
 
 The valley of Granite Creek 672 
 
 Configuration ...-_, 672 
 
 Present stream gravels 672 
 
 Bench gravels .- 672 
 
 Older gravels.. 673 
 
 Gravel on the Boise Range 675 
 
 Basalt _ '.... 675 
 
 Fineness of the gold 676 
 
 Water supply... : 676 
 
 Moore Creek 676 
 
 Grimes Creek ... 677 
 
 Granite Creek 677 
 
 Ground available for future work ... 677 
 
 The monazite sands 677 
 
 Relation between placers and quartz veins 680 
 
 CHAPTER IV. The Idaho Basin (continued) 681 
 
 The pre-Tertiary rocks ^. 681 
 
 Granite - 681 
 
 Dikes associated with the granite 682 
 
 The quartz veins 684 
 
 The Idaho City gold belt 684 
 
 The Elaine vein 684 
 
 The Chickahominy vein. 684 
 
 The Illinois vein 684 
 
 The Populist vein 685 
 
 The Cleveland vein... 685 
 
 The Gambrinus (Surprise) vein 686 
 
 The Boulder vein 686 
 
 The Mona MacCarthy vein. 687 
 
 The Sub-Rosa or Forest King vein 687 
 
 The Elkhorn vein... 689 
 
 The Summit vein 689 
 
 The Quartzburg-Grimes Pass gold belt 689 
 
 The Ebenezer vein.. .". 690 
 
 The Gold Hill vein 691 
 
 The Iowa vein 692 
 
 The Carroll veins ..._.- 692 
 
 The Kennebec claim 693 
 
 Veins at head of Wolf Creek 693 
 
 The veins in the porphyry dike east of Wolf Creek 693 
 
 Claims near Grimes Pass _. 694 
 
 Mining districts east of the basin 695 
 
 Fineness of the quartz gold 696 
 
 The geological history of the Idaho Basin 696 
 
 CHAPTER V. The mining districts of the Boise Ridge 699 
 
 Neal mining district 699 
 
CONTENTS. 621 
 
 CHAPTER V. The mining districts of the Boise Ridge Continued. p age . 
 Neal mining district Continued. 
 
 Location 699 
 
 Topography 699 
 
 Geology 700 
 
 The veins 701 
 
 Black Hornet mining district 703 
 
 Topography 703 
 
 Geology 704 
 
 Mineral deposits. 704 
 
 Boise mining district 705 
 
 Shaw Mountain mining district. 707 
 
 Mining districts of Willow Creek and Rock Creek 707 
 
 Location and topography 707 
 
 Geology 708 
 
 Granitic rocks 708 
 
 Dike rocks 710 
 
 The Payette formation 711 
 
 Rhyolite. 712 
 
 Basalt 712 
 
 The ore deposits. 712 
 
 General character .. , 712 
 
 Treatment of the ores 714 
 
 Detailed description 714 
 
 Silver deposits .. 718 
 
 Placers of the Boise Ridge 718 
 
 Recent placers : 718 
 
 Neocene placers 719 
 
 APPENDIX: The fossil plants of the Payette formation, by F. H. Knowlton. 721 
 
 Systematic enumeration of species 721 
 
 Discussion of the flora and its bearing on the age of the beds 735 
 
ILLUSTRATIONS. 
 
 Page. 
 
 PLATE LXXXVII. General map of the lower Snake River Valley, Idaho-... 625 
 LXXXVIII. Head of Boise Valley, 8 miles southeast of Boise, look- 
 ing northwest, showing basalt table and Pleistocene 
 
 terraces 632 
 
 LXXXIX. Upper canyon of . Brainard Creek, Jerusalem Valley, 
 Boise Ridge, showing tilted basalt flows resting on 
 
 granite 636 
 
 XC. Types of gold-bearing fissure veins GoO 
 
 XCI. The Idaho Basin, looking east from the Jerusalem Road 
 
 west of Quartzburg __ 656 
 
 XCII. Lower Valley of Moore Creek, 3 miles above its mouth, 
 
 showing basalt flow cut through by the creek 658 
 
 XCIII. Idaho City from Gold Hill, looking southwest, showing 
 
 tailings and bench gravels 660 
 
 XCI V. Working bench gravels by the hydraulic process at Idaho 
 
 City 662 
 
 XCV. Gravel bank with underlying lake bed at Plowman's 
 
 claim, East Hill, Idaho City, looking southwest 664 
 
 XCVI. Geological map of the Idaho Basin In pocket 
 
 XCVII. Map of the Neal mining district, by F. D. Howe 700 
 
 XCVIII. Map of the Willow Creek and Rock Creek mining dis- 
 tricts 708 
 
 XC1X. Fossil leaves, Pay ette beds 738 
 
 C. Fossil leaves, Payette beds 740 
 
 CI. Fossil leaves, Payette beds 743 
 
 GIL Fossil leaves, Payette beds 744 
 
 FIG. 55. Gravel benches, 1 miles below Idaho City 681 
 
 56. Section of highest bench, 1 J miles below Idaho City 662 
 
 57. Section across lake beds and gravels at Idaho City 663 
 
 58. Exposure of lake beds and auriferous gravel, l miles south of 
 
 Idaho City. 665 
 
 59. Bench gravel and lake beds at mouth of Granite Creek, 2 miles 
 
 west of Idaho City 666 
 
 60. Bank of bench gravels, one-fourth mile north of Pioneerville, 
 
 level of Grimes Creek 671 
 
 61. Bank at the Ranch Company's claim, Placerville 674 
 
 62. Diagram of fault in the Cleveland vein 686 
 
 63. Section of Mountain Chief vein, east end of claim 690 
 
 64. Breast of drift, Carroll vein 693 
 
 65. Cross section of vein in the Neal mining district 701 
 
 623 
 

 
THE MINING DISTRICTS OF THE IDAHO BASIN AND THE 
 BOISE RIDGE, IDAHO, 1 
 
 By WALDEMAR LINDGREN. 
 
 CHAPTER I. 
 GENERAL TOPOGRAPHY AND GEOLOGY. 
 
 GEOGRAPHICAL POSITION. 
 
 The region shown in PI. LXXXVII includes a portion of the lower 
 Snake River Valley and the mountains adjacent on the northern side. 
 The total area is about 13,500 square miles. It embraces, besides a 
 part of the Snake River, almost the whole drainage of the Payette, 
 Boise, and Wood rivers, and, in the northeastern corner, a part of 
 that of the Salmon River. The irregular mountain complex within 
 the drainage of the Boise and the Payette rivers is designated the 
 "Boise Mountains; " along the parting between these rivers and the 
 Salmon River drainage rise a series of sharp peaks, usually referred 
 to as the " Sawtooth Range." The " Boise Ridge " extends from the 
 Boise to beyond the Payette just west of longitude 116, and attains 
 elevations of over 7,000 feet. The Idaho Basin is an interniontane 
 valley in the Boise Mountains south of latitude 44 and east of longi- 
 tude 116. 
 
 The map shows the positions and names of the quadrangles repre- 
 sented by the topographic sheets issued by the United States Geolog- 
 ical Survey. It also shows, in a somewhat generalized way, the geology 
 of a part of the area. 
 
 SNAKE RIVER VALLEY. 
 
 The discussion of the geology of this district necessitates a short 
 reference to the large Snake River Valley and an abstract of previous 
 work relating to its remarkable geological features. The Snake River 
 Valley stretches across the whole width of southern Idaho in a broad 
 curve opening toward the north and having a radius of 160 miles. The 
 length of this valley from the base of the Tetons to Weiser, where the 
 river enters into a narrow canyon, is over 400 miles, while its width 
 
 1 The field work upon which this report is based was done during the summer and fall of 1896 
 by the author, assisted by Dr. E. C. E. Lord. 
 
 18 GEOL, PT 3 40 625 
 
626 IDAHO MINING DISTRICTS. 
 
 ranges from 50 to 125 miles, its total area being about 34,000 square 
 miles. The grade of the river is moderate. At Blackfoot the eleva- 
 tion is 4,505 feet, and 350 miles lower down, at Weiser, it is 2,125 feet, 
 giving an average grade of less than 7 feet per mile between these 
 places. On both sides of this. valley rise higher ranges, chiefly of 
 granite in the lower valley, of granite and Paleozoic and Mesozoic 
 rocks in the upper valley. The lower slopes of these ranges are often 
 flanked by Tertiary lake deposits. The larger part of the valley is 
 occupied by vast flows of basalt, frequently resting upon and covered 
 by fluviatile and lacustrine accumulations contemporaneous with the 
 flows. The basalt of the Snake River Valley bears evidence of being 
 throughout of the same age approximately, though consisting of a great 
 number of individual flows, and has generally been regarded as Plio- 
 cene. The eruptions did not originate from large volcanoes. Ashes 
 and other fragmentary rocks are generally absent, and the basalt evi- 
 dently flowed out quietly and without explosions from numerous local 
 vents along the margin of the valley or within the valley itself. This 
 volcanic action is usually referred to as fissure eruption, but it must not 
 be inferred that these fissures were long or large. It appears rather as 
 if the vents had the character of rounded local orifices, hardly exten- 
 sive enough to be classed as fissures. The basalts often flowed down 
 from the foothills of older rocks, closely following the present can- 
 yons, though the streams have since then generally succeeded in 
 wearing through the filling in their bottoms. Thus it is, for instance, 
 along the Boise River. 
 
 It will be shown that the Snake River Tertiaries consist of a thick 
 series of early Neocene (Miocene) lake beds, with which are associated 
 vast masses of eruptives distinct from the Snake" River basalts proper, 
 and another series of deposits of late Neocene age (Pliocene), consist- 
 ing of the Snake River basalts and associated sedimentary rocks. 
 These two terranes represent successive stages of the Neocene lake 
 and are often difficult to separate. 
 
 LITERATURE. 
 
 The upper Snake River Basin has been described by Messrs. 
 Hayden, 1 Bradley, 2 Peale, 3 and St. John, 4 in the reports of the United 
 States Geological and Geographical Survey of the Territories. 
 Hayden describes the basalt flow along the present line of the Utah 
 and Northern Railroad, mentioning that there were several flows of 
 basalt, or at least two, separated by somewhat tilted Pliocene depos- 
 its of slight depth. St. John and Peale describe the basalt flows east 
 of this, near the headwaters of the Snake River. Peale states that a 
 number of extinct craters exist, that there were several flows of 
 
 1 U. S. Geol. and Geog. Surv. Terr., Kept. 1871, pp. 25-30. 
 
 2 Ibid., Kept. 1872, p. 190. 
 
 3 Ibid., Rept. 1877, p. 543. 
 4 Ibid.,Eept. 1877, p. 323. 
 
LINDOREN.] SNAKE RIVER VALLEY. 627 
 
 basalt, and that the basalts are generally horizontal in position and 
 fill the valleys and the more depressed portions of the basins. There 
 appear to have been two periods of basaltic flows, one at the close of 
 the Pliocene, the other at the beginning of the Pleistocene. The 
 Pleistocene age is inferred from exposures at Marsh Valley, near 
 Red Rock Pass, where Pleistocene beds were somewhat eroded before 
 the basaltic flow. 
 
 According to Gilbert, however, this Pleistocene is older than the 
 highest stage of Lake Bonneville, during which the lake found an 
 outlet at Red Rock Pass. The river draining the lake at this time 
 appears to have flowed over the surface of the basalt. 
 
 According to Hague, 1 the latest eruptions in the Yellowstone 
 National Park are of basalts, which stretch far into Idaho in somber, 
 monotonous beds. These basalts are pre-Glacial, and their eruption 
 is referred to the Pliocene. 
 
 About 1869 Mr. Clarence King visited the lower part of the Snake 
 River basin and collected a number of fossils from beds beneath the 
 basalt at Castle and Sinker creeks, tributaries from the south, joining 
 the river about due south of Boise. The fossils have been described 
 in detail, while no description of the localities was ever published, a 
 fact which has led to some confusion. A few notes regarding this 
 occurrence are contained in King's Systematic Geology 2 and may be 
 quoted : 
 
 In the basin of Snake River . . . there were basaltic eruptions in the middle 
 of the Pliocene period which overflowed the earlier lacustrine beds of the period, 
 and in turn were themselves overlaid ... by the main, later Pliocene series. 
 . . . Sections obtained along the plains between the Owyhee Mountains and Snake 
 River show that a considerable portion of the beds of the valley, which consist 
 chiefly of white sands and marls carrying numerous well-defined Pliocene forms, 
 were overlaid by large accumulations of basaltic flow, and that subsequently a 
 second period of lacustrine deposition took place, likewise characterized by Plio- 
 cene forms, the latter representing a more advanced stage of development and 
 more recent type than those beneath the basalt. 
 
 King further states that near Shoshone Falls the basalt rests on 
 the eroded surface of a trachytic soft rock which he considers of pre- 
 Miocene age. 3 From the collections of King and the later collections 
 of Wortman, Cope has described an extensive fauna of fresh-water 
 fishes, and proposed for the sediments in which these are contained 
 the name Idaho formation.* 
 
 The locations given are very vague, as "Catherine Creek," " Castle 
 Creek," or "Southern Idaho," and no description of the beds is 
 vouchsafed. The fauna consists of 22 species, all differing from 
 existing species so far as known. Professor Cope thinks that the 
 
 1 Am. Jour. Sci., 4th series, June, 1896, Vol.1, p. 455. 
 U. S. Geol. Expl. Fortieth Par., Vol. 1, 1878, pp. 418, 440. 
 a Ibid., p. 593. 
 t Proc. Phila. Acad. Sci., 1883, pp. 153-166. 
 
628 IDAHO MINING DISTRICTS. 
 
 evidence clearly indicates a Pliocene age. From the same beds 
 were obtained three species of crawfishes specifically distinct from 
 all others described from the West. Mammalian remains were also 
 collected by King from similar beds on Sinker Creek, which were 
 determined by Leidy to be Mastodon mirificus and Equus excelsus, 
 both of which belong to the Niobrara Pliocene fauna. A few mol- 
 lusks have also been found in the same deposits on Sinker Creek. 
 Thus Meek 1 described Sphaerium (?) idahoense Meek from Castle 
 Creek, collected by King. Gabb 2 described two species, Melania 
 taylori Gabb and LHhasia antiqua from a "Deposit on Snake River 
 on the road from Boise to the Owyhee mining country;" thus probably 
 from Walters Ferry. The same forms have been found, according 
 to Mr. George II. Eldridge, at Glenns Ferry, 120 miles above Walk- 
 ers Ferry. Dr. White describes the same two species and another, 
 Latia dallii, from a point 50 miles below Salmon Falls, Snake River, 
 which probably refers to Glenns Ferry, and states that these forms 
 differ considerably from any known fresh-water fauna of America 
 either fossil or living. 3 Both Meek and White are in favor of corre- 
 lating these Tertiary beds with King's Truckee Miocene. To this the 
 utterances of King are directly opposed, and it is, indeed, from 
 stratigraphic grounds, improbable that these beds are of Miocene 
 age. Near Glenns Ferry beds of sand and clay occur intercalated 
 between the basalt flows, and it is probable that the fossils came from 
 this locality and that all of them were collected in beds very closely 
 associated with the late basaltic eruptions, from which it would 
 follow that they should be placed in the latest Pliocene. 
 
 Prof. O. C. Marsh states (oral communication, January, 1897) that 
 a large amount of Pliocene mammalian remains was found in a bluff 
 about 100 feet above the Snake River, some distance below Weiser, at 
 the old crossing of the stage road to Oregon, on the Oregon side of the 
 river. 
 
 None of these localities were visited during the field season of 1896 
 on account of pressing economical and areal work in other sections ; 
 but from the area studied it was possible to read in its chief features 
 the later geologic history of the lower part of the Snake River basin. 
 The correlation of these results with the older work remains for the 
 future. 
 
 TOPOGRAPHY. 
 
 The chief topographic features of the region, of which the geology 
 is shown on PI. LXXX VII, are as follows : 
 
 Broad flat mesas of basalt and Pliocene lake beds spread on both 
 sides of Snake River, though chiefly on the northern side. Through 
 these mesas the river has cut an abrupt canyon, bordered by basaltic 
 
 1 Proc. Phila. Acad. Nat. Sci. 1870, p. 57. 
 
 3 Paleontology of Gal., Vol. II, p. 13. 
 
 ' Proc. U. S. Nat. Mus. 1882, Vol. V, p. 99. 
 
UNI-"!";*.-! TOPOGRAPHY OF THE REGION. 629 
 
 cliffs, to a depth of from 200 to 700 feet. The low mesas, surmounted 
 by several buckles or domes of basalt a few hundred feet high, rise 
 gradually toward the edge of the mountain. Near the mouth of the 
 Boise River the basalt mesas cease, and from here down to Weiser, 
 where the great Snake River canyon begins, several large tributaries 
 enter, such as the Payette and the Owyhee, and, at elevations of from 
 2,200 to 2,700 feet, level bottom lands and broad low terraces flank 
 the water courses. 
 
 Between the mouth of the Boise and Weiser flat-topped hills of soft 
 sandstones rise on both sides of the Snake River to a height of 600 to 
 800 feet. Similar complexes of higli sandy mesas rise between the 
 lower courses of the Boise and the Payette and north of the Payette. 
 The mountains of older rocks surrounding the tectonic trough of the 
 Snake River Valley rise gradually, on the north side of the river, 
 beyond the sloping mesas of Tertiary rocks, their margin having a 
 northwesterly direction in this vicinity. The transition between 
 mountains and mesa is abrupt only at the Boise River, near Boise, 
 and the abruptness is here due to the extensive erosion of the Payette 
 sandstones by the river. 
 
 The mountain region extending up to the Sawtooth Range, dividing 
 with a north-northwesterly trend the waters of the Boise and the south- 
 ern branches of the Payette from those of the Salmon, has an average 
 width of 5,5 miles and culminates in summits with an elevation of from 
 10,000 to 11,000 feet. This mountain complex, which is made up chiefly 
 of granitic rocks, does not form a well-defined range, but rather a 
 broad uplift dissected deeply and in the most intricate manner by the 
 forks of the Boise and the Payette. The summits of the narrow ridges 
 generally form gently sloping lines. If a surface were constructed 
 containing all these lines it would be of undulating, curved character, 
 sloping gently from elevations of 9,000 down to 4,000 feet. From the 
 southwestern edge a steeper slope carries the granitic rocks below the 
 surface of the Tertiary rocks of the Snake River Valley. The can- 
 yons of the Boise and the Payette have cut down in the uplift to a 
 maximum depth of 3,000 feet, and are joined by deep lateral canyons, 
 dividing the whole region into a maze of narrow aretes. The grade of 
 the main rivers is relatively low, from 10 feet up to 50 feet per mile, 
 and only well up toward the head waters are grades of 100 feet per 
 mile attained. The grades of the lateral canyons are also often rela- 
 tively slight in their lower course, but extremely steep cirques rise 
 near their head waters. The Idaho Basin quadrangle offers excel- 
 lent illustrations of these relations, which are the result partly of a 
 considerable antiquity of the drainage, partly of the crumbling char- 
 acter of the granite. At the main divide (Bear Valley quadrangle) 
 the broad valleys and gentler slopes of the Salmon River drain- 
 age contrast strongly with the deeply incised canyons of the Boise 
 and Payette. The latter streams are continually capturing territory 
 
630 IDAHO MINING DISTRICTS. 
 
 belonging to the former, and the divide is in process of migration north- 
 eastward. The whole region may be regarded as an uplifted sloping 
 plateau deeply dissected by a drainage system, whose origin evidently 
 antedates the Miocene period. Smaller individual ranges occur in a 
 few places, as in the Boise Ridge, rising to elevations of 7,500 feet 
 and extending due north, dividing the Idaho Basin from the waters 
 of the Payette. This range also crosses the South Fork of the Payette 
 and continues for some distance north of it. Within this mass of 
 mountains several depressions or basins with gentler slopes also exist, 
 such as the Idaho Basin, the Dead wood Basin, and Smiths Prairie, 
 which have been created or emphasized by more recent orographic 
 movements. Evidences of glacial topography occur only near the 
 Sawtooth and Trinity mountains. 1 The lower area here specially 
 described has never been covered by ice. 
 
 GEOLOGICAL HISTORY. 
 
 The vicinity of Boise River, where it debouches from the mountains, 
 proved to be an exceptionally fortunate location for the study of the 
 geological history of this part of the Snake River drainage, for the 
 record left by the river of successive geological events back to a cer- 
 tain date is remarkably clear and easy to read. 
 
 PRE-TERTIARY. 
 
 The oldest rock exposed is the granite of the Boise Mountains. This 
 forms an extremely large area, embracing, so far as known, the whole 
 of the upper drainage of the Boise and Payette rivers and extending 
 northeastward beyond the Sawtooth Mountains and eastward as far 
 as Wood River, where it is adjoined by sedimentary rocks of probr 
 ably Carboniferous age. 2 This rock is largely a typical, coarse gran- 
 ite of gray or yellowish-gray color, consisting of orthoclase in often 
 large crystals, plagioclase, quartz, biotite, and sometimes muscovite. 
 Pegmatite dikes are common in many places. Locally the granite 
 contains hornblende, and is by gradual transition connected with 
 intermediate rocks standing between granite and diorite, and also, 
 though more rarely, with diorites. Narrow dikes of light-colored 
 granite-porphyry and dark lamprophyric dike rocks, chiefly minettes, 
 are abundant and present a great variety of structural types. A belt 
 characterized by dikes of coarse quartz-diorite, porphyrites, and occa- 
 sional occurrences of gabbro and diabase extends, with one short inter- 
 ruption, from the vicinity of Wilson Peak, east of the Idaho Basin, by 
 Quartzburg, to the Willow Creek mining district. All of these dikes 
 are probably connected with the granite eruption that is, they were 
 intruded shortly after the consolidation of the granite. Within the 
 area described the granite is remarkably unaltered and massive, no 
 
 1 George H. Eldridge, Sixteenth Ann. Kept. U. S. Geol. Survey, Part II, 1895, p. :*>:!. 
 
 2 George H. Eldridge, loc. cit. 
 
LINDOKEN.] PRE-TERTIARY ROCKS. 631 
 
 bodies of schist appearing in connection with it. It weathers easily 
 and crumbles to a coarse sand which largely covers the hillsides. 
 Only in the higher mountains and along the bottom of the canyons 
 are satisfactory exposures found. The age of this granite, which is 
 clearly of igneous and intrusive origin, is an open question. Messrs. 
 Becker 1 and Eldridge 2 assign to it provisionally an Archean age, but 
 a thorough study of its contact with surrounding formations is neces- 
 sary before its age can be determined. The granite is in many places 
 traversed by shear planes, giving it a jointed or sheeted structure, 
 and often these planes coincide with the direction of the fissures on 
 which mineral veins occur. It is probable that these two features 
 are of the same and contemporaneous origin. Nearly all of the pri- 
 mary mineral deposits are contained in the granite or allied porphy- 
 ries. By far most of them have a direction ranging from E.-W. to 
 ENE.-WSW., and dip to the south at angles from 40 to 85 from the 
 horizontal. While it is probable that all of them belong to the same 
 period of formation, there are few definite clews to their age. It is 
 likely, however, that they are post-Carboniferous, and it is certain 
 that they antedate the Miocene lake deposits. A Cretaceous or early 
 Tertiary age may provisionally be assigned to them. The mode of 
 their occurrence indicates beyond doubt an origin by deposition from 
 mineral waters, probably ascending hot springs: A slight recurrence 
 of the vein-forming activity occurred after the Neocene period. 
 
 Before the beginning of the Neocene the chief features of the topog- 
 raphy were outlined the broad uplift of the Boise Mountains and the 
 depression of Snake River Valley. The latter is not unlikely a sunken 
 area separated by old fault lines from the mountains to the north. 
 At that time the basalt flows and the lake beds did not exist, but the 
 drainage of the Boise, and probably also of the upper Payette River, 
 was outlined in practically its present form. The granitic range pre- 
 sented a bold scarp facing the valley, and the canyon of the Boise 
 R^ver was, at its debouchure from the mountains, cut to practically 
 the same depth which it has at present. It had not, of course, cut 
 back so far toward the Sawtooth Range as at present, and many 
 features of the drainage, notably in the Idaho Basin, were different 
 from those existing now. As substantiating this it will be shown that 
 the Miocene lake beds fill the old canyon at the gate of the moun- 
 tains, 10 miles southeast of Boise, and that in front of it lie enormous 
 masses of coarse Neocene gravel and conglomerate. Thus the time 
 immediately preceding that from which the first records date was one, 
 first, of uplift and subsidence, during which the rough features were 
 blocked out, and second, one of long-continued erosion, during which 
 the Boise Mountains were dissected and the debris from the excavated 
 canyons deposited in the basin of the Snake River Valley, where it is 
 
 1 Tenth Census, Precious Metals, p. 54. 
 
 2 Loc. cit. 
 
632 IDAHO MINING DISTK1CT8. 
 
 now deeply covered below later formations. If we should venture 
 tentatively to go back one step further, it might be suggested that 
 the uplifted surface of the Boise Mountains is probably the result of 
 a far older erosion, of early Tertiary or Cretaceous age, which planed 
 down a more ancient range to gentler outlines, or to a peneplain. 
 
 THE PAYETTE FORMATION. 
 
 During the earlier part of the Neocene (Miocene) a large fresh- 
 water lake occupied at least the lower part of the Snake River Val- 
 ley, and its sediments are now prominent features of the region. 
 For these lake beds the name Payette formation is proposed, and 
 their age is determined as upper Miocene. This formation is prob- 
 abty not the same as Cope's Idaho formation, to \fhich a Pliocene age 
 was assigned and which appears to be connected with the later basalt 
 flows. 1 
 
 The extent of the formation is shown in PI. LXXXVII, from which 
 it is seen that it lies in front of the Boise Mountains and occupies the 
 whole lowei* part of the ridge between the Boise and the Payette. It 
 extends over large areas to the north of the Payette, along the flood 
 plains of the Snake River, and is seen to occupy vast areas in Oregon 
 between the mouth of the Owyhee River and Weiser, where the 
 Snake River Canyon begins. On both sides of the lower Snake River 
 the bluffs of the Payette formation attain a height of over 800 feet. 
 In the Payette Valley south of Emmett the sharply defined bluff of 
 Payette beds rises 600 feet above the alluvium. Smaller masses, 
 detached by erosion or uplifts, lie in the intermontane valleys as far 
 east as the Idaho Basin. 
 
 Along the Boise Mountains the Payette beds rest against the irreg- 
 ularly eroded and sharply sloping surface of the granite, and the top 
 stratum attains a height of 4,100 feet. A total thickness of 1,000 feet 
 is exposed near Boise, and wells bored show several hundred feet of 
 similar strata below the surface. Over the larger part of its extent 
 the formation lies nearly horizontal or dips only a few degrees. Near 
 the mountains dips of 8 to 10, generally westward, are noted, and the 
 smaller detached masses in the intermontane valleys are still more 
 disturbed, generally dipping westward at angles up to 50. This is 
 particularly marked in the long arm of sediments of the Payette for- 
 mation filling the valleys of Horseshoe Bend and Jerusalem, on the 
 Payette. 
 
 As might be expected from the character of the land mass from 
 which the sediments were obtained, the latter consist chiefly of granitic, 
 light-colored sands, locally cemented by hot-spring deposits to hard 
 
 1 From the results of more extended surveys during the summer of 1897, it has become evident 
 that the Payette and Idaho formations represent two successive stages of the lake, the often 
 deformed shore-line of the former being found at elevations of from 4,200 to 5,000 feet, and those 
 of the latter at a maximum elevation of 3,000 feet. To separate the deposits of the two forma- 
 tions is not always easy. 
 
LIN DORK N.I 
 
 PAYETTE FORMATION. 633 
 
 sandstones (as at Table Mountain near Boise; see PL LXXXVIII) 
 or clayey semiconsolidated sandstones. Heavy masses of conglomer- 
 ates and gravels begin to appear at Table Mountain, and reach their 
 greatest development opposite the mouth of Boise River, in the high 
 ridge extending in a westerly direction. Purely clayey deposits are 
 rarer, occurring only in convenient sheltered locations near the shore 
 line or in places where volcanic eruptions took place. The basal part 
 of the formation contains, at Horseshoe Bend, Jerusalem, and other 
 localities along the Payette, small coal seams. In the clay accom- 
 panying these coal seams vegetable remains are of frequent occur- 
 rence. The following forms were identified by Professor Knowlton: 
 
 Two miles southeast of Marsh post-office, on the Payette, is a small 
 coal prospect. The disturbed beds of the Payette formation lie here 
 on a sharply sloping surface of granite. At this place the following 
 forms were found, together with many new species : 
 
 Sequoia angustifolia ? Lx. 
 Quercus consimilis Newb. 
 Acer trilobatum productum ? Heer. 
 
 One mile southeast of Marsh, along the road to Willow Creek, a few 
 hundred feet above the river, is an outcrop of yellowish-gray "chalk," 
 or diatomaceous earth, intercalated in the Payette beds and capped 
 by basalt. In this the following forms were found, in an excellent 
 state of preservation : 
 
 Salix angusta Al. Br. 
 
 Quercus consimilis Newb. 
 
 Q. simplex Newby. 
 
 Platanus aspira ? Newb. 
 
 From Cartwright's ranch, on Shafer Creek, 4 miles southeast of 
 Horseshoe Bend post-office, the following forms were identified, together 
 with several new species. This is an excellent locality, and the leaves 
 embedded in a dark clay shale are beautifully preserved. 
 
 Sequoia angustifolia Lx. 
 Salix angusta Al. Br. 
 Ficus ungeri Lx. 
 
 This area is separated from the main one by a small ridge of gran- 
 ite, but that the two formations are identical admits of no doubt. 
 The beds are here disturbed, dipping west at 20 to 25. The plants 
 were obtained near the base of the series, of which about 800 feet of 
 alternating, fairly consolidated shale and sandstone are exposed. 
 The elevation is 3,500 feet. 
 
 .Near Idaho City another detached mass of lake beds is preserved 
 at an elevation of from 4,000 to 4,500 feet, the occurrence of which is 
 described more in detail in Chapter III. From the middle of a series 
 800 feet thick the following plants were obtained: 
 
 Sequoia angustifolia Lx. 
 
 Ulmus speciosa Newberry. 
 
 Betula angustifolia Newberry. 
 
634 IDAHO MINING DISTRICTS. 
 
 From these data Professor Knowlton draws the conclusion that the 
 age is Upper Miocene, contemporaneous with the flora of the aurifer- 
 ous gravels and the lone formation of California, the Lamar flora 
 of the Yellowstone National Park, and the John Day formation of 
 Oregon. The paleobotanical evidence confirms the conclusion, confi- 
 dently drawn from the field work, that all these smaller detached 
 masses of lake beds are of practically the same age. 
 
 During the time of the maximum extension of the Payette Lake its 
 surface stood at the present elevation of 4,200 feet. Its deposits, over 
 1,000 feet thick near the shore, rested against the abrupt slope of the 
 Boise Mountains, and filled the old canyon of the Boise to the same 
 depth. The canyon must have formed a fiord, the branches of which 
 reached as far back as the Idaho Basin, and in which vast quantities 
 of gravel and sand accumulated. Isolated occurrences of well- washed 
 gravel on the summit of high ridges in the lower Moore Creek drain- 
 age, at elevations of 4,500 feet, confirm the above conclusions. The 
 data are not at present sufficient to determine the extent of the Payette 
 Lake, though it is probable that it was confined to the Snake River 
 Valley, inclosed on the west by the Blue Mountains and on the east 
 by the divide toward the Salmon River. 
 
 EARLY NEOCENE VOLCANIC ACTIVITY. 
 
 Near the base of the Payette formation sheets of rhyolite and 
 rhyolite-tuff occur, but this eruption was of limited extent. The 
 best exposures are found near Boise and in the Willow Creek mining 
 district. After the rhyolitic eruptions there occurred enormous out- 
 pourings of basaltic lavas, distinctly different from and earlier than 
 the Snake River basalts. The rocks are in part normal basalts, but 
 have usually a somewhat andesitic habit. In large areas the outcrops 
 generally have a reddish-brown color, distinct from the somber black 
 of the later flows. These early Neocene eruptives are to some extent 
 represented near Boise, but become more abundant northward. Many 
 exposures are seen along the lower Payette from Marsh post-office to 
 Horseshoe Bend and Jerusalem Valley, and the conspicuous sharp 
 ridge of Squaw Butte, rising just north of the Payette above the lake 
 beds to an elevation of 5,800 feet, is composed entirely of these older 
 effusive rocks. Squaw Butte is well visible from the railroad near 
 Nampa and Caldwell as a rugged, reddish-brown peak, contrasting 
 with the white lake beds. The evidence shows that these flows were 
 contemporaneous with the deposition of the Payette beds, and are 
 underlain and covered by sandstones. In some places they break 
 through the lower lake beds and metamorphose them. The vents 
 were located chiefly along the margin of the old lake. At Jerusalem 
 (see PI. LXXXIX) arid in Squaw Butte the whole volcanic series in 
 the latter place consisting of countless flows, attaining a thickness of 
 several thousand feet has been disturbed and uplifted, and now 
 
LINDOBEN.] POST-PAYETTE PHENOMENA. 635 
 
 dips to the west at angles ranging from 10 to 35, the monoclinal 
 uplifts vividly recalling those in eastern Washington described by 
 Professor Russell. 1 There, however, the Miocene beds lie only on 
 top of the volcanic flows of the Columbia formation, while here they 
 lie both below and above similar igneous masses. 
 
 On both sides of the Snake River, from Caldwell to Weiser (near 
 the upper edge of the map, PL LXXXVII), the beds do not contain 
 much evidence of volcanic activity, though from Parma a few vol- 
 canic buttes are visible from the railroad, far to the west, among the 
 lake beds in Oregon. But a few miles beyond Weiser the white bluffs 
 of lake beds begin to assume red or orange colors, and contain streaks 
 of intercalated tuffs. The valley contracts, and at the entrance of 
 the canyon basaltic rocks appear, partly interstratified with the lake 
 beds, partly underlying them. Near Huntington the deep and nar- 
 row canyon is composed entirely of basic volcanic rocks, clearly con- 
 nected with the early Neocene lake beds, and assuredly different from 
 the later basalts from the upper valley. How far down this volcanic 
 canyon extends is not known. 
 
 POST-PAYETTE EROSION. 
 
 After attaining its highest stage, the lake was drained by the 
 establishing of the present course of the Snake River below Weiser. 
 The lake receded as the canyon was rapidly cut by the mighty vol- 
 ume of water, and erosion has steadily proceeded since the end of the 
 Miocene or the beginning of the Pliocene. The broad valleys of the 
 Boise, the Payette, and the lower Snake were eroded in the soft lake 
 beds. A new course was established for the Payette River, which 
 evidently did not debouch at its present position before the Payette 
 epoch. The Boise River, on the contrary, maintained its old course. 
 The accumulated gravels were scoured out from its canyon, and, 
 before the Pliocene basaltic eruptions, its channel in the canyon 
 was deepened nearly to its present level. There was, however, at 
 least one temporary check in this process of draining. For a consid- 
 erable interval of time the lake remained stationary, at a present 
 elevation of from 2,800 to 3,000 feet. The deposits and basalt flows 
 of this epoch are regarded as late Neocene (Pliocene) and belong to 
 the Idaho formation of Cope. 
 
 POST-PAYETTE OROGRAPHIC DISTURBANCES. 
 
 Before the epoch of the Pliocene basalt flows the sediments and 
 flows of the Payette formation were subject to some disturbances, 
 reaching their maximum in the smaller areas in the intermontane 
 valleys. Certain parts of the series acquired a slight westerly dip. 
 More intense orographic movements took place at Squaw Butte and in 
 the Horseshoe Bend and Jerusalem valleys, resulting in monoclinal 
 
 i Bull. U. S. Geol. Survey No. 108, 1893, p. 28. 
 
636 IDAHO MINING DISTRICTS. 
 
 uplifts, the detailed character of which will be discussed in the text 
 accompanying the Boise folio of the Geologic Atlas of the United 
 States. Important movements also took place along the Boise Ridge, 
 which separates the Idaho Basin from the Payette River, and it is 
 probable that it has undergone an extensive uplift. Over the larger 
 part of the area no orographic movements have affected the beds. 
 
 LATE NEOCENE BASALTS. 
 
 When the lake had been partly drained, vast basaltic eruptions 
 began, and in time, intercalated with lake beds, filled the whole of the 
 upper Snake River Valley from the base of the Tetons, near the Wyo- 
 ming line, to a point near the confluence of the Boise and the Snake. 
 Between this point and Weiser no basalts are seen. The basalt flows 
 lie horizontal, filling the plains and the modern canyons. They are 
 also distinguished by their fresh character, black color, and columnar 
 structure. The aggregate thickness probably never exceeds 1,000 
 feet, and is ordinarily much less, individual flows being rarely over 
 100 feet thick. 
 
 As already indicated, the basalts were erupted from a great num- 
 ber of inconspicuous craters, both in the plains and in the adjoining 
 mountains. Their fluidity was remarkable, continuous flows of 50 
 miles or more being noted. Where the Boise River emerges from the 
 mountains the exposures are exceptionally good. There are three or 
 four flows, the principal ones coming down from the South Fork of 
 the Boise. The deepest flow of comparatively small volume is prob- 
 ably the oldest, and lies but a few feet above the present bed of .the 
 river. Deep river gravels accumulated on this flow, and, soon after- 
 ward, two later flows came down the Boise River and filled the canyon 
 near the mouth to a depth of 300 feet. Beyond the mouth the basalt 
 spreads out, and its surface rapidly sinks westward. Still another 
 basalt flow, about 75 feet thick, came down from Moore Creek and 
 joined the large ones at the mouth of the main river. Above the 
 source of this basalt the damming resulted in terraces and bench 
 gravels now lining the upper valleys of Moore Creek and Grimes 
 Creek, described in Chapter III. 
 
 POST-BASALTIC EROSION. 
 
 If the epoch of the basaltic flows be placed at the very close of the 
 Neocene, the events that have taken place since then must be referred 
 to the Pleistocene. Among these are the erosion of the canyons of 
 Snake River and its tributaries to a depth of from 200 to 700 feet and 
 the deposition of extensive flood plains and terraces along the lower 
 Snake, Boise, and Payette. The Boise River has, in Pleistocene times, 
 cut through the 300 feet of basalt accumulated at the mouth of its 
 canyon, and thus laboriously regained the same stage it occupied 
 before the beginning of the Payette epoch. The direction of the chan- 
 nel has gradually changed. During the Payette epoch it had a nearly 
 
LINDGHEN.] 
 
 RESUME OF GEOLOGICAL HISTORY. 
 
 637 
 
 westerly trend, while subsequent events have more and more forced 
 it in a northwesterly direction. PI. LXXXVIII illustrates well the 
 present condition at the mouth of the canyon the basalt flow cut in 
 two and the two Pleistocene flood plains in the widening valley of the 
 river. Pliocene gravel older than the flood plains underlies the basalt. 
 In the right background the Miocene sandstones of Table Mountain 
 are shown, while the background at the extreme right shows the first 
 granitic hills of the Boise Ridge. 
 
 Having thus traced the cycle of events which have taken place in 
 this region since the beginning of the Neocene, it may be well to 
 rapidly review the main points in the history. 
 
 RESUME OF GEOLOGICAL EVENTS IN THE LOWER SNAKE RIVER 
 
 BASIN. 
 
 Pre-Neocene . 
 
 Pre-Neocene or early Neo 
 cene (Miocene) . 
 
 Early Neocene ( Miocene ) , 
 possibly extending over 
 into late Neocene. 
 
 Late Neocene (Pliocene) . . 
 
 Pleistocene ... 
 
 / The depression of the Snake River Valley outlined by 
 I orographic movements. 
 
 f Long-continued erosion, dissecting the Boise Moun- 
 tains. 
 f Boise Canyon eroded to its present depth at its mouth. 
 
 Large fresh-water lake occupying Snake River Val- 
 ley. 
 
 Deposition of thePayette formation at least 1,200 feet 
 thick. 
 
 Highest level reached, 4,200 feet above present sea 
 level. 
 
 Eruptions of rhyolite and andesitic basalts, contem- 
 poraneous with the sedimentation. 
 
 Orographic disturbances of the Payette formation. 
 
 Partial drainage of the lake and epoch of erosion 
 excavating the valleys of the Snake, Boise, and 
 Payette from the Payette lake-beds. 
 
 Basalt flows, filling the Snake River plains and the 
 Boise Canyon. 
 
 Deposition of lacustrine sediments between the flows. 
 (Idaho formation.) 
 
 Complete draining of lake. 
 
 f Erosion of the Snake River basalt canyon above the 
 confluence with the Boise; Boise River cuts down 
 through the basalt to its present depth. 
 
 1^ Terraces, up to 100 feet above the river, and present 
 flood plains along the Lower Snake, Boise, and 
 Payette rivers. 
 
CHAPTER II. 
 THE ORE DEPOSITS IN GENERAL. 
 
 GENERAL FEATURES. 
 
 Throughout the Boise Ridge and the Idaho Basin the primary gold 
 deposits present a certain similarity. They are all contained in gra- 
 nitic rocks or associated dikes. They are all either fissure veins or 
 impregnations connected with fissures. Nearly all of these fissures 
 have a direction ranging from east- west to northeast-southwest, the 
 chief exceptions to this rule being "found in the Black Hornet district. 
 The dip is ordinarily to the south at angles of from 45 to 89, but in 
 the Willow Creek and Rock Creek districts similar dips to the north 
 are found. The prevailing direction of the fissures is the same as 
 that of an often well-developed system of joint planes commonly seen 
 in the Boise Ridge. Finally, the ores are, on the whole, of a similar 
 character, consisting chiefly of auriferous pyrite, arsenopyrite, zinc- 
 blende, and galena in a gangue of quartz or, more rarely, calcite. 
 The fresh ores from deeper levels contain a variable percentage of free 
 gold. Rarely, however, is more than 60 per cent of the total value 
 caught on the amalgamating plates. Gold predominates largely in 
 the value of the ore, though seldom by weight, for in the ordinary 
 ores the weight of the silver considerably exceeds that of the gold. 
 The alteration of the country rock in the vicinity of the veins is 
 throughout of the same character. 
 
 ALTERATION OF THE COUNTRY ROCK. 
 
 A marked change appears in the rock in the vicinity of the veins. 
 The dark constituents, biotite and hornblende, are bleached or disap- 
 pear, and the feldspar is altered to a soft, white, opaque material, 
 only the quartz remaining unaltered. Besides abundant iron pyrite, 
 arsenopyrite also appears in small, scattered, perfect crystals. The 
 width of the altered zone may be from a foot up to 50 or 60 feet. 
 This alteration of the country rock has been noted by Messrs. George 
 H. Eldridge, 1 J. B. Hastings, 2 and F. D. Howe, but has ordinarily 
 been described as kaolinization. The soft, white substance, which 
 often has a greasy feel, is also referred to by the miners as "talc." 
 This change in appearance and composition is without the slightest 
 
 1 Sixteenth Ann. Rep. U. S. Geol. Survey, Part II, 1895, pp. 225, 252. 
 
 2 Idaho Mining News, Vol. L, No. 1, p. 15. 
 638 
 
LINDGRKN.] ALTERATION OF THE COUNTRY ROCK. 639 
 
 doubt directly due to the chemical action of the solutions from which 
 the mineral content of the vein was deposited. The process consists in 
 a sericitization. or replacement of the ferromagnesian silicates, feld- 
 spar, partly also the quartz, by sericite, a fine-fibrous or felted variety 
 of white mica. In composition it is a hydrous silicate of aluminium 
 and potassium, probably identical with muscovite. In many places a 
 carbonatization, or replacement by carbonate of lime and magnesia, 
 goes on at the same time, and sulphides, chiefly pyrite and arseno- 
 pyrite, rarely other minerals, are usually also formed in the rock 
 as minute and perfect crystals. It is certain that this metasomatic 
 process is a common one in fissure veins, 1 audits chemical character 
 is very different from kaolinization. Kaolin, in fact, is a product 
 not ordinarily found on the mineral veins, and talc occurs still more 
 rarely. 
 
 This altered granite, together with the ore and gangue occurring in 
 seams or veins through it, constitutes what miners term a "ledge" and 
 ' ' ledge matter. " This may be many feet wide, and the paying ore may, 
 and in fact does usually, form only a small portion in width of the 
 ledge matter. The altered country rock, though often well filled with 
 pyrite and arsenopyrite, is ordinarily very poor, containing at most 
 one or two dollars in gold. Exceptionally it contains enough gold to 
 be considered an ore, but generally only when adjoining rich vein 
 filling, and large ore shoots; even then it constitutes only second-class 
 ore, and its sulphides are much poorer than those in the vein proper. 
 It rarely contains any free gold. As examples a few typical rocks of 
 this kind may be described. 
 
 The altered dioritic granite from the Checkmate mine, Willow Creek 
 (88 Boise sheet collection), is a granular, white, soft rock, consisting 
 of quartz grains, white earthy grains replacing the feldspar, a few 
 foils of pale-yellowish mica and abundant small and perfect crystals 
 of pyrite, showing the combination GO GO, GO 2, and a few small prisms 
 of arsenopyrite. A few narrow seams, l nnn wide, traverse the rock and 
 carry only blende and galena. The microscope shows quartz grains 
 with undulous extinction, which contain in places a few shreds of 
 sericite, but are on the whole hardly attacked by any metasomatic 
 process. There are a few larger muscovite foils, which evidently rep- 
 resent the biotite of the fresh rock. The space between the quartz 
 grains is filled by a fine-felted sericite mass, which incloses nearly all 
 of the idiomorphic pyrite. Intergrown with and inclosed by the pyrite 
 is a little brown zinc blende and galena in small anhedral grains ; one 
 crystal of arsenopyrite was also noted. No calcite was found. This 
 rock occurs close to a rich ore body, but an assay of it gave only 0. 1 
 ounce of gold and 0.5 ounce of silver per ton. The total replacement 
 
 1 For studies of the metasomatic processes of fissure veins by the author, see Fourteenth Ann. 
 Kept. U. S. Geol. Survey, Part II, pp. 243-284, and Seventeenth Ann. Rept.U. S. Geol. Survey, 
 Part II, p. 144; also Bull. Geol. Soc. Am., Vol. VI, p. 221. 
 
640 
 
 IDAHO MINING DISTRICTS. 
 
 of the feldspars and ferromagnesian silicates and the immunity of 
 the quartz is noteworthy. 
 
 From the Silver Wreath tunnel, Willow Creek district, Boise 
 County, two rocks were collected, analyses of which are given below. 
 The first is a perfectly fresh granitic rock, the ordinary country rock 
 of the district. The second, occurring only a few feet away, is the 
 same granite altered by the vein-forming agencies, and a comparison 
 between the two will show the character of the process. Both rocks 
 are unaffected by atmospheric agencies. 
 
 Analyses of rocks from Silver Wreath tunnel. 
 [Analyst, George Steiger.] 
 
 
 I. 
 
 II. 
 
 SiO 2 
 
 65.23 
 .66 
 16.94 
 1.60 
 1.91 
 trace 
 3.85 
 .19 
 1.31 
 3.02 
 3.57 
 .18 
 .88 
 .19 
 none 
 none 
 .25 
 
 66.66 
 .49 
 14.26 
 .67 
 2.41 
 trace 
 3.37 
 none 
 .95 
 4.19 
 none 
 .36 
 2.16 
 .17 
 none 
 .95 
 3.67 
 
 TiO 2 - . 
 
 A1,O 3 .. .. 
 
 FeiO 3 
 
 FeO . .... 
 
 MnO - 
 
 CaO 
 
 BaO . . . 
 
 MgO 
 
 K,O 
 
 Na,O 
 
 HO below 100 
 
 H 2 O above 100 
 
 PA 
 
 SO, 
 
 s . 
 
 CO* - - 
 
 Less O 
 
 99.78 
 
 100. 31 
 .24 
 
 
 
 100. 07 
 
 I. 79 Boise collection; fresh granitic rock. 
 II. 80 Boise collection; altered granitic rock. 
 
 The unaltered rock is light gray and coarse grained, the average 
 size of the constituents being 5 mm to 6 mm . With the naked eye, white 
 plagioclase, reddish orthoclase, biotite, titanite, and quartz may be 
 distinguished. Under the microscope the quartz proves to be very 
 abundant and is slightly crushed. The plagioclastic feldspars pre- 
 dominate and occur generally in anhedrons, more rarely in roughly 
 prismatic forms. Symmetric extinctions show a maximum of 10. A 
 
LINDOEEN.] COMPOSITION OP THE COUNTRY ROCK. 641 
 
 little orthoclase lies between the plagioclase grains. The biotite 
 occurs in small foils of brownish yellow color. Magnetite occurs 
 sparingly. Titanite is much more abundant, occurring in large crys- 
 tals or anhedrons, sometimes wedge-shaped. It includes small feld- 
 spar grains, but its crystals also project into larger feldspar grains. 
 The structure of the rock is eugranitic. 
 
 An approximate calculation of the analysis of the fresh rock (I) 
 may be made in the following manner : On the basis of a preliminary 
 calculation and estimate there is about 15 per cent of biotite present. 
 For this 1.20 per cent potassa was subtracted. The baryta is calcu- 
 lated as hyalophane, which necessitates a deduction of 0.12 per cent 
 more of potassa. The remainder is calculated as orthoclase. The 
 lime needed for calcite, titanite, and apatite is subtracted from the 
 total lime. The amount of magnetite is estimated. Finally biotite 
 and quartz remain. From the amounts of the bases in this remainder 
 it is estimated that there is 25 per cent free quartz present. 
 
 SiO 2 - 6.51 
 
 A1,O 3 - 1.85 
 
 K,0 - 1.70 
 
 KAlSi 3 O 3 10.06 
 
 SiOi - - 20.78 
 
 . AI 2 O 3 --- 5.90 
 
 -- ---- -- 3.57 
 
 NaAlSi 3 O 3 --.. 30.25 
 
 SiO* --- 6.00 
 
 A1 2 O 3 --- 5.09 
 
 CaO.. 2.79 
 
 CaAl 2 Si. 2 O 8 ..... .. ...... ______ ..... ________ .......... 13.88 
 
 SiO 2 ... ......................... . .......... _________ .59 
 
 A1 2 O 3 ...... . ..... -. ..... ____________________________ .25 
 
 BaO ...... ....... -. ..... ___________ ....... - ......... 19 
 
 K 2 ................... -- .......... --- -- -12 
 
 Ba Al,Si 2 O 8 2KAlSi 2 O 8 __.- ....... . ..... .. ............. 1.15 
 
 PA - .................. --------- ................ 19 
 
 -.-- ...................... - ........ --- ......... 25 
 
 Apatite ....... . ............................... ------- .44 
 
 Ti0 2 ..... . .......... - .......... - ............... --- -66 
 
 Si0 8 _____ .................. _______ ............ - ....... 50 
 
 CaO ........ . ........ -.-- ............. _____ .49 
 
 Titanite ...................................... - ..... 1-65 
 
 FeO ........ ....... . ................. - ............ -20 
 
 Fe 3 O 3 ______________________ .......... 
 
 Magnetite ............ . ........... - ............... -61 
 
 CaO ............................ ..................... 32 
 
 C0 2 ..... i .............. - ........................... -.25 
 
 Calcite . _____ ..... . ........................... ---- 
 
 Quartz. ..... . ....................................... 25.00 
 
 18 GEOL, PT 3 - 41 
 
642 IDAHO MINING DISTRICTS. 
 
 SiO 2 5.85 
 
 .ALA- - 3.85 
 
 Fe 2 3 - - -- i' 19 
 
 FeO.... - 1-71 
 
 MgO 1.31 
 
 K 3 O --- -- 1-20 
 
 H 2 0.. -88 
 
 Biotite..- --- 15.99 
 
 Hygroscopic water . -.- .18 
 
 Total - 99.78 
 
 The biotite would have the following composition: 
 
 Si0. 2 --- - 36.59 
 
 A1 2 0, -- --- 24.08 
 
 Fe,O 3 ---- 7.44 
 
 FeO 10.69 
 
 MgO... - 8.19 
 
 K;O._.- - '--- 7.51 
 
 H 2 O.. 5.50 
 
 100. 00 
 
 The water is somewhat too high, no doubt due to the fact that chlo- 
 rite and other decomposition products are present. 
 
 According to mineralogical composition, habit, and chemical com- 
 position, this rock corresponds closely to the granodiorite of the Sierra 
 Nevada, the only difference being that it contains no hornblende, 
 which in the granodiorite is as a rule abundant. It thus occupies a 
 position between a quartz-mica-diorite and a granite. However, as it 
 grades imperceptibly over into more normal granites, it has not been 
 thought worth while to segregate it from that rock. The plagioclase 
 in the Willow Creek rock is, according to the ratio between albite and 
 anorthite, Ab 2 An, or a basic oligoclase. 
 
 The second rock (80 Boise collection) is grayish white, granular, 
 with a clearly apparent granitic habit. It consists of quartz grains of 
 about the same size as in the fresh rock, while a greenish-gray com- 
 pact mass replaces the feldspar and has a hardness of about 3. The 
 biotite is replaced by a dull- white micaceous mineral. Small crystals 
 of pyrite abound, and the rock is also traversed by a few small quartz 
 veins. In a few places small grains of zinc blende are seen. 
 
 Under the microscope, large grains of quartz with undulous extinc- 
 tion are noted. Between them lies a fine-felted mass of sericite 
 fibers, calcite grains, and in places a little fine-grained quartz. No < 
 feldspar remains, though occasionally the outlines of the grains may 
 still be noted. In places larger muscovite foils appear, evidently 
 representing the original biotite. The quartz is in many places 
 attacked by sericitization, fibers and tufts of sericite and calcite 
 developing in it or projecting into it from the surrounding sericite 
 mass. Titanite, extremely abundant in the unaltered rock, is con- 
 
LINDGREN.] COMPOSITION OF ALTERED GRANITE. 643 
 
 verted into a milky opaque mass, composed of a great number of 
 small crystals. The also abundant apatite is not attacked at all by 
 any metasoinatic process. The idiomorphic pyrite is chiefly contained 
 in the altered feldspars, but also included in the quartz. When the 
 pyrite crystals are larger the quartz in the vicinity often shows very 
 strong undulous extinction, but some small perfect crystals also lie 
 in the fresh, unchanged quartz, usually attached at one side to a 
 bunch of sericite fibers. An assay of this rock gave 0.05 ounce of 
 gold and 0.5 ounce of silver to the ton. 
 
 Analysis II shows the composition of the altered granite. The 
 chemical change is on the whole slight. Silica shows a small increase, 
 alumina a decrease ; a very slight decrease is also noted in the iron 
 oxides, lime, magnesia, and titanic acid, while the whole of the soda 
 and the baryta has been carried away, and the percentage of potash 
 has been considerably augmented. Sulphur and carbon dioxide have 
 been introduced, and the quantity of chemically combined water 
 has been increased. 
 
 With the aid of the data furnished by the microscopic investiga- 
 tion, the analysis may be calculated as follows. The lime has been 
 calculated as carbonate, excepting that necessary for apatite and 
 titanite, the whole of the magnesia likewise as carbonate, and as 
 much of the ferrous oxide as the remaining carbon dioxide would 
 permit. The remainder is sericite and quartz. The amount of free 
 quartz has been estimated according to the quantity of oxides 
 available for sericite. 
 
 S 95 
 
 Fe._ .83 
 
 Pyrite 1.78 
 
 P 2 O, 17 
 
 CaO.- .22 
 
 Apatite ... 
 
 
 .39 
 
 TiO; 
 
 .49 
 
 
 SiO 2 
 
 .33 
 
 
 CaO 
 
 .... .46 
 
 
 
 
 
 Titanite 
 
 
 1.28 
 
 CaO 
 
 2.69 
 
 
 CO 2 - 
 
 2.11 
 
 
 
 
 
 Calcium carbonate 
 
 
 4.80 
 
 MgO - . . .... 
 
 0.95 
 
 
 CO, . 
 
 1.01 
 
 
 Magnesium carbonate 
 FeO 
 
 CO, .. 
 
 Ferrous carbonate 1.45 
 
 Quartz 42.00 
 
644 IDAHO MINING DISTRICTS. 
 
 SiO* 24.33 
 
 A1 2 3 - -.. -- - 14.26 
 
 Fe 2 3 ---- 67 
 
 FeO .44 
 
 K 2 4.19 
 
 H 2 --- 2.16 
 
 Sericite.. 46.03 
 
 Hygroscopic water ... .36 
 
 Total 100.07 
 
 The sericite would have the following composition : 
 
 SiO* - 52.82 
 
 A1 2 3 30.96 
 
 Fe 2 O 3 1.46 
 
 FeO 96 
 
 K 2 9.10 
 
 H 3 O._ 4.70 
 
 100. 00 
 
 The altered wall rock from the Black Hornet mine (60, 63 Boise 
 sheet collection) is a grayish- white, very quartzose rock impregnated 
 with small grains and crystals of arsenopyrite. Though adjoining 
 ore contained from $10 to $20, it was found upon assay to contain 
 neither gold nor silver in appreciable quantities. Under the micro- 
 scope No. 60 appears as a crushed granite or coarse granite-porphyry. 
 The quartz grains are converted into coarse aggregates; the unstri- 
 ated feldspar is filled with sericite fibers and grains of arsenopyrite, 
 some of which have a little adhering chlorite. No. 63 contains unal- 
 tered idiomorphic andalusite, besides crushed large quartz grains and 
 sericitized microperthite, and also a little soda-lime-feldspar. Scat- 
 tered grains of pyrite are associated with foils of sericite. 
 
 The ore of the Black Hornet consists of massive quartz with inclosed 
 sulphides. The preponderating quartz is granular and shows strong 
 evidence of pressure. The ores consist of small, perfect crystals of 
 arsenopyrite and anhedral grains of dark-brown, scarcely translucent 
 zinc blende; inclosed in the latter are many small, distinct foils of 
 sericite. Smaller shreds of this mineral are also scattered through 
 the quartz. 
 
 The granite and porphyries adjoining the veins of the Idaho Basin 
 are altered in a similar manner. Sericitization always takes place, 
 and is often accompanied by the formation of carbonates. A specimen 
 from a seam in the hanging wall of the Boulder mine (19 Idaho Basin 
 sheet collection) consists of a quartz vein 2-g- inches wide, of which 1 
 inch is pure quartz and the rest quartz with much finely divided iron 
 pyrite. This vein is inclosed in a greenish- white, bleached granite, 
 impregnated with a little pyrite and arsenopyrite. 
 
 An assay of the quartz vein gave 2.25 ounces of gold and 1 ounce 
 of silver to the ton, or a total value of $47.21. An assay of the 
 
LINDGBEN.] SILICIFIC ATION. 645 
 
 altered granite immediately adjoining this piece gave only a trace of 
 gold and silver. Under the microscope the altered granite is seen to 
 contain large, partly crushed quartz grains. The feldspar, which is 
 partly orthoclase, partly a soda-lime-feldspar, is filled with sericite 
 foils, chiefly developing on the cleavage planes, and a few grains are 
 almost totally replaced by this material. A few larger muscovite foils 
 probably represent the altered biotite. No calcite is present. 
 
 The diorite-porphyrites and quartz-diorite-porphyrites of the Gold 
 Hill and Pioneer mine at Quartzburg show a similar alteration, chiefly 
 consisting in a conversion of the hornblende and biotite to muscovite 
 foils, calcite, and perhaps also pyrite, while there is a great develop- 
 ment of fine-felted sericite in 'the feldspar phenocrysts and in the 
 groundmass. The abundant pyrite is in sharp cubes, usually lined 
 with sericite foils. Aggregates of secondary quartz also develop in 
 places. 
 
 Silicification. Mr. S. F. Emmons, in his studies of the mineral depos- 
 its of Colorado and other parts of the Rocky Mountains, has admirably 
 and with deserved emphasis brought out the fact that replacement is 
 a process to which many deposits owe their origin, and that it plays an 
 important part in almost all deposits caused by mineral-bearing waters. 
 Carried away with the importance and interest of these results, many 
 geologists and mining engineers have, however, extended the theory 
 of replacement beyond its proper bounds, and speak of every vein- 
 filling and even of veins of solid white quartz as products of replace- 
 ment. Against this view a strong protest should be entered. In this 
 connection it may be of interest to consider, briefly, the processes by 
 which silicification may be produced. 
 
 In the case of ores consisting of carbonates there may often be some 
 difficulty in deciding what is filling and what is replaced country 
 rock, for carbon dioxide and alkaline carbonates are very strong sol- 
 vents, attacking easily nearly every one of the rock-forming minerals 
 and forming pseudomorphs after them. The carbonates may replace 
 a rock completely, wholly changing both composition and structure. 
 As an instance may be cited the coarse-grained mixture of carbonates 
 and mariposite (fuchsite a chromium mica) resulting from the 
 replacement of the serpentine along the Mother lode of California. 
 
 As to quartz, the conditions are wholly different. A solution of 
 silica is comparatively inert and does not easily attack any of the 
 rock-forming silicates. Silicification may take place by two greatly 
 differing processes: (1) Cementation, or filling of the interstices of 
 porous or shattered rocks by quartz deposited from solutions; (2) 
 metasomatic silicification, or a substitution of silica for other miner- 
 als, the silica either being produced by the alteration of the original 
 minerals or deposited pari passu with the dissolving of the original 
 mineral by active reagents in the waters causing the metasomatic 
 action. 
 
646 IDAHO MINING DISTRICTS. 
 
 The first process is often observed in the silicification of various 
 sedimentary, porous rocks, chiefly sandstones or tuff or porous igne- 
 ous rocks, such as certain trachytes and andesites. Silicification by 
 the cementation of shattered rock masses by silica is, of course, a 
 common occurrence in and near quartz veins. But silicification by 
 replacement is a less common process, and is observed chiefly in the 
 case of easily soluble rocks, such as limestone or calcareous shales, 
 when it results in fine-grained or cryptocrystalline aggregates of 
 silica. In the metasomatism of bodies of massive rocks penetrated 
 by chemically active solutions silica is formed in many ways, as by 
 the carbonatization of silicates and sericitization of the feldspars, 
 and if no open spaces are available much of this free silica will be 
 deposited within the rock, usually as fine-grained aggregates more 
 or less mixed with opal and chalcedonite. If no material were added 
 the final result of this would not, however, be a silicification, but 
 merely an increase in the total free quartz of the rock. But in case 
 the rock mass is cut by fissures it appears that most of the resulting 
 free silica is not deposited in the rock, but finds its way out in the 
 open ducts, where, if the solution is supersaturated, it will be depos- 
 ited. In fact, in the metasomatic processes in the ordinary igneous 
 rocks adjoining gold-quartz veins, late investigations have shown 
 that certain elements are added to the rock, while others, notably 
 silica, are frequently subtracted, to be carried away or deposited in 
 available open spaces. 
 
 As for the other possible process of silicification, or a dissolving of 
 the original mineral and a deposition of silica pari passu, it occurs 
 chiefly in easily soluble minerals, such as calcite. In case of the 
 ordinary rock-forming silicates it is apparently not common. The 
 resulting silica is generally in the form of fine, cryptocrystalline 
 aggregates. Rocks silicified by either of these metasomatic processes, 
 or by a combination of both, may occur, but, so far as the writer's ex- 
 perience goes, are not often encountered as wall rocks of auriferous- 
 quartz veins. But neither of these processes can have produced the 
 massive, white, coarse-grained quartz of gold veins belonging to the 
 normal type. This quartz, which contains native gold and sulphides, 
 shows, under the microscope, a peculiar, coarsely granular structure, 
 the grains being partly bordered by crystallographic surfaces. This 
 structure could have been developed only by free crystallization in 
 open spaces. It is scarcely necessary to call attention, in addition, to 
 the frequency of comb structure, etc. , proving also the same kind of 
 origin. This does not necessarily mean that all large bodies of quartz 
 have been deposited in an open space, as large as the volume of quartz 
 now is. Repeated openings of the fissure have doubtless often taken 
 place. 
 
 In nature the complication of the fissure veins is often great, and 
 it is clear, in fact, that it must be so, for the walls are often shattered, 
 
LINDGBKN.] VEIN STRUCTURE. 647 
 
 resulting in alteration of the country rock and deposition of a net of 
 quartz in the interstices. Ground-up mud often fills the fissure, and 
 the result of the action of the solutions on this will be a mass of grains 
 of altered rock, cemented as in a sandstone by quartz. 
 
 STRUCTURE OF THE VEINS. 
 
 The existence of fissure veins is primarily due to one or more fault 
 planes, fissures or seams forming ducts for ore-bearing solutions. 
 The latter have then produced the materials now forming the vein, 
 which may be divided into (1) vein-filling, or minerals deposited in 
 the open spaces along the fissure, and (2) metasomatically altered 
 country rock. Though it is not in every case possible to strictly sep- 
 arate the two classes, as a rule it can be done. Many of the puzzling 
 questions in regard to veins and vein-filling may be solved if this dis- 
 tinction is made and carefully applied. Products of attrition, often 
 present in quartz veins, belong, as a rule, to the second class of 
 materials. The vein-filling which ordinarily constitutes the ore is 
 composed of various sulphides with a gangue of more or less quartz 
 and calcite. Naturally it occurs chiefly along the fault planes and 
 seams. At Willow Creek, for instance, the seams consist of nearly 
 solid sulphides with a little quartz and calcite. These largely rep- 
 resent filling, but are probably, to a minor extent, formed by replace- 
 ment of the country rock immediately adjoining the fault planes. 
 At other localities, as at Black Hornet and Shaw Mountain, the ore 
 consists of quartz-filling exclusively, with scattered grains and masses 
 of rich sulphides and native gold. 
 
 The typical fissure vein may be regarded as a single break or 
 fissure along which, through faulting, more or less continuous open 
 spaces were formed and subsequently filled with ore. On both sides 
 of this filling there is a gradually fading zone of alteration of the 
 country rock. 
 
 In many regions the typical simple fissure vein is relatively rare. 
 The country rock may be cut by one or several fault planes, along 
 which only small open spaces have formed and around which there is a 
 wide belt of altered country rock. The ore, then, mainly accumulates 
 along these planes, largely by filling, partly, also, by metasomatism 
 of the adjoining rocks. Again, there may be a shattered zone adjoin- 
 ing one or more fault planes. The rock is then traversed by a com- 
 plicated system of seams, and large areas of the country rock may be 
 altered. In this case, again, the seams generally contain the gold 
 and the whole seamed rock mass may form a large ore body of low 
 grade. 
 
 On PI. XC (p. 650) a few types of the fissure veins occurring in this 
 region are diagrainniatically represented. 
 
648 IDAHO MINING DISTRICTS. 
 
 MINERAL DEPOSITS OF POST-NEOCENE AGE. 
 
 As has been explained before, there is every reason to believe that 
 all of the more important ore deposits antedate the Payette formation, 
 or that, in other words, they are pre-Miocene. But there is also some 
 evidence of a later period of ore deposition, although of less impor- 
 tance, which occurred after the early Neocene eruptions, and which 
 may be going on in depth even at the present time by means of the 
 hot ascending spring waters found at several places in this region. 
 
 The Neocene rhyolite area occurring on the Idaho City road 3 miles 
 from Boise is somewhat altered in places and is stated, on reliable 
 authority, to contain $1 per ton in silver and a trace of gold. A 
 Neocene sandstone with veins of opal, occurring near this area along 
 the road, was assayed and found to contain 0.50 ounce of silver per 
 ton. The knob of partly altered augite-andesite near the penitentiary 
 at Boise was assayed and found to contain 0.05 ounce of gold and 
 0.50 ounce of silver per ton, a total value of $1.38. 
 
 The Neocene basalt at the mouth of the canyon of Jackass Creek, 
 Jerusalem Valley, contains a quartz vein which is stated to assay 
 about $4 in gold and silver. 
 
PLATE XC. 
 
 649 
 
PLATE XC. 
 
 1. Simple fissure vein with one fault plane and with quartz filling. Altered 
 
 country rock on both sides. Filling only constitutes the ore. 
 
 2. Complex fissure vein with three fault planes. Rich ore as filling along narrow 
 
 openings, partly also by alteration of country rock immediately adjoining 
 fissures. Less altered country rock between and beyond the fault planes. 
 
 3. Simple fissure vein without large open spaces. Ore partly as filling, partly as 
 
 altered country rock. Less altef ed country rock on both sides of fault plane. 
 
 4. Complex fissure vein with two fault planes, along which quartz is deposited as 
 
 filling. Wide sheeted and altered zone between the two fissures. 
 
 5. Irregularly shattered zone between two fault planes. Quartz filling in seams 
 
 and cracks. Extensive alteration of country rock between fault planes. 
 
 6. Single fissure in foot wall of porphyry dike. Dike traversed by stringers from 
 
 hanging wall, shattered and extensively altered. Quartz filling in fissure 
 and seams. Rich ore in quartz vein. Altered porphyry constitutes low- 
 grade ore. 
 650 
 
U. 8. GEOLOGICAL SURVEY 
 
 EIGHTEENTH ANNUAL REPORT PART III PL. XC 
 
 /:/ \--/\-'- / -'-r--#:- 
 
 tft^^y^ 
 
 ::iiiW^MM 
 
 m+^^:m-: 
 
 .F.-Vii 
 
 iiSif ; 
 
 Scale. 
 
 . . '? feel- 
 
 TYPES OF GOLD-BEARING FISSURE VEINS. 
 
CHAPTER III. 
 
 THE IDAHO BASIN. 
 
 GEOGRAPHICAL POSITION. 
 
 The Idaho Basin includes the headwaters of Moore Creek, a tribu- 
 tary of the Boise River, and is located at a distance of 25 miles in a 
 northwesterly direction from the city of Boise, at about latitude 
 43 50' and longitude 115 50'. In comparision to its size this dis- 
 trict has produced a very large amount of gold, chiefly from placer 
 mines, but also considerable from quartz mines. The area embraced 
 in the Idaho Basin that is to say, the productive part of the same 
 does not exceed 150 square miles. Its length from north to south is 
 15 miles and its maximum width about 13 miles. 
 
 DISCOVERY AND HISTORY. 
 
 The placer mines of the Idaho Basin were discovered in August, 
 1862, by a party of prospectors from Walla Walla. During the fall 
 of the same year the party is said to have been attacked by Indians, 
 and its leader, Grimes, killed at Grimes Pass. The party, after 
 ascertaining the richness of the placer deposits, returned to Walla 
 Walla and formed a new expedition of 52 men ; this party reached 
 the basin the same year. The prospectors located first at the pres- 
 ent site of Pioneerville. Subsequently the gold gravels of Centerville 
 were located, and in December of the same year the rich diggings at 
 Idaho City and on Granite Creek were found. Rapidly following 
 these discoveries came explorations of other mineral-bearing parts of 
 Idaho. In 1863 Rocky Bar and the rich mines of Owyhee were found. 
 The influx of miners was extremely rapid after the report of the first 
 discoveries had spread, and one year after the discovery several thou- 
 sand placer miners were operating in the region. From 1862 to the 
 present date placer mining has been carried on continuously, the 
 operation being limited only by the amount of water available. Nat- 
 urally, however, the output has gradually decreased since the first 
 years following the discovery, when, as usual in placer regions, the 
 maximum production was reached. 
 
 At an early date quartz mines began to be exploited, as it was soon 
 seen that the placer deposits led up to the decomposed croppings of 
 numerous quartz veins. At that time, however, quartz mining was 
 in its infancy, and the ores could not always bear the cost of the treat- 
 ment, increased in this case by the long distance over which machinery 
 had to be transported and the high wages demanded for labor. At 
 the present time there is a considerable quantity of gravel still left 
 for exploitation, but these deposits will in time be exhausted, and the 
 gold production will then have to depend on the quartz mines. In 
 1867 and 1868 at least ten mills are reported to have been in operation. 
 
 651 
 
652 
 
 IDAHO MINING DISTRICTS. 
 
 During the last year only a few of the quartz mines and mills were 
 running. 
 
 At the present time the Idaho Basin contains five towns, with an 
 aggregate of 1,200 inhabitants. Idaho City is located on Moore Creek, 
 Centerville and Pioneerville on Grimes Creek, and Placerville and 
 Quartzburg on the different branches of Granite Creek. 
 
 PRODUCTION. 
 
 The total gold production of the basin since its discovery has been 
 the subject of frequent discussion, and it may be said that it is 
 impossible to obtain undisputed data. It is often stated that the pro- 
 duction for the first six years amounted to over $40,000,000, and that 
 the total production exceeds $100,000,000. As will be shown, this 
 estimate must be regarded as extravagant. The following table shows 
 the production of the State of Idaho according to the most reliable 
 estimates, contained in the reports of J. Ross Browne and R. W. 
 Raymond, and the later Mint reports : 
 
 Production of gold and silver in Idaho, 1863-1876. ' 
 
 Year. 
 
 Value. 
 
 Remarks. 
 
 1863. ... 
 
 $7, 000, 000 
 
 Estimate (W. L.). Reports lack- 
 
 1864 
 
 6, 470, 100 
 
 ing. 
 J. Boss Browne, report 1867, based 
 
 1865 
 
 6,581,400 
 
 on Wells-Fargo data; estimates 
 added. 
 Do. 
 
 1866 
 1867 
 1868 
 1869...... 
 1970 
 1871 
 
 8, 023, 700 
 6, 500, 000 
 7, 000, 000 
 7, 000, 000 
 6, 000, 000 
 5, 000, 000 
 
 Do. 2 
 Mint reports. 
 Do. 
 Do. 
 Do. 
 Do. 
 
 1872 
 1873 
 
 2, 695, 900 
 2, 500, 000 
 
 $2,300,000 gold, $400,000 silver. 
 From Eleventh Census, Mineral 
 
 1874 
 
 1,880,000 
 
 Industries, p. 40. 
 Do. 
 
 1875 
 
 1,750,000 
 
 From Eleventh. Census, Mineral 
 
 1876. 
 
 1,600,000 
 
 Industries, p. 40. $1,554,902 in 
 Mint reports. 
 Reports lacking. Estimate by 
 
 
 
 W. L. 
 
 Total. 
 
 70,001,100 
 
 
 1 During these years the defective statistics do not permit the separation of the gold and sil- 
 ver production, but the latter is relatively small, as shown by the figures for 1872. Few silver 
 mines were worked up to 1876. 
 
 2 $17,000,000 in table on p. 40 of Mineral Industries, Eleventh Census. Authority for this doubt- 
 ful statement unknown. 
 
LINDGKEN.] 
 
 GOLD PRODUCTION OF IDAHO. 
 
 Production of gold in Idaho, 1877-1896. 
 
 653 
 
 Year. 
 
 Value. 
 
 Remarks. 
 
 1877 
 
 $1,500,000 
 
 From table in Eleventh Census 
 
 1878 
 
 1, 150, 000 
 
 Mineral Industries, p. 41. 
 Do. 
 
 1879 . 
 
 1, 200, 000 
 
 Do. 
 
 1880 
 
 1,980,000 
 
 Do. 
 
 1881 
 
 1,700,000 
 
 Do. 
 
 1882 
 
 1,500,000 
 
 Do. 
 
 1883 
 
 1,400,000 
 
 Mint reports. 
 
 1884 
 
 1,250,000 
 
 Do. 
 
 1885 . 
 
 1,837,400 
 
 Do. 
 
 1886 
 
 1,798,000 
 
 Do. 
 
 1887. 
 1888 
 1889 
 
 2, 417, 300 
 1,960,000 
 2, 055, 700 
 
 Mint reports; $1,900,000 accord- 
 ing to Eleventh Census table. 
 Mint reports; $2,400,000 accord- 
 ing to Eleventh Census table. 
 Mint reports. 
 
 1890. 
 
 1,696,700 
 
 Do. 
 
 1891 
 1892 
 
 1, 685, 600 
 
 1,721,400 
 
 Do. 
 Do. 
 
 1893 
 
 1,693,600 
 
 Do. 
 
 1894 . 
 
 2, 308, 800 
 
 Do. 
 
 1895 
 1896 
 
 2,594,700 
 2, 323, 700 
 
 Do. 
 Do. 
 
 
 
 
 Total- 
 
 35, 772, 900 
 
 9 
 
 It appears from the tables that the total production of the State for 
 the first six years scarcely exceeded. $41,000,000, according to the Mint 
 statistics, and that consequently the Idaho Basin can not have pro- 
 duced more than a fraction of this amount. Even admitting the more 
 liberal estimates mentioned a few lines below, the total production for 
 this period can not have exceeded $60,000,000. As to the production 
 of the Idaho Basin itself, the data available are still more imperfect. 
 For 1867, 1868, and 1870 there is in Raymond's reports for 1869 and 
 and 1871 an estimation of the total production made by W. A. Atlee, 
 agent of the Wells-Fargo Company at Boise, an authority probably 
 better qualified to judge than anybody else. This includes not only 
 Wells-Fargo shipments, but estimates of all kinds of shipments. 
 
654 IDAHO MINING DISTRICTS. 
 
 Estimation of the total production of the Idaho Basin in 1867, 1868, and 1870. 
 
 District. 
 
 1867. 
 
 1868. 
 
 1870. 
 
 Placerville 
 
 $363, 237 
 
 $340, 515 
 
 $184, 428 
 
 Centerville 
 
 468, 556 
 
 442, 443 
 
 249, 839 
 
 Pioneerville 
 
 494, 931 
 
 552, 604 
 
 250, 000 
 
 Idaho City . - 
 
 3,001,568 
 
 2,961,213 
 
 2, 000, 584 
 
 
 
 
 
 Total 
 
 4, 328, 292 
 
 4, 296, 775 
 
 2, 684, 851 
 
 
 
 
 
 The same authority estimates a total production in Idaho of $9,000, 
 
 000 in 1867, $10,000,000 in 1868, and $6,000,000 in 1870. On this Mr. 
 R. W. Raymond comments that his estimate for the total production 
 in Idaho for 1868 is only $7,000,000, and, admitting the excellent facili- 
 ties which Mr. Atlee had for estimation, still thinks that his values 
 are too high, and is reluctant to allow any increase in his own figures. 
 From 1881 to the present year the statistics are in better condition, 
 and the production of Boise County can be closely estimated. In this 
 production the Idaho Basin furnishes by far the largest quantity of 
 gold; it may be safely said that nine-tenths of the production of Boise 
 County is derived from the Idaho Basin. On the basis of these data 
 
 1 have attempted to construct a table giving the probable production 
 of the Idaho Basin to the present date. It is, of course, only a rough 
 estimate, but it has some value. 
 
 During 1884, Plowman's claim, according to the Mint reports, yielded 
 $25,000, Channel's claim at the head of Willow Creek $10,000, and the 
 Granite Creek Company's claim east of Placerville from $15,000 to 
 $20,000. The Chinese companies were during this period estimated 
 to have produced $25,000 a year. In 1883, Placerville, according to 
 the same authority, produced $25,500, Idaho City $381,500, and the 
 Deadwood Basin, located in the northeast portion of Boise County, 
 $8,000. It will be noticed that the greatest production is always that 
 of the Idaho City district. 
 
LINDGEEN.] GOLD PRODUCTION OF BOISE BASIN. 
 
 Table of probable production of the Idaho Basin, 1863-1896. 
 
 655 
 
 Year. 
 
 Value. 
 
 Remarks. 
 
 
 1863. 
 
 $3, 000, 000 
 
 Estimated (W L ) 
 
 
 1864 
 1865 
 
 4, 000, 000 
 5, 000, 000 
 
 Do. 
 Do 
 
 
 1866 
 
 5, 000, 000 
 
 Do 
 
 
 1867 
 
 4, 300, 000 
 
 Estimated by TV^ A Atlee 
 
 
 1868. 
 
 4, 300, 000 
 
 Ross Browne's report for 
 Do 
 
 1869. 
 
 1869 
 
 3, 000, 000 
 
 Estimated (W L ) 
 
 
 1870 
 1871 
 
 2, 700, 000 
 2, 000, 000 
 
 Estimated by W. A. Atlee 
 mond's report for 1871). 
 Estimated (W.L.). 
 
 (Ray- 
 
 1872 
 
 1,000,000 
 
 Do. 
 
 
 1873. 
 
 800, 000 
 
 Do. 
 
 
 1874 
 
 700, 000 
 
 Do. 
 
 
 1875 
 1876 . 
 
 600, 000 
 600, 000 
 
 Boise County (Raymond's 
 for 1875). 
 Estimated (W.L.). 
 
 report 
 
 1877 
 
 500, 000 
 
 Do. 
 
 
 1878. 
 
 500, 000 
 
 Do. 
 
 
 1879 
 1880 
 
 400, 000 
 300, 000 
 
 Do. 
 Do. 
 
 
 1881 
 
 300, 000 
 
 Boise County, Mint reports. 
 
 
 1882. . 
 
 290, 000 
 
 Do. 
 
 
 1883 
 
 565/000 
 
 Do. 
 
 
 1884 
 
 400, 000 
 
 Do. 
 
 
 1885 . 
 
 619, 000 
 
 Do. 
 
 
 1886 
 
 390, 900 
 
 Do. 
 
 
 1887 
 
 502, 200 
 
 Do. 
 
 
 1888 
 
 283, 000 
 
 Do. 
 
 
 1889 
 1890 
 
 274, 600 
 320, 400 
 
 Do. 
 Do. 
 
 
 1891 
 
 356, 700 
 
 Do. 
 
 
 1892 
 
 376. 400 
 
 Do. 
 
 
 1893 
 1894 
 1895 
 1896. .. 
 
 280, 800 
 32T, 800 
 339, 000 
 326, 000 
 
 Do. 
 Do. 
 Do. 
 Do. 
 
 
 
 
 
 
 Total. 
 
 44,651,800 
 
 
 
 It will be seen from this table that the total production amounts to 
 less than $45,000,000. Allowing for the uncertainty in the data, we 
 may safely say that the basin has not produced more than $50,000,000 
 
656 IDAHO MINING DISTRICTS. 
 
 in gold. Even supposing the admittedly uncertain production of the 
 first four years to be double the amount of estimates here given, the 
 total production would be only $62,000,000. 
 
 While it is not possible to separate the production of the quartz 
 mines from that of the placer mines, it may be said with some confi- 
 dence that the total production of the former does not exceed 
 $4,000,000. 
 
 TOPOGRAPHY. 
 
 The Idaho Basin, the topography and geology of which are shown 
 in PL XCVI, is located in the middle of that great irregular mountain 
 mass extending between the Salmon and the Snake rivers. Defined 
 more closely, it is situated on the ridge between the north fork of 
 the Boise River and the south fork of the Payette. On the west rises 
 the Boise Range, the summits of which are visible from Boise, and 
 which attains elevations of from 7,000 to 7,500 feet. On the east rise 
 the irregular mountain complexes of Sawtooth Range and its pro- 
 jecting spurs. The basin occupies the head waters of Moore Creek, a 
 tributary joining the Boise River 10 miles above where it leaves its 
 canyon and enters the plains of the Snake River Valley. Ten miles 
 from its junction with the Boise River Moore Creek divides in two, 
 the westerly branch being called Grimes Creek. Five miles above 
 this the narrow canyon in which Moore Creek flows widens out to 
 a broad valley, in which the creek meanders with but little fall. At 
 Idaho City the creek branches again, and both forks head in the high 
 mountains near Wilson Peak and Elk Creek Mountain. A long ridge 
 with a southwesterly direction separates the Moore Creek Basin from 
 the depression of Grimes Creek. This ridge, which for a long distance 
 has a nearly level summit, rises to a height of 1,000 feet above Idaho 
 City. To the south and east of Idaho City the rise is much more 
 rapid. From the vicinity of Thorn Creek Mountain a number of very 
 high and narrow ridges project northward, encircling the southern 
 and eastern part by a chain of hills rising 2,000 feet above Idaho 
 City. Six miles above Idaho City, Moore Creek enters this rugged 
 complex of mountains, and 5 miles farther up heads in the precip- 
 itous amphitheaters of Elk Creek Mountain. 
 
 The canyon of Grimes Creek reaches to a point 10 miles above its 
 junction with Moore Creek; then the valley broadens, exactly simi- 
 larly to the valley of Moore Creek, the main branch continuing in a 
 northeasterly direction and heading near Grimes Pass, 4 miles north of 
 Pioneerville. This, pass forms the water-parting between the Payette 
 and Boise rivers. It is comparatively low, attaining an elevation 
 of only 5,000 feet. Immediately east of Pionee.rville and of Grimes 
 Pass the high ridges of Wilson Peak and Summit Flat rise above the 
 more gently undulating country of the valley of Grimes Creek. An 
 important tributary, Granite Creek, enters 4 miles below Centerville 
 and extends in a northwesterly direction toward Quartzburg. Granite 
 
LINDQREN.] TOPOGRAPHY CREEK GRADES. 657 
 
 Creek flows in a similar wide valley with gentle slopes, and passes 
 again lead over to the Pay ette watershed north of Place rville and north 
 of Quartzburg. The lowest pass is the former, which attains an eleva- 
 tion of only 4,700 feet. A short distance west of Granite Creek the 
 Boise Ridge rises very abruptly in the vicinity of Quartzburg, and 
 more gently farther south to elevations ranging up to 7,500 feet. The 
 lowest pass leading across the Boise Ridge, with an elevation of 5,500 
 feet, is found 6 miles west of Centerville. 
 
 One can best appreciate the topographic features of the basin when 
 standing high up on the slopes of the Boise Ridge or on any one of 
 the high peaks rising toward the east. It is seen that the name is 
 extremely appropriate, because it forms a low depression encircled on 
 all sides by a ring of high mountains. Only toward the north, along 
 the water-parting between Boise Ridge and Grimes Pass, is there a 
 lower rim, leading over into the deep canyon of the Payette River. 
 In the accompanying photograph (PL XCI), taken from a point at an 
 elevation of 6,000 feet on the road leading from Quartzburg to Jeru- 
 salem Valley, the encircling rim from Thorn Creek Mountain to "Wil- 
 son Peak is well shown, as are the remarkably level ridges separating 
 the lowest depressions in the basin. 
 
 GRADES OF THE WATER COURSES. 
 
 According to the topographic maps of the United States Geological 
 Survey the grade of the Boise River above and below the mouth of 
 Moore Creek is very slight, being only about 10 feet per mile. 
 Moore Creek for the first 11 miles from its mouth, to the junction 
 with Grimes, has a grade of 40 to 50 feet per mile. The narrow 
 canyon above the mouth of Grimes Creek has a somewhat stronger 
 grade, approximating 66 feet per mile. From Idaho City down to 
 where the canyon begins a grade of 50 feet per mile is obtained; 
 above Idaho City it is for 3 miles 33 feet per mile; beyond this point 
 the grade increases rapidly and is from 100 to 200 feet per mile. 
 
 For the first 9 miles from the junction Grimes Creek averages 40 
 feet per mile; then follow 4 miles of a more abrupt canyon, with a 
 grade of 80 feet per mile. Within the basins of Centerville and 
 Graniteville the creeks have a fall of about 30 feet per mile, which 
 above Pioneerville and Quartzburg rapidly increases to 200 feet per 
 mile. 
 
 TERTIARY AND PLEISTOCENE FORMATIONS. 
 
 
 LOWER MOORE CREEK VALLEY. 
 
 Configuration of the valley. From Boise River up to the junction 
 with Grimes Creek, Moore Creek flows in a somewhat broad and 
 U-shaped valley, the slopes of which rise with increasing steepness 
 to ridges with gentle summit lines 2,000 feet above the valley. The 
 hills are covered with a scant vegetation and the soft crumbling 
 18 GEOL, PT 3 42 
 
658 IDAHO MINING DISTRICTS. 
 
 granite is easily washed down by atmospheric agencies. The width 
 of the valley between the summits is not more than 2 miles. Above 
 the mouth of Grimes Creek the valley contracts and the steep slopes 
 project, the creek forming a more V shaped valley, which continues 
 to 44 miles above the junction. A few small alluvial flats lie in the 
 bottom of this canyon. 
 
 The basalt flow. The valley bottom is filled with a basalt flow rarely 
 over one-fourth of a mile in width ; its top rises to about 100 feet above 
 the creek level. Through this flow the stream has cut down to a depth 
 somewhat exceeding that which it had attained before the basaltic 
 eruption. The joints in the basalt have produced perpendicular 
 cliffs, the whole being an exact illustration of a canyon within a valley. 
 "While much of the basalt flow has been eroded, enough remains to 
 form a nearly continuous fringe of cliffs on either or both sides of the 
 streams, reaching from the mouth of the creek up to 1^ miles above 
 the junction with Grimes Creek. The level top of the flow has been 
 covered by a sloping, sandy wash from the adjoining hills. The 
 character of the valley, the basalt flow and its covering, is well illus- 
 rated in PI. XCII. Above the point mentioned the basalt suddenly 
 ceases, and no more of it, either in outcrops or in pebbles, is seen 
 above. It also extends a few miles up on Grimes Creek, and it is 
 probable that the vent was located at some point in the Grimes Creek 
 Canyon, and that the flow backed up for some distance on Moore 
 Creek. The basalt is about contemporaneous with the flows of the 
 Snake and Boise rivers geologically speaking recent being referred 
 to the late Neocene (Pliocene) period. 
 
 The present stream gravels. The bed occupied by the stream is 
 generally narrow, seldom exceeding 100 feet in width. The bed rock 
 is only rarely exposed. The creek is filled with coarse gravel, largely 
 made up of tailings brought down from the Idaho Basin by the winter 
 freshets. The maximum depth of these tailings is 20 feet. The 
 gravels in the present stream have been and are still extensively 
 washed, mostly by Chinese using the ordinary appliances for river 
 mining dams, Chinese pumps, and derricks. The old channel cov- 
 ered by the recent debris has been exposed by mining at many places, 
 being naturally richer than the tailings. The many basalt bowlders 
 found in it are a considerable obstacle to cheap mining. On Moore 
 Creek, about 4 miles above the mouth of Grimes Creek, a steam 
 dredge was operated in 1896, with the purpose of striking the rich 
 gravel 10 to 20 feet below the surface. The gravel is reported to have 
 been reached, though the large bowlders interfered somewhat with 
 the work. On the whole, the present stream gravels of lower Moore 
 Creek can not be considered to have been extremely rich. 
 
 The gravels below the basalt. The basalt along Moore Creek is 
 found to rest on stream gravels accumulated in the bed before the 
 molten flow poured down the valley. The old channel is sometimes 
 
LINDQEEN.] GRAVELS OF LOWER MOORE CREEK VALLEY. 659 
 
 preserved on the east side of the creek, sometimes on the west side, 
 which makes it necessary to well establish the course of the channel 
 before commencing extensive work. The old gravel is found at ele- 
 vations of from 25 to 75 feet above the creek, and has been exposed 
 by a number of tunnels. The gold is fairly coarse, the particles 
 being about the size of mustard seeds, but it can not be said that 
 these old placers have been shown to be very rich. They have not 
 as yet been extensively worked. At a place 1 mile above Half Way 
 House, on the east side of the creek, 6 feet of granitic gravel, covered 
 by 3 feet of sand, is exposed below 30 feet of basalt. One-half mile 
 farther up the old channel is well exposed by two tunnels on the 
 western side of the creek. The old bed rock lies 25 feet above the 
 stream, and the deposit has been developed by 175 feet of tunnels. 
 Above the bed rock lies 8 feet of coarse gravel with a streak of sand 
 in the middle; 70 feet of solid basalt covers this. The gravel is 
 reported to contain about 65 cents per cubic yard. As the gravel is 
 not extremely compact, and as the basalt forms an excellent roof, it 
 might be possible to profitably exploit many of these small stretches 
 of old channels by underground hydraulic operations. 
 
 High gravels. Though the lower part of Moore Creek has not been 
 thoroughly examined, it has been shown that gravels exist on some of 
 the high ridges within this drainage. The study of these high gravels, 
 which are probably of Tertiary age, is of the highest importance, as 
 it enables us to trace more fully the geological history of the region. 
 The largest of these high gravels was found on the summit of a high 
 and narrow ridge between the two forks of Thorn Creek, at an eleva- 
 tion of 4,500 feet. This deposit, which consists of extremely well- 
 washed gravel of granitic and quartzose character, has been worked 
 to some extent by the hydraulic process and found to contain gold in 
 paying quantities. The extent from east to west is only a few hundred 
 feet. The depth of gravel is probably considerable, although difficult 
 to estimate on account of slides on the steep slopes. Small patches of 
 gravel are also reported to exist on the neighboring ridges. It is 
 probable that during the highest stand of the Neocene lake which 
 occupied the whole lower basin of the Snake River gravel deposits 
 filled the upper parts of Moore Creek and the Boise River. The 
 occurrence of this high gravel will be discussed again later in con- 
 nection with the geological history of the Idaho Basin. 
 
 UPPER MOORE CREEK VALLEY. 
 
 Configuration of the valley. Five miles below Idaho City the form 
 of the valley suddenty changes. From a level bottom the slopes rise 
 gradually, numerous creeks branch, and the whole forms a broad, 
 basin-like depression. The general character is well shown in PL 
 XCIII, looking southwest from Idaho City. Three miles above Idaho 
 City a narrow canyon begins again. Seen from some elevation, the 
 
6 GO IDAHO MINING DISTRICTS. 
 
 three most impressive topographic features are (1) the broad valley; 
 (2) the level ridges between Idaho City and Centerville, between Elk 
 Creek and Moore Creek, and between Granite and Bannock gulches, 
 rising to an elevation of 1,000 feet above the valley; and (3) the 
 encircling rim of high, deeply dissected peaks and ridges, attaining 
 a height of 2,000 or 3,000 feet above the valley. 
 
 The present stream gravels. The alluvial gravels filling the bed 
 of the present stream form broad flats, over which the water course 
 meander's in changing channels. The largest part of these gravels is 
 debris from the hydraulic mining operations carried on in the bench 
 gravels and the high gravels. The width of the tailings below Idaho 
 City reaches 1,000 feet. In two places the channel contracts between 
 low, projecting hills. At Idaho City the maximum width is reached; 
 here the tailings are about 2,000 feet wide, contracting again to a nar- 
 row channel 1 miles above the city. Two and one-half miles above 
 the same place a comparatively narrow canyon begins, and the tail- 
 ings are only up to 200 feet wide. The tailings cover the imperfectly 
 washed original creek bed, and in many places also the first (lowest) 
 terrace or bench. At Warm Springs they are reported to be 15 feet 
 deep; at Idaho City as much as 40 feet. They consist chiefly of 
 granitic and porphyritic pebbles, with much sand. By a natural proc- 
 ess the gold in the tailings is gradually concentrated. At some time 
 the whole creek bed will probably be washed over again to recover 
 this gold and to reach the older bottom gravels, which are supposed 
 to be rich in many places. Probably the only way in which this can 
 be profitably done is by means of hydraulic elevators or dredges. 
 
 The stream gravels were most extensively worked in early days. 
 Moore Creek was very rich up to the mouth of Gambrinus Gulch, 
 though gravels have been washed still higher up. The gulches enter- 
 ing from the south, as a rule, paid only for a short distance from 
 the main creek; their upper courses were nearly barren. On the 
 northern side, Gambrinus and Illinois gulches were extremely rich. 
 Bear Gulch has also been worked extensively. The bottom of Elk 
 Creek in its upper course is generally narrow, but was rich up to 
 Boulder mine; 2 miles below Boulder mine the creek bottom widens 
 to 200 feet, and placer diggings were being operated in 1896. Deer 
 Creek, heading at Summit mine, yielded very heavily, the output of 
 the half mile near the summit being placed at $90,000. Wolf Creek 
 has been worked, but was not so rich. Spanish Creek was also 
 worked, and near its head lies a flat, one-eighth mile wide and one- 
 half mile long, covered by 12 feet of angular wash, which has been 
 extensively worked, the gold being probably derived from small 
 seams or from a gold-quartz vein not yet discovered. 
 
 The gulches entering from the north and south below Idaho City 
 were generally barren beyond the extent of the terraces. 
 
 Bench gravels. Where the broad valley opens, 6 miles below Idaho 
 
LINDGKEN.] 
 
 GRAVELS OF UPPER MOORE CREEK VALLEY. 
 
 661 
 
 City, a series of shelf-like terraces, entirely absent farther down, 
 begin to appear. The width is only a few hundred feet, and rarely 
 are longer stretches of them preserved, each little creek and gully 
 usually cutting the terrace in two. For the first 4 miles most of the 
 gravel patches lie on the northern side of the valley. At least twp 
 terraces may here be recognized, the bed rock of the lower one being 
 50 and of the upper about 10O feet above the creek. The depth of 
 the gravel is seldom over 30 feet, though near the bed-rock slopes 
 much debris has slid down over the gravel. All of these gravel 
 patches have been very rich, and work is still in progress on some of 
 them. The bed rock, as far up as 1 mile below Warm Springs, is 
 granite or granite-porphyry. 
 
 Above Warm Springs the gravel terraces or benches are very pro- 
 nounced and often form continuous streaks of considerable length. 
 The best exposures are found at Turner's claim, 1 mile below Idaho 
 City, on the road to Warm Springs. At this place the gravel ter- 
 races occupy a total width of one-half mile, and rest partly on gran- 
 
 Moore Creek 
 TatfJngs 
 
 Horizontal Sc&te. 
 
 IOOO 
 
 Feel- 
 
 Vei-rlcal Scale. 
 
 ) IOO ZOO 300 
 
 feel- 
 
 FIG. 55. Gravel benches 1} miles below Idaho City. 
 
 ite, partly on Tertiary lake beds, gently inclined westward. Fig. 55 
 shows a profile of the different terraces here exposed. The highest 
 terrace is found at an elevation of 80 feet above the creek bed. 
 Below this there are three others, and possibly four, at intervals of 
 15 and 30 feet. The lowest terrace is said to be covered by the tail- 
 ings. These gravels have been very extensively washed, but a con- 
 siderable amount still remains. The upper terrace, illustrated in 
 fig. 56, is covered by 8 to 12 feet of well-washed gravel, chiefly gra- 
 nitic in character. This contains the largest part of the gold, and 
 rests on the eroded surface of the soft lake beds. This pay gravel 
 is again covered by 12 feet of fine sandy or clayey sediments with 
 occasional carbonaceous seams. In this there is but little gold. On 
 top rests 8 feet of angular surface gravel, washed down from the 
 adjoining hillside. This gravel is barren. The gravel terrace extends 
 in a northeasterly direction along Elk Creek, and is chiefly developed 
 on the western side. The continuous bodies give way to isolated 
 patches, and 2 miles above Idaho City Elk Creek passes into a nar- 
 row canyon. In Idaho City gravel terraces are noted surrounding a 
 
662 
 
 IDAHO MINING DISTK1CTS. 
 
 high body of older gravel called East Hill. A part of this terrace, 
 on which the town stands, has not yet been mined. Opposite Idaho 
 City, and in fact all along the southern side of Moore Creek up to 
 the mouth of Granite Creek, the gravel benches are more or less con- 
 tinuous. The lowest is noted 20 feet above the creek and higher 
 ones are at 50 and 100 feet. Small benches occur on the north side 
 of Moore Creek east of Idaho City. At least three different benches 
 may be recognized at the elevations noted. Most of these bench 
 gravels near Idaho City rest on lake beds of sandy or gravelly char- 
 acter, usually referred to by the miners as ' ' false bed rock. " 
 
 All the small patches of gravel terraces have been extensively 
 washed and are not yet quite exhausted. The thickness of the gravel 
 rarely exceeds 25 feet. 
 
 Above the mouth of Granite Creek, Moore Creek enters a canyon, 
 along which there are but small indications of gravel terraces. At 
 Plowman's sawmill the creek widens somewhat, and from here up 
 the bottom is generally occu- 
 pied by a flat 100 to 300 feet 
 wide, the surface of which is 
 10 to 20 feet above the creek. 
 Upon the sides are occasional 
 benches at an approximate 
 height of 50 feet above the 
 creek. All these low terraces 
 have been washed as high up 
 as the mouth of Gambrinus 
 Gulch, and from the evidence 
 of the old washings it is clear . 
 
 FIG. 56. Section of highest bench, 1J miles below 
 
 that most of the gold came Idaho city. 
 
 down from this gulch. Above 
 
 Gambrinus Gulch the washings are less extensive, and some of the 
 low gravel flats have never been worked, being evidently too poor. 
 Two miles above Idaho City, as stated above, Elk Creek enters a nar- 
 row canyon, and although this widens somewhat farther up, still 
 there are only occasional patches of gravel terraces remaining, at 
 elevations of about 50 feet above the creek. The manner of mining 
 the bench gravels by the hydraulic process is shown on PI. XCIV. 
 
 High gravels. There are several bodies of gravel in the vicinity of 
 Idaho City which in their occurrence differ from the ordinary bench 
 gravels, and which are generally at high elevations above the creeks. 
 While these also are probably former terraces of the valley of Moore 
 Creek, they are much older, and it seems desirable to treat them 
 separately. 
 
 The slope opposite Idaho City is occupied up to 400 feet above the 
 creek by soft lake beds cut up into sharp ridges separated by deep 
 and narrow ravines. The gently sloping tops of these ridges are 
 
 8 r&eh Angular 
 Surface Gravel. 
 
LINUGREN.] 
 
 GRAVELS OF MOORE CREEK VALLEY. 
 
 663 
 
 covered by auriferous gravels which have 
 a thickness of 60 feet or less. The base 
 of these gravels lies, at Barker's claim, 300 
 feet above Moore Creek. This gravel shows 
 excellent fluviatile stratification, and appears 
 to rest in a flat channel eroded in the lake 
 beds. The gravel consists of well-washed 
 granite pebbles, accompanied by some of 
 quartz. Bowlders 2 feet in diameter occur 
 occasionally. This gravel is quite rich, the 
 best pay being found, as usual, on the bed 
 rock, i. e., on the soft lake beds, but there is 
 also gold distributed through the gravel. 
 The gravel and gold has also, of course, slid 
 down the steep hillside, and this material 
 covering the slopes has been washed. Dur- 
 ing the summer of 1896 the claim of Mr. 
 Barker, 1 mile southeast of Idaho City, was 
 worked by the hydraulic process. The pay 
 gravel does not extend southward beyond 
 the lake beds. In these high gravels there 
 occur- somewhat abundant large cobbles up 
 to 1 foot in diameter of quartz stained brown- 
 ish, and which are often rich in gold, one 
 bowlder sometimes yielding $20. The source 
 of this quartz is not known. It certainly does 
 not come from the high hills to the south. 
 Fig. 57 shows the general relations of the 
 high gravels at Idaho City. 
 
 Another important bodj^of the high gravels 
 is found on the hill immediately east of Idaho 
 City. The gravel , which reaches a total depth 
 of 100 feet, forms a body about 2,000 feet long 
 and 1,000 feet wide. It rests throughout on 
 clayey and sandy lake beds, dipping gently 
 westward at an angle of 10. Seen from the 
 south side of the creek, the stratification 
 planes in the gravel appear to have a decided 
 dip westward, amounting to 4, or a little less 
 than the underlying rocks. The gravel rests 
 remarkably evenly on the. lake beds, with 
 but little sign of unconformity. The geolog- 
 ical section in fig. 57 illustrates the occur- 
 rence, while PI. XCV shows the gravel bank 
 and underlying lake bed in Plowman's claim. 
 A marked fluviatile stratification is often 
 
 ^v^- 
 
 1f 
 
 1*1 
 
 ^> 
 
 a 
 
 ? i 
 
 <: 2 
 
 t 
 $] -3 
 
664 IDAHO MINING DISTRICTS. 
 
 visible. The gravel is medium coarse and is made up chiefly of gran- 
 itic bowlders with occasional pebbles of quartz. By tracing this area 
 around, it is found that the bed rock rises gently, being at the 
 eastern end at least 200 feet above the creek. At the western end the 
 exposures are not so good, as tailings and bench gravels lie up against 
 the higher gravels and the underlying beds are not here visible. The 
 gravel on East Hill, as this area is called, has been worked by the 
 hydraulic process for a number of years, and the claim is reported 
 to have produced from $10,000 to $20,000 a year. The largest part of 
 the gold is found resting on the soft bed rock. The upper part of the 
 gravel also contains some gold, but probably not more than about 5 
 cents per cubic yard. The gold is fairly coarse, and has a value of 
 $16.50 an ounce before melting. On the surface of the gravel the gold 
 appears to be more abundant, which is probably caused by a gradual 
 concentration by atmospheric agencies. 
 
 Another large body of gravel is that known as Gold Hill (fig. 57), 
 occupying about 160 acres and situated on the point between the creek 
 and Bear Gulch. The top of this gravel body is 350 feet above Idaho 
 City, and its greatest depth is probably not less than 200 feet. Along 
 Elk Creek and Bear Gulch the gravel rests on the same soft lake beds 
 which crop out on East Hill. Toward the southwest tailings lie up 
 against it. On the northeast side, on the other hand, the gravel rests 
 directly on granite bed rock. Here also the dip of the gravel beds is 
 about 4, while that of the lake beds is 10 W. Good exposures, made 
 by hydraulic mining, are seen on the southwest side. One-fourth 
 mile north of Idaho City the surface of the soft lake beds lies 20 feet 
 above the creek. Above the lake beds lies 15 feet of coarse heavy 
 gravel with many subangular fragments. Above this is 10 feet of 
 sand with clay streaks, sometimes a little coaly, and somewhat 
 resembling the lake beds. Capping this sand is ordinary well- washed 
 gravel. Here, as in the other gravel bodies, the largest pay was 
 found on the surface of the bed rock that is, on the surface of the 
 lake beds and this rich bottom stratum has been mined by the drift- 
 ing process both on the southeast and our the southwest side. A large 
 body of gravel here remains, which can be worked by the hydraulic 
 process, although it is probably of low grade. Owing to some diffi- 
 culty in procuring water, the claims on this hill have not yet been 
 extensively worked. 
 
 On the ridges above these deposits no other gravel masses have been 
 found, but a small body rests on a sidehill to the east of Elk Creek, 3 
 miles northeast of Idaho City, at an elevation of about 200 feet above 
 the creek. On the western side of Elk Creek, opposite Idaho City, 
 small patches of gravel are occasionally found 200 feet above the 
 creek level, and scattered pebbles occur in many places at about this 
 elevation. Still another body of high gravel is that found on the 
 point between Granite Creek and Moore Creek, east of Idaho City. 
 
L1NDGKEM.] 
 
 LAKE BEDS OF MOORE CREEK VALLEY. 
 
 665 
 
 It forms a bench-like deposit 175 feet above the creek, and the larger 
 part of it has been worked by the hydraulic process. 
 
 Lake beds. Near Idaho City, on both sides of Moore Creek, a con- 
 siderable area is covered by soft sedimentary beds of clay, sand, and 
 gravel. These do not bear evidence of being river deposits. The 
 regular stratification and their general character indicate that they 
 have been deposited in a body of water, in all probability a fresh- 
 water lake. These beds do not contain any notable amount of gold, 
 but the fluviatile auriferous gravels just described are deposited on 
 their eroded surface. The dip of the beds proves that that they have 
 been disturbed since their deposition. Recognizing their sedimentary 
 nature, the miners call these lake beds "false bed rock." The lake 
 beds are first met with 1 mile below Warm Springs, where they appear 
 as semiconsolidated white sand and clays. Near Warm Springs they 
 assume the form of coarse yellowish sandstones, evidently cemented 
 by the opaline silica of the hot waters. In fact, sandstone cemented 
 
 Auriferovs Gravel pa rHy washed off 
 
 
 FIG. 58. Exposure of lake beds and auriferous gravel 1J- miles south of Idaho City. Top of 
 gravel, 400 feet above Idaho City. 
 
 by fire opal has been collected on both sides of the creek, and the 
 occurrence is mentioned by Mr. S. F. Emmons. 1 Owing to the very 
 coarse character and rapid accumulation of the debris the stratifica- 
 tion is poorly preserved. Half a mile below the hot springs these sand- 
 stories form a bluff 300 feet high, and also extend east of the road, 
 producing a relatively narrow passage for the creek. A slide has 
 taken place near the creek, covering an older channel, the bed rock of 
 which lies only a few feet above the present creek and which has 
 been mined by several tunnels. At Turner's claim the lake beds form 
 the bed rock and are well exposed. They dip 5 NW. and consist of 
 soft sand and clay with occasional coaly layers. The clay encloses 
 nodules of iron pyrite containing some gold and silver. 
 
 Near Turner's claim a projecting spur of granite reaches to within 
 a few hundred feet of the road, and in the hydraulic cuts the lake 
 beds are seen to rest on it. Between Turner's claim and the citv the 
 
 1 Boise Statesman, March 29, 1896. 
 
666 IDAHO MINING DISTRICTS. 
 
 lake beds are not exposed, but the gravel of the terraces is reported 
 to rest on them. Across Elk Creek from Gold Hill sandy and clayey 
 lake beds again appear, the bench gravels resting on their eroded 
 surface. Granite appears a short distance up on the hillside. 
 
 Around East Hill and Gold Hill the lake beds are well exposed, and 
 consist largely of greenish or gray clay with arenaceous streaks and 
 intercalated beds of black clay with coaly streaks. The dip is 10 W. 
 A few fossil plants were found here, which were identified by Mr. 
 Knowlton. (See Appendix, p. 721.) 
 
 These plants identify the lake beds with the Payette formation of 
 the foothills, a correlation which the field work had shown to be very 
 probable. Considerable masses of fossil wood are reported to have 
 been found in the lake beds at the mouth of Steamboat Gulch, 1 mile 
 southeast of Idaho City. 
 
 The lake beds attain their greatest development south of Idaho City, 
 where they are more than 300 feet thick. Their character is here 
 prevailingly sandy, with some medium-coarse gravels and with occa- 
 sional coaly and clayey layers. The exposure illustrated in fig. 58 
 
 FJO. 59. Bench gravel and lake beds at mouth of Granite Creek, 2 miles west of Idaho City. 
 
 indicates an apparent unconformity in the lake beds. They continue 
 up the creek, decreasing in width, to the mouth of Granite Creek. 
 Good exposures are seen at Brockhausen and Spiro's claim, between 
 Granite and Bannock creeks, where the bench gravels rest on them. 
 Fine gravels here appear in the lake beds, interstratified with clay and 
 sand. At the little bench just south of the mouth of Granite Creek, 
 12 feet of lake beds, dipping 4 W., at first gravelly, then sandy, rest 
 on granite, and on the eroded surface of the lake beds rests a patch 
 of bench gravel 50 feet above the main creek. A few quartz pebbles 
 are present in the gravel of the lake beds (fig. 59). 
 
 A small area of clayey lake beds is said to exist on the high plateau 
 several hundred feet above Moore Creek and about 2 miles east- 
 southeast of the mouth of Granite Creek. 
 
 The contacts of the lake beds with the granite offer points of great 
 interest. It has already been noted that lake beds rest on granite 
 near Turner's claim, at the east end of Gold Hill, and at the mouth of 
 Granite Creek. Everything indicates that they were laid down on an 
 uneven surface, and probably in a valley with configuration similar 
 to that of the present Moore Creek Basin. But at many other places 
 
LAKE BEDS OF MOORE CREEK VALLEY. 607 
 
 it is clear that the lake beds are separated from the granite by 
 normal faults. One mile below Warm Springs, on both sides of 
 Moore Creek, there is evidence that the lake beds abut directly 
 against the granite. The same relation is noted at the sandstone 
 bluff, 300 feet high, back of Warm Springs. Here the almost hori- 
 zontal lake beds abut against a steep granite bluff, and a little lateral 
 valley has formed along the contact. There can hardly be any doubt 
 that this steep bluff represents a fault-scarp. The deeply incised 
 gulch just southward gives similar testimony as to the sharp abut- 
 ment of the two formations against each other. 
 
 A small hot spring is located at a point on this fault, and the large 
 warm springs probably also issue from this fault, though at present 
 they break out through the sandstone a little below it. The water 
 has a very high temperature, and the total quantity is probably not 
 less than 100 miner's inches. The water is not rich in dissolved salts, 
 but has a slight smell of sulphureted hydrogen. Mr. J. B. Hastings * 
 thinks that this fault and the accompanying slipping down of this 
 mass of conglomerate or sandstone caused the damming of a lake and 
 the deposition of the lake beds. This can not be accepted as a cor- 
 rect explanation, for the sandstone is of the same age as the lake 
 beds, the deposition of which was caused by events much farther 
 reaching than a landslide. 
 
 All along the southern contact line of lake beds and granite, from 
 Moore Creek below Warm Springs to beyond Bannock Creek, the 
 evidence of a fault is very decided. Nearly everywhere along this 
 line the lake beds cease suddenly, and south of them the granite rises 
 in a steep bluff, contrasting strongly with the confused topography of 
 the soft and sliding lake beds. The best evidence is found at the 
 contact back of Barker's claim, where the contact plane between 
 granite and lake beds is found to dip at an angle of 45 N. A similar 
 and extremely well-exposed fault is shown on both sides of Elk Creek 
 at the northern end of Gold Hill at the mouth of Lincoln Gulch. 
 
 In conclusion, the lake beds of the Payette formation in the Moore 
 Creek basin form an area of about 7 square miles; they dip west or 
 northwest at angles of from 4 to 14, and they are often separated from 
 the granite by marginal faults. They are probably a remnant of a 
 more extensive area preserved by reason of being sunk in the granite 
 by movement along these faults. 
 
 A total thickness of from 300 to 400 feet is exposed above Moore 
 Creek. The idea that rich gold gravel would be found below the lake 
 beds led in 1894 to the sinking of a shaft and bore hole at Idaho City, 
 only about 20 feet above the level of Moore Creek. One hundred feet 
 of shaft were sunk, and then, when the water became too difficult to 
 handle, a bore hole continued down to a total depth of 516 feet. It is 
 
 reported that granitic bed rock was struck at that depth. Samples 
 
 ; 
 
 1 Eng. and Min. Jour., July 21, 1894 
 
668 IDAHO MINING DISTRICTS. 
 
 of boring show mainly granitic sand and clay, with nodules of iron 
 pyrite occurring at frequent intervals. The total thickness of the 
 lake beds would, then, be not less than 850 feet. A few miners'-inches 
 of saline water flowed from the well, as might indeed be expected, for 
 the geological conditions are such that a typical artesian basin is 
 formed. 
 
 Gold in tine lake beds. It is stated that no gold is contained in the 
 lake beds or the false bed rock. This certainly seems, at first glance, 
 to be a strange state of affairs, considering that the sands, clays, 
 and gravels of the lake beds consist of practically the same material 
 as the auriferous gravels. It would seem, to imply^ that the quartz 
 veins from which the gold was derived were formed between the period 
 of the lake beds and that of the gravels. It will be shown, however, 
 that the lake beds are not entirely void of gold. Those just south of 
 the mouth of Granite Creek, shown in fig. 59, were prospected with the 
 pan. In the lowest bed, consisting of coarse gravel with much sand, 
 nothing was found; but 6 feet above the granite, in a finer gravel 
 admixed with some quartz pebbles, several colors were found in every 
 pan. The gold is extremely fine and of a rather pale color. There is 
 very little black sand in this gravel, but a considerable quantity of 
 monazite. The samples were taken under conditions that made it 
 impossible for any of this gold to have been derived from the rich 
 gravel above. Mr. Brockhausen informed me that in a claim one-half 
 mile below the mouth of Granite Creek a considerable amount of gold 
 was taken out of a bed of gravel dipping below the false bed rock. 
 
 At the mouth of Noble Gulch, opposite Idaho City, there is a bed 
 of gravel a few feet thick dipping below strata of carbonaceous clay. 
 This gravel has been worked and is reported to have yielded some 
 gold. Mr. Barker informs me that a little gold may occur in the 
 gravels of the lake beds wherever quartz pebbles are present. Mr. 
 Kramer, who owns a claim one-half mile below Warm Springs, states 
 that John Wood, former owner of the claim, obtained good prospects 
 in a bed of gravel dipping under the false bed re k at that place. The 
 locality is now covered up. Mr. Turner states that nodules of pyrite, 
 containing a few dollars in gold and silver, are often found in the 
 false bed rock. During the sinking of the artesian well at Idaho City 
 certain strata were found to contain much iron pyrite, which upon 
 being washed out and assayed was found to carry as much as $12 per 
 ton in gold and silver. 
 
 It is conceded, however, that these occurrences of pyrite do not 
 necessarily indicate an original content of gold in the lake beds, as 
 the precious metals may have been leached from the overlying rich 
 gravels and deposited with the pyrite below. 
 
 It is thus certain that free gold occurs in some of the gravel of the 
 lake beds. That there could not be much of it present is clear from 
 the mode of formation of the lake beds, for they were deposited by 
 
LINDOREX.] ROCKS OF MOORE CREEK VALLEY. 6G9 
 
 rapid accumulation in a body of water affording no opportunity for 
 concentration. Moreover, the detritus was mostly derived from the 
 immediately surrounding hills, which are nearly barren of mineral 
 veins, while the overlying gravels were transported, concentrated, 
 and assorted by streams coming from the region of auriferous quartz 
 veins. It is probable that a system of streams existed before the lake 
 beds were laid down. It would naturally be expected that many of 
 these should carry gold, and it is indeed probable that if the lake beds 
 were removed we should find auriferous gravels on the bed rock along 
 these lines of old stream courses. But it is extremely unlikely that a 
 random bore hole would strike any of these deposits. They could be 
 found only by prospecting along the margin of the lake beds and fol- 
 lowing down any rich stratum that might be found. In this case, 
 however, the cost and difficulties of mining would be very great. 
 
 Olivine-basalt (dolerite). One mile above Idaho City, on the north 
 side of Moore Creek, there are peculiar outcrops of a black or dark- 
 green very tough rock, weathering in rounded outcrops, which are 
 commonly referred to as "nigger heads." Decomposing, they yield 
 a dark-red, yellow, or green clayey soil. Gravel benches rest upon 
 this rock, which apparently forms an intercalated bed up to 100 feet 
 thick in the lake beds. The sheet lies flat at the point indicated, 
 crosses Moore Creek in a narrow strait 2 miles above the city, and 
 then, probably being tilted, rises to elevations of 400 feet above the 
 creek near Pine Gulch. Here it is evidently separated by a fault 
 from the granite. The same rock is found again in nearly every one 
 of the small gulches entering Moore Creek opposite Idaho City, and 
 here it is covered by a considerable thickness of lake beds and is 
 exposed only in the bottom. It is a medium-grained, dark-green 
 rock, with abundant scattered crystals of greenish-yellow olivine. 
 Under the microscope it is seen to be a coarse olivine-basalt (dolerite), 
 and to consist of large phenocrysts of olivine and small crystals of 
 magnetite as the earliest product of consolidation. There is, further, 
 a large amount of violet-brown augite in large anhedral individuals, 
 forming a sort of base, in which are embedded the irregularly distrib- 
 uted laths of a basic feldspar (labradorite). The olivine decomposes 
 to brownish-red products, also to serpentine; the augite to chlorite, 
 with beautiful radial structure. The structure of the rock is really 
 that of a diabase. This rock was evidently poured out on the surface 
 as a lava at the time of deposition of the lake beds. 
 
 THE VALLEY OF GRIMES CREEK. 
 
 Configuration. Four miles below Centerville the canyon widens to 
 a broad valley with gentle slopes, similar to that of Moore Creek, 
 extending in an east-northeasterly direction for 11 miles. Above this 
 Grimes Creek makes a sudden bend, and, separated only by a low 
 ridge from the deep canyon of the Payette River, finally reaches its 
 
670 IDAHO MINING DISTRICTS. 
 
 headwaters at Summit Flat. Only two tributaries join it Clear 
 Creek, heading in the rugged mountains near Wilson Peak, and 
 Muddy Creek, heading a few miles northwest of Pioneerville. 
 
 Present stream gravels. A large amount of tailings lies nearly all 
 along Grimes Creek. At Centerville they are 900 feet wide ; farther 
 up they narrow considerably, where the hills approach closer to the 
 creek, to widen again near Pioneerville; above this place the creek 
 enters a rather narrow canyon. A great mass of tailings also lies in 
 Muddy Creek. Clear Creek has never been washed, and the original 
 wide alluvial grassy flats are here preserved in the lower course of 
 the creek. Concerning the gold content of these tailings, the same 
 remarks apply here which were made in relation to those of Moore 
 Creek. They can doubtless be worked profitably in many places by 
 means of hydraulic elevators or dredges. The difficulty is to obtain 
 a sufficient water supply. The beds of Grimes Creek and Muddy Creek 
 are reported to have been rich throughout, while Clear Creek did not 
 pay well. Only a few of the side gulches contained gold in paying 
 quantities. Willow Creek was rich, and contained near its head a body 
 of angular gravel, known as Channel's claim, which has yielded much 
 gold. Henry Creek, leading up to Summit mine, was also rich. The 
 bulk of the gold appears to have come down from the headwaters of 
 Grimes and Muddy Creeks. 
 
 The tailings are very sandy, being composed of almost 60 per cent 
 sand and 40 per cent cobbles, and the maximum depth is 15 to 20 feet. 
 The lower part of the tailings and benches of Grimes Creek, up to 3 
 miles below Centerville, is owned by the Grimes Creek Bed Rock 
 Flume Company ; the upper part, as far as several miles above Pio- 
 neerville, by the Wilson Company, which for many years has carried 
 on active operations near Pioneerville. The creek has been worked 
 as far up as the big bend at Grimes Pass, where the gravel is charac- 
 terized by a great many heavy bowlders of porphyrite. Many similar 
 cobbles of porphyries also occur farther down on Muddy and Grimes 
 creeks. Pebbles of obsidian have been found on Muddy Creek. 
 
 Bench gravels. As along Moore Creek, gravel benches occur at 
 different elevations all along Grimes Creek. The two most prominent 
 benches are at elevations of 30 and 60 feet above the present creek 
 bed, but scattered gravel occurs at higher elevations also. Such is 
 the thin gravel occurring near Centerville up to 150 feet above the 
 creek. These bench gravels have been very extensively worked, and 
 but little remains of them near Centerville. A short distance above 
 Centerville, at a place called Bummer Hill, they were of unusual 
 richness. Above the narrow canyon the bench gravels appear again 
 in the open valley; where Muddy, Clear, and Grimes creeks join the 
 same kind of benches are noted and hydraulic work has been actively 
 prosecuted. Pioneerville is situated on the lower bench, 25 feet 
 above the creek. A low bench gravel, one-half mile above town, 
 
LINUGUEN.] 
 
 DEPOSITS IN GRIMES CREEK VALLEY. 
 
 671 
 
 ! Sand and Gravel 
 
 Fine Gravel 
 
 worked in 1896, is illustrated in fig. 60. The bed rock is at the creek 
 level, and the work was done by means of hydraulic elevators, which 
 have been extensively utilized by this company. The gold, which is 
 generally of the size of mustard seeds, lies often on the higher bed 
 rock instead of in the potholes. The lower gravel carries all the gold. 
 
 Older gravels. The low terrace 'separating Muddy and Grimes 
 creeks, one-fourth mile northwest of Pioneerville, and covered by 
 later bench gravels, is partly made up of granite, partly of an older, 
 somewhat cemented, granitic gravel. This belt is only about one- 
 fourth mile wide, and the gravel abuts against the granite on the 
 northern side, showing that it is separated from it by a fault. It is 
 evidently an older gravel sunk down along a fault-line. On the 
 southern side it apparently rests on granite. The same fault is well 
 shown in the creek on the eastern side, one-fourth mile above the 
 town. It is reported that a shaft 100 feet deep was sunk in this gravel 
 some twenty years ago, without reaching the underlying granite. The 
 gravel contains some 
 coarse gold. The side 
 hill immediately east 
 of this fault is wholly 
 composed of granite, 
 but above, on the nar- 
 row ridge separating 
 Grimes and Clear 
 creeks, lies a body of 
 somewhat similar 
 gravel, attaining an 
 elevation of 200 feet 
 above the creek. Gran- 
 ite bed rock is found 120 feet above the creek, and on it rests a 
 bed of coarse gravel containing some gold. Much of this gravel has 
 been worked by the hydraulic process. 
 
 Lake beds. ~No extensive areas of lake beds occur in this vicinity, 
 but in the valley of Muddy Creek, 2 miles north of Pioneerville, a 
 small patch of a rather remarkable deposit is found. For a distance 
 of a mile the creek runs in a narrow canyon, which then opens to a 
 somewhat wider valley. Here lie, chiefly along the western side of 
 the creek, beds of soft white sands, gravels, and clays, with a little 
 lignite. In one place where the stratification could be made out the 
 layers seemed to dip 20 W. This small mass of sedimentary deposit 
 has a lacustrine character, and should probably be correlated with the 
 lake beds of Idaho City; it does not contain any gold, but the surface 
 gravels resting on it are said to have been unusually rich, the softer 
 beds having acted as riffles, catching the gold. On all sides the 
 granite rises rather steeply. At Bummer Hill, one-half mile above 
 Centerville, a granitic sand, which may possibly also belong to this 
 lacustrine series, forms the bed rock. 
 
 FIG. 60. Bank of bench gravels one-fourth mile north of Pio- 
 neerville, level of Grimes Creek. 
 
672 IDAHO MINING DISTRICTS. 
 
 Volcanic rocks. A small dike of andesite occurs a short distance 
 west of Grimes Pass, and fragments of obsidian have been found in 
 Muddy Creek. 
 
 THE VALLEY OF GRANITE CREEK. 
 
 Configuration. Granite Creek, joining Grimes Creek 3 miles below 
 Centerville, extends from this point in a north-northwesterly direction 
 for a distance of 8 miles, heading at the low pass north of Quartz- 
 burg. A number of tributaries join it from east and west, produc- 
 ing, in the middle course of the creek, a large, basin-like depression. 
 North of Granite a narrow canyon begins. Ophir Creek, Boyles 
 Gulch, and Wolf Creek head at the relatively low divide toward the 
 Payette drainage, while Fall Creek, Trail Creek, and Canyon Creek 
 head in the Boise Ridge and carry a great deal of water. A broad 
 ridge, only 400 feet high, separates Granite Creek and Grimes Creek. 
 
 Present stream gravels. As in the districts already described, the 
 larger part of the present stream gravels consists of tailings. They 
 are one-fourth mile wide at the junction with Grimes Creek, but only 
 a few hundred feet in width from that place to half a mile below the 
 mouth of Ophir Creek. Here they widen and attain a maximum 
 width of 1,500 feet. The tailings also reach far up on Ophir, Boyles, 
 and Wolf creeks, but narrow down to 100 feet or less a short distance 
 above Granite. Along the lower courses of Canyon Creek, Trail 
 Creek, and Clear Creek, as far as 2 or 3 miles above their mouths, are 
 stream gravels and low terraces, attaining in some places a width of 
 1,000 feet. These creeks have yielded scarcely any gold, and their 
 gravels and terraces show well the character of the river courses of 
 the basin before the gold discoveries. Clear Creek was entirely bar- 
 ren in its upper course. A little gold was found in one or two places 
 along the creek which Hawkins toll road follows from Star ranch 
 westward. Canyon Creek has produced a little gold, and Fall Creek 
 a considerable amount. The main creek has been rich from the 
 junction up to Quartzburg, while no gold is found above that town. 
 Ophir, Boyle, and Wolf creeks were very rich up to their headwaters. 
 The east fork of Alder Creek, which flows into the Payette and heads 
 opposite Wolf Creek, has also produced some placer gold. It appears 
 to be the only creek on the Payette side which is auriferous. The 
 gulches running into Ophir Creek from the east have produced 
 scarcely anything. In fact, most of the broad ridge separating Grimes 
 and Ophir creeks is singularly barren. As to the working of the 
 tailings in Granite Creek, the same remarks apply as have been 
 made in the case of the other tailings mentioned above. 
 
 Bench gravels. Benches are found at intervals all along Granite 
 Creek as far up as half a mile above Granite; also for some distance 
 up Ophir Creek, and up Wolf Creek as far as Placerville. There are 
 usually two well-pronounced horizons, the bed rock of the lower one 
 
LINDGREN.] GRAVELS OF GRANITE CREEK. 673 
 
 being 20 to 30 feet above the creeks and that of the higher one at an 
 elevation of 50 feet. Near Granite and Placerville bowlders of por- 
 phyritic rocks are abundant. The benches opposite Granite also con- 
 tain many basaltic bowlders and pebbles, which are probably derived 
 from the basaltic areas high tip on the summits of the Boise Ridge, 
 referred to later. On the broad flood plain of Fall Creek the bench 
 gravels are very extensive, and reach an elevation of 4,380 feet above 
 the sea, or 50 feet above Fall Creek. All of the benches along Granite 
 Creek and its tributaries from the northeast have been worked for 
 gold. 
 
 Older gravels. Near Placerville and Granite are several very inter- 
 esting occurrences of gravels belonging to a stream system which dif- 
 fered considerably from the present one and giving evidence of having 
 undergone disturbances since their deposition. Two small and iso- 
 lated gravel patches occur close together one-fourth mile northwest of 
 Placerville, on Sailor Gulch. Each contains but a few acres. Both 
 have been worked by the hydraulic process. The exposures show a 
 30-foot bank of medium-sized gravel with excellent fluviatile stratifi- 
 cation. The gravel contains a great number of porphyry bowlders 
 similar to the rock cropping near Quartzburg. The granitic bed rock 
 slopes gently westward, and extends down to the present creek. The 
 bed rock is 150 feet above the level of Wolf Creek at Placerville. A 
 small area of similar gravel lies at the same elevation near the Pio- 
 neerville road, 1 mile east-northeast of Placerville. 
 
 Opposite Placerville lies the Ranch Company's claim, which has 
 been extensively washed of late years and has produced much gold. 
 This is a mass of older, compact gravels resting in a channel-like 
 depression, and on which, along the creek, the later bench gravels 
 have accumulated. In the early years this gravel was considered 
 "false bed rock," and it was not generally supposed that it could be 
 profitably worked. The gravel body lies on the ridge separating 
 Boyles Gulch from Wolf Creek, the top of it being one-fourth mile 
 wide and reaching an elevation of 200 feet above the level of the tail- 
 ings at Placerville. It fills a depression or channel, the bed rock ris- 
 ing rapidly northward and southward. The lowest bed rock is exposed 
 in the present diggings, and is at the bank 75 feet above the tailings 
 at Placerville, sloping from there gradually down to the debris-filled 
 stream-bed at the rate of 6 feet per 100 feet. The character of the 
 gravel is shown in fig. 61. The gravels bear every evidence of having 
 been accumulated in a stream of considerable size. They are coarse 
 at the bottom, very well rounded, and contain abundant cobbles of 
 the peculiar altered porphyry occurring near Quartzburg. No basalt 
 bowlders were found. The gold is fine and evenly distributed through 
 the mass of the low r er gravel. On the eastern side of the ridge there 
 are also hydraulic pits, and the deepest bed rock lies 135 feet above 
 the creek bed at Placerville. At this point the channel suddenly 
 18 GEOL, PT 3 43 
 
674 
 
 IDAHO MINING DISTRICTS. 
 
 ceases. Across Ophir Creek the bed rock rises rapidly in all direc- 
 tions, and no possible continuation can be suggested except down the 
 narrow canyon of Ophir Creek. Furthermore, the nature of the peb- 
 bles indicates that the stream came from some point to the northwest, 
 whereas the present grade of the bed rock is in exactly the opposite 
 direction. The conclusion is almost unavoidable that the channel 
 has been cut off by a fault and its grade reversed. 
 
 On the point between Wolf Creek and Boyles Gulch a little of the 
 same compact gravel occurs just at the edge of the tailings. Placer- 
 ville appears to be built on a similar compact gravel, in which narrow 
 benches were cut by the present stream, though just below the town 
 granite bed rock appears at the edge of the tailings. Due southwest 
 of Placerville, on the slope up to the summit of the level ridge between 
 Granite and Wolf Creek, no bed rock appears to have been found. 
 Neither has there been any bed rock found on the opposite slope from 
 this ridge down to Granite Creek. A broad, low bench fringes the 
 northeast side of Granite Creek below Granite. Bed rock has never 
 been found for some distance below Granite in the creek. All this 
 
 appears to indicate 
 
 I 
 
 12 feef, Granite Sand 
 
 8 feeh, C/ay 
 reef', Coarse Gravel 
 
 FIG. 61. Bank at the Ranch Company's claim, Placerville. 
 
 that the Ranch 
 Company's channel 
 continues with grad- 
 ually sinkin'g bed 
 rock across Granite 
 Creek. 
 
 Interesting c o n - 
 ditions also obtain 
 across Granite Creek 
 on the broad flood plain of Fall Creek, where it emerges from the nar- 
 row canyon in the Boise Ridge, here suddenly rising as a steep escarp- 
 ment facing west. This place, called Norwegian Flat, at present 
 worked by the Kennedy Company, is extensively covered with rich 
 bench gravels up to the mouth of the canyon. This bench gravel, which 
 is rarely over 25 feet in thickness, does not rest on granite, but on a 
 harder, more compact gravel, which contains some gold and which is 
 of the same general character as the Ranch Company's gravel. At 
 the upper end of the claim, near the mouth of the canyon and the foot 
 of the escarpment, this "false bed rock" is found to suddenly abut 
 against the granite, strongly suggesting that it is cut off by a fault. 
 No shafts have ever been sunk in this lower gravel. It is probable 
 that it is the same channel continuing across Granite Creek, and that 
 it is cut off at both ends by faulting. On the hills to the right and 
 left of Fall Creek a similar compact gravel also occurs, seemingly con- 
 tinuous with that of the deepest chanuel. Thus the low ridge between 
 Fall and Canyon creeks is covered, up to an elevation of 80 feet above 
 Fall Creek at the upper end of Kennedy's claim, and a similar body 
 
IJNDGEEN.] GRAVEL AND BASALT OF THE BOISE RIDGE. 675 
 
 reaches high up on the ridge between Fall and Granite creeks nearly 
 to the Newburg or Lawyer quartz claim. It is said to be quite rich 
 here, though hard, and difficult to work on that account and because 
 of the scarcity of water. On this ridge the older gravel distinctly 
 rests on the granite, and its thickness reaches a maximum of 200 feet. 
 Its highest elevation on the ridge near this quartz mine is 4,900 feet, 
 or 500 feet above the upper end of Kennedy's claim. 
 
 Gravel on the Boise Ridge. A very remarkable occurrence of 
 gravel was found on the summit of Boise Ridge 3 miles west-north- 
 west of Quartzburg. The broad, flat summit extends northward from 
 Hawkins Pass, with a winding direction, caused by the deeply incised 
 gulches, and an elevation of from 6,500 to 7,300 feet above the sea. 
 North-northwest of Quartzburg lie, on the summit, several hundred 
 feet of scoriaceous basaltic flows, which extend down into Jerusalem 
 Valley on the west. In this basalt there occurs, at an elevation of 
 6,900 feet, one-half mile south of the sharp point, with an elevation 
 of 7,200 feet, a small body of gravel. It could not be determined 
 whether this gravel is intercalated between the basalt beds or forms 
 an inclusion in the same, but the former is more probable. At any 
 rate, the gravel is well washed, of granitic character, and is said to 
 contain some gold. This occurrence is of the greatest interest, as it 
 clearly indicates that a very great disturbance has taken place since 
 the eruption of these basalts, for the gravel could not possibly have 
 been formed with the present topographic features. Considered in 
 connection with the faulted old gravels at the eastern foot of the 
 escarpment, 2,700 feet lower, it points to a great disturbance along 
 the eastern base of the Boise Ridge. 
 
 Basalt. The whole of the high portion of the Boise Ridge south of 
 the latitude of Quartzburg is remarkably free from any late erup- 
 tions. At the locality mentioned in the preceding paragraph, culmi- 
 nating in the hill with an elevation of 7,200 feet north-northwest of 
 Quartzburg, the very even, flat surface of the granitic ridge is capped 
 by 300 feet of massive basalt. Above the massive basalt lie 200 feet 
 of tuff and scoriaceous basalt, again covered by 100 feet of fresh and 
 massive olivine-basalt. These basaltic flows slope rapidly westward, 
 and the ridge on the north side of Brainard Creek is, as seen in PI. 
 LXXXIX, composed of a great number of superimposed thin basaltic 
 flows, all dipping northwest at angles of 30 or 35. The photograph is 
 taken from a gap in the ridge between Brainard and Porter creeks, 3 
 miles west-southwest from the high basalt peak in the Boise Ridge. 
 Taken in connection with the probable fault along the eastern side of 
 the range at Granite, it certainly appears as if a westward tilting had 
 formed part of the orographic movements in this vicinity since the 
 time of the deposition of the lake beds. The basalt is much older 
 than the basalt of the lower Moore Creek, and in all probability is 
 contemporaneous with the lake beds. 
 
676 
 
 IDAHO MINING DISTRICTS. 
 
 Other small basalt areas were noted near Hawkins toll road, 2 miles 
 west of Star Ranch. This basalt forms a dike on the high ridge 
 between the toll road and Clear Creek, follows the road for some dis- 
 tance near longitude 116, and appears again on the ridge north of 
 the road. Here it is in part vesicular, and appears to have flowed out 
 from the dike. This basalt is probably also of Tertiary age. 
 
 FINENESS OF THE GOLD. 
 
 The fineness of the placer gold varies from 770 to 912. The follow- 
 ing list gives the value at some of the principal localities : 
 
 Value and fineness of placer gold at principal localities. 
 
 Locality. 
 
 Value before 
 melting. 
 
 Fineness 
 per mill. 
 
 Idaho City Turner's claim (bench gravels) 
 
 $16. 75 
 
 
 Idaho City, East Hill (high gravels) 
 
 16.50 to 16.75 
 
 
 Idaho City, Barker's claim (high gravels) 
 
 
 850 
 
 Pioneerville (bench gravels) 
 
 15.35 
 
 770 
 
 Placerville, Ranch Company claim (old 
 channel gravel) . 
 
 
 912 
 
 Placerville Granite Creek (bench gravel) 
 
 
 850 
 
 Placerville, Fall Creek 
 
 
 775 
 
 Placerville, Ophir Creek .. . 
 
 
 910 
 
 Placerville, Wolf Creek 
 
 
 910 
 
 
 
 
 WATER SUPPLY. 
 
 The water available for placer work is not abundant; in fact, usu- 
 ally the working season is only from three to four months. The 
 streams are not large and do not head among very high mountains, 
 so that the flood from the melting snows soon subsides. It would be 
 possible, but hardly practicable, to carry a ditch to the basin from 
 the headwaters of the Boise or the Payette. The principal ditches 
 are as follows : 
 
 MOOEE CREEK. 
 
 1. The upper Moore Creek ditch. Takes water from Moore Creek 5 miles above 
 
 Gambrinus Gulch. Capacity, 600 miner's inches. 
 
 2. The Lambing ditch. Dam below Illinois Gulch. Capacity, 350 miner's inches. 
 
 3. The Christie ditch. Dam above mouth of Granite Creek. Capacity 1,100 
 
 miner's inches. These three are on the northwest side of Moore Creek. 
 
 4. Thorn Creek ditch. Takes its water from Thorn Creek, dumping it across the 
 
 divide into Pine Creek; used for the high gravels south of Idaho City. 
 
 5. Channel ditch. Dam on Elk Creek one-half mile above Elkhorn Mill. Capac- 
 
 ity, 600 miner's inches. Covers divide between Elk and Grimes creeks. 
 
 6. Mann's ditch. On south side of Elk Creek. Dam 1 mile above Forest King 
 
 Gulch. Ten miles long. Covers Gold Hill at Idaho City. 
 
LINDQREN.] WATER SUPPLY AND WORKABLE GROUND. 677 
 
 7. Anderson ditch. Takes water from Elk Creek below Boulder mine. 
 
 8. Cuddy ditch. Takes water from Elk Creek below Boulder mine. 
 
 9. Dunn ditch. Takes water from Elk Creek below Boulder mine. 
 
 GRIMES CREEK. 
 
 The water supply is here largely controlled by the Wilson Company. 
 The principal ditches are as follows: 
 
 1. Wilson ditch. 12 miles long, on west side of Grimes Creek. Dam located 1 
 
 mile below Charlotte Gulch. Capacity, 2,000 miner's inches. 
 
 2. Gold Trap ditch. 7 miles long, also on west side of Grimes Creek. 
 
 3. American ditch. 6 miles long, west side of Grimes Creek. Dam at Charlotte 
 
 Gulch. 
 
 4. Mountain ditch. 8 miles long, west side of Grimes Creek. Also two shorter 
 
 ditches from Clear Creek. 
 
 GRANITE CREEK. 
 
 The water supply is here controlled by the Ranch Company and 
 the Kennedy Company. The Ranch Company's ditch is 14 miles long, 
 and takes water from Granite Creek above Quartzburg. Capacity, 
 1 ,000 miner's inches. Other ditches lead from West Fork, Fall Creek, 
 and Canyon Creek. 
 
 The hydraulic washings use a pressure of from 100 to 350 feet. 
 There are rarely more th/in 600 miner's inches used in each monitor. 
 Hydraulic elevators have been used by the Wilson Company to work 
 low-bench gravels and tailings. The gravel is elevated from 10 to 25 
 feet. Five hundred miner's inches are here used for the monitors. 
 
 GROUND AVAILABLE FOR FUTURE WORK. 
 
 The largest amounts of gravel remaining near Idaho City are on 
 East Hill and Gold Hill. Though some of the bench gravels remain 
 they are getting rapidly worked out. In the Grimes Creek drainage, 
 some bench gravels still remain near Pioneerville. In the Granite 
 Creek drainage there is a considerable area of low-bench gravels yet 
 untouched near Granite, on both sides of the creek. Considerable 
 gravel remains at the Ranch Company's ground near Placerville. If 
 the conclusions in this paper are correct, there is also a large amount 
 of gravel on the ridge between Wolf Creek and Graniteville. 
 
 In all three drainage branches there are vast amounts of tailings 
 which, with suitable appliances, may be worked over again. But 
 there is no doubt that the placers in course of time will be exhausted. 
 That they are not already exhausted is due to the limited water 
 
 supply 
 
 THE MONAZITE SANDS. 
 
 The sand of the gravels and lake beds of the Idaho Basin is entirely 
 derived from the granite and associated dike rocks. It consists of 
 relatively angular and sharp-edged grains, indicating its manner of 
 formation by extremely rapid accumulation from ,the deeply disinte- 
 
678 IDAHO MINING DISTRICTS. 
 
 grated rocks. The heavy minerals found in the granite are also 
 found in the sand, and may be easily separated by washing in the 
 miner's pan; they are always deposited in the sluice boxes with the 
 gold. 
 
 In all parts of the basin a yellow or brownish-yellow mineral forms 
 a considerable quantity of the heavy substances remaining with the 
 gold. It is usually referred to as "yellow sand," and is also given the 
 picturesque name of "Bummer Hill sand," from a locality near Cen- 
 terville, where it was particularly abundant, but I am not aware that 
 its true character has ever been investigated. 
 
 The mineral has been shown to be monazite, this being the first 
 time its occurrence has been noted from the Western States. As is 
 well known, it occurs abundantly in the granite and gneissoid rocks 
 and gold-placer mines of the Southern Appalachians, and in several 
 of the North Atlantic States, also in Brazil, the Ural Mountains, and 
 other places. There is no doubt that it forms an original constituent 
 of the granite of the Idaho Basin. 
 
 One of the samples was obtained in washing a few pans of the sandy 
 lake beds occurring as "false bed rock" in a gravel bench at the 
 junction of Moore Creek and Granite Creek, 3 miles east of Idaho 
 City (see fig. 59). The heavy residue consisted largely of small yellow 
 grains and amounted to about 2 grams per pan of 8 kilograms, which 
 would correspond to 0.025 per cent. The microscope revealed the fol- 
 lowing minerals: Ilmenite in sharp hexagonal crystals, but no magne- 
 tite; zircon, also in extremely sharp crystals of a slightly brownish 
 color, and abundant yellow or greenish-yellow grains rarely showing 
 crystallographic faces. The refraction and double refraction of the 
 latter mineral were very high; the hardness not much over 5. The 
 ilmenite was eliminated by the electro-magnet, and the remaining pow- 
 der, containing about 70 per cent of the yellow mineral, was analyzed 
 by Dr. W. F. Hillebrand. The result showed it to be a phosphate of 
 the cerium metals, the approximate amount of the oxides of the latter 
 being 48 per cent; in these approximately 1.20 per cent of thoria was 
 found. This result identifies the mineral with monazite, the only 
 other similar mineral being xenotime, which is mainly a phosphate of 
 yttrium with but little cerium. The samples also contained a con- 
 siderable amount of titanium, which would indicate that some titanite 
 is present. Practically all of the ilmenite was extracted by the 
 magnet. 
 
 Another sample, furnished me by Mr. T. Myer, of Placerville, 
 came from the alluvial gold washings in Wolf Creek, near that town. 
 Cleaned from quartz, etc., it appeared as a heavy dark sand consist- 
 ing of a black iron ore (ilmenite), rounded crystals of red garnet, 
 sharp crystals of zircon, and irregular grains of a dark yellowish- 
 brown mineral with waxy luster, sometimes showing crystallo- 
 graphic faces. It was found impossible to extract more than a small 
 
THE MONAZ1TE SANDS. 679 
 
 part of the iron ore by the magnet. There was practically no magne- 
 tite present. This sand was examined qualitatively by Dr. Hille- 
 brand, who found phosphoric acid, cerium metals, and thorium. The 
 yellowish-brown material is therefore, in all probability, monazite. 
 
 Monazite has, as is well known, a certain economic value, as the 
 oxides of the rare earths contained in it are used for the preparation of 
 the incandescent gaslights of the Welsbach and other burners. A 
 considerable amount of monazite sand has been produced during the 
 last few years in the Southern Atlantic States, chiefly North Caro- 
 lina, and in Brazil. The prices have varied from 3 to 25 cents per 
 pound, according to the purity and the percentage of thoria. The 
 North Carolina monazite contains between 0.17 and 6.20 per cent of 
 this rare earth. Mr. Waldron Shapleigh, chemist for the Welsbach 
 Light Company, kindly gives (March, 1897) the following information 
 in regard to present production and price: 
 
 At present the monazite sand market is very dull; hardly any demand, and only 
 in lots of a few tons. The present price in North Carolina is 6 cents per pound, 
 but it can be bought a little lower than this. Brazilian sand is quoted in New 
 York at 4f cents per pound, fully equal to the North Carolina sand, in 5 or 10 ton 
 lots. Larger orders can be placed in Brazil at a much lower figure. The price 
 has been steadily downward, as the supply from the mines now opened is far 
 greater than the consumption. It is not generally known that during the first 
 eighteen months or two years of this new industry enough sand was mined and 
 purchased by the largest manufacturers to last several years to come, as so far it 
 has but the one use. The manufacturers did not know how extensive the sand 
 deposit was; therefore were desirous of securing a large and safe stock at the start. 
 
 The largest purchasers are the Welsbach Light Company of Vienna, supplying 
 Europe, and the Welsbach Light Company of Philadelphia, which supplies 
 America. I should hardly think that Western localities could compete with 
 North Carolina and Brazil, unless the mineral is of a very superior quality or a 
 by-product. 
 
 At present there would be no difficulty in placing an order for several thousand 
 tons per year in Brazil and having it filled. 
 
 The widespread occurrence of monazite in considerable quantities 
 in the Idaho Basin raises the question whether the deposits can be 
 profitably worked. The present low price and the high cost of trans- 
 portation and labor make this very doubtful, unless it be saved as a 
 by-product in the placer mines. It will be necessary to extract all 
 ilmenite by strong electro-magnets. In this manner a comparatively 
 pure product may be obtained. It is not practicable to entirely sep- 
 arate the zircon and garnet from the monazite. The purest material 
 was obtained from near Idaho City, while that from Placerville and 
 vicinity contains a large amount of ilmenite and garnets. Many data 
 in regard to the character and production of monazite may be found 
 in a paper by Mr. H. B. C. Nitze, in the Sixteenth Annual Report of 
 the United States Geological Survey (1894-95), Part IV, pp. G67-693. 
 
680 IDAHO MINING DISTRICTS. 
 
 RELATION BETWEEN PLACERS AND QUARTZ VEINS. 
 
 The dependence of the gold placers upon the occurrence of gold- 
 quartz veins is very strongly brought out by a study of the occurrences 
 of both. While there are many small quartz seams occurring through- 
 out the granite, some of which may contain a little gold, it is perfectly 
 evident that there are two regions in which quartz- vein deposits are 
 concentrated. These are, first, the Gambrinus mining district, on 
 the ridge between Elk Creek and Moore Creek, continued by the Elk- 
 horn mining district, at the headwaters of Elk Creek; and second, 
 the gold belt extending from the Boise Ridge near Quartzburg to 
 Grimes Pass. Every creek and ravine leading up to these .deposits 
 has been rich, while the watercourses rising in other parts of the 
 range are comparatively barren. It seems clear beyond doubt that 
 most of the gold in the gravels near Idaho City came down the Illinois 
 and Gambrinus gulches; above these Moore Creek becomes compara- 
 tively poor. What gold there is has doubtless been derived from the 
 more distant veins at the very head of Moore Creek, near Summit 
 Flat. In nearly every case an exceptionally rich ravine has been 
 found to lead up to a quartz vein. Thus it is clear that the recently 
 discovered Summit mine, on the ridge between Elk and Grimes creeks, 
 furnished the gold found in Deer Creek and Henry Creek. The only 
 occurrence to which some doubt is attached as to the derivation of 
 the gold is that of the rich angular gravels at the head of Spanish 
 Fork and Willow Creek, but it is probable that they are derived from 
 local seams and veins. 
 
 The headwaters of Grimes Creek furnish a most convincing argu- 
 ment in favor of the derivation of the gold from the quartz belt. 
 Every gulch heading along the line of that belt is rich, while every 
 one not crossing it carries only extremely small quantities of gold. 
 
 The conclusion is that practically all of the placer gold in the dis- 
 trict has been derived from the quartz Veins in these two districts. 
 
 On an average the fineness of the gold in the quartz veins is a little 
 less than that in the placers. This has generally been the experience 
 in most mining districts, and is accounted for by a dissolving of the 
 silver and baser metals from the surface of each grain of gold. The 
 highest grade of quartz gold is found near Quartzburg, and in the 
 gravels of Placerville, derived from the Quartzburg mines, the placer 
 gold is of unusual fineness. 
 
CHAPTER IV. 
 
 THE IDAHO BASIN (CONTINUED). 
 
 THE PRE-TERTIARY ROCKS. 
 GRANITE. 
 
 The Idaho Basin forms a part of the great granite area of the Boise 
 and Payette drainage, and the pre-Tertiary rocks consist exclusively 
 of granite, together with a number of porphyritic dikes, probably 
 intruded shortly after the granitic intrusion. It has been stated 
 before that the age of this granite is unknown. If Archean, as has 
 been supposed, the slight amount of compression and change it has 
 undergone is certainly remarkable. A shearing is often noticeable, 
 dividing the rock into sheets or plates upward of a foot thick. The 
 direction of the shearing varies considerably, and is sometimes paral- 
 lel to the general direction of the quartz vein. In Gambrinus and 
 Sub-Rosa gulches a strike of -N. 20 to 24 W. and a dip of 70 E. or W. 
 were noted. In the Ranch Companj^'s claim at Placerville the sheet- 
 ing is parallel to the direction of the Quartzburg gold belt; strike, N. 
 45 E. ; dip, 60 SE. On Hawkins toll road, on the western slope of 
 the Boise Ridge, the strike is N. 60 to 70 W. and the dip 70 to 80 N. 
 or S. Conjugated systems of shear planes, having the same strike, 
 but dipping in opposite direction, thus occur here. In the depres- 
 sions and low ridges of the basin the granite is disintegrated to con- 
 siderable depth, so that it is very difficult to secure good specimens. 
 The disintegrated granite forms a coarse, yellowish-gray sand, the 
 individual grains of which have undergone but very little decompo- 
 sition, and which is easily swept down into the creeks by the rain 
 storms. Fresher and harder rocks crop out on the high ridge between 
 Elk and Moore creeks, upon which the Forest King and other mines 
 are located. The outcrops form brilliant white rounded masses ; but 
 even here the disintegration has made rapid progress. On the Boise 
 Ridge the granite is ordinarily soft and crumbling. The deepest 
 disintegration is probably found about the head of Muddy and Ophir 
 creeks, where a good outcrop is only rarely seen. The granite area 
 extends northward across the Payette River and far to the north of it. 
 
 The granite has a coarse grain, the average size of the constituents 
 being 3 nim . The reddish orthoclase crystals are often very prominent. 
 
 681 
 
682 IDAHO MINING DISTRICTS. 
 
 The rock is composed of gray quartz, white or reddish feldspar 
 partly orthoclase, partly an acid soda-lirne-feldspar and small biotite 
 flakes, the incipient decomposition of which usually gives the rock a 
 rusty aspect. Hornblende is rarely found. Muscovite often occurs 
 in the more acid varieties. Of accessory constituents, which are best 
 studied by washing the decomposed sandy granite, there are: Ilmen- 
 ite in often perfect crystals (though little or no magnetite appears to 
 be present), apatite, zircon in extremely sharp, slightly brownish 
 crystals, small garnets, titanite, and brownish or yellowish imperfect 
 crystals of monazite. For description of the monazite sands, see pp. 
 677-679. 
 
 DIKES ASSOCIATED WITH THE GRANITE. 
 
 The granite is traversed by 'dikes, which in some places become 
 very numerous and large. Dikes of granite-porphyry and aplite are 
 common, though rarely very long and wide. Many such dikes, to- 
 gether with others of pegmatitic character, occur; for instance, along 
 the road southwest of Idaho City and on the hill, with an elevation of 
 6,200 feet, due south of the town. 
 
 Dark-colored, lamprophyric dike rocks, which generally belong to 
 the minettes, were noted in a few localities. These dikes are, as a 
 rule, narrow, and their occurrence is closely connected with that of 
 the veins. From the Sub-Rosa and Forest King mines dark-gray, fine- 
 granular dike rocks were collected, generally rich in black inica. 
 In thin section the former appears as typical minette, consisting of 
 biotite, augite, magnetite, and orthoclase, with pauidiomorphic struc- 
 ture. The feldspar crystals show a tendency to radial or spherulitic 
 arrangement. A similar minette, consisting of biotite, hornblende, 
 and orthoclase, was collected at the Gold Dollar tunnel, 1,000 feet east 
 of the pass leading from Placerville to Garden Valley. The dikes 
 evidently antedate the veins. 
 
 The Bois"e Ridge south of Quartzburg contains scattered dikes of 
 granite-porphyry and diorite-porphyrite, but near the latter locality 
 begins a very important belt of dikes intimately connected with the 
 Quartzburg belt of gold deposits. The rocks are in all respects simi- 
 lar to those which appear at Willow Creek mining district; the latter 
 may in fact be regarded as the westward extension of the Quartzburg 
 belt, having the same direction and lying in its continuation to the 
 west-southwest, but a distance of 8 miles, barren of mineral deposits 
 and dikes, separates them. The dikes do not follow the mineral 
 deposits in detail and are very irregular, sometimes only a few hun- 
 dred feet wide, then again expanding to a width of over a mile. 
 Owing to unusually deep residuary soil on the divide toward Payette 
 River, the contact of granite and porphyries is generally difficult to 
 trace, and the areal extent indicated on PI. XCVI must be regarded 
 as only approximately correct. 
 
LI.VDGREN.] DIKES ASSOCIATED WITH THE GRANITE. 683 
 
 The porphyry begins at the Mountain Chief and Belzazzar mines, 
 where it occurs as a wide belt extending across the vein and forming 
 a considerable part of the hill to the east of the mines. Large masses 
 of a similar porphyry occur in the lower part of Fall Creek, and it 
 continues eastward toward Quartzburg as a narrowing belt. The 
 rock in this area is a characteristic light-colored hornblende-porphy- 
 rite, consisting of white plagioclase in stout prisms up to l cm long, 
 and idiomorphic hornblende crystals up to 5 ram in length, embedded 
 in a fine-grained groundmass of feldspar, hornblende, and a little 
 quartz. 
 
 At Quartzburg the porphyry belt is only a few hundred feet wide 
 and has undergone great thermal alteration, secondary minerals like 
 pyrite, muscovite, and calcite being abundant. On the Gold Hill 
 mine dump specimens of fairly fresh rocks were collected. Some of 
 them are very similar to the above-described rock. The abundant 
 large white feldspars are labradorite, according to extinction of 
 numerous Carlsbad twins. There is no hornblende left undecom- 
 posed, but there is some light-brown biotite in process of conversion 
 to chlorite. The groundmass is micropoikilitic, consisting of quartz 
 and unstriated feldspar. Another variety, greatly altered, of a yel- 
 lowish color and impregnated with pyrite, is characterized by large 
 corroded quartz crystals, up to l cm in diameter, and large porphy- 
 ritic labradorite, greatly altered by sericitization. The groundmass 
 is fine-granular, probably micropoikilitic, of quartz and feldspar, but 
 now greatly filled with sericite. 
 
 East of Gold Hill the porphyry belt widens considerably. Quartz- 
 burg Hill is composed of quartz-diorite-porphyrite. This rock, similar 
 to that described from the Belzazzar mine, forms the largest part of 
 the area. It crosses Wolf Creek as a wide belt, and is here accom- 
 panied by dikes of more basic rocks. Two miles north of Placerville 
 a dike of norite-gabbro crosses the road and a dike of normal diabase 
 appears in the same vicinity. East of Wolf Creek the area widens 
 still more and reaches its maximum width. At Sweet's Claim, one- 
 half mile west of Grimes Pass, the porphyry is narrower. A specimen 
 from the Northern Star shaft shows the same idiomorphic large feld- 
 spar and hornblende crystals. The former are very fresh and consist 
 of labradorite ; the latter are sharply idiomorphic and partly chlori- 
 tized. The groundmass is microcrystalline allotriomorphic, being 
 made up of quartz and unstriated, clouded feldspar. 
 
 This porphyry belt was not followed east of Grimes Pass, but it is 
 apparent that it attains great development among the high hills rising 
 beyond it. Clear Creek contains a great abundance of porphyiy 
 bowlders. They are practically the same quartz-diorite-porphyrite 
 which is described above. Quartz is evidently always present in the 
 groundmass, and sometimes also as porphyritic crystals. 
 
684 IDAHO MINING DISTRICTS. 
 
 THE QUARTZ VEINS. 
 THE IDAHO CITY GOLD BELT. 
 
 In the immediate vicinity of Idaho City very few quartz veins occur, 
 and none of importance. Mr. Plowman states that a big quartz vein 
 was found on Wallula Flat, 2 miles east of Idaho City, on the northern 
 side of the creek. A narrow streak in this vein carries gold. About 
 1 mile due south of Idaho City the Keystone mine was located on a 
 large but apparently barren vein. 
 
 Six miles northeast of Idaho City, on the ridge between Moore 
 Creek and Elk Creek, is the Gambrinus mining district. 
 
 The Elaine vein is situated on the Moore Creek side of the ridge. 
 The developments are small, though some fair ore has been extracted 
 and milled. There is a 5-stamp mill on the property. 
 
 The Chickahominy vein lies a little higher up on the ridge and a 
 few hundred feet south of the Blame. It was worked in the early 
 days, and a large mill was erected on Moore Creek 4 miles above 
 Idaho City. 
 
 The Illinois vein. This important deposit, which can be traced for 
 If miles, is located three-fourths of a mile above the Blaine, and 
 crosses the ridge at an elevation of 5,100 feet. The vein has an aver- 
 age strike of a few degrees north of west and dips to the south at an 
 angle of from 45 to 50. It is inclosed in granite throughout, though 
 smaller dikes of porphyry occur occasionally in this granite. The 
 vein is one of the strongest in the basin, and it is very clear that it 
 has furnished a large portion of the placer gold in Moore Creek. It 
 contains a great deal of finely distributed gold all along, and some 
 good pay shoots besides. Illinois Gulch, draining this vicinity, is 
 reported to have been extraordinarily rich. 
 
 The Eureka claim lies at the eastern end of the vein. Its production 
 amounts to $30,000, and besides much was taken from surface diggings 
 near the vein. A 10-stamp mill stands on the claim, which has not 
 been worked since about 1880. The vein is a large, composite one, 
 similar to the Illinois, to be described later. At the time of its 
 exploitation an ore shoot in this vein was worked down to a small 
 depth, where it is said to have been lost. The developments are 
 slight, consisting only of a tunnel and a shaft 60 feet deep. 
 
 The Lucky Boy adjoins on the west. The developments consist of 
 only a few prospect holes. The strike is N. 81 W. and the dip 50 S. 
 The exposures show 8 feet of decomposed and sheeted granite, with 
 small quartz seams. Some pay ore is found on the foot wall. Two 
 parallel veins exist, one 30 feet south and the other 200 feet north of 
 the main fissure. 
 
 The Illinois, consisting of two claims, is the principal producer of 
 the vein. It was located in the early days, as it was soon seen that 
 
LINDGEEN.] IDAHO CITY GOLD BELT 685 
 
 the rich placers led up to the vein. The production is stated to be 
 $225,000, which has been chiefly taken out in small batches of very 
 rich ore. Some ore from this claim was crushed in 1895 in the Elaine 
 mill. The deposit is characteristic of many veins in the Idaho Basin. 
 Large masses of quartz are hardly ever seen. The strike is N. 71 W. 
 and the dip 40 S. The vein consists of a wide zone of sheeted and 
 fractured granite, with abundant small quartz seams between the 
 joints of the sheets or ramifying through them. These small quartz 
 seams carry the gold, while the granite between them, though usually 
 altered, soft, and decomposed, contains no pay. This sheeted zone 
 is here 30 to 40 feet wide and contains gold throughout. The princi- 
 pal pay shoot is, however, 400 feet long, and one streak, 2 feet wide, 
 in this pay shoot is particularly rich. The deposit has been sluiced 
 off on the surface and then worked by means of a crosscut tunnel 
 from the gulch. A cross seam, also carrying some gold, joins it in 
 Illinois Gulch, and a parallel vein is also said to exist. The ore is 
 practically all free milling on the surface. Even when sulphurets 
 are met with in depth it is probable that a larger proportion of the 
 gold will remain in free condition. The developments may be said to 
 be very slight and unsatisfactory, but it is probable that if properly 
 opened the vein would furnish great amounts of low-grade ore, which, 
 with suitable and cheap methods of extraction and reduction, might 
 be made to pay. The width of the vein and the soft character of the 
 rock would make mining somewhat expensive and difficult. 
 
 The Chicago claim, on which but a slight amount of development 
 work has been done, adjoins on the west, beginning near the road on 
 the summit of the ridge. 
 
 The Populist vein. This vein is situated 1 mile west-northwest of 
 the Illinois. It has a similar strike and dip, and some work has been 
 done on it recently. 
 
 The Cleveland vein. This relatively small vein is locHted 5 miles 
 north-northwest of Idaho City, on the south side of Forest ,King Gulch, 
 at an elevation of 5,030 feet. It is a single-fissure vein, about 1 to 2 
 feet wide, inclosed in granite, striking a little north of west and dip- 
 ping 60 S. A rich shoot 100 feet long was found on it a few years 
 ago, which yielded a considerable sum of money; it has not been 
 followed below the present tunnel level. The mine is of interest as 
 showing plainly the result of faulting, illustrated in fig. 62. The vein 
 is thrown a distance of GO feet horizontally in the hanging wall. At 
 least two faults of this character are known. If movements in only 
 a vertical direction have taken place, this fault is certainly an over- 
 thrust, the hanging wall having moved up relatively. As, however, 
 lateral movements may also have occurred, it is possible that the 
 present position of the vein may be due to an oblique movement to 
 the southwest, the direction of which makes with the horizontal an 
 angle of between and 60, the hanging wall having moved down 
 
686 
 
 IDAHO MINING DISTRICTS. 
 
 relatively. While this is possible, the probabilities are strongly in 
 favor of an overthrust. 
 
 Tlie Gambrinus (Surprise] vein. This large deposit is situated 5^ 
 miles north-northeast of Idaho City, on the summit of the ridge 
 between Elk and Moore creeks and near the foot of the steep Forest 
 King Hill. The elevation is 5,480 feet. It was discovered in 1864, 
 and the principal work was done between 1864 and 1865. The total 
 production is $263,000. The strike of the vein is N". 61 W., and the 
 dip, measured on the exposed foot wall, is 45 S. It can be traced for 
 some distance westward, and the Buckeye forms the western exten- 
 sion. The vein has a maximum width of 40 feet, and isjof the same 
 composite type as the Illinois, consisting of a sheeted zone in granite 
 with a great many small and rich quartz seams between the joints, 
 these seams containing all the pay. The surface is very greatly 
 decomposed arid has been extensively sluiced. Two chimneys or 
 shoots of rich ore were found close together, dipping east on the plane 
 of the vein, at first steep and then more gentle. These shoots were not 
 
 nearly so long as the Illi- 
 
 Norfh 
 
 
 
 r 
 
 ^ 
 
 Vein 
 
 ^. 
 
 Vein 
 
 rOrifr 
 
 7 
 
 FIG. 62. Diagram of fault in the Cleveland vein. 
 
 nois ore body, but richer. 
 The ore contains antimo- 
 nite, and this mineral ap- 
 pears to be closely associ- 
 ated with the gold. The 
 vein has been developed 
 only by short tunnels and 
 small shafts, riot over 100 
 feet deep, and appears, 
 like the Illinois, to deserve 
 much more extensive pros- 
 way of water and heavy 
 
 pecting. The same difficulties in the 
 ground will probably be met with in depth. 
 
 The Boulder vein. This deposit is located on Elk Creek, 6 miles 
 north by east of Idaho City, at an elevation of 4,830 feet. Prepara- 
 tions were made a few years ago to exploit this vein on a large scale, 
 and an excellent 30-stamp mill, to be driven by water power, was 
 built. It was run for only a short time, the ore probably being of 
 too low grade to handle profitably; neither was there much ore in 
 sight, so that it would have been necessary to sink below the creek 
 level almost immediately. The vein, which crops for only a short 
 distance and is marked on the canyon slope by quartz croppings sev- 
 eral feet thick, strikes on the surface N. 75 W. and dips 50 S. It is 
 opened by a tunnel 900 feet long. The general character is the same 
 as the Gambrinus and the Illinois, being a very wide (up to 40 or even 
 60 feet) zone of sheeted granite filled with many small seams of quartz 
 carrying pyrite, arsenopyrite, and zincblende scattered through it. 
 As it was necessary to mine the whole width, though the pay was 
 
LINDOREN.] IDAHO CITY GOLD BELT. 687 
 
 only in the narrow seams, and as the ground was very soft and heavy, 
 square timbering had to be used. Underground the vein appears to 
 strike N. 20 W., from which disagreement with the surface strike it 
 would appear that the vein has been considerably disturbed. A nar- 
 row vein in the hanging wall of the big deposit was mined during 
 189G and furnished small quantities of very rich ore. This was not 
 much decomposed, and indicated what the character of the ore will 
 be in depth. It contained bunches of pyrite," arsenopyrite, and 
 blende, with a gangue of quartz and some calcite. The fresh sul- 
 phurets contained much coarse gold, the ore being free milling to 70 
 per cent of its value. It is probable that most of the vein in the 
 Crambrinus mining district will remain largely free milling as depth 
 is attained. The value of the coarse gold in the sulphurets is $15 to 
 $10. The fineness of the amalgamated bullion is 680 to 718. 
 
 Mona MacCarthy is the name of a small vein located three-fourths 
 of a mile west of the Boulder, on the high side, and lying between the 
 Boulder and the Forest King veins. Some work has been done on it. 
 Many small seams are found between this vein and the Forest King. 
 
 The Sub-Rosa or Forest King vein. This vein is traceable for a 
 distance of 2 miles from the Washington mine on the east to beyond 
 the Forest King on the west. It crops in hard granite throughout, 
 though at several places dark-green, dioritic dikes appear near it or 
 cross it. Though narrower than the Illinois and the Gambrinus, it 
 has produced some good pay shoots. 
 
 The Forest King was located in 1875, and a 10-stamp mill was erected 
 on it in 1884. The elevation of the mill is 6,280 feet. The United 
 States mineral monument of the district is indicated by an iron rod in 
 an outcrop close by. No work has been done on the vein during the 
 last few years. The vein shows on the surface in quartzose crop- 
 pings, which do not contain any pay. It is opened by a tunnel 900 
 feet long, through granite, which shows several seams dipping south- 
 ward. The vein consists of a zone, several feet wide, of crushed gran- 
 ite with smaller quartz seams. It strikes N. 56 W., and dips 60 S. 
 The drift on the vein extends several hundred feet east and west. 
 Three hundred feet west a dike, 20 feet w T ide, of a dark, syenitic rock 
 (probably a minette) apparently cuts across the vein ; but from the 
 fact that the dike is full of small quartz seams, which all contain a 
 little gold, it is probable that the dike is really older than the vein, 
 and that the difference in appearance of the vein in the two rocks is 
 due to the difference in their resistance to the dislocating force. A 
 dike of the same rock, 1 foot wide, occurs in the crosscut, and is par- 
 allel to the vein in dip and strike. A 50-foot winze was sunk below 
 the tunnel level, some distance west of the crosscut, in the bottom of 
 which was found altered granite, with sulphurets and small quartz 
 seams, giving assay values of $80 to $100 per ton. 
 
 A location called the Northern Light, on which some work has been 
 
688 IDAHO MINING DISTRICTS. 
 
 done, adjoins the Forest King on the east. The Sub-Rosa, also called 
 the Confederate, is a claim on the same vein, 1,500 feet long, and 
 located on the steep side hill toward Moore Creek. The topography 
 is very rugged, owing to the depth to which the gulches have been 
 incised in the granite. At the line between the Sub-Rosa and the 
 Washington the elevation is 5,500 feet. The vein was worked many 
 years ago by Mr. William Hooten, who extracted a considerable 
 amount of very high grade ore from a comparatively small shoot. 
 Then the mine lay idle for many years, until 1896, when work was 
 resumed with the intention of finding the continuation of the pay 
 shoot from a lower tunnel level. The strike of the vein is N. 56 W., 
 and the dip is, as usual, to the south. The vein is several feet thick, 
 consisting of a very soft clayey mass of altered granite with quartz 
 seams. Many smaller dikes of lamprophyric rocks, chiefly minettes, 
 occur near, the vein. In one of the older tunnels it is clearly seen 
 how one of these dikes is sharply cut off and faulted by the vein. 
 The exposures in the lower tunnel of 1896, 300 feet below the old 
 workings, are interesting. A small portion of the vein was found in 
 about normal position, but on following it toward the west, in the 
 direction of the ore shoot, it was found to be cut off by a dike of 
 minette 20 to 30 feet wide, across which solid granite again was met. 
 At first glance it would appear as if a later dike had cut across the 
 vein and faulted it, but upon close inspection of the dike it is seen 
 to be extremely crushed and separated from the vein by fault planes, 
 and the probability is that the dike was intruded before the vein was 
 formed, and that a subsequent fault has thrown the vein in the hang- 
 ing wall, just as happened in the Cleveland vein. This is made the 
 more probable as extensive explorations had previously failed to find 
 it in the foot wall. 
 
 The Washington claim adjoins the Sub-Rosa on the east. This 
 part of the vein was exploited a few years ago, and a considerable 
 amount of gold was extracted. The mine is equipped with a 10-stamp 
 mill, and is developed by a tunnel following the vein for 290 feet and 
 a vertical shaft sunk to 316 feet at the mouth of the tunnel; three 
 levels are turned from the shaft, and extend, the first to 400, the sec- 
 ond to 250, and the third to 170 feet toward the east. The vein is 
 vertical, and has about the same strike as the Sub-Rosa. An ore 
 shoot 45 feet long and from 1 to 6 feet thick was found, and has been 
 stoped from the 200-foot level up to the surface. The yield is reported 
 to have been $90,000 from 4,300 tons, or $20 per ton. The ore was 
 practically all free-milling and consisted of fresh quartz. A little 
 pyrite occurred in depth. The shoot was cut off in depth by a small 
 vein carrying silver, and its continuation beyond this is not known. 
 Forty feet north of the gold vein, and separated from it by altered 
 granite, is a strong vein of solid quartz, from 8 inches to 4 feet wide, 
 which has been exposed by crosscuts from all levels. This vein 
 
LINDGEEN.] IDAHO CITY GOLD BELT. 689 
 
 carries silver only as chloride on top, stephanite and ruby silver in 
 depth the average assays showing values of from 33 to 90 ounces per 
 ton. Ore of the latter kind carries only $1 of gold. Though much of 
 this silver ore is in sight, none has yet been extracted. Four hun- 
 dred and fifty feet beyond the breast of the tunnel another ore body 
 is said to show on the surface and to carry both gold and silver. This 
 is one of the few occurrences of silver veins in the basin, and is of 
 great interest, as the two veins evidently represent separate periods 
 of vein filling, the silver vein probably being the later. 
 
 The Elkhorn mining district adjoins the Gambrinus and is situated 
 on upper Elk Creek. 
 
 The Elkhorn vein is an old location at the junction of Elk Creek 
 and Ross Fork, at an elevation of about 5,300 feet. Discovered in 
 early days, it was worked during 1867 and 1868, and, intermittently, 
 later. Some prospecting was done on it in 1896. It has produced a 
 total of $500,000. The developments consist of a tunnel 1,400 feet 
 long, and stopes above it. It is a well-defined vein, about 18 inches 
 wide, with a northwesterly strike, and carrying decomposed quartz 
 without sulphurets. The ore body was large and the ore high grade, 
 containing up to $40 per ton in gold. The ore shoot was very large, 
 but at a depth of 100 feet it was cut off by a fault plane carrying soft, 
 decomposed granite. There are several other veins in the vicinity, 
 which, however, can show no production. 
 
 The Summit vein is a recent discovery on the ridge between Elk 
 and Grimes creeks, found by tracing the placer gold of Deer Creek 
 up to its source. The vein is inclosed in granite, and strikes a little 
 north of west, dipping 45 SW. There is a zone, 18 feet wide, of 
 crushed granite, carrying 4 feet of pay ore, composed of the same 
 broken granite and quartz seams, and which assays from $10 to $40 
 per ton in gold. The ore shoot is said to be 60 feet long on the sur- 
 face. As usual, the vein carries much water and is difficult ground 
 to timber. Prospecting was in progress in 1896, and it was proposed 
 to sink a shaft 400 feet deep. Between the Summit vein and Center- 
 ville lie, near the road, two quartz claims, called the Golden Fleece 
 and the Golden Star. A 10-stamp mill was built long ago to work 
 the ore, but the results proved unsatisfactory, and the property has 
 long been idle. 
 
 THE QUARTZBURG-GRIMES PASS GOLD BELT. 
 
 The whole lower drainage basin of Granite Creek and Grimes Creek 
 is singularly void of gold-quartz veins. Three miles north of Center- 
 ville, at Crane's claim, a deposit carrying much sulphurets contain- 
 ing gold and silver is being prospected. On Clear Creek, 3 miles 
 south-southwest of Star Ranch, at an elevation of 4,475 feet, are two 
 narrow quartz veins (Jackson's claim), inclosed in granite and carry- 
 ing silver only. A small quantity of rich silver sulphides was found 
 18 GEOL, PT 3 44 
 
690 
 
 IDAHO MINING DISTRICTS. 
 
 on them, and stains of copper and arsenic were noted. The strike is 
 north to south and the dip steep to the east. 
 
 Two and a half miles southwest of Quartzburg the gold belt begins, 
 at the Ebenezer claim. It is not known to extend west of this point, 
 though gold-quartz float has been found 2 miles farther on, along 
 Dead Man's Gulch. The direction of the gold belt westward would 
 carry it directly to Horseshoe Bend, where the Willow Creek belt 
 begins. The high Boise Ridge is very brushy and difficult of explora- 
 tion, and it is by no means impossible that quartz veins will be found 
 in the intervening stretch. 
 
 TJie Ebenezer vein. This vein is continuous for a distance of nearly 
 a mile across the gap in the ridge between Canyon and Fall creeks, 
 and three important claims are located on it. The Ebenezer claim 
 lies on the Canyon Creek side, and is said to have produced $150,000 
 from sluicing and surface workings. The vein strikes northeast and 
 
 southwest and dips to the 
 southeast, and is encased in 
 granite. It is about 5 feet 
 wide, and consists of sheeted 
 granite traversed by many 
 small and rich quartz veins. 
 The surface ore was very rich, 
 but at a slight depth the gold 
 was contained in sulphides, 
 which did not readily yield 
 it to simple amalgamation. 
 
 Scale. 
 
 feet 
 
 has 
 last 
 
 FIG. 63. Section of Mountain Chief vein, east end of 
 claim. 
 
 Only assessment work 
 been done during the 
 years. 
 
 The Mountain Chief ad- 
 joins on the northeast, ex- 
 tending to the summit of the ridge, at an elevation of 6,000 feet, and the 
 vein is similar to the one just described. It is stated that 10 tons of its 
 ore were milled in 1895, yielding $100 per ton, and much gold has been 
 obtained by sluicing the surface. Sulphurets appear here also in 
 depth. In a surface cut the section of the vein was as shown in fig. 63. 
 The Belzazzar claim lies on the Fall Creek side and has been opened 
 by sluicing and a tunnel, 200 feet below the summit. Bodies of heavy 
 sulphurets, chiefly pyrite, are exposed along the vein. The western 
 part of the vein lies in hornblende-porphyrite, while the eastern end 
 has granite in the foot wall and the same porphyrite in the hanging 
 wall. 
 
 A slightly divergent vein, called the Centennial, lies a few hundred 
 feet southeast of the Mountain Chief, on the summit of the ridge. 
 This vein carries more silver than gold, and shows heavy iron pyrite 
 in a 6-inch seam. 
 
LINDQBEN.] QUARTZBURQ-QRIMES PASS GOLD BELT. 691 
 
 The Gold Hill vein. This is probably the continuation of the 
 Ebenezer vein, though it has not been traced across Fall Creek. It 
 is continuous from the Newburg, on the divide between Fall Creek 
 and the west fork of Granite Creek, to at least some distance east of 
 Quartzburg. 
 
 The Newburg claim, at an elevation of 5,000 feet, was worked exten- 
 sively by surface sluicing during the early days, then abandoned, and 
 again located. It is developed to some extent by tunnels aggrega- 
 ting several hundred feet in length. The vein consists of a shattered 
 and decomposed zone in a belt of quartz-porphyrite, and reaches a 
 width of 70 feet. Narrow seams extremely rich in gold traverse this 
 shattered zone, giving to the whole an assay ^lue variously stated 
 from $4 to $12. The ore body is evidently extensive. 
 
 The Homeward Bound, Elizabeth, and Mayflower adjoin the New- 
 burg on the northeast across West Fork. Considerable surface work 
 with sluices and arrastreshas been done on them. The vein is about 
 5 feet wide, and is said to contain sulphurets in large quantities in 
 depth. A narrow streak of quartz- porphyrite follows it. The Con- 
 federate and the Dunlap adjoin Gold Hill on the west, and have a 
 strike of N. 65 E. The developments are not extensive, but some good 
 ore is reported to occur on them. ' 
 
 The Gold Hill and Pioneer claims constitute the most important 
 quartz mine in the Idaho Basin, and the only one which has been 
 extensively and systematically worked, having been in operation with 
 short interruptions since 1864. The Gold Hill was first worked and 
 yielded for a long time ore averaging $20 per ton. It was first 
 exploited by tunnels on the northeastern side of Granite Creek, but 
 in 1875 work began below water level in a shaft just below Quartz- 
 burg on the eastern branch of the creek, the total depth attained 
 being 400 feet. In late years the Gold Hill vein has been abandoned 
 and work concentrated on the Pioneer, a claim adjoining on the south- 
 east. The total amount extracted from the Gold Hill and Dunlap 
 claims from 1869 to 1894 is stated to have been $1,280,000, and the 
 production from the Pioneer claim from 1884 to 1895 is stated to have 
 been $498,000. The total production of the claims mentioned, all of 
 which was not recorded, is believed to have been at least $2,225,000. 
 
 In the mint reports the following data are found : Raymond's report 
 for 1872 states that Gold Hill produced $300,000 since September, 1869. 
 In 1881 it is stated that 150 tons of ore from the Gold Hill yielded 
 $25,000 in gold. In 1883 the Gold Hill produced $76,800; in 1884 the 
 production was $50,000. The property was equipped with a 25-stainp 
 mill in 1875. No work was in progress in 1896, pending a sale of the 
 mine. The Gold Hill vein is a well-defined quartz vein with an aver- 
 age strike of N. 70 E., and a dip of 70 S. The foot wall is generally 
 sharp and well defined and consists of granite. In the hanging wall 
 lies a dike of quartz-porphyrite several hundred feet wide, described 
 
692 IDAHO MINING DISTRICTS. 
 
 in connection with dike rocks (p. 682). The vein is of very irregular 
 width, from a few inches up to 6 feet, and has a great tendency to 
 throw out stringers in the porphyry in the hanging wall; these when 
 followed were found to be rich, but soon gave out. The ore consists 
 of free gold and sulphurets, the latter chiefly iron pyrite, also some 
 antimonite, which is said to be intimately associated with gold. Small 
 traces of tellurium are also reported. About 50 per cent of the value 
 is in free gold, and this proportion is likely to remain stable as depth 
 is attained. _ The sulphurets are reported to be of high grade. The 
 old workings of Gold Hill extend up on the steep hill northeast of 
 Quartzburg. 
 
 The Pioneer claim adjoins the Gold Hill on the south. A vertical 
 shaft 400 feet deep is sunk on it. It is located on a fissured zone in 
 the same porphyry dike which forms the hanging wall of Gold Hill, 
 and which contains a great number of small seams with very rich ore, 
 the whole forming a large body of low-grade ore. The porphyry is 
 yellowish and decomposed, filled with pyrite, sericite, and some cal- 
 cite. The sulphurets of the Pioneer are of much lower grade than 
 those of Gold Hill. 
 
 A short distance below the Pioneer there are several claims on a 
 vein crossing the creek, the principal one being called Mountain Girl. 
 The ore consists chiefly of sulphides without any free gold, but some- 
 times contains much silver, being similar to the Centennial, which 
 lies in a similar position in front of the Mountain Chief vein. 
 
 Immediately adjoining the Gold Hill on the northwest is a flat vein 
 called the Lone Star, from which, in early days, much gold was 
 obtained by surface sluicing. 
 
 The Iowa vein. This vein lies a short distance north of the Gold 
 Hill, and was opened in 1896 by an 800-foot tunnel starting from the 
 10-stamp mill one-eighth of a mile north of Quartzburg. The tunnel 
 is driven through granite, which near the vein is much decomposed. 
 The vein is a narrow seam in granite filled with a soft clay gouge and 
 containing streaks extremely rich in gold. There is also some pyrite. 
 
 In the extension of the Iowa lie the Yellow Jacket and other claims 
 which have been less developed. 
 
 The Carroll veins. A group of five claims lies at the head of Cali- 
 fornia Gulch, 1 miles northeast of Quartzburg. The surface in this 
 vicinity was extremely rich and has been extensively washed. It 
 can not be said that the direction and extent of the veins have been 
 definitely established, but that rich veins exist in this ground is not 
 to be doubted. On the Ivanhoe claim some work was done in 1896, 
 the vein being opened up by means of a tunnel several hundred feet 
 long and exposing a good ore shoot. In this tunnel the vein dips south 
 at a steep angle, and lies entirely in soft, decomposed granite. Outside 
 of the ore shoot the vein is indicated only by a black-clay seam. The 
 character of the ore in the shoot is illustrated in fig. 64, showing the 
 
LINDGREN.] 
 
 QUARTZBURG-GRIMES PASS GOLD BELT. 
 
 693 
 
 breast of the tunnel. The valuable part consists of 2 feet of decom- 
 posed granite with seams 3 to 5 inches wide of pyrite. This contains 
 considerable free gold, some of which appears to be in the decomposed 
 wall rock. Outside of the principal shoot there are many streaks of 
 iron pyrite, which do not contain any free gold. 
 
 The Kennebec claim. This property, situated one-half mile from 
 the Carroll, yielded some very rich ground for sluicing. Of the vein 
 but little is definitely known. 
 
 Veins at head of Wolf Creek. From the Iowa a string of claims 
 extends through the Carroll and Kennebec and then farther through 
 the Black Bear, Mountain Queen, and others up toward a high, promi- 
 nent point on the divide. All these claims lie in granite, though 
 occasional dikes cut the principal rocks; the main belt of porphyry 
 lies a little to the south. On none of them has much work been 
 done. The Black Bear lies at an ele- 
 vation of 5,000 feet a short distance 
 to the west of the pass between Pla- 
 cerville and Garden Valley. The 
 strike is N. 70 E., and the dip 50 
 to the south. The vein is a well- 
 defined fissure with a pay streak of 
 good ore 4 to 5 feet wide, which has 
 been followed down for 40 feet. The 
 ore is free-milling, at present at least, 
 and contains a little galena. North- 
 east of the pass lie a number of more 
 or less prominent veins. The Gold 
 Dollar is a perpendicular vein, the 
 ore of which carries no free gold, and 
 it is said to run from $2 to $20 per 
 ton. Near by lies another vein, with 
 flatter dip of from 20 to 40, carry- 
 ing some free gold. The Monumental 
 and Mountain Queen are on a nearly vertical, heavy vein striking N. 
 81 E. It has no distinct walls, but consists of streaks of quartz and 
 heavy iron pyrite in decomposed granite cut by some porphyry dikes. 
 The Etna, lying a short distance southwest of the pass, is said to 
 consist of a streak in porphyry impregnated with auriferous seams 
 and pyrite. 
 
 Veins in the porphyry dike east of Wolf Creek. On the summit 1 
 mile east of the pass is the Golden Chariot, at an elevation of 5,300 
 feet. The wide dike of quartz - hornblende - porphyrite forms the 
 country rock. In the tunnel the vein appears as a vertical streak, 
 2 feet wide, of brown decomposed rock, said to assay well. A similar 
 deposit, called the Buena Vista, lies a little to the south. Half a mile 
 eastward are the Big Six and the Mineral Hill group of claims, in 
 
 mmm 
 
 FIG. 64. Breast of drift, Carroll veins. To 
 the left, 2 feet of altered granite with 
 rich seams of massive pyrite; to the 
 right, 3 feet of altered granite with 
 poorer seams of quartz and pyrite. 
 
694 IDAHO MINING DISTRICTS. 
 
 the same porphyritic dike. The Big Six appears as a brown, much 
 decomposed vein, 1 to 2 feet wide, chiefly made up of limonite; it 
 strikes N. 55 E. and dips steeply toward the northwest, this dip being 
 an unusual one for the vicinity. The claim is developed by a small 
 shaft, and some fair assays were obtained from it, one sample contain- 
 ing $10. 33 in gold and $0. 50 in silver. The Mineral Hill group adjoins 
 on the northeast, being situated on the headwaters of Ophir Creek, at 
 an elevation of about 5,000 feet, and consists of five claims. The sur- 
 face is extremely decomposed to a brown loam, and luxuriant vege- 
 tation covers all outcrops. These claims have not yet been prospected 
 enough to determine their character, but the pay appears to be con- 
 tained in streaks in the porphyry, impregnated with pyrite and carry- 
 ing free gold on the surface at least. Near the Mineral Hill claim a 
 large extent of surface is said to contain gold. The ore is a soft, 
 decomposed rock, principally composed of limonite, one selected sample 
 of which assayed $154 in gold, $1.71 in silver. Lead carbonate also 
 occurs in the ore. Where sulphurets are found they are said to be of 
 low grade. It is probable that these deposits are similar to that of 
 the Pioneer claim, near Quartzburg. 
 
 Claims near Grimes Pass. For 3 miles beyond the Mineral Hill 
 group, in a northeasterly direction, no mineral deposits are known, 
 though the deep soil covering the region makes it probable that no 
 thorough prospecting has ever been undertaken. About three-fourths 
 mile. west of Grimes Pass, on the summit of the ridge dividing the 
 waters of the Payette and Boise rivers, at an elevation of 5, 000 feet, 
 lie a number of claims called the Morning Star group. There are 
 eight claims laid out along two adjoining lines. The deep surface 
 soil makes prospecting difficult, and the exact character of the deposit 
 is not known. Over a large extent the surface gives good prospects, 
 and many little shafts demonstrate the presence of a considerable 
 body of low-grade free-milling ore. The ore has always the appear- 
 ance of streaks, 4 to 6 feet wide, of decomposed and brownish por- 
 phyry, striking a trifle north of east. The deposits lie in a dike, 
 several hundred feet wide, of quartz-hornblende-porphyrite, continu- 
 ing from the vicinity of Quartzburg, but the contacts of the dike with 
 the granite are difficult to trace. Samples of the ore washed in pan 
 gave good prospects of free gold, with some lead carbonate. On the 
 Morning Star a shaft 232 feet deep has been sunk. A long tunnel 
 has been started on the Payette side, 600 feet vertically below the 
 shaft, and is calculated to strike the vein 1,700 feet from the mouth. 
 In 1896 it had been driven as far as a point vertically below the shaft, 
 but work had to be suspended on account of financial difficulties. 
 Three hundred feet back from a point perpendicularly below the 
 shaft the contact of granite and porphyry was struck in the tunnel. 
 The deposits are evidently similar to those of the Pioneer mine and 
 the Mineral Hill group, and consist of a more or less shattered zone 
 
LINDGEEN.] MINING DISTRICTS EAST OF THE BASIN. 695 
 
 in porphyry, which has been impregnated with auriferous sulphides 
 by thermal action. The ore will probably be base in depth, but near 
 the surface a considerable amount of free-milling ore exists. 
 
 The Mountain Queen mine lies on Grimes Creek, 3 miles above the 
 Pioneer, at the southern edge of the porphyry dike and about one- 
 fourth mile from the Morning Star claims. It is probably not the 
 extension of the latter, but a more southerly vein. A few years ago 
 a 20-stamp mill, driven by water power, was constructed on this prop- 
 erty .and ran two years. At first the ore is said to have been taken 
 from a well-defined quartz vein, but later the mineralized porphyry 
 was mined and milled and was found too poor for profitable work. 
 
 The porphyry dike extends eastward toward the high hills east of 
 Grimes Pass, but was not followed and examined any farther. At 
 Charlotte Gulch, on the east side of Grimes Pass, are many claims 
 which on the decomposed surface carried much free gold. The 
 veins contain pyrite, galena, and blende, with a small amount of free 
 gold. Mr. Woods, of Placerville, states that there is evidence that 
 those veins have been much disturbed by faulting. 
 
 MININ& DISTRICTS EAST OF THE BASIN. 
 
 The Summit Flat mining district lies on the headwaters of Elk 
 Creek, Clear Creek, and Moore Creek, at elevations of from 6,000 to 
 8,000 feet, and 12 miles north-northeast of Idaho City. At the head- 
 waters of Elk Creek are the Barry, Peerless, King, and other veins, 
 while the Wilson group of claims lie a little farther north. The veins 
 generally strike east to west, or a little north of east, and dip south 
 at steep angles. In character they are apparently well-defined, wide 
 fissure veins carrying much quartz, chiefly free milling, though 
 bunches of sulphurets may occur. The Mammoth claim in the 
 Wilson group is opened by means of an incline 325 feet deep, expos- 
 ing a considerable body of ore. There are two small mills in this 
 mining district. This region was not visited by the writer in 1896. 
 
 Between Summit Flat and Kempner, 10 miles to the east, are many 
 prospects with only slight developments, partly carrying gold ores, 
 partly silver ores. Placer deposits occur at many places along Lost 
 River and Bear River near Kempner. Twenty-two miles northeast 
 of Idaho City the silver mines of Banner are located, which produced 
 considerably before the recent fall in price of silver. Between 1882 
 and 1894 the total silver production of this district probably 
 amounted to $1,500,000 or 12,000,000, reaching a maximum of over 
 $200,000 in 1892. At present these mines are shut down. The 
 deposits are large, well-defined quartz veins carrying rich silver 
 sulphides. 
 
 Gold-quartz veins have been found on the southwestern slope of 
 Sunset Mountain, and several claims have lately been located on 
 
696 
 
 IDAHO MINING DISTRICTS. 
 
 upper Rabbit Creek, draining into Boise River 8 miles east of 
 Idaho City. 
 
 Fineness of quartz gold. 
 
 Mine. 
 
 Value per ounce. 
 
 Fineness. 
 
 G-ambrinus 
 
 $15. 50 
 
 
 Boulder 
 
 15. 50-16. 00 
 
 680 to 718 
 
 Forest King 
 
 
 700 
 
 Washington 
 
 15.00 
 
 
 Illinois .. 
 
 15.00 
 
 
 Ebenezer 
 
 16.50 
 
 
 Gold Hill 
 
 a 17. 50 
 
 800 to 910 
 
 
 
 
 a Average. 
 THE GEOLOGICAL HISTORY OF THE IDAHO BASIN. 
 
 The succession of geological events to which the existence of the 
 basin and of the gold-bearing gravels is due is neither simple nor easy 
 to decipher. In a large degree this is owing to the very monotonous 
 structure of the bed-rock series, which gives few clews, except those 
 indicated by the topography, to the character of the movements that 
 have taken place, for it soon becomes apparent, during a study of the 
 district, that erosion alone, unaided by orographic movements, can 
 not have produced this peculiar depression situated on the divide 
 between two main rivers. 
 
 The doubtful age of the granite, which alone constitutes nearly the 
 whole pre-Tertiary series in the basin, has already been alluded to. 
 It has further been stated that a surface laid through the ridge lines 
 of the Boise Mountains in general probably forms part of an old pre- 
 Tertiary peneplain or land mass planed down by erosion; and, still 
 further, that the erosion succeeding the uplift which differentiated 
 the Boise Mountains and the Snake River plains had, prior to the 
 lake period, cut far into this uplifted surface, so far, indeed, that 
 the Boise Canyon at its mouth was cut to its present depth at the 
 beginning of the Neocene. All this does not account for the depres- 
 sion of the basin, which lies much below the general level of that 
 surface. It seems probable that the present upper valleys of Grimes 
 and Moore creeks have been excavated by erosion, but this again 
 does not account for the basin as a whole. In it the river valleys 
 are separated by low ridges, the summits of which form, if extended, 
 an undulating surface considerably above the creeks, it is true, but 
 still much below the general surface of the surrounding country, as 
 is well shown by PI. XCI. The extent of this surface determined 
 the existence of the basin in the first place, and as a probable work- 
 ing hypothesis to account for this it may be assumed that this earlier 
 
LINDGREN.] GEOLOGICAL HISTORY OP THE IDAHO BASIN. 697 
 
 basin was caused by a sinking of a portion of the Boise Mountains 
 along curved fault lines between the Boise Ridge on the west, Wilson 
 Peak and other elevations on the east, and the Thorn Creek Hills on 
 the south. The age of the quartz veins in the basin can not be defi- 
 nitely indicated, but is most likely Cretaceous or Eocene. They 
 were certainly formed before the deposition of the Payette lake beds, 
 and it is to be expected that the rivers and creeks of the pre-Payette 
 period of erosion in the basin carried detrital gold derived from 
 these veins. These stream gravels are now either completely eroded 
 or buried below the lake beds at Idaho City. As has been ex- 
 plained in the detailed description, there is slight chance of finding 
 them by boring, and still slighter chance of mining them profitably 
 if found. 
 
 The surface of the Payette lake attained a height above the present 
 sea level of 4,200 feet at the mouth of the Boise Canyon. If the eleva- 
 tions and the topography were then the same as at the present time, 
 the lake would have reached up as far as Centerville in Grimes Creek, 
 and 4 miles above Idaho City in Moore Creek. It is almost certain, 
 however, that the relative elevations are not the same, for near Idaho 
 City we find the Payette lake beds at 4,400 feet, and there forming 
 part of a smaller area which has settled down between parallel fault 
 lines just how much is not known. From this it appears that the 
 basin has increased its elevation somewhat relatively to the country 
 at the mouth of the Boise Canyon. High up near the divide, on Muddy 
 Creek, a small remnant of inclined lake beds occurs, but it is perhaps 
 a small local accumulation. At any rate it is certain that the Payette 
 lake covered the lower part of the basin in early Neocene times. 
 
 The lake beds were rapidly accumulated in the bay then occupying 
 the basin, and as no concentration of the material took place, it was 
 natural that their content of native gold should be very slight. 
 
 The raising of the base level to the present elevation of over 4,000 
 feet would naturally produce extensive accumulations of gravel in 
 the creeks draining to the lake. It is probable, indeed, that at this 
 time of maximum lake extension the lower valleys opening into the 
 basin were choked with gravel; and as an evidence of this may be 
 cited the occurrence of auriferous river gravel on the summit of a 
 ridge in the Thorn Creek drainage, at an elevation of 4,500 feet. 
 Vast eruptions of basic lavas took place on the summit and western 
 side of the Boise Ridge, and to less extent in the basin. All of these 
 earlier lavas probably flowed out during the deposition of the lake 
 beds. As the lake receded stream courses were established over its 
 deposits, and the streams which headed near quartz veins began to 
 carry down their precious load and concentrate the gold on the bed 
 rock. These fluviatile deposits, which were formed very shortly after 
 the Payette lake beds, or perhaps in part contemporaneously with 
 them in valleys draining into the lake, have been described as "older 
 
698 IDAHO MINING DISTRICTS. 
 
 gravels." Among them are the deposits of Gold Hill, East Hill, and 
 Barker's claim at Idaho City, as well as the Ranch Company's claims 
 and other gravels near Placerville. They rest partly on the lake 
 beds, partly on granite; and while these gravels at Idaho City may 
 have been deposited by Moore Creek as very high bench gravels, the 
 gravels at Placerville form a part of a drainage system differing from 
 the present one. 
 
 During the period of general erosion following the retreat of the 
 Payette lake important events took place. The lower canyon of 
 Moore Creek was scoured of its accumulated gravels. The lake beds 
 were disturbed and acquired a decided dip to the west. One block 
 of them at Idaho City sunk down between fault lines, being thus pre- 
 served from the erosion which destroyed the larger part of them.- 
 The gravels laid down on the lake beds also show a tilting westward, 
 though at slighter angles than the latter. Near Placerville and 
 Granite there were extensive disturbances, which greatly changed 
 the old drainage. Along the eastern side of the Boise Ridge these 
 disturbances, it would .appear, took the form 'chiefly of faulting, for 
 along this line the old gravels are cut off; but the amount of this 
 faulting is not easy to establish. In this connection the occurrence 
 of a little gravel on the summit of the Boise Range is of great inter- 
 est, and it is difficult to explain.. It is not believed, however, that 
 the disturbance was so great as to create the whole of this ridge at 
 this time. 
 
 Finally, at the close of the Pliocene came the eruption of the Snake 
 River basalts. The Moore Creek flow originated at some point on 
 Grimes Creek a few miles below the basin, and as it dammed the 
 stream to an elevation of 100 feet the natural result was the accumu- 
 lation of bench gravels above by the checking of erosion. As the 
 creek gradually wore through the basalt filling, the level at which 
 bench gravels were formed gradually sunk. Thus the bench gravels, 
 lining the stream up to 100 feet above their beds, are directly due to 
 the Pliocene basaltic eruption, and represent in the basin the deposit 
 of the Pleistocene times. 
 
CHAPTER V. 
 THE MINING DISTRICTS OF THE BOISE RIDGE. 
 
 NEAL MINING DISTRICT. 
 LOCATION. 
 
 The Neal mining district is situated south of the Boise River, just 
 east of Three Point Mountain, on the head of Wood Creek, in Elmore 
 County, 15 miles southeast of Boise, in the southwest corner of the 
 Idaho Basin quadrangle. 
 
 The district embraces about 10 square miles, but the productive area 
 has been confined to the heads of Wood and Bender creeks. The camp 
 was discovered in 1889, and has been worked since during the summer 
 months, producing about $200,000 in gold. Three mills have been 
 erected, a 10-stamp for the Homestake, probably the oldest mill in the 
 State, having been first used in Idaho Basin; a 5-stamp for the Alice 
 mine, now a custom mill ; and a 10-stamp for the Lilly mine on Black 
 Creek, now idle. 
 
 Placer mining has been confined to a few bars and the creek beds, 
 but the product from this source forms a very inconsiderable part of 
 the camp's output. The largest amount extracted from the placers is 
 said to have been $800. 
 
 The western half of the district is bare of timber, and except in the 
 main streams there is during the summer months a scarcity of water. 
 The eastern half is better timbered. 
 
 PI. XCVII, drawn by Mr. F. D. Howe, shows the topography, 
 dikes, veins, and mining claims of the central part of the district. 
 
 TOPOGRAPHY. 
 
 The main topographic feature is the high ridge which, with a 
 WNW.-ESE. trend, divides the Snake River from the South Fork of 
 the Boise, and which only reaches an elevation of about 5,000 feet. 
 At Three Point Mountain this ridge swings to a northerly direction, 
 and culminates 4 miles farther north in a point 5,400 feet high, 
 between Birch and Grouse creeks, overlooking the mouth of Moore 
 Creek and the forks of the Boise River. A number of deep canyons 
 separated by narrow ridges radiate from the vicinity of Three Point 
 Mountain. To the southwest extend, at the foot of Three Point Moun- 
 tain, the Tertiary formations of the Snake River Valley. The direc- 
 tion of the creeks seem, in some measure, to follow the lines of faults 
 and jointing that is, they extend from north-northwest to south- 
 southeast and from east to west. 
 
 699 
 
700 IDAHO MINING DISTRICTS. 
 
 GEOLOGY. 
 
 The prevailing rock is the normal gray granite of the Boise Moun- 
 tains, composed of orthoclase, plagioclase, quartz, and biotite ; horn- 
 blende is of rare occurrence in it. A jointed structure or sheeting is 
 often noted, the direction (N. 50 to 80 E.) and dip (up to 45 S.) 
 roughly corresponding to those of the veins. Numerous dikes cut the 
 granite, and may be divided into several classes. 
 
 Some of the dikes consist of a harder gray granite, which carries 
 some muscovite. Less frequent are dikes of coarser and more mica- 
 ceous character than the general mass. Along the north side of Wood 
 Creek are several dikes of a pyritiferous granite, occurring at one 
 place as foot wall to a vein. 
 
 The most prominent dikes are those which crop so boldly on Black 
 Creek, about 3 miles southwest of the Homestake mine, and which, 
 according to Mr. Howe, continue for a long distance northward with 
 a general trend of N. 5 W., one of them, the most easterly, showing 
 on the map Their width is up to 200 feet. The rock, which has a 
 somewhat porous character, is dark gray in color with brownish spots; 
 phenocrysts of feldspar are abundant, and are usually about 5 mm long. 
 It is almost impossible to obtain fresh rock. The microscope shows 
 the rock to consist of sanidine phenocrysts; small, brownish, decom- 
 posed foils and prisms, probably decomposed biotite; and a holocrys- 
 talline groundmass, of spherulitic and micropegmatitic character, of 
 orthoclase and some quartz. The rock should probably be classed as 
 a syenite-porphyry. 
 
 Normal granite-porphyry is common and forms dikes, more rarely 
 irregular masses, with a general direction of N". 20 to 30 W. , several 
 occurring on the divide between Wood and Grouse creeks. 
 
 Lastly, there are narrow dikes of lamprophyres, dark-green, dense 
 rock, in which small foils of black mica are often seen. These vary 
 from 18 to 30 inches in width and often trend with the vein N. 78 E. 
 
 A specimen of thislamprophyric dike rock from the Hidden Treasure 
 mine is a panidiomorphic granular rock composed of brown horn- 
 blende, augite, and soda-lime feldspar in slender, lath-like forms; 
 probably also some orthoclase. The rock is very similar to certain 
 camptonites, or, perhaps, stands between a minette and a camptonite. 
 Similar dikes also occur in the Homestake mine, and in the foot wall 
 of the High Five is a dike 15 feet thick, of lamprophyric rock with 
 abundant black mica and porphyritic orthoclase crystals. These 
 dikes are sometimes the hanging wall of the veins, at times appar- 
 ently not affected by the vein processes, at others partially or entirely 
 replaced by ore. At one place in the Homestake mine a part of this 
 dike, crushed and altered, lies in the middle of a 4-foot vein. Mr. 
 Howe concludes from his observations that the lamprophyres are the 
 oldest dikes, followed by the large dikes of syenite-porphyry, and 
 
LINDGRKN.] 
 
 VEINS OF NEAL MINING DISTRICT. 
 
 701 
 
 these again by the granite-porphyry. It is probable that all of them 
 antedate the veins. Remains of a glassy rhyolite are found on Three 
 Point Mountain and the ridges northward. 
 
 THE VEINS. 
 
 The Neal district was visited in October, 1896, but only two days 
 could be devoted to it, and I therefore gladly availed myself of the 
 offer of the following notes by Mr. F. D. Howe, superintendent of 
 the Hidden Treasure mine, who is thoroughly familiar with the dis- 
 trict and with whose statements my own observations in the principal 
 mines fully agree. Credit for many of the above data regarding the 
 dikes of the district is also due to Mr. Howe. 
 
 The veins of the district have the common N. 70 to 83 E. trend and the same 
 general dip to the south, and for form may be referred to three classes: First, veins 
 filling larger fault fissures, on which are located the principal mines; second, veins 
 along the minor shearing planes of the granite, more or less irregular, but gen- 
 erally carrying high-grade 
 ore; and third, veins of a 
 hard white quartz, called by 
 the miners "bull quartz," 
 carrying no values. 
 
 The veins on the fault 
 fissures are often displaced 
 by faults of a north-south 
 trend, which occurred sub- 
 seqtient to the vein filling. 
 The position of the north- 
 south faults is often shown 
 on the surface by gulches of 
 greater or less size. The dip F IG . 65. Cross section of vein in the Neal mining district, 
 is to the south, ranging from 
 
 30 to 54, somewhat steeper than that of the foliation. The granite of the foot 
 wall for some little distance away from the vein has suffered a decomposition of 
 its mica, is harder, and is cut by cross jointing planes, in which are thin seams 
 of a talcose mineral, giving it a blocky appearance. Garnets occur on this side of 
 the fissure and may be of secondary origin. On the hanging- wall side the granite 
 is darker, and the main joints follow the fissure and no cross jointing appears. 
 On this side only appear the oxides of manganese. Beyond the sheeting or joint- 
 ing of this side there is a zone of structureless granite (fig. 65). 
 
 The vein filling is separated from the walls by thin seams, but in places the 
 mineralization extends into both walls, in which case the gold in the walls is 
 coarser than that of the vein proper. 
 
 The vein matter consists of quartz, sulphides, and partly replaced country rock. 
 The ordinary structure is, next the hanging wall, a clear quartz, more or less 
 honeycombed and stained by the oxidation of the iron pyrites; next, a zone of 
 replaced country rock, granite or one of the dark rocks described above, carry- 
 ing much pyrite and other sulphides. 
 
 Pyrite often occurs in the dike rock in detached kidneys and sometimes as par- 
 tial replacements. The width of the veins varies from 2 to 13 feet. The gold 
 occurs free in the quartz; partially free in the pyrites. It varies from microscopic 
 
702 IDAHO MINING DISTRICTS. 
 
 to shot size, and in some of the very rich pockets the oxidation of the pyrites has 
 left a semicrystalline form. It is worth $15 per ounce from the retort, the alloy 
 being silver. The associated sulphides are iron pyrites and galena, and a little 
 zinc blende appearing on the surface as iron oxides and cerussite. From the 
 pure galena silver values as high as 160 ounces per ton have been obtained, one 
 assay showing 0.7 ounce of gold and 44 ounces of silver. The pyrites contain as 
 high as 21 ounces of gold per ton. An assay of clean zincblende contained 1.4 
 ounces of gold per ton. The pyrites constitute from 3 to 10 per cent of the ore 
 as broken; the galena less than 1 per cent. From 40 to 65 per cent of the gold 
 is saved by amalgamation. The values of the milled ore range from $10 to $120 
 in gold per ton, the larger part being between $10 and $35. Concentrates carry 
 about 2.5 to 4 ounces in gold and 5 to 6 ounces in silver per ton. 
 
 The veins of the second class have less development', and with two or three 
 exceptions have produced but little ore. They occur nearly parallel to the fissures 
 at some distance on either side, and differ in having less dip, little or no complete 
 replacement of the country rock, and less regularity to the ore bodies. Generally 
 the values are high. Where they have been productive the veins occur along the 
 line of dike contacts, as at the High Five and Golden Star. The foot wall is here 
 a granitic porphyry and apparently lies parallel with the jointing or sheeting. 
 
 The veins of the third class are the most prominent in the way of outcropping, 
 the hard white quartz having suffered but little from surface decomposition. 
 Occasionally the quartz is heavily stained by the iron oxides, and in places scat- 
 tering pyrites are found, but the values are low. In places along the sides of this 
 "bull quartz " have been found streaks of high-grade ore, but there has been no 
 development to determine whether the hard quartz caps softer ore, as it does in 
 other parts of the State. 
 
 Several prospects are found northwest of Three Point Mountain, in Charcoal 
 Ravine. The main developments have been on the Jackson property a narrow 
 dike, 8 to 12 feet, of quartz-porphyry, with quartz veins on the joint and contact 
 surfaces. The quartz carries a coarse gold, and there is some impregnation of the 
 porphyry mass. 
 
 In the central belt the principal vein is the Homestake-Hidden Treasure. On the 
 Homestake claim one shoot of ore, varying in length from 75 to 125 feet and in 
 width from 4 to 12 feet, has been mined through tunnels to a depth of 350 feet. 
 To the west the vein is cut by a fault, striking N. 19 W. and dipping 60 E. 
 Beyond this fault the vein was recently found again, thrown 100 feet to the south. 
 Four hundred feet to the east, in which distance another shoot is opened, a section 
 of the vein is faulted 200 feet to the north. This faulted section is another ore 
 shoot, and is about 250 long. Beyond this, to the east, another shoot has been 
 mined to a depth of 100 feet. The term "ore shoot" refers only to ores yielding 
 $10 per ton and over; if made to include ores from $5 per ton and up, the vein so 
 far as opened is practically one shoot. The greatest depth attained below the 
 surface is 350 feet. 
 
 On the Hidden Treasure, the easterly extension of the Homestake, the vein has 
 been opened for 450 feet, to a depth of 165 feet, varying in width from 1 to 13 feet. 
 Several small displacements by north-south faults, between 4 and 12 feet, are 
 shown, and one with a displacement of 60 feet. The entire top of the vein has 
 been moved to the south on a fault plane dipping 6 or 8 to the northeast, between 
 60 and 100 feet. In one place this plane was filled with ore. About 90 per cent of 
 the production of the camp has been from these two properties. 
 
 In the High Five and the Golden Star a vein has been opened, with the granitic 
 porphyry for a f oo twall. It apparently dips with the foliation. The high-grade 
 ores occur in lenticular masses of greater or less extent. The value or extent of 
 the rest of the vein material has not been determined. 
 
LINDOREN.] VEINS OF NEAL MINING DISTRICT. 703 
 
 The vein is in width from 2 to 6 feet, and in form and character of ores is bnt 
 little different from the Homestake vein. 
 
 On the Corder property (Sunshine) an ore shoot has been developed on a fault 
 fissure, with the ordinary dip and trend; and 120 feet to the north a parallel vein, 
 dipping 30 to the north, has been opened. Each vein averages 4 feet, and the 
 ores are similar in character and value to the type ores of the camp. 
 
 On Indian Creek, 5i- miles southeast of Neal, a vein has been opened on the 
 Stevens and Beck properties for 6,000 feet along its trend. It is a fault fissure 4 
 to 8 feet wide and carries ores similar in character and value to those of Neal. 
 
 On Black Creek, 4 miles southwest of Neal, several veins have been opened and 
 some little production made. Work on them has been done only at odd times. 
 The values are high and the limited developments indicate strong veins. 
 
 Two miles east, along Wood Creek, are two recent developments, the North 
 Star and the Clements mines, both being of the common type of the district. In 
 the first named arsenopyrite occurs. 
 
 Milling charges have been $5 per ton; transportation, from $1 up, and the mill 
 saving not over 55 per cent that is, only the free gold thus requiring 12 to $15 
 ore to pay the outside expenses only. To the smelter the charges aggregate $28 to 
 $35 per ton. It would be safe to say that nothing less than $25 rock would return 
 more than wages to the owner unless he had a mill. The average claim owner 
 had either to make the claim pay or limit the development to the annual assess- 
 ment, carelessly done. The work in the camp is a result of this condition and 
 fully illustrates it. 
 
 To these full notes of Mr. Howe should be added only the statement 
 that the alteration of the country rock adjoining the veins is of the 
 same character as that at other places within the region described. 
 The black mica is bleached, being converted to carbonates and to 
 white mica. The feldspars are converted to an opaque white matter, 
 which is neither kaolin nor talc, but sericite in extremely fine-grained 
 aggregates. The quartz grains remain unaltered in general, and 
 pyrite and arsenopyrite are often introduced. The principal value 
 of the veins is in the filling that is, in the solid quartz accompanied 
 by sulphides. But the altered granite next the filling here sometimes 
 also carries good value. 
 
 BLACK HORNET MINING DISTRICT. 
 TOPOGRAPHY. 
 
 This district and its continuation northward (the Deer Creek min- 
 ing district) is on the eastern side of the Boise Ridge, on the slope of 
 the ridge culminating in Lucky Peak. It is 8 miles east-southeast 
 of Boise, and is situated at elevations ranging from 4,500 to 5,500 
 feet. The topography is very accentuated; deep, sharply incised 
 V-shaped canyons score the slope of the Lucky Peak, draining to 
 Boise River and to Moore Creek. 'Scattered timber covers the hill- 
 sides at higher elevations. The topography is indicated in a some- 
 what generalized way on the Boise sheet. 
 
704 IDAHO MINING DISTRICTS. 
 
 GEOLOGY. 
 
 The geological structure of the Lucky Peak ridge is very simple. 
 It consists nearly entirely of the normal granite of the Boise Moun- 
 tains. A number of dikes vary the monotony, but consist almost 
 exclusively of light-colored granite-porphyry, which have in general 
 a northwesterly trend and a width occasionally attaining 100 feet, but 
 usually much less. Placer deposits hardly found place to accumulate 
 in the steep gulches and cut no figure in the production of the camp, 
 
 MINERAL, DEPOSITS. 
 
 A number of gold-quartz veins are found in the Black Hornet dis- 
 trict; and they are not confined to the district. Scattered small veins 
 occur in the granite between this region and the Neal mining district, 
 9 miles to the southeast. West and southwest from Lucky Peak scat- 
 tered prospects are also found; likewise to the north and northwest, 
 connecting in the latter two directions with the Shaw Mountain and 
 the Boise districts. The northern part, or the Deer Creek district, 
 has been known for a long time. On the Montana claim an arrastre 
 was built and worked many years ago by Mr. Plowman, of Idaho City. 
 But the southern and lately most productive part, near the Black 
 Hornet mine, has been known only during the last few years. 
 
 The production has been confined almost entirely to ore shipped to 
 smelting works from the Black Hornet or Ironsides mine. During 
 1895 and 1896, 200 carloads are said to have been shipped, averaging 
 $40 per ton, which would give a total product for the camp of about 
 $24,000; the total production is probably $30,000. 
 
 The veins in this vicinity differ markedly in direction and dip from 
 those at other camps on the range. Instead of a strike ranging from 
 east-west to northeast-southwest, we here find veins striking north- 
 south or northwest-southeast, and with a dip of 45 to 50 to the west. 
 Though base ores prevail, some of the veins carry a notable percent- 
 age of free gold. 
 
 The more prominent claims begin at the Viola mine and extend for 
 2^ miles northward. South of the Viola are a number of prospects, 
 some of which, such as the Fraud and the Ruby, are reputed to be 
 promising. 
 
 The Black Hornet vein extends through the Viola and Ironsides 
 claims, but can hardly be traced any farther. Having at first a direc- 
 tion of N". 20 W., it changes in the Ironsides claim to N. 40 W., the 
 dip being to the southwest at 50. The vein crops along a ridge lead- 
 ing up to Lucky Peak, and a sharply cut ravine several hundred feet 
 deep offered excellent place for tunnels to tap the vein. The Viola 
 shows on the crumbling granite on the surface as a strong vein of 
 white quartz. It is developed by a crosscut tunnel 200 feet long 
 
LIXDOKKN.] DEPOSITS OF BLACK HORNET MINING DISTRICT. 705 
 
 and a drift following the hanging wall north. A width of several 
 feet of quartz is shown, and near the northern end of the claim a pay 
 shoot exists 100 feet long and said to be 9 feet wide, carrying an ore 
 which averages $15, of which about half is in free gold. The ore is 
 is similar to that of the Ironsides. The Ironsides or Black Hornet 
 adjoins on the north, and its principal pay shoot lies near the line of 
 the Viola claim. It is developed by a cross cut striking the vein 
 about 100 feet below the croppings and a winze sunk 100 feet deep 
 ear the southern end-line in the drift. The pay shoot extends 200 
 feet north from the end line, but only 70 feet of it consists of shipping 
 ore. Along the pay shoot the quartz reaches a width of 10 feet or more. 
 This block of ore between tunnel level and surface was stoped and 
 shipped, averaging, it is said, $40 per ton, almost entirely in gold. 
 
 North of the richest pay shoots are large amounts of lower-grade 
 ore. The vein shows as a body of massive, fine-grained white quartz, 
 from 2 to 10 feet wide, and contains sulphides irregularly distributed 
 through it. The sulphides, which in the pay shoot will amount to 8 
 per cent of the ore, consist of arsenopyrite, pyrite, and zinc blende. 
 The value is by no means exclusively in the sulphides, for a specimen 
 of massive zinc blende and arsenopyrite assayed only 0.40 ounce of 
 gold and 4.60 ounces of silver; a total value of $11.50. A sample of 
 the quartz with scattered iron pyrite yielded 0.45 ounce of gold and 
 1 ounce of silver; a total value of $10. The walls are often ill defined 
 and without a clay selvage, and consist of shattered granite and 
 granite-porphyry altered by thermal processes. The feldspar is 
 largely converted to sericite or white mica, and the rock contains, for 
 a few feet on each side of the vein, much scattered arsenopyrite. 
 This altered wall rock contains, in strong contrast to the filling, only 
 a trace of gold and silver. The Ophir vein lies one-half mile north 
 of Ironsides and has a similar direction. But little work has been 
 done on it. Near the Ophir vein a long vein begins, and extends, 
 with a westerly dip, due north across Dead Dog Creek to Deer Creek. 
 The following claims are located on it, beginning at the southern 
 end: Mclntyre, Gray Eagle, Sorrel Horse, Golden Rule, and Montana. 
 Most of them are but superficially developed, and the ore, though 
 free milling on the surface, grows base at a slight depth. The Mon- 
 tana is opened by a cross cut 270 feet long. 
 
 BOISE MINING DISTRICT. 
 
 At a distance of from 3 to 5 miles east and east-northeast from 
 Boise are a number of prospects which have never produced much, 
 yet are worthy of mention. The country rock is normal granite 
 throughout, cut by a few dikes of granite-porphyry with a general 
 north-northwesterly direction. Dikes of dark lamprophyric rocks 
 also occur. 
 
 18 GEOL, PT 3 45 
 
706 IDAHO MINING DISTRICTS. 
 
 Three miles east of Boise, on the north side of the stage road in 
 Cottonwood Creek, are several claims, Morning Star, Last Chance, 
 and First Chance, located on a narrow vein striking northeast-south- 
 west and dipping south, the developments consisting only of two tun- 
 nels 100 feet long. High assay values in silver have been found on 
 the first claim, while the others chiefly contain gold. One and a half 
 miles further east, just north of the road, is another claim said to 
 have yielded some rich decomposed silver ore. 
 
 On Picketpin Gulch, 5 miles east of Boise, are the Golden Star loca- 
 tion and a great number of other claims. The Golden Star claim is 
 said to cover two parallel veins and a cross vein, but the openings do 
 not show the character of the deposit very clearly in the decomposed 
 granite. 
 
 An arrastre wa built on this claim many years ago and the soft 
 decomposed ore treated in it is said to have yielded $33 per ton. A 
 small mill was erected a few years ago, but it did not run long. Man} 7 
 of the veins in this vicinity show no quartz, but only a streak of ther- 
 mal alteration on each side of a fault plane. Mr. Eldridge 1 mentions 
 at this same locality "several narrow dikes of lamprophyre, trending 
 N. 50 to 70 W. and dipping 45 to 80 SW. A vein of quartz lies 
 between two of these." The dark-green, fine-grained dike rock from 
 this locality is panidiomorphic granular, and consists chiefly of brown 
 hornblende and orthoclase with some soda-lime feldspar. It appears 
 to be a syenitic lamprophyre connected with the vogesites. In the 
 lower part of Fivemile Creek many strong quartz veins appear, all of 
 them having an east-west direction and a southerly dip of from 50 
 to 60. The Scorpion is a well-defined vein showing 2 to 3 feet of 
 solid quartz between granite walls. A tunnel 100 feet long has been 
 driven in this vein in the western side of the creek. The quartz, 
 which contains scattered iron pyrite and arsenopyrite, is said to assay 
 up to $8 per ton. A dike of fine-grained, dark-green minette, a 
 species of syenitic lamprophyre, was cut in the lower tunnel and 
 appears to lie nearly parallel to the vein. The dike is considerably 
 altered, filled with calcite, sericite (white mica), and pyrite, and car- 
 ries about $1.65 in gold. Claims adjoining on the same vein are the 
 Elevator and Hattie, while parallel to it and adjoining northward 
 are the Badger and Free Gold. Parallel veins also lie on both sides 
 of the Idaho City stage road at the mouth of Fivemile Creek, and 
 scattered prospects extend eastward to Shaw Mountain district. The 
 Tornado and Blizzard claims are situated 1 mile northeast of the Scor- 
 pion, and carry heavy sulphide ore, zinc blende, galena, and pyrite, 
 having high assay value but containing no free gold. 
 
 1 Sixteenth Ann. Bept, U. S. Geol. Survey, Part II, 1895, p. 335. 
 
LINDGREN.] SHAW MOUNTAIN MINES. 707 
 
 SHAW MOUNTAIN MINING DISTRICT. 
 
 The veins in this district, apparently forming a continuation of 
 those on Fivemile Creek, were discovered in 1877. The veins are 
 located on the high ridge just north of the Idaho City stage road, 8 
 miles N. 80 E. from Boise, at elevations of about 5,000 feet. The 
 mines were prospected only on a small scale in 1896. The country 
 rock is normal granite, with a few smaller masses of granite-porphyry. 
 A strong sheeting of the granite is noted in many places between 
 Fivemile Creek and Shaw Mountain, the joints having the same 
 strike and dip as the veins. The Rising Sun vein is the most promi- 
 nent, and crops as a well-defined fissure vein of white quartz for 1 mile 
 near the summit of the ridge with a general east-west direction and 
 dip of 45 to 80 S. Four claims are located on it, from west to east, 
 as follows: Rising Sun, Paymaster, North Star, and Daisy. On the 
 first of these a 10-stamp mill was erected in 1879. It is developed by 
 several tunnels, the lowest 400 feet below the croppings and 500 feet 
 long. From the upper levels at least 500 tons were extracted, yield- 
 ing from $14 to $100 per ton; in the lowest tunnel heavy sulphide ore 
 was found which did not contain much free gold. From a sample of 
 this, collected from the dump and containing pyrite, arsenopyrite, 
 blende, and galena, an assay of 11 ounces of gold and 4 ounces of 
 silver was obtained, a total value of $230 per ton. The pay shoot is 
 stated to be 120 feet long, the width of the vein being not over 2 feet. 
 Some ore of similar character has also been extracted from the Pay- 
 master. The North Star, showing strong croppiugs of white quartz 
 on the summit of the sharp ridge, is said to contain five smaller shoots 
 of ore, and is opened by a tunnel 280 feet long, giving backs of 180 
 feet. A few hundred feet south of this vein, on two smaller parallel 
 veins, lie several claims, among which are the Kessler, Gold King, 
 and Levi. These veins, on which some good ore is said to have been 
 found, carry the same clean white quartz as the North Star; samples 
 of this barren-looking material gave $2 in gold and $0.49 in silver. 
 
 Near the vein the granite has undergone the usual alteration due to 
 thermal waters. The brown mica (biotite) is converted to white mica 
 (muscovite), and! the feldspars are changed to a white opaque mass, 
 which is muscovite (sericite) in an extremely fine-grained aggregate. 
 Aggregates of coarse muscovite sometimes occur in the quartz from 
 this vicinity. 
 
 MINING DISTRICTS OF WILLOW CREEK AND ROCK CREEK. 
 LOCATION AND TOPOGRAPHY. 
 
 The Willow Creek district lies in Boise County, 18 miles distant 
 from Boise, in a direction N. 20 W., and is adjoined on the northeast 
 by the Rock Creek district, the two extending in an east-northeast 
 
708 IDAHO MINING DISTRICTS. 
 
 direction for 8 miles. The elevation ranges from 3,000 to 5,000 feet 
 above sea level. A ridge with northwesterly direction and culminat- 
 ing in Crown Point (elevation 5,300 feet) separates the two districts 
 and also the watershed of the Boise from that of the Payette. Most 
 of the mines of Willow Creek are located in the steep gulches at the 
 head of the North Fork of the same creek. On the eastern side a 
 steep descent leads down to Rock Creek, draining due northward into 
 the Payette. The eastern end of Rock Creek district lies on the north- 
 easterly trending ridge separating the Payette from the branches of 
 Shafer Creek. The mining towns of Pearl and De Levan are located 
 on Willow Creek. During the past summer there were probably 150 
 men in the districts. A small Huntington mill is erected on the 
 Easter claim, and two smaller custom mills are also built lower down 
 on Willow Creek. 
 
 While placer deposits were worked in the vicinity of Willow Creek 
 long ago, and one of the mines of the district, the Red Warrior, was 
 worked in 1870, the majority of the locations have been made during 
 the past few years, especially in 1894 and 1895. The productive 
 mines of the districts are at present those in Willow Creek, and the 
 total output is probably about $80,000 in gold, all extracted within 
 the last few years. The output of 1896 is estimated at $50,000. 
 Among the producers are the De Levan group, the Checkmate, 
 Friday, Leviathan, Birthday, and Lincoln. 
 
 GEOLOGY. 
 
 GRANITIC ROCKS. 
 
 The formation of chief importance as containing all the veins is 
 the granite and associated dike rocks. A few miles west of Pearl the 
 first granite hills emerge from under the cover of the Payette sand- 
 stones and rise rapidly eastward, extending thence uninterruptedly 
 in a northeasterly direction. The larger part of the area is occupied 
 by a granitic rock, which is a local modification of the normal granite 
 of the Boise Mountains. 
 
 The rock crumbles and disintegrates very easily, and the slopes of 
 the mountains are covered by a deep mantle of disintegrated rock. 
 During the winter rains the erosion goes on very rapidly, and deep 
 gulches are often excavated in a remarkably short time. It is possi- 
 ble to obtain the fresh rock only from exposures in the bottom of the 
 canyons or in prospect tunnels. The rock is of a light-gray color and 
 has a coarse-grained structure, the average grain having a diameter 
 of from 3 to 6 mm . It is composed of white feldspar, quartz, biotite, 
 and sometimes hornblende. Brown titanite in small grains is uni- 
 versally present. Occasionally larger grains of light-red orthoclase 
 appear among the prevailing white plagioclase. Under the micro- 
 scope the following minerals are noted : Hornblende appears in brown- 
 

 u 
 
 
 e 
 
 n 
 
 Z r^ 
 
 
 .2 
 
 
 UJ 
 
 
 z 
 
 o 
 
 
 
 
 z 
 
 O 
 
 
 a 
 
 8 
 
 z 
 
 
 c 
 
 UJ 
 
 o 
 
 UJ 
 1 
 
 LEISTO 
 
 a. 
 
 c 
 
 3 
 I 
 
 ver terr 
 
 NEOCE 
 
 O. 
 Z 
 
 ,c 
 
LINDGEEN.] 
 
 ROCK OF SILVER WREATH MINE. 
 
 709 
 
 ish-green anhedral grains, and biotite as irregular, yellov/ish-brown 
 foils. The quartz occurs in abundant anhedral grains, frequently 
 exhibiting undulous extinction, due to pressure. The feldspar, also 
 in irregular grains, is quite predominantly a soda-lime feldspar, gen- 
 erally an oligoclase or andesine, though some labradorite was found 
 in a specimen from the Payette River Canyon. Small plagioclase 
 crystals are ' sometimes embedded in the biotite. Orthoclase and 
 microcline both occur in the specimens from the Silver Wreath mine 
 and near the Checkmate, but are practically absent in other speci- 
 mens from the Payette River Canyon, 3 miles east of Marsh. A lit- 
 tle magnetite and apatite always occurs. Titanite is present in larger 
 quantities, and sometimes, as at the Silver Wreath mine, makes up a 
 notable percentage of the rock. In this rock it occurs in idiomorphic 
 wedge-shaped crystals protruding in feldspar grains and also includ- 
 ing small prisms of the same mineral. An analysis of the rock from 
 the Silver Wreath mirie is given below, and a calculation of the 
 analysis may be found on page 641 : 
 
 Analysis of rock from the Silver Wreath mine. 
 [Analyst, George Steiger.] 
 
 SiO 3 . --- 
 
 65.23 
 
 TiO 2 
 
 .66 
 
 ALO, 
 
 16.94 
 
 Fe 2 O 
 
 1.60 
 
 FeO 
 
 1.91 
 
 MnO . . -- - 
 
 trace 
 
 CaO - - - 
 
 3.85 
 
 BaO - 
 
 .19 
 
 MffO 
 
 1.31 
 
 K 2 O - - 
 
 3.02 
 
 Na,O - - 
 
 3.57 
 
 H 2 O below 100" 
 
 .18 
 
 H 2 O above 100 - --- 
 
 .88 
 
 p,O 
 
 .19 
 
 CO 2 
 
 .25 
 
 
 
 
 99.78 
 
 According to these data, it is clear that the granitic rock is more 
 closely related to a quartz-inica-diorite than to a granite, and shows 
 great similarity to the granodiorite of the Sierra Nevada in California. 
 Being, however, only a local modification of a large area of normal 
 granite, with which it is connected by transitions, the name granite 
 has provisionally been retained. More basic dioritic rocks, contain- 
 ing an abundance of hornblende, sometimes appear as irregular 
 streaks and masses near Pearl. This is well shown in the tunnel at 
 
710 IDAHO MINING DISTRICTS. 
 
 the Easter mine, as well as in the bottom of the creek near the Silver 
 Spray claim. 
 
 A still more basic facies occurs at Horseshoe Bend on both sides of 
 the river, and extends for a distance of 3 miles down along the can- 
 yon, bordering on the south against the porphyritic dike subsequently 
 described and on the north against the dioritic granite, with very indis- 
 tinct and ill-defined outline. This rock varies much in appearance, 
 from dark-gray, medium-grained, or slightly porphyritic to coarse- 
 granular, the latter consisting apparently of white feldspar and rather 
 abundant green. hornblende. The peculiarity of these dark, granular 
 rocks is that besides being poor in quartz they also carry augite, and 
 may be designated pyroxene-diorites. The rock at the Horseshoe 
 Bend bridge carries imperfectly idiomorphic augite and a little 
 hypersthene, the crystals being of a maximum length of l mm , but 
 usually less. There is also a little biotite. These three constituents 
 are embedded in a clear feldspar mass, which consists of short prisms 
 of labradorite, with zonal extinction, cemented by smaller anhedral 
 grains of probably the same feldspar. The structure in this, as in 
 other specimens, is hypidiomorphic granular. The coarse-granular 
 rock three-fourths mile west of Horseshoe Bend consists of white 
 feldspar, green hornblende, and a smaller amount of biotite in large 
 sheets. The microscope shows a few large, irregular grains of ortho- 
 clase, in which are embedded smaller prisms of labradorite. In this 
 specimen there is a little quartz between the large feldspars. Most 
 of the feldspar grains doubtless consist of labradorite. The augite 
 is largely converted into hornblende, and but little of the original 
 mineral remains. 
 
 DIKE ROCKS. 
 
 A series of dikes extends diagonally across the districts. Begin- 
 ning as narrow dikes near the Horseshoe Bend post-office, these rocks 
 extend in a widening belt over toward Rock Creek, there attaining 
 their maximum development at the crossing of Rock Creek. The 
 belt is here fully one-fourth mile wide, and practically forms one 
 dike, though with smaller included masses of diorite. From Rock 
 Creek this same dike extends up toward Crown Point Hill, but gradu- 
 ally contracts and ends before reaching the summit. Scattering dikes 
 are, however, found on that hill, and appear to continue from there 
 in a southwesterly direction, the last prominent dike appearing near 
 the Dynamite claim at Pearl. 
 
 The dike rocks are of somewhat varying character. Pegmatitic dikes 
 hardly occur at all, and light-colored granite-porphyry, so common 
 elsewhere, is not abundant here. The usual dike rock is a coarse 
 diorite-porphyrite. The rock occurring on the river hill between 
 Horseshoe Bend and Rock Creek is prominently porphyritic by large 
 white feldspar crystals, up to l cm long, and by smaller crystals of 
 
DIKE ROCKS ON ROCK CREEK. 711 
 
 hornblende and biotite, all embedded in a reddish ground mass. 
 Under the microscope the feldspars are shown to be a plagioclase of 
 medium basicity. The hornblende and the biotite are of normal char- 
 acter, while the groundmass is microcrystalline, consisting of quartz 
 and unstriated feldspar. The structure of the groundmass often is 
 approximately micropoikilitic. In certain of these porphyrites horn- 
 blende is very abundant and occurs also as small prisms embedded 
 in the groundmass. 
 
 Another kind of porphyry contains quartz as rounded phenocrysts, 
 and in this variety no quartz occurs in the groundmass. At the cross- 
 ing of Rock Creek the dike is wide and fresh and the rock is of 
 somewhat different character. It is dark green and fine grained, with 
 feldspar prisms up to 8 mm in length and a few black, shining crystals 
 of hornblende. The feldspar is chiefly labradorite in sharp, short 
 . prisms and very fresh. The crystals are of all sizes, grading down 
 to those which form a part of the groundmass. Augite occurs as 
 idiomorphic crystals, many of them decomposed; a little hornbler.de 
 is also present, and magnetite is quite abundant. Between the closely 
 crowded feldspars lies very little groundmass of quartz and unstriated 
 feldspar. The structure of this rock is intermediate between holo- 
 crystalliiie porphyritic and panidiomorphic granular. The rock is 
 thus an augite-diorite-porphyrite, closely connected with the lampro- 
 phyric dike rocks. 
 
 At the Dynamite claim, near Pearl, dense, dark-green dikes appear, 
 consisting of clouded and altered feldspar in lath-like form, between 
 which lie the decomposed ferromagnesian silicates replaced by chlo- 
 rite and epidote. This rock has somewhat the appearance of an 
 altered, fine-grained diabase. Scattered dikes occur in other parts of 
 the district, one large dike cropping on the road to Marsh, 1 miles 
 north of Pearl. On the whole, the dikes may be said to be most 
 abundant for a distance of half a mile north and half a mile south of 
 the main belt of porphyritic rocks above described. 
 
 THE PAYETTE FORMATION. 
 
 The loose sandstones of the Payette formation (early Neocene) are 
 laid down upon the very irregular granitic surface and begin at the 
 western edge of the Willow Creek district, extending far westward. 
 Sandstones and fine gravels of the same age are also found high up in 
 the vicinity of Prospect Peak, and cover, in fact, the pass leading from 
 Willow Creek to Boise. A branch of the Payette sandstones extends 
 in a northeasterly direction as far as Horseshoe Bend. The Payette 
 formation locally contains gold placer deposits, as at Church's ranch, 
 at the southern edge of Marsh Valley. The gold in these placers has 
 doubtless been washed down from quartz veins on the northern slope 
 of Crown Point Hill. Other placer deposits occur 1 mile southwest 
 of Marsh in the sands and conglomerates of the Payette formation. 
 
712 IDAHO MINING DISTRICTS. 
 
 These placers also probably have their origin in the gold veins of 
 Crown Point Hill. 
 
 RHYOLITE. 
 
 The sharp point of Prospect Peak and the hill 1 mile to the west of 
 it consist of rhyolite. They are necks from which large flows of the 
 same rock poured down the southern slope of the ridge during the 
 period of the Payette lake beds. In South Willow Creek the sand- 
 stone is seen to overlie the rhyolite. A smaller flow of rhyolite 
 reached down as far as one-fourth mile south of Pearl. The rock is 
 usually reddish or reddish-gray, and is of the ordinary compact lith- 
 oidal variety. In the last-mentioned flow occur, associated with it, 
 rhyolite glass and loose tuffs. 
 
 BASALT. 
 
 The eruption of rhyolite was followed, during the same early Neo-> 
 cene period, by extensive eruptions of andesitic basalt. Smaller 
 masses and necks of this black massive rock occur on the ridge one- 
 fourth mile west of Prospect Peak, near the Leviathan, and at several 
 other places to the west. 
 
 The Payette formation and accompanying eruptives are later than 
 the mineral deposits, and contain no veins. 
 
 THE ORE DEPOSITS. 
 
 GENERAL CHARACTER. 
 
 The gold deposits in the Willow Creek and Rock Creek districts are 
 fissure veins of somewhat varying character. Most of them occur in 
 a belt parallel to that of the porphyry dikes, extending in a north- 
 easterly direction, and being in no place much over 1 mile in width. 
 The veins at Willow Creek are most frequently entirely in the dioritic 
 granite. Sometimes a vein follows a porphyry dike for some distance 
 in foot or hanging, but rarely for a long distance. Again, a vein 
 may cut through a dike, in which case it often splinters up. The 
 porphyry dikes are evidently all older than the veins. The fis- 
 sures which carry gold strike east- west or northeast-southwest. In 
 the Willow Creek district the dip is always to the north from 45 to 
 80 and the direction east- west, but toward Rock Creek the direction 
 gradually changes to northeast-southwest. Toward Horseshoe Bend 
 the direction changes again to east-northeast to west-southwest, and 
 the dip is frequently steep to the south. The individual veins can 
 rarely be traced for a long distance, and though it is probable that 
 some of the veins are a mile long, this can rarely be satisfactorily 
 proved. Narrow veins predominate in the Willow Creek district, 
 while wider deposits occur on Rock Creek. The best exposures are, 
 however, found in the former district, owing to more extensive devel- 
 opment. In Rock Creek the developments are relatively slight, and 
 
LINDOHEN.] GOLD DEPOSITS OF WILLOW AND. ROCK CREEKS. 713 
 
 the decomposed surface material does not always allow satisfactory 
 conclusions as to the character of a deposit. A large number of loca- 
 tions have been made in both districts, which, in fact, contain a very 
 great number of veins. The ordinary type of the "Willow Creek 
 deposits consists of one or more fault fissures, on both sides of which 
 there is a zone a few feet wide in which the country rock has been 
 thoroughly altered (see Chapter II) and impregnated with pyrite. 
 Along the main fissure, or, if there are two or more, chiefly along the 
 foot wall, there are narrow seams filled with sulphides (pyrite, zinc- 
 blende, arsenopyrite, and galena), which constitute the ore. The 
 altered country rock, though often studded with pyrite crystals, usu- 
 ally contains only $1 or $2 in gold, while the value of the solid sul- 
 phides in the seams may reach $100 per ton or more. The deposit 
 may thus be characterized as narrow veins of high-grade sulphide, 
 ore. There is usually but little gangue along these seams ; calcite 
 and quartz both occur. In other deposits the zone of altered diorite 
 or granite is traversed irregularly by numerous small seams carrying 
 arsenopyrite, blende, and galena, and in this manner the wider depos- 
 its of medium-grade ore are formed. The veins of Rock Creek are 
 generally wider than those of Willow Creek. 
 
 The surface decomposition attains 50 to 100 feet in depth. In this 
 zone the vein matter forms a brown ferruginous mass, which contains 
 free gold and partly decomposed sulphides, often also lead carbonate. 
 In many cases the fresh sulphide ore is found less than 50 feet from 
 the surface. The fresh ore contains a very small percentage of free 
 gold, and sometimes, in rich ore, not even a color is obtained by the 
 pan. It follows from this that the amalgamation process, is, as a 
 rule, applicable only to the surface ores, though some veins will be 
 found to contain more free gold than others. At present the rich 
 ore all above $30 is sacked and shipped to smelters. 
 
 The minerals consist of the following combination, so common in 
 the Boise Ridge: pyrite, arsenopyrite, zinc blende, and galena; chal- 
 copyrite is rare. The first two often occur as crystals. The zinc 
 blende is black, brown, or greenish-yellow, usually not crystallized. 
 The galena is less common than the others, and is considered an indi- 
 cation of rich ore. Ruby silver is reported as a rarity from the 
 Shamrock and the Lincoln. 
 
 Shipping ore often contains 5 ounces of gold and 5 ounces of silver 
 to the ton. A sample of pyrite, arsenopyrite, and galena from one 
 of the best mines gave 0.85 ounce of gold and 28.35 ounces of silver 
 per ton, a total of $37.42. Some galena carries 60 to 70 ounces of sil- 
 ver, and generally also much gold. Much of the arsenopyrite and 
 zincblende is poor. The principal value appears to be in the pyrite 
 and galena. Of the extent and direction of the ore shoots but little 
 is known at present, but it is clear that the high-grade shoots are not 
 of great lateral extent and that they are rather irregular. 
 
714 IDAHO MINING DISTRICTS. 
 
 TREATMENT OF THE ORES. 
 
 At present only the shipping ores can be utilized, and the question 
 how to make $10 to $20 ore pay is one of the greatest importance to 
 the camp. If it should contain any notable amount of free gold, amal- 
 gamation and concentration will probably be found most economical. 
 Experiments should be made as to the applicability of the cyanide 
 process to these ores. In the absence of notable amounts of copper 
 and antimony the process might be of advantage, but experiments 
 are necessary to prove this. 
 
 DETAILED DESCRIPTION. 
 
 The Lincoln vein is one of the most westerly locations in Willow 
 Creek, being situated about a mile south-southwest of Pearl. The 
 strike is N. 76 W. and the dip steep to the north, the vein being 
 traceable in granite for a distance of one-fourth mile, with good ore 
 at close intervals. The tunnel shows 2 to 10 feet of altered and 
 pyritic granite, with smaller streaks and veins (1 to 6 inches wide) of 
 pyrite, arsenopyrite, and blende, associated with a little drusy quartz; 
 ruby silver has been noted. The developments consist of a crosscut 
 tunnel 200 feet long, with drifts on the vein, and a small winze. 
 Fifteen tons of ore were shipped, averaging $100. A sample of poor 
 ore gave 0.1 ounce of gold and 5.30 ounces of silver, a relatively large 
 amount of silver for this camp. 
 
 The Shamrock is situated a few hundred feet southwest of Pearl 
 post-office, and is developed by an 80-foot crosscut from the creek 
 level, from which drifts extend on the vein. The country rock is 
 very much disturbed granite containing rich but irregular seams of 
 ore. Some tons of the latter were shipped to smelters. 
 
 The Pinto lies a short distance north of the Bishopric mill, in 
 Pearl, and has been opened by 225 feet of tunnels and a 50-foot winze. 
 Sixty tons of ore are said to have been milled, yielding $23 per ton. 
 The vein is about 2 feet wide. The Pearl claim, showing some very 
 good ore, is located in this vicinity. 
 
 The Dynamite, said to be the extension of Pinto, is situated on the 
 north side of Willow Creek, a short distance east of Pearl, the crop- 
 pings being 250 feet above the stream. The vein is opened by a 
 tunnel 200 feet long, strikes N. 68 W. and dips 45 N., and shows 
 16 inches of decomposed vein-matter in granite. A large porphyry 
 dike lies close by to the north. 
 
 The Easter lies very nearly in the continuation of the Dynamite, 
 and is one of the producing veins of the district. The croppings lie 
 in granite 250 feet above the creek and the vein is developed by a 
 tunnel 100 feet below the croppings. Another tunnel was started at 
 the creek level, but has not yet reached the vein, work being sus- 
 pended in 1896 on account of litigation. A considerable amount of 
 
LINDGBEN.] MINES ON WILLOW CREEK. 715 
 
 ore was sloped and milled in 1895. The vein strikes N. 81 W., dips 
 60 N., and shows 2 to 3 feet of decomposed vein matter which, in the 
 pay shoot, yielded, it is said, $38 per ton of free gold. Pockets carry- 
 ing extremely rich ore occurred at intervals. On the west side the 
 vein is said to splinter up in a porphyry dike. 
 
 The Iron Dollar is located a short distance east of the Easter, and 
 is probably the continuation of the same vein. The development 
 consists of short tunnels and surface cuts. A few tons have been 
 milled, yielding $58 in free gold. The vein, which strikes N. 71 W. 
 and dips 60 N., lies in granite with occasional porphyry dikes in the 
 hanging wall. The decomposed ore consists of altered granite, with 
 streaks of arsenopyrite, pyrite, and galena, as well as a little calcite 
 and quartz. A sample of good ore gave 2.50 ounces of gold and 7.15 
 ounces of silver to the ton, a total of $56.68. 
 
 The Judas lies a few hundred feet north of the Iron Dollar, and is 
 at present (1897) being developed by a shaft intended to reach a 
 depth of 400 feet. Excellent ore is reported to have been milled from 
 this vein. The strike and dip are nearly the same as in the Iron 
 Dollar, and the vein shows from 1 to 2 feet of decomposed granite 
 carrying rich seams. 
 
 The Checkmate crops in granite on the south side of Willow Creek, 
 due south of the Judas. This vein is one of the productive proper- 
 ties, shipping ore during the whole summer of 1896. It is reported 
 that 300 tons, averaging $80 per ton, have been shipped. The mine 
 is developed by a tunnel 100 feet long on the level of the creek, giving 
 about 100 feet of backs. The deposit consists of a zone several feet 
 wide of altered and pyritic granite, containing rich seams of heavy 
 sulphides, arsenopyrite, pyrite, blende, and galena. At the time the 
 mine was visited most of the ore came from a seam of solid sulphides 
 4 to 6 inches wide. The strike is 1ST. 84 W. ; the dip to the north. 
 
 A short distance east of the Checkmate is the Silver Spray, from 
 which some good ore has been shipped. The vein is opened by a short 
 tunnel, and strikes east-west, dipping 40 N. The country rock is 
 dioritic granite, with streaks of dark diorite and dikes of diorite- 
 porphyrite. The character and the minerals are similar to the 
 Checkmate. 
 
 A little farther east is the Golden Chest, showing a wide zone of 
 altered and pyritous granite with narrow seams of zinc blende. 
 
 South of Willow Creek, opposite the last-named claim, lies the Red 
 Warrior, the oldest location in the district. No work was done on it 
 in 1896. 
 
 One mile southeast of Pearl, on the summit of a ridge, lies the 
 Leviathan claim. This is developed by a shaft 75 feet deep, and a 
 few tons of rich ore have been shipped. The width of the mineralized 
 granite is 13 feet, with seams of pay ore on both walls. In the con- 
 tinuation of this claim lie the Middleman and the Sacramento, which 
 
716 IDAHO MINING DISTRICTS. 
 
 have the same east- west strike. Both of these claims have shipped 
 some rich ore, containing much galena. The pure galena, assays 8 
 ounces of gold and 67 ounces of silver to the ton. The developments 
 are slight. 
 
 The Friday is located on a flat 100 feet south of the Leviathan and 
 is developed by a 100-foot shaft and drifts on the vein. Thirty tons 
 of ore are said to have been shipped and some rich surface ore has 
 been milled. The deposit shows 8 feet of altered granite, with a seam 
 of heavy sulphides on the foot and hanging -walls. The ore contains 
 pyrite, arsenopyrite, and blende, with much calcite. This vein is said 
 to be nearly vertical. The mine was not accessible during the present 
 examination. 
 
 Beyond the claims mentioned, for a distance of about 1,000 feet, there 
 are but few locations, but a number of strong veins are found on the 
 summit of the ridge separating Willow Creek from Rock Creek. 
 
 Beginning on the north, the Emmett vein is located near the summit 
 of Crown Point Hill, on the southwesterly slope. Good ore is reported 
 to have been found in this claim and shipments were made during 
 the winter of 1896-97. An incline shaft is sunk to a depth of 100 feet. 
 
 The Ida lies on the Rock Creek slope, at an elevation of 4, 700 feet, 
 and appears to be a wide vein in a dike of mineralized porphyry. It 
 is developed by 175 feet of tunnels and shaft, and excellent assays 
 have been obtained from average samples. The Blaine, on the 
 Willow Creek side, a short distance north of the road to Rock Creek, 
 is a promising prospect from which some ore was shipped in 1896. 
 The Alexander, located on the divide, showed some good ore, a brown 
 decomposed mass containing lead carbonate and milling $40 per ton. 
 The vein is 4 feet wide, striking N. 74 E. and dipping north. 
 
 The Birthday, a few hundred feet south of the Blaine, has produced 
 some rich shipping ore, composed of solid pyrite, zinc blende, and 
 galena. 
 
 The Silver Wreath lies on the Willow Creek side, three-fourths of 
 a mile southeast of Crown Point Hill, and is opened by a crosscut 
 170 feet long, cutting the vein at a depth of 75 feet. The croppings 
 show distinctly by quartz, colored greenish by arsenic. The strike is 
 N. 79 E. and the dip steep to the north. The deposit consists of a 
 zone of decomposed dioritic granite, 8 feet wide, containing seams of 
 the usual minerals. Some ore shipped yielded $40 per ton. 
 
 The IXL is situated on the Rock Creek side, three-fourths of a mile 
 east-southeast of Crown Point Hill. An incline shaft is being sunk 
 on this vein, and has at the present writing attained a depth of 200 
 feet. The vein, which strikes on an average northeast and dips 
 50 N. , is contained in granite with a dike of granite-porphyry in the 
 hanging wall. Four feet of brown decomposed vein matter are shown 
 in the shaft. About 25 per cent of the total value is in free gold, and, 
 according to average samples, there is a considerable body of medium- 
 
UKDQBKN.] MINES ON WILLOW AND ROCK CREEKS. 717 
 
 grade ore. A tunnel is located on the eastern extension, 900 feet east 
 of the incline. It is claimed that several ore bodies occur between 
 the incline and the shaft. The vein is one of the longest in the dis- 
 trict, being traceable for at least 2,000 feet. 
 
 The Zena, Stella, and Ella claims are located 600 feet south of the 
 IXL, about in the continuation of the Birthday and Silver Wreath, on 
 the Willow Creek side, and are opened by several short tunnels. The 
 Zena shows a well-defined fissure with a dike of diorite-porphyrite 
 5 feet wide in the hanging. The ore consists of narrow streaks of 
 blende, pyrite, and arsenopyrite in an altered and pyritous granite. 
 The ore appears fresh near the surface, in contrast to the decomposed 
 ledge matter of the IXL and the Alexander. 
 
 A number of veins are located along Rock Creek. The Black Crook 
 lies ITJ- miles northeast of Crown Point Hill, and is opened by a drift 
 on the vein 140 feet long. The vein strikes N. 62 E. and has a maxi- 
 mum width of 8 feet. It has diorite-porphyrite in the hanging wall 
 and granitic graiiite-diorite in the foot wall. The gangue is a grayish 
 quartz and a pink calcite colored by manganese. The ore body was 
 reported to be large but of low grade. Some assays show a relatively 
 large amount of silver in the ore. The Vein is reported to be traceable 
 for a long distance eastward. 
 
 The Blue Bucket lies 1,500 feet farther down the creek, at an eleva- 
 tion of 3,500 feet, in diorite and dioritic granite. Some very rich ore 
 is said to have been taken from it, but the claim was not worked 
 during the examination of the district. 
 
 East of Rock Creek lie a large number of claims, on most of which 
 but little work had been done in 1896. Among them is the Anticlinal, 
 under the Liberty Cap Hill, and the Lambertine, Bobtail, and Mint 
 claims, three-fourths of a mile east of Rock Creek. On the Bobtail 
 claim a tunnel 200 feet in length has been run, cutting an 8-foot vein 
 of good ore. 
 
 Many claims are also located on the ridge between Shafer Creek 
 and the Payette River. There appear to be two principal lines of 
 deposits. One begins one-half mile southwest of Horseshoe Bend 
 post-office, where the granite emerges from the Payette lake beds and 
 continues in a west-southwest direction up to the summit of the ridge. 
 Among the claims located along this line are the Sunny Side and the 
 Ballentyne, both on the same vein. The vein dips 70 to 80 S. and 
 is about 2 feet wide. The vein matter is soft and decomposed, carry- 
 ing free gold and some lead carbonate. The country rock is granite, 
 but in the foot wall lies a dike of quartz-diorite-porphyrite a few feet 
 wide. Another vein lies a short distance southward. A large num- 
 ber of prospects are found on the steep river hill toward the Payette, 
 about one-fourth mile north of the Ballentyne and opposite McFar- 
 land's ranch on the river. The following claims are located on this 
 vein system, from east to west: Mammoth, Apex, Atlanta, Claggett, 
 Topeka, Kentuck. These are at an elevation of about 1,000 feet above 
 
718 IDAHO MINING DISTRICTS. 
 
 the river. Hall's claim lies a little lower down, about 700 feet above the 
 river. Some of these claims appear to be promising properties, but 
 the developments are slight. The ores are decomposed, carrying on 
 the surface a considerable amount of free gold. Some antimonite, 
 carrying no gold, was also found in this vicinity. 
 
 The above are by no means all of the claims and prospects of the 
 district, but only such as showed any notable development or pro- 
 duction of ore. It is quite possible that some of these prospects may 
 develop into paying mines. 
 
 . SILVER DEPOSITS. 
 
 The Boise Mountains contain many notable silver deposits, chiefly 
 well-defined quartz veins with finely distributed rich sulphides and 
 antimonides. But it is not intended to take up the study of them in 
 this paper. The principal locality where silver mining has been car- 
 ried on is at Banner, 25 miles northeast of Idaho City. 
 
 Many scattered quartz veins with silver ores, either galena or rich, 
 silver sulphides, occur in the area here described, but none of them 
 have produced much. A few deposits of this kind occur along the 
 Idaho City road 3 or 4 miles from Boise, and another' in north fork of 
 Dry Creek a few miles southwest of Shafer Butte. Other silver pros- 
 pects are located 2 miles south of Church's placers, in Marsh Valley, 
 and at several places near Horseshoe Bend, notably on the western 
 side of the Payette 2 miles north of the bridge. Many silver pros- 
 pects occur 1 mile east of Halfway House in the Moore Creek Valley, 
 and some of them are said to contain rich ore (Sunlight group). 
 
 The occurrence of occasional silver deposits in the Idaho Basin has 
 already been mentioned in the detailed description in Chapter IV. 
 
 PLACERS OF THE BOISE RIDGE. 
 RECENT PLACERS. 
 
 The bars of the Boise and Payette rivers were worked in the early 
 days, and on some of them work is still progressing. The large 
 gravels of the lower reaches of both rivers contain a little gold, but 
 scarcely enough for profitable working. A dredger built some years 
 ago to work the gravels of the lower Payette near Marsh proved a 
 failure. The placers of the Moore Creek drainage were discussed in 
 Chapter III. Most of the creeks of the Boise Range have carried a 
 little gold, but few of them have been rich. 
 
 Benches along Dry Creek and Willow Creek are worked at inter- 
 vals, even now, when water is available. Shafer Creek, at least the 
 branch heading near Cartwright ranch, carried a little gold. The 
 richest placers probably occur at the northern base of Crown Point 
 Hill at Church's in Marsh Valley; but the whole output of the recent 
 placers of the Boise Ridge is, if we except the basin, of small 
 importance. 
 
UNDGHBN.] PLACERS OF THE BOISE RIDGE. 719 
 
 NEOCENE PLACERS. 
 
 The shore and old gulch gravels resting on granite in the early Neo- 
 cene Payette formation carry a little gold at many places for instance, 
 in several gulches about 2 miles eastward from Boise, north and south of 
 the Idaho City stage road. Similar old placer deposits are found in 
 the Payette formation at Church's, in Marsh Valley, and the old grav- 
 els at Johnson's, 1 mile southwest of Marsh, contain some gold which 
 has been concentrated in the gulches and washed by the hydraulic 
 process. 
 
 Gold-bearing gravels of late Neocene (Pliocene) age are found below 
 the remnants of the several basalt flows on both sides of Boise River, 
 those in Moore Creek having already been mentioned. The top of the 
 lowest flow, which is probably the oldest, lies at the ' ' New York House," 
 10 miles southwest of Boise, at the level of the river, and is not visible 
 farther west. Eastward it rises slowly, and near the mouth of Moore 
 Creek is 40 feet above the river (in August). Below this flow, which 
 is about 20 feet thick, lie 2 to 10 feet of coarse, heavy gravel, resting 
 on granite. This gravel is in places rich in coarse gold, part of which 
 probably conies from seams and small veins in the surrounding gran- 
 ite. There are only a few exposures of this low flow below the mouth 
 of Moore Creek, and it is reported that only one or two are known 
 above. The flow came down the south fork of the Boise. At low 
 water this gravel below the basalt has been mined with profit at sev- 
 eral places, notably at the Holy Terror mine, 2 miles below the mouth 
 of Moore Creek, and at Tarents, 2 miles farther down. There is only 
 a limited amount of this gravel below the lower flow. The two other 
 flows, 30 to 60 feet thick, are at elevations of 120 and 300 feet above 
 the river. Underlying both of them, wherever they are preserved, 
 hanging along the banks of the canyon, are heavy masses of late Neo- 
 cene gravels, 20 feet or more in thickness. This gravel contains some 
 gold throughout, and though much of it is fine, it may in places be 
 found rich enough for the hydraulic process wherever water can be 
 brought to it. In 1896 an attempt was made at the mouth of the 
 canyon, 8 miles southeast of Boise, on the northeast bank of the river, 
 to mine the heavy mass of gravel and sand here underlying the basalt 
 flow, and should this attempt be successful there are probably many 
 other similar deposits a little farther up the river which could be 
 worked in the same manner. 
 
THE FOSSIL PLANTS OF THE PAYETTE FORMATION. 
 
 By F. H. KNOWLTON. 
 
 The following report is based on a collection of fossil plants obtained 
 during the past season by Mr. Waldemar Lindgren from the lake beds 
 of the Snake River, in western Idaho, to which the name Payette for- 
 mation has been given. The matrix in which the plants are preserved 
 is in general a fine-grained clay, which has retained their outline and 
 nervation with remarkable fidelity. 
 
 Following is a list of localities from which the plants were obtained : 
 
 1. Two miles southeast of Marsh post-office, Boise County, Idaho. 
 From a coal prospect. 
 
 2. One mile southeast of Marsh post-office, Boise County, Idaho. 
 From a canyon on the road to Willow Creek and several hundred 
 feet above the Payette River. 
 
 3. Robb's coal prospect, 1 mile south of Horseshoe Bend post-office, 
 Boise County, Idaho. 
 
 4. Cartwright's ranch, on Shafer Creek, 4 miles southeast of Horse- 
 shoe Bend post-office, Boise County, Idaho. 
 
 5. Near Idaho City, Boitee County, Idaho. 
 
 SYSTEMATIC ENUMERATION OF SPECIES. 
 
 DRYOPTERIS IDAHOENSIS n. sp. 
 PL XCIX, figs. 1, 2. 
 
 Outline of frond unknown; frond twice pinnate, pinnse approxi- 
 mate, subopposite, deeply pinnate, the segments oblong, obtusely 
 acuminate, or upper pinnse lobed at base, the remainder entire or 
 undulate; secondary rachis strong, curved upward; each segment 
 with a strong midvein giving off forked veins. 
 
 As may be seen from the figure, this species is represented only by 
 a fragment, which, were it not for the fact that it is so distinctly 
 unlike any previously described American form, would be almost too 
 fragmentary for notice. The original form of the frond can not be 
 determined. The specimen consists of a portion of the rachis with 
 parts of four pinnse, only two of which are approximately perfect. 
 The pinnae are close together, subopposite in attachment, and slightly 
 18 GEOL, PT 3 46 ? 21 
 
722 IDAHO MINING DISTRICTS. 
 
 arching upward. The lowest pinna is lanceolate, deeply cut, with 
 oblong, obtusely acuminate segments. It is 2 cra in length. The other 
 most perfect pinna is 1.5 cm in length, and is also lanceolate in outline, 
 but has only one pair of segments at base, the remainder being merely 
 undulate. The nervation consists of forked veins arising from a 
 rather strong midvein in each segment. 
 
 As no fruit is preserved, its proper generic reference becomes ques- 
 tionable, and dependence must be placed on its resemblance to the 
 described forms of which the systematic position is known. It has, 
 for example, some resemblance to what has been described as Las- 
 trc&a fischeri Heer, from the Swiss Tertiary, and also John Day Val- 
 ley, Oregon, but differs in being hardly one-half the size and in 
 having forked instead of simple nerves. 
 
 On the whole, this appears to approach most closely certain species 
 of Aspidium (now Dryopteris) from the Tertiary of Switzerland. 
 Among them may be mentioned A. filix-antiqua Heer, A. meyeri 
 Heer, and A. elongatum Heer, all described and figured in Heer's 
 Flora Tertiaria Helvetia?, Vol. I, PI. XL 
 
 Locality: One mile southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 EQUISETUM sp. 
 
 There are several Equisetum stems in the collection. They are all 
 underground portions of stems, showing the scars of rootlets. From 
 one stein that is shown in cross section it appears that they are about 
 12-ribbed. They vary in width from l cm to 2 cm . 
 
 These stems appear to most resemble E. ivyomingense Lx., 1 from the 
 vicinity of Green River, Wyoming, also identified by Newberry 2 at 
 probably the same locality, but there are differences, which make it 
 advisable to keep them apart. I have not given a name to this form, 
 hoping that more and better material could be obtained. 
 
 Locality: Idaho City, Idaho. 
 
 PlNUS Sp. 
 
 PI. XCIX, fig. 3. 
 
 The collection contains a single nearly perfect fruit. 
 Locality: Idaho City, Idaho. 
 
 SEQUOIA ANGUSTIFOLIA ? Lx. 
 
 PI. XCIX, fig. 4. 
 Sequoia angustifolia Lx., Cret. and Tert. Fl., p. 240, PI. L, fig. 5, 1883. 
 
 This species was described by Lesquereux from Elko Station, 
 Nevada, in strata supposed to be of Green River Group age. He also 
 reported the same species from Corral Hollow, California. The figure 
 
 Tert. PL, p. 69, PL VI, figs. 8-11. 
 a Of. plates ined., PL LXV, flg. 8. 
 
KNOWLTON.] PLANTS OF THE PAYETTE FORMATION. 723 
 
 of a specimen from this last locality, as cited above, agrees closely 
 with the one under discussion, but it does not appear to be identical 
 with the Elko specimens. It is likely that on a revision of American 
 fossil Sequoias this will have to be made a new species, unless it can 
 be correlated with some known form. 
 
 Localities: Two miles southeast of Marsh post-office, Boise County; 
 Cartwright's ranch, on Shafer Creek; Idaho City. 
 
 SEQUOIA, Cones of. 
 
 The collection contains a single example, which bears three broken 
 cones that appear to belong to this genus. They are too fragmentary 
 to make an identification of value. 
 
 Locality: One mile southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 JUGLANS HESPERIA n. sp. 
 
 PI. XCIX, fig. 8. 
 
 Leaflet coriaceous, elliptical-lanceolate in outline, unequal-sided at 
 base, probably acuminate at apex (broken); margin finely serrate; 
 petiole short, thick; midrib thick; secondaries numerous, about 
 eighteen pairs, opposite below, alternate above, emerging at a low 
 angle, but curving upward, and running along the border and send- 
 ing weak branches to the teeth; intermediate secondaries numerous, 
 often two between secondaries, either soon lost, or running nearly to 
 the margin; nervilles numerous, mainly percurrent; finer nervation 
 quadrangular. 
 
 This fine species is represented by the single example figured. It 
 is nearly perfect, lacking only the apex. The part preserved is 8 om 
 long and was probably 10 om or ll cm in length when perfect. It is 
 broadest in the middle, at which point it is 3.75 cm in width. It 
 is broadly lanceolate, rounded and unequal-sided at base, and prob- 
 ably acuminate at apex. The margin is finely serrate, with rather 
 obtuse teeth. 
 
 This species is closely related to, if not, indeed, identical with, Jug- 
 lans oregoniana Lx. , from the Chalk Bluffs of California. Almost 
 the only difference is that J. oregoniana is enlarged upward, whereas 
 the one under discussion is narrowed above and enlarged below. The 
 configuration of the base, the serrate margins, and the nervation are 
 very similar. There are, however, no intermediate secondaries in J. 
 oregoniana. On account of these differences, slight though they are, 
 and from the further fact that the material is very scanty, it has been 
 thought best to regard them as distinct, at least for the present. 
 
 Locality : Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
724 IDAHO MINING DISTRICTS. 
 
 MYRICA LANCEOLATA n. sp. 
 PI. XCIX, figs. 5, 6. 
 
 Leaf of firm texture ; linear-lanceolate, tapering below into a long 
 wedge-shaped base which passes into a thick petiole l cm to 2 cm long; 
 apex broken but apparently long acuminate; margin irregular, faintly 
 toothed; midrib very thick, straight; secondaries obscurely preserved, 
 but apparently alternate, at an acute angle, and passing up for long 
 distances near the margin ; finer nervation hot retained. 
 
 This species is based on the two fragments figured, both of which 
 represent the basal portion. The smaller of the two specimens (fig. 6) 
 is 6.5 cm in length including the petiole (1 CJU ), and was probably at least 
 9. 5 cm in length when perfect. Its width is abont . 75 cm . The nervation, 
 with the exception Of the thick midrib, is not preserved. The larger 
 leaf has only 5.5 cm preserved, including the petiole of 2 cm . Its length 
 must have been at least 12 cm . The midrib is very thick and straight, 
 as in the other. The width of this specimen is a little more than 1. 5 cm . 
 
 This species is very closely allied to a species not yet published, 
 from the Lamar flora, in the Yellowstone National Park. The leaves 
 are of about the same size, the main point of difference being the 
 more pronounced teeth in the Lamar species. 
 
 Locality: Cartwright ranch, on Shafer Creek, Boise County, Idaho. 
 
 MYRICA ? IDAHOENSIS n. sp. 
 PI. XCIX, fig. 7. 
 
 Leaf thickish, obovate-lanceolate, obtuse at apex, narrowed below 
 to a wedge-shaped base and a long, thick petiole; margin obscurely 
 crenate ; midrib thick, straight. 
 
 This leaf is preserved entire, and is 9 cm in length, including the 
 petiole, which is 2 cm . In outline it is long, obovate-lanceolate, with 
 obtuse apex, and narrowed from above the middle to a long, wedge- 
 shaped base. The petiole is thick and much curved to one side. The 
 margin is rather remotely and faintly crenate, the teeth short and 
 obtuse/ The midrib is the only nervation preserved., and this is thick 
 and straight. 
 
 In absence of better nervation there is some doubt as to the generic 
 reference of this leaf. It has been referred to Myrica provisionally, 
 until better material can be obtained. It has considerable resem- 
 blance to the living M. cerifera L. (common wax-berry), but it is impos- 
 sible to carry the comparison beyond similarity of shape, dentation, 
 and midrib. 
 
 Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
KNOWLTON.] PLANTS OF THE PAYETTE FORMATION. 725 
 
 POPULUS LINDGRENI n. Sp. 
 PL C, fig. 3. 
 
 Leaf of firm texture, coriaceous, nearly circular in outline, being 
 only a trifle broader below the middle, whence it is rounded to a trun- 
 cate base, and above to a very obtuse apex; margin somewhat irreg- 
 ularly but finely crenate-toothed, the teeth obtuse; petiole over 2 cm 
 in length, very large, flattened; palmately five-nerved or ribbed from 
 the top of the petiole, the central or midrib strongest, very thick, 
 the two lateral ribs also strong, the lowest pair being the slightest; 
 the central or midrib with two pairs of subopposite secondaries high 
 above the middle ; the large lateral pairs of ribs each with about six 
 secondaries on the outside, emerging at a very low angle and arch 
 ing near the margin ; finer nervation obscure. 
 
 The fine specimen figured is the only one obtained of this charac- 
 teristic species. It is nearly circular in outline, being 5.25 cm in length 
 without the petiole, and nearly 5.5 cm in width at the broadest portion, 
 which is just below the middle. The petiole is a little more than 2 cm 
 in length, 2 mm in width as it emerges from the base of the leaf, and 
 3.5 mm in width at the other end. It appears to be preserved entire 
 and is clearly flattened. 
 
 The margin of the leaf is closely crenate-toothed, the teeth being 
 obtuse. The nervation is markedly five-ribbed from near the top of 
 the petiole, the three central ribs being by far the stronger. The 
 lowest lateral ribs or nerves are small and soon lost in the blade of 
 the leaf. 
 
 Among living species this appears to approach most closely to P. 
 balsamifera candicans. It differs in being much more obtuse, in 
 having a more marked crenate border, and in the stronger nervation. 
 The relationship is, however, quite marked, the two leaves being of 
 the same type, but with strong specific differences. 
 
 There is no fossil American species with which this is to be closely 
 compared. There are several with approximately the same shape, 
 yet differing clearly in serration, nervation, etc. 
 
 I take pleasure in naming it after Mr. Waldemar Lindgren, of the 
 United States Geological Survey. 
 
 Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 POPULUS EOTREMULOIDES n. Sp. 
 PI. C, figs. 1, 2; CI, figs. 1, 2. 
 
 Leaves membranaceous yet firm-textured, broadly ovate in outline, 
 rounded regularly to the base and contracted above to an obtusely 
 acuminate apex; margin entire for lower fourth of leaf, remainder 
 obscurely crenate-toothed ; petiole very long, flattened; midrib rather 
 
726 IDAHO MINING DISTRICTS. 
 
 strong; secondaries about four or five pairs, the lowest pair arising 
 from the very base of the blade, thin, soon lost in the blade ; second 
 pair very strong, arising from the petiole some distance above the 
 base and arching up for two-thirds the length of the leaf, probably 
 branched outside; the other secondaries, probably two or three pairs, 
 arising some distance above, strong, alternate, at an angle of 45 ; 
 finer nervation not retained. 
 
 This well-marked species is represented by the four specimens fig- 
 ured. The larger of these (fig. 2 of PL CI) is 10.75 cm in length with- 
 out the petiole, which is 5.25 cm long. The margin is not all preserved, 
 but the leaf appears to have been about 7 cm in width. The other 
 nearly perfect leaf (fig. 1) is a little less than 10 cm in length -and is 
 6.5 cm in width. About 3.5 cra in length of petiole is preserved, but it 
 is not all present. 
 
 The leaves are all broadly ovate, with rounded bases and obtuse 
 apices. The margin is crenate-toothed from above the base. The 
 petiole is very long, as may be seen from the figures, and is obviously 
 flattened. The nervation is not well preserved, but enough can be 
 made out to show its general character. The strong pair of second- 
 aries arise some distance above the base, while the thin basal pair 
 arise near the top of the petiole. There are also two or three pairs of 
 secondaries arising from the midrib some distance above the strong 
 pair. None of the ultimate nervation is retained. 
 
 Among living species the relation of this fossil form is unquestion- 
 ably with P. tremuloides Michx. In the herbarium of the National 
 Museum there is a specimen, consisting of a young seedling plant of 
 this species, collected on the Aquarius Plateau, Utah, at an altitude 
 of 9,000 feet, that can hardly be distinguished from the fossil leaves 
 under consideration. The size, outline, petiole, and nervation are 
 practically identical. The only difference, and this is of minor im- 
 portance, appears to be in the margin. In the fossil form the teeth 
 are absent from the lower fourth of the leaf, while these specimens 
 of P. tremuloides are toothed from base to apex and the teeth are 
 rather larger. The leaves of this seedling differ somewhat from the 
 normal mature leaves of the species, but it would seem, in view of 
 their evident relationship to the fossil leaves, that they represent a 
 reversion to an ancestral type, or perhaps rather a survival of this 
 type, which disappears in the mature plant, There certainly can be 
 no doubt of the intimate relationship between the living and fossil 
 leaves. 
 
 There seems to be no fossil American species with which it is at all 
 intimately related. It is perhaps closest to P. zaddachi Heer, but 
 differs markedly. 
 
 I have given this species the name eotremuloides in view of its 
 evident relation to the well-known tremuloides. 
 
 . Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
KNOWLTON.] PLANTS OF THE PAYETTE FORMATION. 727 
 
 POPULUS OCCIDENTALS n. Sp. 
 PI. XCIX, fig. 14. 
 
 Leaves evidently of firm texture, long-ovate in outline, rounded 
 below to a truncate base and narrowed above (apex broken) ; petiole 
 not preserved; margin faintly or rather obscurely crenate-toothed, 
 with obtuse teeth; midrib slender, straight; secondaries seven or 
 eight pair, subopposite, at an angle of about 45, curving upward ; 
 finer nervation not preserved. 
 
 This species is represented by the single example figured. The 
 part preserved is 8 cm long and was probably not far from 10 cm in length 
 when perfect. It is broadest at a point much below the middle, where 
 it is 6 cm broad. Both base and apex are wanting, but it appears that 
 it was rounded or truncate at base and acuminate at apex. The mar- 
 gin is rather obscurely crenate-toothed, the teeth obtuse. The nerva- 
 tion consists of about eight pairs of subopposite secondaries. 
 
 This species seems to approach quite closely to Populus monilifera 
 Ait. , the cottonwood so abundant in the West. It differs slightly in 
 dentation of the margin, and in the fact that the secondaries arise at 
 a greater angle and apparently do not anastomose near the margin. 
 
 Among fossil species it is somewhat related to P. balsamoides Gopp. , 
 from the Miocene of California. 1 But this differs in being more heart- 
 shaped at base, more obtuse at apex, and more strongly dentate at 
 margin. 
 
 Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 SALIX ANGUSTA Al. Br. 
 
 PL XCIX, fig. 12. 
 
 There are a number of somewhat defective leaves that are referred 
 with little doubt to this species. 
 
 Localities: One mile southeast of Marsh post-office, Boise County; 
 Cartwright's ranch, on Shafer Creek, Idaho. 
 
 BETULA ANGUSTIFOLIA Newby. 
 Proc. U. S. Nat. Mus., Vol. V, p. 508, 1883; plates ined., PI. XL VI, fig. 5. 
 
 This was described by Newberry from Bridge Creek, Oregon. The 
 specimen here referred to it is broken, but is probably correctly 
 identified. 
 
 Locality: Idaho City, Idaho. 
 
 BETULA, Fruit of. 
 PI. XCIX, fig. 9. 
 
 Fruit (pistillate ament) cylindrical, 3 cm in length, 9 mm in diameter; 
 bracts rather few, acutish, about 3 mm long. 
 
 1 Lx., Cret. and Tert. Fl., p. 348, PL LV, figs. 3, 5, 1883. 
 
728 IDAHO MINING DISTRICTS. 
 
 This appears to represent the pistillate ament of a Betula, agreeing, 
 for example, quite closely with the living B. alba, B. papyracea, etc. 
 This view is further strengthened by the finding of leaves of Betula 
 in the same beds. 
 
 I have not thought best to name it specifically, as it is somewhat 
 obscure and better material is necessary for the determination of the 
 minute characters. 
 
 Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 BETULA ^QTJALIS? Lx. 
 
 PL Oil, fig. 5. 
 
 Betula cequalis Lx., Mem. Mus. Comp. Zool., Vol. VI, No. 1, p. 2, PI. I, figs. 
 2-4, 1880. 
 
 I am somewhat in doubt as to the correctness of this reference. 
 There is but a single specimen in the collection, and this, as may be 
 seen from the figure, is not perfect, lacking the apex and most of one 
 side and the base. It, however, agrees quite closely with Lesquereux's 
 figures, being only a little more obtuse. The base appears similar as 
 far as can be made out. 
 
 Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 QUERCUS SIMULATA n. 8p. 
 PL CI, figs. 3, 4; Oil, figs. 1, 2. 
 
 Leaves coriaceous, lanceolate-acuminate, slightly unequal sided at 
 base, obtuse or obtusely acuminate at apex; margin undulate or 
 remotely shallow-toothed; petiolate, petiole short, thick; midrib 
 strong, straight; secondaries numerous, 12 to 16 pairs, alternate or 
 subopposite, at an angle of 20 to 45, irregular, camptodrome, each 
 joined by a simple bow to the one next above; intermediate second- 
 aries occasional, soon vanishing; ultimate nervation obscure, but 
 apparently quadrangular. 
 
 These leaves appear to have been quite abundant in the beds, for 
 four or five very perfect examples, and numerous more or less frag- 
 mentary ones, occur in the collection. They were evidently thick, 
 coriaceous leaves, suggestive at least of having been evergreen. They 
 range considerably in size, the smallest being 3 cm in length and l cm in 
 width, and the largest 9 cm in length and 2.25 cm in width. The average 
 size, represented by figs. 1 and 4, is about 8 cm in length by 2 cm in 
 width. In the smaller specimens the petiole is scarcely 2 m long, 
 while in the larger ones it is nearly or quite l cm in length. They are 
 slightly unequal-sided at base, and obtuse (fig. 1) or somewhat acumi- 
 nate (fig. 4) at apex. The margin is undulate, or very slightly and 
 remotely toothed. 
 
KNOWLTON.] PLANTS OF THE PAYETTE FORMATION. 729 
 
 The nervation is marked at once by the great number of close camp- 
 todrome secondaries that arise at various angles from perhaps 20 to 
 45. The finer nervation is obscure. 
 
 Among living species this appears to approach most closely to 
 Q. imbricaria MX., which has the same shape, the inequilateral base, 
 and the undulate margin. The differences in the primary nervation 
 are, however, marked. In Q. imbricaria the secondaries are not 
 nearly so numerous ; they emerge at a more acute angle and are more 
 irregular in their course. They are camptrodrome, somewhat as in 
 Q. simulata. 
 
 Among fossil species the one under discussion approaches Q. sim- 
 plex Newby., from Bridge Creek, Oregon, 1 which differs in being nar- 
 rower, with more acuminate apex, and in having fewer secondaries. 
 Ours is also somewhat like Q. convexa Lx. , of the auriferous gravels 
 of California, which differs, however, in being rather oblanceolate 
 with more obtuse apex. The nervation is of the same character in 
 both, and they are evidently related. 
 
 Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 QUERCUS CONSIMLLIS Newby. 
 
 PI. Oil, fig. 6. 
 
 Quercus consimilis Newby., Proc. TJ. S. Nat. Mus., Vol. V, p. 505, 1883; plates 
 
 ined., PI. LXIII, figs. 2-5. 
 Quercus breweri Lx., Cret. and Tert. Fl., p. 246, PI. LIV, figs. 5-8, 1883. 
 
 This species is represented by the very perfect figured specimen 
 and also a number of equally well preserved but broken specimens. 
 There can be no doubt as to its belonging to Newberry's species, 
 which is from Bridge Creek, Oregon. 
 
 Localities: Two miles southeast of Marsh post-office; 1 mile south- 
 east of Marsh post-office, Boise County, Idaho. 
 
 QUERCUS IDAHOENSIS n. sp. 
 PL Oil, fig. 4. 
 
 Leaves coriaceous, broadly oblong in general outline, rather abruptly 
 rounded at base, obtusely acuminate at apex, margin sharply serrate 
 to just below the apex; the teeth large, almost bristle-pointed, directed 
 upward, sinuses deep, rounded; midrib rather thin, straight; second- 
 aries about 10 or 12 pairs, straight, parallel, craspedodrome, entering 
 the larger teeth, arising at an angle of about 45, subopposite; finer 
 nervation not preserved. 
 
 This species is represented by the single example figured. It is 8 cm 
 long and 3 cm wide. It lacks only a very small portion of the base. It 
 
 Proc. U. S. Nat. Mus., Vol. V, p. 505, 1883; Plates ined., PI. XLIII, flg. 6. 
 
730 IDAHO MINING DISTRICTS. 
 
 is quite a striking leaf, being made so by the regular, sharp-pointed 
 teeth and the parallel craspedodrome secondaries. 
 
 This species is closely allied to the preceding species, Q. consimilis, 
 and it is possible that it may belong to it. It appears to differ in its 
 larger size, larger and stronger teeth, and particularly in being toothed 
 entirely to the base, whereas Q. consimilis is without teeth for nearly 
 or quite one-third of its length. A larger series may show them to 
 be identical. 
 
 Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 QUERCUS SIMPLEX Newby. 
 Proc, U. S. Nat. Mus., Vol. V, p. 505, 1883; plates ined., PI. XLIII, fig. 6. 
 
 There are two or more fairly well preserved examples that appear 
 to belong to this species. 
 
 Locality: One mile southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 QUERCUS PAYETTENSIS n. sp. 
 
 PL CII, fig. 9. 
 
 Leaves of firm texture, lanceolate in outline ; margin deeply sinuate- 
 toothed, the teeth rather obtuse, the sinuses deep, rounded; midrib 
 strong; nervation craspedodrome; secondaries as many pairs as there 
 are teeth, alternate, at an angle of about 45, passing straight to and 
 entering the teeth ; finer nervation not retained. 
 
 This species is founded on the example figured and one or two addi- 
 tional fragments. The figured specimen is the most perfect, though 
 lacking both base and apex. It is now about 4.5 cm in length and 
 1.75 cm in width. It was probably not far from 7 cm in length when 
 perfect. 
 
 This species has comparatively little resemblance to either of the 
 species of Quercus detected thus far in the Payette formation. It is 
 perhaps closest to Q. consimilis Newb. (PI. IV, fig. 6), but differs 
 markedly in being longer, narrower, and in having much stronger 
 teeth. Quercus furcinervis Rossm., 1 from Bridge Creek, Oregon, is 
 somewhat similar, being, however, very much larger and with rela- 
 tively much smaller teeth. 
 
 Locality: Silicified shale, Jackass Creek, 1 miles above its junction 
 with the Payette River, Boise County, Idaho. 
 
 QUERCUS ? sp. 
 
 There is a single fragment that appears to belong to this genus, but 
 it is too much broken to permit identification. It is a leaf that must 
 have been 12 cm or 14 cm in length and about 5 cm in width. The basal 
 
 i Lx., Cret. & Tert. PI., PI. LIV, fig 2. 
 
KNOWLTON.] PLANTS OF THE PAYETTE FORMATION. 731 
 
 portion only is preserved. The leaf appears to have been obovate- 
 lanceolate, extending below into a wedge-shaped base. It appears to 
 have been entire in the lower portion and toothed above. 
 
 Locality: One mile southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 ULMUS SPECIOSA Newby. 
 
 Proc. U. S. Nat. Mus., Vol. V, p. 507, 1883; Plates ined., PI. XLV, fig. 8. 
 
 A single, somewhat fragmentary specimen, but with no doubt this 
 species. 
 
 Locality: Idaho City, Idaho. 
 
 FlCUS UNGERI Lx. 
 Pi CI, fig. 5. 
 
 Lesquereux, Suppl. to Hayden's Ann. Rept. 1871, p. 7 (1872); Tert. Fl., p. 195, PI. 
 XXX, fig. 3; Cret. & Tert. Fl., p. 163, PI. XLIV, figs. 1-3. 
 
 The collection contains three specimens that undoubtedly belong 
 to this species, being especially like fig. 2 of PL XLIV in the Cretaceous 
 and Tertiary Flora. They are of about the size of this, and have the 
 slightly unequal base and identical nervation. 
 
 Locality: Cartwright's ranch, on Shafer Creek, Boise County, Idaho. 
 
 CASSIA OBTUSA n. sp. 
 PL C, figs. 4, 5. 
 
 Leaflet small, of firm texture, elliptical; margin entire, obtuse at 
 apex, obtuse or subcordate at base; petiole short, thick; midrib 
 thick, straight ; secondaries numerous, about 14 pairs, the lowest pair 
 short, nearly at right angles to the midrib, the others alternate, at an 
 angle of 20 to 30, probably curving and anastomosing at their 
 extremities; finer nervation not preserved. 
 
 The two examples figured are all of this species that were contained 
 in the collection. The smaller is about 3.5 cm in length and 1.5 cm in 
 width. It is nearly regularly elliptical in outline, with obtuse base 
 and relatively obtuse apex. The petiole is a little more than l mm in 
 length and is rather thick. The midrib is also thick and carries 
 about fourteen pairs of alternate parallel close secondaries. The 
 other specimen is a little longer, with a subcordate base, but is other- 
 wise similar. 
 
 There seems to be no American ^species with which this can be 
 closely compared, but in the Swiss Tertiary a number of forms 
 approach it quite closely. Thus Cassia phaseolites Heer 1 suggests 
 this, but differs in size and in the fact that it is more wedge-shaped 
 at base and apex. The nervation is quite similar. C. ambigua Heer 2 
 
 i Fl. Tert. Helv., Vol. Ill, PI. CXXXVII, figs. 1-13. 
 "Loc. cit., figs. 29, 32. 
 
732 IDAHO MINING DISTRICTS. 
 
 is also similar, but differs in outline and in having fewer secondaries. 
 As nearly as can be made out, the leaflets under consideration belong 
 to this genus and are provisionally so placed. 
 
 Locality : Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 PLATANUS ASPERA ? Newb. 
 Proc. U. S. Nat. Mus., Vol. V, p. 509, 1883; Plates ined., PI. XLII, figs. 1-3. 
 
 The collection contains several fragments of Platan us leaves, but 
 hardly enough to be certain of their reference to this species. It is 
 probable, however, that the identification is correct. 
 
 Locality: One mile southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 CELASTRUS LINDGRENI n. sp. 
 PL XCIX, fig. 13; C, fig. 6. 
 
 Leaf membranaceous ; lanceolate-oblong in outline, narrowed below 
 into a wedge-shaped base and prolonged above into an acuminate 
 apex; margin obscurely serrate, the teeth small, obtuse; midrib 
 rather thick and strong; secondaries about 10 or 12 pairs, suboppo- 
 site, emerging at an angle of 45 or more, camptodrome, each arched 
 and joined to the one above by a broad loop some distance within the 
 border, with one series of smaller loops outside from which weak 
 branches pass to the teeth; intermediate secondaries occasionally 
 present, soon lost; nervilles much broken, forming large, irregular 
 areolse. 
 
 The somewhat fragmentary leaves figured are the only specimens of 
 this form in the collection. The smaller appears to have been about 
 6.5 cm in length, and a little more than 2 cm in width at the broadest 
 point, which is a little below the middle of the leaf. The larger leaf 
 was 8 or 9 cm in length, and is about 3.8 cm in width. The nervation of 
 both is finely preserved, and is quite characteristic of the genus 
 Celastrus. 
 
 The species with which this is to be compared is Celastrus frax- 
 inifolius Lx./from Florissant, Colorado. The general resemblance is 
 very marked, the differences being rather of minor or specific impor- 
 tance. They are as follows : In C. fraxinifolius the leaves are broad- 
 est below the middle, the petiole is winged (broken in C. lindgreni), 
 the teeth are fewer and stronger, .and the secondaries fewer. 
 
 Among the numerous new species of this genus found in the Yel- 
 lowstone National Park, but still unpublished, there are several to 
 which this is evidently related. 
 
 Locality : Idaho City, Idaho. 
 
 ' Cret. and Tert. Fl., p. 184, PI. XXXIII, figs. 2-4; XL, fig. 10. 
 
KNOWLTON.] PLANTS OF THE PAYETTE FORMATION. 733 
 
 ACER TRILOBATUM PRODUCTUM ? Heer. 
 PL CII, fig. 3. 
 
 The collection contains only the single specimen figured of this 
 form. It is unfortunately broken at the apex, so that its reference to 
 this variety of Acer trilobatum is more or less uncertain. From the 
 configuration of the part preserved there is, however, little doubt as 
 to its correctness. 
 
 Locality : Two miles southeast of Marsh post-office, Boise County* 
 Idaho. 
 
 RHUS PAYETTENSIS n. sp. 
 
 PI. CI, figs. 6, 7. 
 
 Leaflet coriaceous, ovate in outline, abruptly rounded or truncate 
 at base, and slightly unequal-sided, obtuse (?) at apex; margin nearly 
 entire on one side, remotely toothed on the other, the teeth small, 
 sharp, pointing upward; midrib thin, somewhat irregular; seconda- 
 ries about 6 or 7 pairs, opposite or subopposite, emerging at an angle 
 of 35, much curved upward, and ending in or sending weak branches 
 to the few marginal teeth; nervilles strong, mainly percurrent; finer 
 nervation quadrangular. 
 
 The smallest leaflet is 5.25 cm in length as now preserved, and was 
 probably not far from 6 cm in length when perfect. It is just 3 cm in 
 width. The whole base is unfortunately not preserved^ but from the 
 configuration it appears that it was slightly unequal-sided. 
 
 This species is referred to the genus Rhus on the strength of its 
 resemblance to the living Rhus toxicodendron, the common poison ivy. 
 This small leaflet resembles certain small forms of this species in 
 quite a marked degree. The living form has usually more strongly-cut 
 leaflets, but in general outline and nervation they are quite similar. 
 
 This species does not appear to be particularly close to any of the 
 numerous fossil species that have been described from similar beds. 
 
 Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 TRAPA AMERICANA n. sp. 
 PL CII, fig. 7a. 
 
 Fruit two-horned, the horns long, slender, acuminate, pointing 
 upward at an angle of about 45 ; central prominence between the 
 horns obtuse, prominently striate ; body of fruit thick, wedge-shaped 
 below. 
 
 This fruit belongs to the two-horned Asiatic type of the genus. It 
 is obverse-deltoid or broadly wedge-shaped in outline. The distance 
 from base to extremity of horn is just 2 cm , while the distance between 
 
734 IDAHO MINING DISTRICTS. 
 
 the horns is about 17 mm . The length from base to tip of central promi- 
 nence is 16 mm . The length of the horns is about 7 mm , and the length 
 of the central prominence about 4 mm . 
 
 Thus far only two specimens of Trapa have been described from 
 North America T. borealis Heer, 1 from the Eocene of Port Graham, 
 Alaska, also detected by Dawson in the Laramie of Red Deer and 
 Rosebud rivers, Canada, and Trapa (?) microphylla Lx., 2 described 
 from Point of Rocks, Wyoming, and since detected near the mouth 
 of the Yellowstone River in Montana, in the Yellowstone National 
 Park, in the Ceratops beds of "Wyoming, and along the Red Deer and 
 Rosebud rivers in Canada. Some doubt attaches to the correctness 
 of the reference of the last to Trapa, as the specimens are leaves or 
 leaflets only; but as they have been found by Dawson associated with 
 fruit, it may be correct. 
 
 The ordinary form of T. borealis, as described and figured by Heer 
 (loc. cit.), is quite different from the one in hand, being very thick 
 and obtuse at base, with irregular horns and a greatly enlarged cen- 
 tral projection. One of Heer's figures (op. cit., fig. 11), however, is 
 quite like ours in shape, but is more than twice the size. 
 
 The species from Idaho is perhaps more like T. silesiaca Gopp., 
 described from Schossnitz, Silesia, and also detected by Heer in Por- 
 tugal. 3 It is about the same size, but differs slightly in the slenderer 
 horns and entire central prominence. 
 
 Locality: Idaho City, Idaho. 
 
 TRAPA ? OCCIDENTALIS n. sp. 
 PL Oil, fig. 7b. 
 
 Fruits two-horned, or in effect three-horned, the lateral horns slen- 
 der, acute, at right angles to the central prominence or horn, which 
 is nearly twice the size of the lateral ones; body of the fruit but little 
 prolonged below the plane of the lateral horns, slightly wedge-shaped. 
 
 These fruits are decidedly anomalous. They are deltoid or trian- 
 gular in general outline. The width is 2 cm , each lateral horn being 
 5 or 6 mm in length and 2 mm in width at the base. - The central pro- 
 jection is 1.5 cm in length and about 5 mm in width at the base. 
 
 I am much in doubt as to whether these fruits should be referred 
 to the genus Trapa. They are found in the same piece of matrix as 
 the one previously characterized, and in fact, as may be seen from 
 the figure, one of them overlaps one of the horns of T. americana. 
 Close association of unconnected fossils does not, of course, argue 
 affinity, but these are so close together and have such a general 
 
 1 PI. Poss., Alaska, p. 38, PI. VIII, figs. 9-14 
 
 5 Bull. U. S. Geol. and Geogr. Surv. Terr., Vol. I, p. 369, 1875; Tert. PI., p. 295, Pl.'LXI, figs. 
 16-lTa; Ward, Bull. U. S. Geol. Surv. No. 37, p. 64, PI. XXVII, figs. 3-5, 1887. 
 3 Contr. PI. Poss. Portugal, p. 37, PI. XXII, fig. 11, 1881. 
 
KNOWLTON.] PLANTS OP THE PAYETTE FORMATION. 735 
 
 resemblance that it has been thought best to describe them under 
 this name. A more obvious affinity will be accepted if pointed out. 
 For geological purposes this species will serve admirably. 
 Locality: Idaho City, Idaho. 
 
 PHYLLITES FLEXUOSUS n. sp. 
 PL Oil, fig. 8. 
 
 Leaf membranaceous, outline probably broadly lanceolate; base 
 and apex destroyed ; margin undulate-toothed ; midrib strong, straight ; 
 secondaries many pairs, alternate, straight or oftener very flexuose, 
 camptodrome or subcraspedodrome, entering the obscure blunt teeth; 
 finer nervation not retained. 
 
 This is only a fragment, and perhaps should not be given a name, 
 but it appears to be quite characteristic, and hence has been given 
 this preliminary name pending the discovery of more perfect material. 
 The width is about 6.5 cni . 
 
 No attempt has been made to search for affinities, as it is too frag- 
 mentary to afford satisfactory diagnostic characters for comparison. 
 
 Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. 
 
 PHYLLITES OBSCURUS n. sp. 
 PI. XCIX, figs. 10, 11. 
 
 Leaves small, elongated-elliptical, with entire margins; petiole 
 long, thick; midrib thick, straight; other nervation not preserved. 
 
 The two little leaves figured are all that were contained in the 
 present collection. The smaller is 2 cm in length, and about 6 mm wide. 
 The petiole is about 4 mm in length. The larger leaf was about 3.5 om 
 in length and about 8 mm in width. The petiole is about 8 mm in 
 length. 
 
 As the nervation is not preserved, it is impossible to refer these 
 leaves to a known genus with any degree of certainty. They are 
 consequently not of great importance. 
 
 Locality: Two miles southeast of Marsh post-office, Boise County, 
 Idaho. ' 
 
 DISCUSSION OF THE FLORA AND ITS BEARING ON THE 
 AGE OF THE BEDS. 
 
 As here enumerated, the flora of the Payette formation embraces 32 
 forms. Of this number, 17 are described as new, while 5 are not spe- 
 cifically named, thus leaving only 10 species, or nearly 33 per cent, 
 
736 
 
 IDAHO MINING DISTRICTS. 
 
 having an outside distribution. The following table shows graphically 
 the distribution of these species : 
 
 Distribution of the flora of the Payette formation. 
 
 
 Carbon, Wyoming. 
 
 Sedalia, Colorado. 
 
 * 
 
 st 
 
 2a 
 
 a 
 
 B 
 
 
 a 
 
 Auriferous gravels, 
 California. 
 
 1 
 1- 
 
 t* o 
 
 O to 
 f 
 
 M 
 I 
 
 m 
 
 
 
 
 
 1 
 
 >a 
 Kfi 
 
 && 
 1 
 
 -a 
 
 Sequoia angustifolia Lx 
 
 
 
 x 
 
 x 
 
 
 
 Salix angusta ? Al. Br 
 
 
 
 x 
 
 x 
 
 
 
 Betula angustifolia Newb - 
 
 
 
 
 
 x 
 
 
 Betula aequalis Lx 
 
 
 
 
 x 
 
 
 
 Quercus simplex Newb ... 
 
 
 
 
 
 x 
 
 
 Quercus consimilis Newb 
 
 
 
 
 
 x 
 
 x 
 
 Ulmus speciosa Newb 
 
 
 
 
 
 x 
 
 
 Ficus ungeri Lx. 
 
 
 
 x 
 
 
 
 
 Platanus aspera Newb 
 
 
 
 
 
 x 
 
 
 Acer trilobatum productum ? Heer 
 
 x 
 
 x 
 
 
 
 
 X? 
 
 
 
 
 
 
 
 
 From this table it appears that 9 of the 10 species are found in the 
 lone formation (auriferous gravels) of California, or the Miocene of 
 Bridge Creek and the John Day Valley, Oregon, and that 6 of the 
 species have never before been found outside of these places. Of the 
 3 species also reported from the Green River group, Sequoia angusti- 
 folia, as reported from California, is probably not the same as the 
 original from Nevada, as stated in the systematic portion. Salix 
 angusta is open to more or less question, being difficult of positive 
 identification at all times. The remaining species, Ficus ungeri, 
 appears to be found in the Green River group and the Payette. Acer 
 trilobatum productum is doubtfully identified from the collection 
 under discussion, and is therefore entitled to but little consideration. 
 
 Several of the species here described as new to science are related, 
 in some cases closely, to certain Miocene species. Thus, Quercus ida- 
 hoensis is close to Q. consimilis Newb. ; Populus occidentalis is related 
 to P. balsamoides Gopp. ; Quercus simulata is somewhat like Q. sim- 
 plex Newb. ; Myrica lanceolata and Celastrus lindgreni are clearly 
 related to species not yet published from the Lamar flora of the Yel- 
 lowstone National Park. 
 
 The evidence of the fossil plants points, therefore, to the Upper 
 Miocene age of the Payette formation, a view which is confirmed by 
 the stratigraphy. In fact, the close relation brought out between this 
 flora and that of Bridge Creek and John Day Valley and the fact 
 that the western limit of these beds as now explored is in the direc- 
 tion of these localities make it more than possible that they may be 
 parts of a formation of wide extent. 
 
PLATE XCIX. 
 
 18 GEOL, PT 3 47 737 
 
PLATE XCIX. 
 
 Page 
 
 FIG. 1. Dryopteris idahoensis n. sp 721 
 
 FIG. 2. Dryopteris idahoensis. Fragment 721 
 
 FIG. 3. Pinus sp._ 722 
 
 FIG. 4. Sequoia angnstif olia Lx 722 
 
 FIGS. 5, 6. Myrica lanceolata n. sp _ . . 724 
 
 FIG. 7. Myrica idahoensis n. sp 724 
 
 FIG. 8. Juglans hesperia n. sp 723 
 
 FIG. 9. Betula, fruit of 727 
 
 FIGS. 10, 11. Phyllites obscurus n. sp 735 
 
 FIG. 12. Salix angusta? Al. Br 727 
 
 FIG. 13. Celastrus lindgreni n.sp 732 
 
 FIG. 14. Populus occidentalis n. sp._ 727 
 
 738 
 
U. S. GEOLOGICAL SURVEY 
 
 EIGHTEENTH ANNUAL REPORT PART III PL. XCIX 
 
 13 
 
 FOSSIL PLANTS OF THE PAYETTE FORMATION. 
 
PLATE C. 
 
 739 
 
PLATE C. 
 
 Page. 
 
 PIGS. 1, 2. Populus eotremuloides n. sp 725 
 
 Fio. 3. Populus lindgreni n. sp 725 
 
 FIGS. 4, 5. Cassia obtusa n. sp 731 
 
 FIG. 6. Celastrus lindgreni n. sp 732 
 
 740 
 
U. 8. GEOLOGICAL SURVEY 
 
 EIGHTEENTH ANNUAL REPORT PART III PL. C 
 
 FOSSIL PLANTS OF THE PAYETTE FORMATION. 
 
PLATE CI. 
 
 741 
 
PLATE CI. 
 
 Page. 
 
 FIGS. 1, 2. Populus eotremuloides n. sp -.. 725 
 
 FIGS. 3, 4. Quercus simulata n. sp 728 
 
 FIG. 5. Ficusungeri Lx 731 
 
 FIGS. 6, 7. Rhus payettensis n. sp 733 
 
 742 
 
U. S. GEOLOGICAL SURVEY 
 
 EIGHTEENTH ANNUAL REPORT PART III PL. Cl 
 
 FOSSIL PLANTS OF THE PAYETTE FORMATION. 
 
PLATE On. 
 
 743 
 
PLATE OIL 
 
 Page. 
 
 FIGS. 1,2. Quercus simulata n. sp 728 
 
 FIG. 3. Acer trilobatum productum ? Heer 733 
 
 FIG. 4. Quercus idahoensis n. sp 729 
 
 FIG. 5. Betulasequalis? Lx 728 
 
 FIG. 6. Quercus consimilis Newby 729 
 
 FIG. 7a. Trapa americana n. sp 733 
 
 FIG. 7b. Trapa? occidentals n. sp 734 
 
 FIG. 8. Phyllites flexuosus n. sp 735 
 
 FIG. 9. Quercus payettensis n. sp 730 
 
 744