r ^4 C 3 ^ STATE OF CALKORNIA DEPARTMENT OF NATURAL RESOURCES Geology of the Macdoel Quadrangle « California BULLETIN 151 1949 nimnM— innnnnrinniinMiwi— Mnini DIVISION OF MINES PERRY BUIlDINa SA« fSANCISCO BBBoeooaBnaB COLLEGE OF AGRICULTURE DAVIS, CALIFORNIA . STATE OF CALIFORNIA EARL WARREN, Governor DEPARTMENT OF NATURAL RESOURCES WARREN T. HANNUM, Director DIVISION OF MINES FERRY BUILDING. SAN FRANCISCO OLAF P. JENKINS, Chief SAN FRANCISCO BULLETIN 151 NOVEMBER, 1949 GEOLOGY OF THE MACDOEL QUADRANGLE By HOWEL WILLIAMS and Circular Soil Structures in Northeastern California By PETER H. MASSON UNIVfcKSIfY OF CAUFORNIA LIBRARY ^OLLECE OF AGRICULTURE DAVIS LETTER OF TRANSMITTAL To His Excellency The Honorable Earl Warren Governor of the State of California Dear 8ir : I have the honor to transmit hereAvith Bulletin 151, (icoJfxjn of the Macdocl Quadrangle, ])repared under the direction of the Chief of the Division of ]\Iines, Olaf P. Jenkins. The bulletin includes colored geologic and economic mineral maps and other pertinent data on a specific area in Siskiyou County, north of Blount Shasta and bounded by the Oregon border. The report describes deposits of building stone and crushed rock, diatomite, ornamental and gem stones, copper and molybdenum, and coal. It represents one of a series of such quadrangle reports which the DiAision of Mines is engaged in publishing. The field work was done on a cooperative basis with a faculty member of the University of California. The author of this bulletin on the Macdoel quadrangle, Howel Williams, is head of the Department of Geological Sciences, University of California. As an eminent volcanologist, Dr. Williams' treatment of the geology is of particular interest, since this area is covered largely by volcanic rocks. Included with the report is an article on the origin of certain interesting rock rings concerning which frequent queries have been received by the Division of j\Iines. This article. Circular Soil Struc- tures in Northeastern California, has been prepared through field inves- tigations by a graduate student of the University of California, Peter H. Masson. Kespect fully submitted, WARREN T. HANNUM, Director Department of Natural Resources Julv 1949 67420 CONTENTS GEOLOGY OF THE MACDOEL QUADRANGLE, CALIFORNIA, BY HOWEL WILLIAMS 7 I CIRCULAR SOIL STRUCTURES IN NORTHEASTERN CALI- FORNIA, BY PETER H. MASSON 61 (->) GEOLOGY OF THE MA.CDOEL QUADRANGLE, CALIFORNIA By Howkl Williams * OUTLINE OF REPORT Page ABSTRACT S INTRODICTIOX 9 Lofjitioii and accessibility 9 Tt)p<)<;rai)liy 11 Cliinafe and vpsetation 12 AckiiDwUdgnifiits lo DESCRIPTIVE GEOLOGY 13 I're-Cretaceons bedrocks 14 Upper Cretaceous (Chico) beds 16 Eocene (T'mpqua) sediments 18 Western Cascade series 20 The bedded rocks 21 Lavas 21 Pyroclastic rocks 23 Sediments 25 Volcanic necks, domes, and dikes 27 Rhyolite domes 27 Necks of andesite, dacite, and basalt 28 Dikes and sills 32 Arc and mode of deposition of the Western Cascade series 32 Earth movements at the close of the Miocene epoch 33 High Cascade series : Pliocene to Recent 3.") Plio-Pleistocene volcanoes 35 Basaltic" shield volcanoes 35 Basaltic intrusions 38 Hornblende-bearing andesites and dacites ( V) 39 Pyroxene andesite lavas 40 Recent eruptions 41 Deer Mountain volcano 41 Eruptions near the base of Mount Shasta 41 Whaleback volcano 42 Kegjc. Soule Ranch, .ind Horsethief Butte cones 42 Pluto's Cave basalt 42 Butte Valley basalt 44 Little Deer Mountain volcano 45 Butte Creek basalt 45 Alder Creek ba.salt—- 46 Eruptions near Copco Dam 47 Goosenest volcano 48 Last flows of Shasta and Shastina 40 Summary of the petrography of the High Cascade lavas 50 Moraines and fluvioglacial deposits 50 • Chairman, Department of Geological Sciences, University of California, Berke- ley, California. Manuscript submitted for publication January 19 49. ( T) 8 MAC'DOEL QT'APRAXGLE [BllU. 151 Page STRT'CTrKE HI Folding ni Faulting i>2 GROl xn WATKU 55 BP:SWICK "CRATERS" 56 ECONOMIC GEOLOGY - 57 Coal 57 Copper and molylidenum 58 Building stono and ctusIkxI rock 58 IM;itomite 59 Ornamental and gem stones 59 LITERATIRE CITED 60 ILLUSTRATIONS Fignre 1. Index map showing location of Macdoel (niadrangle, and area covered l»y sketch map along Highway 0!) from Weed to Hilts 10 -. .Microdrawings showing Western Cascade rocks 22 3. Looking east across Shasta Valley to the High Cascades 26 4. Microdrawings showing rocks from volcanic necks 28 5. A'iew from near Little Shasta, looking south 30 f). View from 2 miles west of Little Shasta, looking east 34 7. Microdrawings showing lavas of the High Cascades 38 8. Microdrawings showing lavas of tiic High Cascades 46 riate 1. Geologic map of Macdoel Quadrangle In jiocket 2. Econr)niic mai) of Macdoel (luadrangle. In i)ocket .3. fJeologic sections across Macdoel (piadrangle In pocket 4. Sketch map of geology along Highway 99, Weed to Hilts In i»>ped on a .scale of 1 :125.(>09. To|>ogr:ii)hic:i]l\ it JMchides parts of Sh:ist;i Valley and I'utte V:illey, along with the intervening Cascade Range and ;i portion of the v.-illey of the Kl.'iniath Kiver. The oldest rocks in the (luadrangle are metacherts iind qtiartzites. proh.ihly of Paleozoic age, which are intruded by fpiartz nionzonite of Jurassic age. Similar rocks are widesi)read in the jidjacent p.irt of the Yreka (inadrai^gle to the west, where they are ac<-oiMi)anied by .Jurassic (V) inlrusions of serpentine and metadiabas(>. In that quadr.'ingle these bedrocks ;ire overlain with profound uiuonforniity by lu.arine. l'i>per Cretjiceous (Chico) bed.s ; these are not exposed in the Macdoel (piadrangle but they underlie most of Shasta Valley and may extend lienejith the Cascade Range. Resting on the Cretaceous rocks jire freshwater Eocene sediments belonging to the I'lnpipia forni.-ition which outcrop at tiie northern cnil and along the eastern edge of Shasta Valley. With the exception «>f these small exposures of Eocene sediment and the still smaller outcro|)s of pintonic and metamorphic bedrocks jireviously meutioncHl. virtually the wiiole of I lie (piadrangle is occupiec! by \(ilc;inic materials. These belong to two series, lirst tiie Western Cascade series. r;inging in agi' Iroin I'ocene to Miocene, and second, the High Cascade series of IMiocene, I'leistocene, and Recent age. Tiie older .series cover.s most of the western half of the ipiadrangle, and is made up chiefly of andesitic lavas, with subordinate flows of basalt and (!acite, beds of rhyolite tuff. 1049] OEOLOOY 9 and a fow (loniicMl protnisions of rhyolitio liivii. Xo tract" rciiiiiiiis df tin' i>ar«Mit cones, l)Ut several necks mark llie sites of tlie central vents of some of the vanished volvanoes. In brief, the topojirapliy in this hell of Western Cascade rocks is entirely erosioiial in oriiiin. At the close of the Miocene period this older series was gently tilted to the east and northeast, and was cut by faults that border long, narrow horsts trending slightly west of north. At the same time the ancestral Cascade Range was formed by regional uplift. Subsequently, a north-trending chain of volcanoes was built along the crest of the range ; their products form the High Cascade series. Here the topography is almost wholly constructional, and even the oldest cones r( tain much of their original shapes. During Pliocene and I'leistocene times, l)roa(l, H:ittish shield volcanoes were formed by (piiet elTusions of olivine i)a.salt, while eruptions of andesite and perhaps of dacite built steeper cones alongside the shields. Among the andesitic cones produced mainly during the Pleistocene, the largest by far is Mount Shasta which adjoins the quadrangle on the south. After the close of Pleistocene time, while the glaciers of Shasta were shrinking to their present size, many new volcanoes of andesite and basalt developed in the High Cascades, and copious floods of basaltic lava issued from fissures to inundate much of Butte and Shasta Valleys and the ciinyons of Butte and Alder Creeks, while other basaltic flows were discharged near Copco Dam, impounding the Klamath River to produce a large lake in which much diatomite was deposited. Many of the Recent flows are not more than a few thousand years old, and perhaps the final eruption within the area took place within the present millennium. Shasta Valley is a structural depression bordered on the east by a fault of great displacement, developed at the end of Miocene time. Butte Valley is al.so a downdropped block, but of much later origin, being surrounded by well-preserved fault scarps of late Pleistocene and Recent age. Known economic mineral deposits are few. Copper and molybdenum are found in plutonic rocks on Yellow Butte, and a little coal has l»een mined in the IJmpqua formation near Ager. Lavas and tuffs of the Western Ca.scade series, and basaltic cinders from younger volcanoes have been utilized for building materials and road metal. Opal and chalcedony have been collected for ornamental purposes. INTRODUCTION Location and Accessibility The Maedoel quadrangle, scale 1 :125,000, lies in Siskiyou County (fig. 1). Its northern boundary is the Oregon-California state line, and its southern boundary the parallel 41°30' North. The other limits are the meridians 122° and 122°30' West. The area thus enclosed covers approximately 940 square miles. The small villages of Maedoel and Mounf Hebron, close to the eastern edge of the quadrangle, are the principal settlements, but most of the population is scattered on farms in Butte and Shasta Valleys. Yreka, the county seat, lies a short distance to the west; Weed and Dorris, two important sawmill towns, lie a short distance to the south and east, respectively. IT. S. Highway 97, connecting Weed with Klamath Falls, cuts across the southeastern portion of the area, following close to the main line of the Southern Pacific Railroad. U. S. Highway 99, linking Weed with Yreka and ]\ledford, lies a few miles to the west of the quadrangle. The Siskiyou branch of the Southern Pacific Railroad, after skirting the western edge of the area from Gazelle to Montague, enters the quad- rangle at Snowdon, then passes through Ager to leave the area close to the northwestern corner (pi. 4). Many secondary roads branch from the two main highways just mentioned, and a close network of oiled and gravelled roads facilitates access to the flat farming country. Tavo good roads, one from Hornbrook 10 MACDOEL QUADRANGLE [Bull. 151 Kir. 1 Index map showinp location of Macdoel quadrangle, and area covered by sketch map (plate 4) alonp Hisliway ;•» from Weed to Hilt. 1;)4}>J GEOLOOY 11 to the Copoo Dam. and tlic dtluM- from A^or to Bcswick. open up the valley of the Klamath Hiver. The mountainous, eentral j)art of the re}.M()ii is erossed by the road between Monta<:ue and Mount Hebron, and much of it is traversed by Forest Service and lo^j;ing roads. Topography The Macdoel quadranjxle is divisible into four topographic units, namely, Shasta Valley. Butte Valley, the intervenin«; Cascade Kange, and the valley of the Klamath Kiver. Shasta Valley is an approximately oval basin, about 30 miles long in a north-south direction and 15 miles in greatest width, bordered on one side by the Siskiyou Mountains and on the other by the Cascade Range. Most of it lies between elevations of 2.40U and 2,80U feet. The eastern, flatter half is occupied by a vast flow of basaltic lava recently erupted from the flank of Mount Shasta; the western half consists of older vol- canic rocks eroded into a myriad of hillocks that range from a few feet to 200 and rarely to 300 feet in height. Most of these hillocks are domical, some are conical, others are mesas and a few are long, hogback ridges. Together they form a strange landscape, deceptively like the products of recent volcanic activity. Between the hillocks lie many small ponds and marshes and the alluvial flats of slow, winding streams. Chief among these streams are Shasta Kivei- and its tributary Parks Creek which rise among the Siskiyou Mountains to the south. After feeding the Dwinnell Reservoir and meandering between the aforementioned hillocks, the Shasta River passes out of the quadrangle to continue its sluggish course for another 9 miles before plunging into the deep, rocky gorge through which it hurries to join the Klamath River. In the eastern half of Shasta Valley, owing to the porous nature of the lava floor, there are few streams, most of the subterranean drainage emptying into ponds and lush meadows in the lower, northern end. On the opposite side of the Cascade Range lies Butte Valley, the bed of an ancient lake, a featureless plain covering more than 150 square miles, lying at an elevation of approximately 4,200 feet. Meiss Lake is all that now remains of the original body of water that formerly drained northward through Sam's Neck to the Klamath River. It has no outlet and its size varies greatly with the seasons. Abundant ground water is found all over the valley at shallow depths. The principal streams enter- ing the basin are Butte Creek from the south and Prather Creek from the west ; the former sinks underground soon after entering the basin, while the latter empties into Meiss Lake to augment the water discharged by adjacent springs. The valley itself is a huge, structural trough almost encircled by youthful fault scarps, and several flat-floored grabens, including Sam's Xeck and Pleasant Valley, project beyond the main depression between parallel horsts. Separating Butte from Shasta Valley is the third toj^ographic unit, the High Cascades. Near the southern edge of the (|uadrangle this includes the foothills of Mount Shasta; then, in a broad, north-south belt, follows a series of giant volcanoes. Some of these, for instance ^liller and Eagle Rock Mountains, are considerably eroded, while others, like the Goosenest and Whaleback, are so recent in origin that they have been modified only slightly by dissection. Their summits rise to elevations of 12 MACDOEL Ql'ADRAN'fJLE [Bllll. 151 approximately 7,000 to S.oOO feet. Tliose built of basaltic lavas have gentle slopes that contrast strikingly with the steep flanks of the andesi- tic cones. In the High Cascades the topography is almost wholly construc- tional, the land-forms resulting chiefly from the outpouring of lava during Pliocene and later times; to the we.st, on the other hand, where Eocene, Oligocene. and Pliocene volcanic rocks are exposed, the topogra- phy is entirely erosional and bears no relation to the shapes of the original cones from which the lavas and ashes were erupted. This topographic contrast is accentuated by a pronounced difference in vegetation, for the young volcanoes of the High Cascades are heavily wooded while the older volcanic roeks, being for the most part thickly mantled with soil, form i-ounded. grassy slopes and cultivated fields. The foiiitli topographic unit is the valley of the Klamath River. Wiiere it is iiK-ised into the older volcanic rocks, the landscai)e is mature and the streams flow in V-shaped channels between branching, narrow- crested ridges ; where it crosses the High Cascades, on the other hand, the topography is youthful and the streams occupy deeper, narrower canyons bordered by plateaus and flat-toppod spurs. The course of the Klamath Kiver, like that of the Kogue and the Umpqua, was already established in broad outline before the older volcanic rocks were raised and tilted to the east, and before the uplift of the Klamath-Siskiyou Mountains. Prior to Pliocene time, the rivei- already flowed westward tlirough a broad valley crossing the eastward-ilipping lavas, and although the bed- rock region to the west rose spasmodically the river maintained essentially its present course by incising a deep canyon through the Klamath ]\Ioun- tains. In brief, the Klamath River is an antecedent stream. Climate and Vegetation Except that the winter temperatures are lower, the climate of Shasta Valley resembles that of the Sacramento Valley. At Yreka, the mean annual rainfall appi-oximates 18 inches, and at Montague it is about 12 inches, the rainy season lasting from October to A'pril. "The mean annual tempei'ature is 31.3 F. During the rainy season it averages about 40°F. It drops to zero at times, and snow falls nearly every winter .... From May to October, inclusive, the avei-age is 62°F. Summer temperatures above lOO'^F. are often rccoi'dcd, although these extremely hot periods do not last long .... The climate is well suited to stock raising and grain growing, whicli are the princij)al industries." ^ The climate of P.iiltc \'alley conforms closely to that of the Great Pasiii i-cgion of Oregon. .Vt Klamath Falls, about 20 miles north of Putte \'alley, the raiiit'all averages appi'oximately 15 inches a year; at ^lacdoel the annual rainfall is about the same, while the seasonal snowfall averages approximately 44 inches. Most of the precipitation falls during the winter months; between .June and September only about half an inch falls per month. in the High Cascades the rainfall is considerably heavier and winter snows ai"e conunon, I lere t he mountains are covered with a heavy growth of yellow pine, Douglas spruce, white fir, incense cedar, and tamarack l)ine, and scattered groves of asjx'n, maple, and oak. Where these forests 'Watson, K. U., Wank, U. K., ami Smith, Alfrt'il, Soil sm v» y ni" tlie Sha.<:ta Valley ai'.a, ('allfurnlu : T. S. Di-pl- AKricullurc, Hur. Soils, li»:2:t. 1949] (MOLOdV 13 have boeu destroyed by fire, as on Ka^'le Kock and Willow Creek Moun- tains, tliey have been rephieed by \vi(b' areas of brnsli that are diffieult of access. Butte and Shasta Valleys and the hills bordering the Klamath River are ram of study of the southern Cascades. During 1I)4S, six weeks were spent in completion of the work. Thanks are recorded to the Board of Research of the University of Cali- fornia for funds that helped to defray expenses. For much information concerning the local geology and for pleasant companionship in the field, 1 am grateful to Messrs. Walter Pollock, Sr. and Jr., of Yreka, and to Mr. C. B. Kay of Montague. DESCRIPTIVE GEOLOGY The oldest rocks in the jMacdoel quadrangle are metacherts and quartzites exposed on Yellow Butte, part of a narrow fault block at the foot of I\Iount Shasta. Similar rocks, accompanied by siliceous schists and marbles and intruded by sills of metadiabase and serpentine are wide- spread along the edge of the Siskiyou Mountains, immediately to the west of the quadrangle (pi. 4). The age of the metamorphic rocks is prob- lematical, but probably Paleozoic. On Yellow Butte they are intruded by quartz monzonite, presumably of Jurassic age. No Cretaceous rocks outcrop within the Macdoel area, but the pres- ence of many salt-water wells and springs in and around Shasta Vallej^ suggests that marine Cretaceous beds underlie much of the quadrangle. A short distance to the west, near Yreka and Montague, and to the north- west, in the valley containing Ilornbrook and Hilt, Upper Cretaceous (Chieo) sediments are widely exposed. Everywhere they rest with pro- found unconformity on the plutonic and metamorphic bedrocks. Tjying upon the Cretaceous beds are Eocene sediments that belong to the Umpqua formation. In the Coast Ranges of Oregon, around Rose- burg and farther north, these beds are marine and include abundant flows of pillow basalt, but to the south, in the Medford, Yreka, and Macdoel quadrangles, they are all of freshwater origin and consist mainly of shales, sandstones, and conglomerates with a few thin beds of coal. They outcrop in two parts of the ^Macdoel region, one at the northern end of Shasta Valley, and the other close to the eastern edge, at the foot of Miller ^Mountain. By far the greater part of the Macdoel quadrangle is occupied by Tertiary and Quaternary volcanic rocks. The western half is made up principally of lavas and pyroclastic beds that range in age from Eocene to Miocene. These belong to the Western Cascade series - which forms the eoastward flank of the Cascade Range throughout its length. Within this belt the landscape is entirely erosional in origin; no trace remains 2 Callaghan, Eugene, Some features of the volcanic sequence in the Cascade Range in Oregon : Am. Geophysical Union Trans., pp. 243-249, 1933. 14 MACDOEL QUADRANGLE [Bull. 151 of the cones and craters from -which tlie flows anrl ashes were discharged, and only a few plugs are left to mark the sites of the central pipes of some of the vanished volcanoes. At the close of the Miocene epoch, the Western Cascade series was gently tilted toward the east and northeast and cut by faults trending slightly west of north. Subse(|nently a broad, north-south chain of large volcanoes was built. Because these form the crowning peaks of the Cas- cade Range, their products are grouped together as the High Cascade series. During Pliocene and early Pleistocene times the eruptions were mostly of olivine basalt and oliviiu'-bearing basaltic andesite. These pro- duced such huge, flattisli shield volcanoes as .Miller and Eagle Rock Moun- tains. At the same time, viscous flows of andesite and dacite ( ?) were discharged by other volcanoes along the crest of the range. Mount Shasta itself was built mainly during the Pleistocene epoch, at first almost wholly by effusions of andesitic lava, but in the final stages by eruptions of dacite and ba.salt as well. After tlic close of the Pleistocene epoch, while the glaciers of Shasta were retreating to tlieir present position, many new volcanoes were formed and many of the older shield volcanoes, particularly along the borders of Butte \'alley, were nnu-h modified by block faulting. Among these younger volcanoes, the Whaleback and Deer Mountain were the first to develop; subsequently the Tjittle Deer ^Mountain and Goosenest volcanoes became active. Long flows of olivine basalt flooded the canyons of Butte aiul Alder Creeks and others spread over the eastern half of Shasta Valley. Still later, the Klamath River was dammed by eruptions of basalt near Cojico Dam. The final eruptions within the area may have taken j>Iace Avithin the last millennium; certainly numerous flows issued no more than a few thousand years ago. The last explosions of the neigh- boring Mount Shasta probably occurred in 1786.^ Pre-Cretaceous Bedrocks The only exposures of the pre-Cretaceous basement within the quad- rangle are on Yellow Butte, at tlie northern base of Mount Shasta, where they form part of a narrow, north-trending fault block bordered by Pleistocene and Recent lavas. This bedrock island consists mainly of dense, almost porcelanic, pale bluish-white (|nartzitcs, in ])lai'cs finely banded in .shades of i)ale gray and black. In part, at least, they are metacherts. The bedding rarely departs moi'e than 10 from the vertical, and the strike, while dominantly north. rang(^s from north-noi'theast to north-northwest. Near the south- ern (Mid of the l)Utte, thin beds of mica schist and slate accomj)any the quart/.ites. Along the eastern flank, the metamorphie rocks are cut by coarse-grained liornblende-biotite quartz monzonite and thin dikes of aplite. By analogy with the bedrocks of the Siskiyou Mountains, the nu^ta- morpiiie rocks are assigned to the Paleozoic, and the plutonic rocks are refei'rcd to the Jurassic period. Attention is dii-ected next to the bedrocks that border the Macdoel (piadrange on the west, the distribution of which is shown in plate 4. The ^ WIMI.-inis, llowi'l, Mciiiiit Sha.stfi, n Ca.'scado volcano: Jour. Oeolopv, vol. 10, pp. 417-I2!t. T.i.'l2. Williams, Ilowel, Mount Shn.sta, California : Zolt.schr. fiir Vulkanologie, vol. l.S, pp. 225-253,1934. 1949] GEOLOGY 15 hills exteiulinj,' southeastward Iroiii Vreka to (Jreiiada consist chiefly of siliceous luetaseclinioiits overlain hy Cretaceous sandstones and c()ng:lom- erates. Predominant amoniz: the luetaniorphic rocks ai'e banded meta- cherts and dense ([uartzites, some of wiiich cany a little "rraphite. Next in order of abundance are jnile jrray and buflf ({uarlz-sei-icite schists and pale arallels the road. ai)|)ro.\imately 2 miles south of the summit of r>o«ziis ^Mountain. In this, phenocrysts of jrreen hornblende, up to 3 millimeters lon«r. make up between 10 and 1") jiercent of the bulk. Flakes of bnnvn biotite (2 pel-cent), and jihenoi-rysts of zoiumI acid labradorite-basic andesine (20 percent ), accom))aiiy the hornblende in a microfelsitic base rich in (piartz. No Hows of rhyolite were observed, aithonirh rhyolite tiitf is abundant and rhyolitic lava forms many domes. Ximierous chemical analyses would be recpiired to determine the |)ii)|i(irtion of basaltic lavas in the "Western Cascade series, for in the iichl it is seldom jiossible to distinjiuish between them and the dark " In this description an<1 in other petrogrnphic descriptions in this paper, the author has u.'^i-d the term "ore" with reference to the dark opaque minor accessory minerals a|>pearing under the microscupe. l!)4i)J fiK()I-()» Wells, F. G., op. cit. 26 MACDOEL QT-ADRAXGLE [P>nll. 151 m pi>.; -■ ^ •.^'»' - . V> • '. - r \ I ■T. 'J CS iV . • f • - .> \ . : v\^ v^ 1 1 -<^-:.2 \vV; ■r- ■-'hi •i ■ ■•* 5 . • *. -* . - ■ ■■': i 1^ .- o y. r" i* y c _ i i K . _5r ~c- -2 TJ S . c - c S j= i: -c t; = ■= ? " J) o ?---_■ ^ W *^ — . _ "T W ~ E £ -f' "S U -" - - — r -u c ^« - ■' - _ o - - cC ■S ?■ ^ " S o ■" > r ■- ?• ca ■.J r^ ^ — . — i^ o S. p iL- x.ti— t- - 4) T.. ■f. it O i ? — ■33 y c ell O w-C C - IJ - ~ ii 1, n ? • ■ c : oj ^ L. (_ — — ■^ r; CO <« ;> ^ r C f- O ^ 1* ? c ^ Y . i'r.T. a i~ : 1949] OEOLOOY 27 and C()iinuM-ate are proscnt dose to tlio base of the series near Klania- thoii and Ilonihrook and in the valley of AVillow Creek, and occasional rounded pebbles and boidders in the tulVs thereabouts testify to stream action duriujr deposition. Small lenses of voleanic confrlomerate also occur locally in the ujiper part of the series, as alonp: Davis (Julch. Layers of diatomite. such as are found in the series in Orejron. are lackin V F ' - • 1 -!r ' i '''■ ' : ''."': • T-'.*. * . ■_ \ r ^ .?.' H f ^ ^ i •. , p-: ^4 ■ P'* T ' n ■ -^ •" J V \i '• -K \ r -^ / 'I' ;- ^ ; fM\ 1 ^ ^ "7 f-'iiS 1 - f . ^"- ; - ; : -V JK i : j^i ^'ci '3a-'; 1 ' '' ', /?;^ :^^V V -■■* ' /v ■' /-^^ T ''. -'t rnf/ Jft 1 5> J'j /.'.-^JSU^ 1 ' ^ J 4 > IS- s. r^^€l^^ Is • ? • ^: s- »V \KP H ; ^" S . ■ "5^ \ ■«;•■■.'■•,■"» fi ;■ \ \^A i'f ^- -{S '• ^ ffM ' V l.'/t . ■. ''4^ ^jM te\"v Mr ii '■ ; ^a ~<^ *' V V. ■ .'A 1 w^'m iS- ''' /^ Pi '^ 3 '.; "''-' *i p Si'= ^' '-'- r;^^ vSh ' Vj- A4| l a> c u u _o <0 rt « X » ■«-' 3 !_ 73 1/ o ,g; ^ 7i ■*-• u rt ^-J O o 2 ttJ 4-1 4-) »; rt u k! !< 5 o .22 0) 5 •"■ <«M .Ti > u x: M •n X 01 > iw "3 irj M o C TO 4) u "1 0)4-1 c -C fc o c 4* 7 y iE ■y a •/. j: -^ — i;)491 OKOLOOY 31 lUH-U is oval, inoasiirinj; a|)|)r()xiiiiatt'ly ;{.')() yards in a north-south iliree- tion antl 21)0 yards in inaxiiuuin width. riittiii feet in width. Alonjr the niai-;.;ins of the neck, and for a short distance iinvard from the southern edjic, these dikes are arranged concentrically and either stand vertically or dip outward at angles of more than 60°, after the manner of ring dikes. In the core of the neck, on the other hand, the dikes trend northward or almost so, and all are vertical. Some dikes cross others at low angles, but most of them are parallel, multii)le intrusions. No iloubt the neck served as a feeder to a long succession of surface flows. Under the microscope the basalt is seen to have a texture varying between intcrsertal and diabasic. Api)i-oximately 5 percent consists of golden-brown chlorophaeitc, sonic of it di'velopcd from por{)hyritic oliv- ine and some occurring in irregular patches throughout. Pale green, anhedral grains of diopsidic augite, up to 1 millimeter in diameter, total 30 percent of tlie volume ; hypersthcne is found only in the cores of a few of the larger augites, never as discrete crystals, and amounts only to 1 percent of the bulk. Roughly 5o percent of the basalt consists of basic labradorite laths up to 1 millimeter in length. Small, euhedral grains of magnetite (3 percent), and clear, butt'-colored glass (n = 1.525 ± .002) make up the rest. Among the necks in Shasta Valley, the largest forms Gregory Moun- tain, on the outskirts of Montague, a short distance west of the Macdoel quadrangle. This consists of hornblende andesite. Another large neck rises from the flats near Cedar Lake (fig. 5). In plan, this one is oval, measuring a mile along the major and half a mile along the minor axis, and it rises to a height of approximately 750 feet. Throughout it is com- posed of massive, gray and olive-green, hornblende- and biotite-bearing pyroxene dacite, thoroughly propylitized by hydrothermal solutions. No flow-banding was observed within it, nor was any regular pattern of joints detected. A similar, almost structureless neck forms the hill known locally as the Camel, close to Little Shasta (fig. 6). This is made up of uniform, coarsely porphyritic, hornblende-rich pyroxene andesite. Unfor- tunately talus conceals its relations to the adjacent bodies of rhyolite, but almost certainly it represents another denuded filling of a volcanic pipe. A high conical butte, referred to locally as Mary Peak and shown on the geologic map (pi. 1) as 3267 Ilill. lies north of Snowdon. Its flanks are composed mainly of Ump(|ua sediments, but the top consists of fine-grained, black basalt. Where the basalt is columnar, the columns dip outward, locally at angles as low as 4:0°, suggesting that the cap is either the remnant of a flow that moved down a steep-sided valley in the Umpqua beds or the filling of a neck with inward-dipping sides. The presence of sporadic, small inclusions of milky quartz in the basalt favors the second view, for these can only have been picked up from Cretaceous conglomerates at depth. Perhaps the small patch of hydrothermally altered andesite on the northeast shoulder of the peak, and the patches of silicified and limonitized rhyolite on the opposite side also represent necks ; if so, there must have been three closely spaced volcanoes in line, one of basalt, a second of andesite, and a third of rhyolite. 32 MACDOEL QUADRANGLE [Bull. 151 Two oval hillocks, each about 50 feet high, form islands in the flood of Recent basalt near Big Springs, in the eastern half of Shasta Valley. One is about 2,000 and the other 1,500 feet long. They consist of massive, unhanded, coarse-grained hypersthene andesite porphyry. The presump- tion is that these hillocks mark the feeding pipes of two more eroded volcanoes. Dikes and Sills Minor intrusions are surprisingly rare in the Macdoel quadrangle considering their abundance in the Yreka and Medf ord areas. Several vertical and steeply dipping dikes of olivine-bearing pyroxene andesite cut the coarse tuff-breccias on Sheep Rock. A vertical dike of andesite, with divergent, curving columns, cuts the lavas near Low Wood School, on the bank of Klamath River, and another columnar dike of andesite, trending N. 80° W. for almost a mile and dipping at angles of 20°-60° N., cuts the lavas near the northwest base of Eagle Rock Mountain. A 4-foot dike of andesite traverses the tutt'-breccias above the artesian wells near the western foot of Miller Mountain, and, as mentioned already, there is a dike of rhyolite near Bogus School that probably served as a feeder for the eruption of welded tuff. These are the only minor intrusions seen among the Western Cascade series. Sills may be present between some of the flows, but none was surely identified. Several steeply dipping to vertical dikes, a few inches to about a 3^ard in width, cut the underlying Umpqua sediments between Willow School and the former site of Snowdon School, as well as on the Cooley Ranch, south of Mary Peak. But these intrusions are few and small compared with those to be seen farther north, in the valley between Horn- brook and Hilt (see pi. 4). Most of these intrusions are sills rather than dikes, and they range in composition from dacite porphyry to basalt porphyry, the commonest ones being propylitized augite- and liypers- thene-andesite porphyries. Some in the Medford quadrangle show a density stratification, a lower gabbroid facies passing upward into diorite, as discussed by Merriam.-^ AVells and Waters -- have described basic intrusions in the Blackbutte-Elkhead-Nonpareil area in Oregon, some of which they consider to have been feeders to basaltic flows in Umpqua formation. Age and Mode of Deposition of the Western Cascade Series Elsewhere the writer -^ has summarized the available evidence relat- ing to the age of the AVestern Cascade series, concluding that the beds range from upper Eocene to the top of the IMiocene. Volcanism had already begun in the Roseburg and Medford areas during middle Eocene (TImpqua) time, and some tuff is present in the upper part of the Umpqua formation in the Yreka quadrangle. During upper Eocene time, volcanism became more widespread, and vents became active in the Macdoel region. ^ Merriam, Richard, Magmatic differentiation in gabbro sills near Ashland, Ore- gon : Am. Jour. Sci., vol. 243, pp. 456-465, 1945. "Wells, F. G., and Waters, A. C, Basaltic rocks in the Umpqua formation: Geol. Soc. America Bull., vol. 46, pp. 961-972, 1935. ^ Williams, Ilowel, The geology of Crater l^ake National Park, Oregon : Carnegie Inst. Washington, Pub. 540, 1942. . . . The ancient volcanoes of Oregon: Condon Lec- ture, Pub. 1, Oregon State System of Higher Education, 19 48. 1949] GEOLOGY 33 Among the tuffs foniiintr tlio loAvermost 40 feet of the Western Cascade series near lIornhrt)uk, })etrilied wood and fossil leaves are ])lentiful. and these, according to Chaney,^"* indicate an upper Eocene or Oligocene age. Abundant petrified wood is also present among the tuffs in the Maedoel {{uadrangle, but no leaves have yet been found there. There is no reason to doubt, however, that the lowermost volcanic rocks are equivalent to the leaf-bearing tuff's near Hornbrook. Chancy 's analj^sis ^^ of the Western Cascade floras shows that during late Eocene time, mild and humid, semitropical conditions pre- vailed. Avocados, cinnamons, figs, and persimmons flourished in the lowlands, while on the higher hills and cones more temperate forests grew, rich in redwood, alder, tan oak, and elm. A mild and humid climate also prevailed during the Oligocene period. Even far inland, beyond the Cascade Range, the conditions were uniform, so that red- woods remained predominant in the forests. Nearer the coast, in sheltered bays, warm temperate and subtropical forms persisted. By the end of Miocene time, writes Chancy, the forests were "like those of today in the valleys of Michigan and Ohio, in the Redwood Belt of California; they were essentially like those which had lived in the uplands during the Eocene. ' ' The occurrence of fossil redwoods east of the Cascade Range in late Miocene beds indicates that the range was still not high enough to check moisture-bearing, ocean winds and thus to reduce the rainfall on the lee side by more than a few inches. And this despite the fact that lavas and pyroclastic ejecta had accumulated to a thickness of more than 10,000 feet. The conclusion is inescapable : the area now occupied by the AYestern Cascade series must have subsided many thousands of feet as the volcanic eruptions continued. From top to bottom of the series, there is no evidence of deep erosion during accumulation. All signs suggest that the lavas and tuff's were laid down on a surface of low relief. Beds of conglomerate are found chiefly near the base of the series; at higher horizons, the interbedded sediments consist prin- cipalh' of tuffaceous shales and rare seams of lignitic coal such as would be formed in bogs and on alluvial flats. The absence of any marked angular unconformities between the volcanic rocks also indicates that the topography was one of gentle relief. If high cones existed they must have lain to the east of the present outcrop of the Western Cascade series, and their remains must now be buried beneath the younger lavas of the High Cascades. Surprisingly few volcanic necks have been discovered in the West- ern Cascades considering the great volume of erupted material. Indeed they are more numerous in the Maedoel quadrangle than in any other part of the belt. Considering also the scarcity- of Tertiary intrusions among the bedrocks of the Klamath-Siskiyou Mountains, it can onh' be supposed that most of the Western Cascade volcanoes lay far to the east. Many flows may have been erupted from fissures rather than from cones; in such event the chances of locating their sources are much reduced. Earth Movements at the Close of the Miocene Epoch Reference has already been made to Wells' discovery of a pro- nounced angular discordance between the Umpqua formation and the -^ Personal communication. -" Chaney, R. W., Ancient forests of Oregon : Carnegie Inst. Washington, Pub. 501, Cooperation in Research, 1938. 3—9172 34 MACDOEL QT'ADRAXGLE [Bull. 151 p-fll m\ m O - C P — : o 4> ^ > .i^ Cz — •/. - — K - ^ - ■•'^■^ — " ? V .1^1 = ■£ "Ma/" 7-. r d:; 1, 5^j: X 7. — ^ " -- . y. i >■ ~ o^ y. !^ 1* c td (u . o o Si: -^ ii ^ a- O y. Ji i :, ^- C " . -■' yj~ ci~ < > ^^i : •' >. 5 >. - = °-= y. .- ~ J= t- -1 - c o j; E c ' ~ 3 • 1 c y. i' - fc 3 eS t. " C t. 4) , i;)49J OEOLOOY '\7) earliest of the Western Cascade lavas i)i tlie ^ledford (|ua(lraii ]ireseut Ilijih Cascades. At tlu' same time, the bedrock area of the Klamath-Siskiyou Mountains was slowly ri.sinrr as it was eroded. Siu'h a coupling; movement accounts for the easterly and north- easterly dips of the Western Cascade series and Tor the diminution in the anule of dip in those directions. At the close of the Pliocene epoch, the entire Cascade belt was prreatly upheaved ; it was then, for the first time, that the country to the east Avas depi-ived of sufiicient rainfall to ]iermit continued f>Towth of red- wood forests. This upheaval was accompanied by the formation of several faults trending- slightly west of north, and by the opening of north- trending fissures along and m^ar the crest of the range. It was from these fis.sures that the Pliocene and younger lavas were erupted to build the giant cones of the High Cascades. High Cascade Series: Pliocene to Recent Plio- Pleistocene Volcanoes Basaltic Shield Volcanoes Throughout the southern i)art of the High Cascades in Oregon and California, Pliocene and early Pleistocene times were characterized by the growth of a north-south chain of large, flatfish shield volcanoes built by quiet etfusions of fluid olivine basalt and basaltic andesite. Great diversity had marked the behavior and products of the volcanoes that produced the Western Cascade series; on the contrary, the volcanoes now to be described were extremely uniform in their activity ; f ragmental explosions seldom interrupted the quiet outflow of lava, and the flows themselves varied only slightly in composition despite their wide extent. The principal Plio-Pleistocene basaltic volcanoes of the Macdoel quadrangle are Miller Mountain, the partly buried shields under the lavas of Willow Creek I\Ionntain and the Goosenest, Ball Mountain, Eagle Kock ^Mountain, McGavin Peak, and Secret Spring Mountain. East of these, along the edge of Butte Valley, there are several coeval basaltic volcanoes, much modified by faulting, that form part of the well-known block-fault country extending northward into the Klamath Falls region. There is no certainty as to the precise order in which these coalescing volcanoes began to grow; most of them were active simultaneously for a long period. Probably the southernmost, iMiller Mountain, which is the most deeply eroded, was the first to become extinct. The flanks of some, such as Ball ^lountain, Tkes Peak, and the Eagle Rock volcano are so little dissected that their final eruptions may not date back further than late Pleistocene time. Although patches of red scoria, the relics of former summit cones, cap Ball ^Mountain and the peak to the south, and may also be seen near the top of the basaltic shield north of Copco Dam, the craters of all the Plio-Pleistocene basaltic volcanoes have been destroyed by erosion. Never- theless, because none of the volcanoes was ever glaciated, they are much less denuded than coeval shields in the High Cascades of Oregon, many 36 MACDOEL QUADRANGLE [Bull. 151 of which have been dissected sufficientlj^ to reveal the fillings of their cen- tral conduits. It is chiefly around their margins that the Macdoel shields have suffered denudation, for the flanks have been driven backward by the sapping action of springs and streams that cut readily into the less resistant rocks of the underlying Western Cascade series. This process accounts, for example, for the abrupt termination of the lavas of the Eagle Rock volcano along the rims of the canyons of the Klamath River and of Bogus and Shovel Creeks. It accounts also for the large amphi- theater on the north side of Secret Spring Mountain and for the huge embayment cut into the western flank of the Miller Mountain shield. Where least modified by faulting and erosion, the basaltic shields have much gentler slopes than those of the adjacent andesitic volcanoes. For instance, the Eagle Rock shield has slopes that range from 5° to 7°, whereas the neighboring andesitic cone of Willow Creek Mountain has slopes of 10° to 13°. A glance at the geologic map (pi. 1) will show that most of the basaltic shields are oval in plan rather than circular. Thus the Eagle Rock shield is elongated in a north-south direction, while the Ball Moun- tain, ]\Iiller Mountain, and Mount Hebron volcanoes are elongated in directions between northwest and N. 30° W. These elongations, coupled with alinement of the shields themselves, suggest groAvth over a major set of north-south fissures and a minor set inclined at angles of 30°-45°, and it is noteworthy that tliese are also the directions of the younger fault scarps that border Butte Valley. The eastern shields never extended much farther than at present, but the larger, western shields, such as the Eagle Rock volcano, which still covers 60 square miles, the Miller Mountain volcano, and the two shields under the Goosenest and Willow Creek Mountain must formerly have been much more extensive, for remnants of their flows spread far down the valley of the Klamath River and into Shasta Valley. Before any of the shields began to develop, a north-trending ridge of Western Cas- cade rocks already existed, roughly coincident Avith the line of the pres- ent High Cascades. On the west this ridge rose 3,000 to 4,000 feet above Shasta Valley ; on the other side, it was probably much lower. The drain- age at that time was mostly toward the- west, and the Klamath River already flowed in that direction through a broad and shallow valley. Evidence for the old drainage lines may be seen in the distribution of the outliers of basaltic lava. For example, the patches of basalt near Bogus School are relics of a flow from the Eagle Rock volcano that poured west- ward down a steep-sided, boulder-strewn valley, and the patches perched on the walls of the Klamath River clearly indicate the form of an ancient channel. More striking are the outliers of basalt related to the shield volcano beneath Willow Creek Mountain. Four residual caps rest on the spur between Dewey Gulch and Dry Creek, at elevations of 4,000 to 4,500 feet. Two miles to the southwest, a fifth outlier forms Solomon's Temple, at an elevation of approximately 3,900 feet. West of this are two more outliers forming Table Rock, at elevations of between 3,550 and 3,700 feet, that rest on coarse fluviatile conglomerates charged with boulders of quartzite. Taken together these seven outliers mark tbe course of an old stream-channel trending southwestward into the ancestral Shasta Valley. At Table Rock two successive flows followed the channel. Other 1949] GEOLOGY 37 basaltic flows spread westward inlo the ancestral Shasta Valley from the Miller Mountain volcano. LiihoJogy. By far the dominant lava of all the shields is a massive, pale g'ray, microvesicnlar, liolocrystalline basalt liberally sprinkled with granules of olivine. Flows that contain a little glass are generally darker and more coarsely vesicular, while the glass-rich tops and bottoms of a few flows are black and scoriaceous. Most of the flows vary in thickness between 10 and 50 feet; exceptionally they reach a thickness of 100 feet. Few^ are auto-brecciated and the crusts of most are smooth. In many places, particularly along the rims of the Klamath River, Bogus and Shovel Creek canyons, columnar jointing is well developed. The two valley-filling flows of Table Kock show coarse eolinnnar jointing in their upper parts, while toward the base they exhibit a platy jointing that curves upward from the horizontal to the vertical. In addition they are cut by throughgoing vertical joints alined parallel to the direction of flow and showing horizontal mullion structure. Both the platy and the longitudinal joints are to be ascribed to shearing of the lava as the mar- ginal and basal portions, owing to greater viscosity, were impeded in their advance relative to the more fluid, interior parts. Save for the relics of summit scoria cones already mentioned, there is little trace of ex])losive activity on any of the shields. Thin beds of red- dish cinders separate some of the flows of the Secret Spring Mountain volcano, but elsewhere no fragmental layers were observed between the lavas. Nor were any interbeds of diatomite detected, such as are common between the basaltic flows of coeval shields in the vicinitv of Klamath Falls. Petrography. The typical lava of the shield volcanoes is a fluidal, intergranular, olivine-augite basalt. The volume percentage of olivine phenocrysts varies between 2 and 10. In some flows the mineral is fresh; in others it is partly altered to iddingsite, or, less commonly, to bowl- ingite. Normally this alteration is confined to the margins of the crystals, but in some of the Ball Mountain lavas the rims of the olivines are fresh while the cores are replaced by iddingsite, suggesting that oxidation and enrichment in iron took place at an early stage of consolidation. Occa- sionally, and particularly in scoriaceous basalts reddened by fumarolic action, the olivine crystals are partly converted to magnetite and hematite. Augite forms phenocrysts only in a few flows, chiefly among those of the eastern shields. Rarely it forms ophitic plates partly enclosing the feldspars. Characteristically, however, the mineral occurs as minute anhedral grains in the dense groundmass, and it varies in amount between 25 and 35 percent of the bulk. It is a pale green, diopsidic variety with optic angles of approximately 50'' -55°. Minute prisms of hypersthene are present in most flows, but only in very minor amount. Phenocrysts of plagioclase are exceptional, although in some lavas, as on McGavin Peak, sporadic crystals of bytownite reach 1 millimeter in length. Typically the feldspar occurs in subparallel microliths less than half as long. In composition these range from medium labradorite to acid bytownite. AYhere present, interstitial glass composes no more than 5 percent of the volume, and its color varies from dark brown to black according to the content of finely divided magnetite. A little cristobalite and/or 38 MAfDOFX QUADRA \(!LE A B [Bull. 151 Fig. 7. MiciMdra wings showing lavas of the High Cascades. .1, Olivine-beariiig hypersthene andesite 151) from halfway up the north Hank of the tjoosenest volcano. Phenocrysts of olivine, hypersthtnc, and labradorite, in a matrix of brownish-black glass charged with sodic labradorite microliths and grains of pyroxene. B. Pyroxene andesite (nlS) from the youngest flow of Shastina, on l'. S. Highway 97, near B.M. 3471. Phenocrysts of augite and hypersthene : gi-oundniass of medium labradorite laths, pyroxene grains (chiefly hypersthene), opaiiue ore minerals, and interstitial glass. C, Pyroxene andesite (."iH) from summit of Willow Creek Mountain cone. Phenocrysts of hypei'sthene and augite, the former predominating, together with labradorite, in a gjroundmass of microlithic felds|)ar, specks of pyroxene and opaque ore minerals, and a little trid>niite. tridymite is almost invariably ]iros(Mit. \\\\\\ or without opal, lininhax(;le [Bull. 151 floAv and cone are older than Haystack Butte since the latter shows no cover of cindery ejecta. Whaleback Volcano The larg:est of the Recent volcanoes in the Macdoel quadrangle is the "Whaleback, an iniposinjj, steep cone that rises 3,000 to 4.000 feet above the surrounding country. It is composed almost entirely of dark, vesicular flows of basalt, usually devoid of porphyritic feldspar but witii 4 to 6 percent of olivine phenocrysts and, especially on the western flank of the volcano, abundant crystals of diopsidic augite (2V — 55° ; Z to c — 56°) up to 3 millimeters in length. In flows devoid of augite, hypersthene is usually present in minor amomit. Sub-parallel micro- liths of basic labradorite average about 40 percent of most specimens. All these constituents lie in a base of opaque black glass, constituting another 40 percent by volume. On the summit of the main lava cone there are two lava-scoria mounds on a north-south line, the larger of which exceeds 500 feet in height and has a well-preserved crater. On the eastern flank there is a third mound of lava and scoria, apparently without a crater. Erosion has scarcely modified the form of the Whalebac.'v and the flows nowhere show traces of having been glaciated. Kegg, Soule Ranch, and Horsethief Butte Cones The preci.se position of these cones in the sequence of Recent erup- tions is uncertain, although all are older than the Little Ueer ^lountain volcano. The Kegg cone, on the eastern edge of the quadrangle, has been almost wholly removed by quarrying. It consists of red and black, basaltic cinders crowded with lapilli and bombs, some of which measure 4 feet across. The (luaquaversal dips of these .ejecta indicate that originally the cone was a low, oval mound, the vent of which lay near the center of the f|uarry. A few irregular stringers of basalt cut the cinders; these j)robably are fillings of fissures tln-ough which short flows of lava escaped to the surface. Aj)proximately 3 miles to the southwest, near the SoiUe Handi, there is another cinder cone almost eviscerated by (piarrying. Here the ejecta are composed for the most part of red scoriaceous lumps between half ail inch and a yard across. Above the well-stratified cinders lie patches of aggliif iii;i1(' formed by fragments that were pasty enough when they lauded from flight to adhere to each other. As in the Kt>gg cone, the vent of this one also lies close to the center of the cjuarry. A stumpy flow of olivine basalt issued from the foot of the cone on the south side. Tlic lower flanks of the cone are covered to a deptii of a few feet by boiiidcry. fluvioglacial outwash. E(|uiilistant from the two cones just described are two others tliat coalesce to form Horsethief Butte. Both are made up of olivine basalt scoria. Wlietliei- or not they were built before t)ie adjacent fault scarps were formed is uiu'crtain owing to slides of talus. Pluto's Cave Basalt The eastern half of Shasta \"alley is occupied by a sheet of olivine basalt referred to lien- as the Pluto's Cave flow, after the large lava I!)4f)l OEOLOGY 4.'^ tiil)(' near its soutlxM-ii t'lid, at tlic localitN' uaiiu'd The Caves on tin- }*eok)jrie' map. plate 1. 'I'liis llow eoviM's nioi'e than ")() scpiafe miles and exeeeds 20 miles in ltMi;^tli. It is tlins by far th^' lar^^est tlow of any n^' in the ^Maedoel (piadranj^de. It seems to have issued from fissures close to tlie northeast base of Mount Shasta. F'or the first 5 miles, as far as the Southern I'aeifie Railroad, the surface of tlie H(nv lias an inclination of 5° ; for the next 5 miles, to Pinto's Cave, the slope dimiiiish(^s to 'A ; then, for another "> miles, it diminishes to approximately l'^, tinally heeominy almost horizontal. Evidence concerning the thickness of the flow is meager. Before the lava was erupted, the eastern half of Shasta Valley was a broad depres- sion ('ontainin«i- hillocks of andesite like those to he seen in the western half. A few of these hillocks still rise as islands within the tlood of basalt. Almost certainly the Shasta Kiver and Parks Creek Howed through this dej^ression before being diverted to their present channels by the outfiow of lava. In ]>art the depression was floored by dai'k volcanic sand, for Mr. C. B. Kay reports an outpouring of such material from an arte- sian well suuk through the basalt. The thickest portion of the flow is undoubtedly the median part that extends northwestward through Pluto's Cave, for here the lava is piled into a high ridge elongated parallel to the direction of flow. A short distance to the north of the cave, accord- ing to ]\Ir. Kay, basalt was cut to a depth of a])i)roximately 2!)() feet in a well, and it may be that locally the lava attains a thickness of 400 feet. Beyond the Big Springs road the thickness diminishes rapidly, until in T.ittle Shasta Valley it is reduced to a few tens of feet. The narrow ribbon that spread into the Shasta River must also be extremely thin. Not only did the lava force Shasta River and Parks Creek into new chan.nels, but it deranged the drainage elsewhere. South of the Big Springs road the marginal parts have been largely covered by fluvio- giaeial oiilwash from the slopes of Mount Shasta, as well as by cinders blown from younger cinder cones. Large fans of pebbly and sandy out- wa.sh are now spreading over the edge of the lava east of Dwinnell Reser- voir, and the finer materials in them are being winnowed by the winds to form dunes in the vicinity of Pluto's Cave. The main topographic features of the basalt are the median ridge in its up})er. constricted part, the caves or lava tubes in the same area, the schollendomes or oval mounds formed bj' hydrostatic pressure of liquid lava under the congealed crust, the pressure-ridges along the mar- gins and the collapse-depressions in the lower part of the flow. Of the lava tubes, the largest is Pluto's Cave itself. It was discovered in ISG'i, and, according to AVells,-*^ the "succession of halls and caverns" can be traced for a distance of between one and a half and two miles. Today it is doubtful if it can be followed for more than half a mile. It trends approximately northwestward, lying close to and parallel to the axis of the flow. In several places the roof has collapsed so that entry is easy. Most of the tube has a diameter of 30 to 50 feet, but the floor is thickly covered by debris fallen from the ceiling and by sand blown from the dunes on the surface. Locally the diameter reaches 80 feet. The walls reveal three, and in places four supei-iniposed flows with cliidcery tops and bottoms. These do not represent (listinct effusions separated by intervals M Wells, H. T>., Hi.stnry of Siskiyou County, Oakland, 1881. 44 MACDOEL QUADRANGLE [BuU. 151 of quiet, but simply "flow-units" or lobes extruded through the front of the advancing lava.-' No lava stalactites hang from the ceiling, and only crude strand linos were loft on the walls by the obbinci' of the lif|nid interior as it drained to lower levels. Oval schollendomes, a few feet to 20 feet high, are scattered at random over the surface of the lower half of the flow. ^Marginal pressure ridges, many of which have gaping fissures on their crests, are most numoi-ons along the eastern edge, as in the vicinity of the Hart Ranch. Collai)se depressions are distributed spoi-adicall}' over the flow, but espe- cially near the margins of the lower part. Some are elongated trenches bordered by low cliffs, like the one near the eastern foot of Drop-off. Others are approximately circular, like the one close to and almost in line with Pluto's Cave. Still others are irregular in outline, and many are occupied by ponds and marshes. The majority were formed by col- lapse of lava-crusts over tubes emptied b\ di-ainage, but some are being produced today while others are being doei)enod by removal of sand and gravel from beneath the lava bv subterranean streams. Lithologically, the basalt is ({uite uniform. All of it is black, vesicular, olivine-rich augite basalt with a fairly smooth crust marked by gentle swells and hollows. Pahoehoe skins are exceptional. A description of the microscopic features of two samples Avill suffice. One of these, typical of the crust of the basalt, has a hyalojulitic texture and consists of the fol- lowing: olivine crystals, up to 1 millimeter in length, 12 percent; laths of basic labradoi-ite, also measuring U]) to 1 millimeter long, 50 percent; minute, auhodral grains of augite, 2 ])ercont ; interstitial black glass, 15 ]iorcent ; and amygdules filled Avith radiating calcite and a little opal, 21 percent. The othei- sample is re])resontative of the holocrystalline lava beneath the glassy crnst. In tiiis, olivine makes up 5 percent of the volume, whereas .snudl pi'isms and aidiedral grains of augite total ajiproximately 25 percent. Laths of basic labi-adorite. composing (JO percent of the bulk, are nuich smallei- than in the glassy basalt, few measuring more than 0.2 of a millimetei- in nuixinuim dimension. Granular opaque ore minerals account for 8 percent of the whole, and interstitial cristobalite makes up the remainder. Butte Valley Basalt The southern end i>\' \'>\\\\r \':\\\r\. aiound Jerome, is occupied by an almost lioi'i/.ontal sheet of lilack. \-esicnhii' olivine basalt dotted with schollendomes, almost identical in appeai'ance with the Pluto's Oave lava just described. Us visible extent in tlie iMacdoel (piadrangle is shown on the geologic map, plate 1, but it exteiuls far to the oast, and probably to the north also beneath a cover of alluvium. How far to the north the basalt sjtroad is uncertain. Several wells near Maedool, after passing through ;{() to 50 feet of sediment enter basalt, although this may be of Pleistocene age rather than lu'cent. Put that the Pntle \'alley basalt (lid extend as far as ]\Iount llehroii Slat ion .seems likely because a well at that locality jiassc'd through 47 IV'-t of l)asalt, beginning at a depth of ;{0 feet, before continuing thi'ongh 24 feet of cindei's and then cutting clay, sand, and gravel J'or another ll;{ feet. Since no sediments are i)res- enl in the Plio-Pleistocene succession, the iid'erence seems justified that -•' NIchol.s, R. L., Klow-unUs in b.i.salt : .Iniir. Oeolog:>-, vol. II, pp. f.17-630, 1936. 1949] OKOLOOY 45 tlu> hiisiiltic lavii here is of lu'cciit orJLiiii. At .limipor Lod^c. wliicli lies at lli(> l)()tt(»iu of the .Mount ilchrou jrniili' on ('. S. Ili^^liway 97, the liiitte ValU'v basalt is 80 feet thick ami unclerhiiu by (hirk voleaiiic sand. Similar basalts, pi-obably of about the same a<;e, are widely exposed utNir r>ray. Their source, like that of the I'uttc \'alh'y hiva, lies in fissures east of the Maedoel (luadranj^le. Little Deer Mountain Volcano The upper pait of Little Deer Mouutaiu is a cone of red, bi'oAvu, and black cinders between .")()() and (iOO feet hiiih, breached on the south side. Surroundinxtent. .lud^inetween the.se minerals there is a matrix of black glass heavily charged with dusty opaque ore minerals. Alder Creek Basalt From anotlier fissure, near the top of the precijiitous north wall of Alder Creek cannon, a younger flow of basalt "-ascaded 1.700 feet on to the canyon floor, then continued for 2 miles, entling with a steep front as it spread over the Butte Creek ba.salt. The surface features of this speetaculai- flow are so well preserved that if the forest cover were 1!U91 r.KOLooY 47 roni()\0(l oiu' iiiiirlit sui)p()st' tliat the hivn luid been discliai'^cd only a few cltH'iuK's ajro. Almost t'ci-tainly it was tTuptod within the present or the preeediiifi millennium. In contrast with the smooth-ernsted Butte Creek basalt, tliis tlow lias a bloeky to scoriaeeous crust, and instead of olivine the most consijicuous ])lieM(HTysts are of au^icall\", the Goosencst Hows are extremely uniform. All are true block lavas, that is to say they have crusts composed of smooth-faced blocks, up to several yards across, that pass downward through a shat- tered layer into massive, unbroken lava. In jilaces the siirticial blocks are piled ill stecji mounds, many more tlian .lU feet hiyh, and in ridges dis- posed parallel and perpendicular to the directions of flow. Petrographically, tlie lavas are hyperstheue-rieh andesites or per- haps basaltic andesites, markedly vesicular and with a glassy matrix. l*henocrysts of olivine, up to 1 millimeter long, make up oidy 0.5 to 1 percent of three samples studied microscopically. Porphyritic augite is equally rare. Phenocrysts of hypersthene, on the other hand, constitute between .") and 8 ]iert'eut of the bulk. Laths of zoned, medium to basic labradorite, few of which exceed a length of 1 millimeter, total between 40 and 50 percent. The remainder consists of brownish-black glass charged with dusty opaque ore minerals, minute needles of acid plagio- elase, and specks of pyroxene. Last Flows of Shasta and Shastina The snouts of two Keeent flows of andesite erupted from the flanks of Shasta and Shastina lie within the Macdoel quadrangle. The older flow may be seen a short distance to the east of the Dwiunell Reservoir. It is a blocky to scoriaceous, hypersthene-augite andesite with steep margins and a rugged top marked by arcuate ridges and gullies arranged normal to the direction of advance. Along its western side, it overrides the terminal moraines of the Shasta glaciers, but its top is bare of glacial debris and is mantled only by a thin veneer of cinders. The younger flow, whose high, block}- front is skirted by U. S. High- way 97, is probably the last to be discharged by Shastina. Only a small part of it extends into the Macdoel quadrangle, the entire flow covering approximately 20 square miles. This great flood poured from a series of fissures at elevations of 9,000 to 9,500 feet, not far below the crater rim of Shastina. And they escaped after the formation of two cinder cones, one of which w^as encircled by the lava while the other deflected its course. Some of the source-fissures are arcuate ; others lie radially with respect to the flanks of Shastina. One, illustrated in an earlier report,-^ is a sinuous trench from 30 to 50 feet wide and up to 100 feet deep, with almost vertical Avails. As to the age of these thick, blocky flows, there is evidence that the glaciers of Mount Shasta had dwindled practically to their present extent before the lavas were erupted. Indeed one gush of lava issued from the end moraine of the AYhitney glacier, only a short distance below the present front of the ice. If further proof of their youth were needed, it might be found not only in their perfectly preserved, steep fronts, but also in the paucity of vegetation on their tops. The almost complete lack 28 Wells. H. L,., op. cit =» Williams, Howel, Mount Shasta, California: Zeitschr. fiir Vulkanolocie, vol. 15, pp. 225-253. 1934. 4—9172 50 MACDOEL QUADRANGLE [Bull. 151 of large trees suggests that some of the lava is no more than a few cen- turies old. Thev are mantled onlv bv a light sprinkle of pumice blown from Shasta in 1786.-'^o Petrographically, these last flows of Shastina are olivine-free and olivine-poor, pyroxene andesites, generally devoid of porphyritic feld- spar. A sample from the snout of the longest flow, near U. 8. Highway 97, is selected for description. In this, few feldspar laths exceed 0.25 millimeter in length, most of them measuring less than 0.1 of a milli- meter. They show a strong Huidal alinement. In composition they vary little, all being of medium labradorite. Together they make up 55 percent of the volume. Phenocrysts of diopsidic augite (2V — 55° ; Z to c — 42°), mostly between 0.2 and 0.4 of a millimeter across, but occasionally 1 millimeter long, make up approximately 6 percent. Porphyritic hypers- thenes, of about the same size, total only 2 percent. Among the pyroxene microliths, which constitute 5 percent, hypersthene is much more plenti- ful than augite. The remaining 82 percent of the lava consists of trans- lucent, brown glass (n=1.508±.002;=68 percent SiOg) lightly stippled with granular opaque ore minerals. Summary of the Petrography of the High Cascade Lavas The volcanic rocks of the Western Cascade series, as noted already, range in composition from olivine basalt to potassic rhyolite. Those of the High Cascades show much less variation, being for the most part olivine basalts, olivine-bearing basaltic andesites, and pyroxene andes- ites. Some hornblende-bearing andesites are present, and perliaps some of the Haight Mountain lavas are dacites. But rhyolites are absent. During Pliocene time almost all the lavas were olivine basalts or basaltic andesites. Subsequently, andesites and perhaps dacites were also erupted. In other words, no regular sequence can be detected. With few exceptions, individual volcanoes discharged only one type of lava, but Little Deer Mountain, after erupting olivine basalt throughout most of its activity, discharged flows of pyroxene andosite during the final stages, and Mount Shasta, after growing almost to its full height by effusions of pyroxene andesite, began to erupt dacite and basalt as well. As in other parts of the High Cascades, the Pliocene and younger lavas of the ]\Iacdoel quadrangle belong to the Pacific or calc-alkaline igneous suite. Moraines and Fluvioglacial Deposits Moraines. At their maximum extent, which was presunuibly at the climax of the Tioga stage of the Wisconsin glaciation of the Pleistocene epoch, approximately 25,000 years ago, the glaciers that descended the northwest slopes of Mount Shasta spread into Shasta Valley to an eleva- tion of about 2,800 feet. Their length was then slightly more than 18 miles. Their end moraines are to be seen along tlic shores of the Dwinnell Reservoir, and their recessional moraines form the cluster of ridges that extend thence southward to Weed. The limits of the glaciers that formerly covered the northern flank of Shasta are obscured by younger lavas and by fluvioglacial fans, but probably the ice did not extend far beyond U. S. Highway DT, to eleva- 30 417-420 225-2511, VJiA Willlam.s, Ilowel. Mount Sha.stn, a Ca.scade volcano: Jour. Geology, vol. 40, pp. , 1932. . . . .Mounl Shasta, ("alifnniia : Zoitifclir. fiir Viilkanologle, vol. 15, pp. 1040] OKOLOGY 51 tioTis h(>l()\v 4, ()()() I'lH't. Thoro arc no siako National Park, Oregon: Carnegie Inst Washington, Pub. 540, 1942. 1940] GEOLOOY 5.1 Umpqna beds inside the horst. and tliat three bodies of lava, probably the fillinpfs of voleanic neeks, are present near the southern end of the horst, just where the displacements reaeh a niaxinmni. The second liorst, which may l)e referred to as the YcHow Butte horst. is a mucli more important strncture. It is traccabh^ for approx- imately 8 miles, wideninj]: northward from abont half a mile to at least three times that width. The fault boundiufr the horst on the east, althoufrh larfrely covered by Ixccent lavas and fjULdomcrates, is marked in places by sjiriufifs and artesian wells and l)y tlic abi-ujit termination of Umpqna sediments aprainst the Western Cascade series. Owing to renewal of movement on the fault within very recent times, the trace is further defined by a straiirht scar]), u]) to 15 feet hiiih, that cuts the Pluto's Cave basalt and the iidiers of Shasta andesite a short distance north of Yellow Butte. Southward the fault i)asses through the gully on the east side of Yellow Butte and disappears beneath the Shasta lavas close to U. S. Highway 97. T'^nfortunately the amoiuit of throw on the fault cannot be determined accurately, partly because the relief of the pre-volcanic surface is unknown, partly because rapid lateral variations within the AVestern Cascade series make correlations hazard- ous, and partly because there is doubt as to wliat part of the Umpqna formation is present within the horst. But if the pre-emption surface was one of low relief, and the Umpqua beds exposed within the horst represent the topmost part of the formation, the downthrow on the fault near the Conrad Ranch approximates 600 feet. Undoubtedly the throw increases southward, since the metamorphic and plutonic bedrocks are revealed inside the horst on Yellow Butte. Thereabouts the throw may be several thousand feet. The probable position of the fault bordering the Yellow Butte horst on the Avest is shoAvn on the geologic map, plate 1. Unfortunately the exact position is concealed by the Pluto's Cave lava. As in the case of the eastern fault, the throw diminishes northward, but the precise amount of displacement cannot be told. The trouble is that the Western Cascade lavas in the western half of Shasta Valley show no well-defined dips, and in the other half they are buried by Recent flows. But if the older lavas dip northeastward at angles that diminish in that direction from 15° to 5°, as they do elsewhere, then the throw on the fault in the latitude of Big Springs is not less than 10,000 feet. Opposite Yellow Butte the throw must be much more if the bedrocks there were formerly covered by Cretaceous and Umpqua sediments and by the full thickness of the Western Cascade series. South of Yellow Butte, the converging fauUs that border the horst are concealed by andesitic flows from jMount Shasta. They nuist continue southward for a considerable distance, and it may not be fortuitous that if they maintain the trends they have on either side of Yellow Butte they must come together close to the central vent of Shasta. From the foregoing it appears that Shasta Valley is a large struc- tural depres.sion, limited on the east by a fault of great displacement. Already, before the first Pliocene eruptions of the High Cascade vol- canoes, there was a broad, north-south depression that coincided approx- imately with the present valley, bordered on the east by a high ridge of Western Cascade rocks. But the drainage of tlie depression was then quite different from that of today. Proof of this is to be found in the 54 MACDOEL QUADRAXr.LE [Bull. 151 boulders of quartzite beneath the Table Rock basalts, for these were laid down in the bed of a westward-flowinp: stream, 700 to 800 feet above the ju-esent edge of Sliasta Valley, despite the fact that the l)Oulders could only have been derived from far to the west, from the Klamath- hiiskiyou ^lountains. Pebbles and cobbles of bedi'ock are also present in the upper reaches of "Willow Creek valley, and there are broad terraces mantled Avith bedrock detritus at the northern end of Sliasta Valley, oast and north of Snowdon. The presumjition is that the Shasta River formerly ran close to the edge of the High Cascades and it probably continued northward through what is now the valley of AVillow CreeK to join the Klamath River about 8 miles above its present confluence. Where the former channel of the river passed by ^liller Mountain it was bordei'ed by huge fans of bouklcry detritns. u]) to .UK) feet in thickness, that merged upw^ard into pediments, relics of which are still preserved 1,000 feet above the present valley. Today, Shasta River makes a right-angle bend on leaving the Dwinnell Reservoir, and Hows approximately i)arallel to the margin of the Pluto's Cave basalt for the next 10 miles. There can be little doubt that this course was established only a few thousand years ago, when tile original channel was filled by the Pluto's Cave lava. The ancestral Shasta Valley and the two horsts adjacent to it were pi-obably formed at the close of the ]Miocene ei)och, prior to the growth of the Pliocene shield volcanoes. But Butte Valley and the adjoin- ing fault-scar]is were formed much later. i\lost of Ilies<> scari)s i)robably (late back to late Pleistocene time, but many aiH' so well-jireservei,! as to indicate either renewal of movement or origin in Recent times. The scarps follow two principal directions, one north and the other ap])rox- imately northwest. As far as can be judged the two sets were formed simultaneonsly. In several places, as near the }.Ieiss Ranch, the scarps show abrnpt changes in trend where the diagonal fanits meet the meridional ones. Butte Valley itself is a complex, down-faulted basin, deepest along its western side. Between JMacdoel and Dorris, in see. "I'A, T. 47 X., K. 1 W., a well passed through 18 feet of sandy soil, then through 173 feet of clay before entering a bed of cinders. A well at jMouiit Hebron Station ended in sediments at a dejith of 184 feet. But apparently the full thick- ness of the valley-fill has nowhere been ]ienetrnted by borings. Sam's Neck and Pleasant Valley are two graben ]ii'ojecting beyond the margins of the main de]>ression. The adjacent hoi-sts are tilted west- W'ai'd at angles of 10° or less. .\1 1lie southern em! of Sam's Xeck. approximately 2 miles east of Spring School, a sulphur spring occurs at the intersection of two faults. ()rr Lake and the two dry lakes shown on the geologic map. i)late 1, occupy graben, and like IVIeiss Lake tlie two dr\- ones lie on the western side of t he depi-essions containing them, suggesting that the down-dropjted blocks are tilted in that direction. Innnmeralile small displacements cut the Westei'ii Cascade series, so that slickensided lava surfaces are extremel\- abundant, hut the trends of these iiiinur fiacluics and the directions of movement along them are highly \arial>le ovei- short distances. A recent fault cuts the upper flow of ha.salt foi-ming Table Rock, trending appro.ximately noi-thwest- ward and with a downthrow' to the west of aboi.t 15 feet. 1949] oKOLonv 55 GROUND WATER At the soiithorn end ol" Shasta N'allcy, nmv Pluto's Cave, tlie water table lies at a dciitli of approximately :U)0 Teet. Nortliward it approaches the surfaee rapidly so that many lai-^'e sprinjrs issue from the basaltic lava, and in Little Shasta Valley ponds and lush meadows occupy the depressions. Several wells in the valley disehar«,'e artesian water from shallow deitths. Two artesian wells antl several artesian sprin<;s, ineludiiif,' the copious one that feeds Spring Creek above Conrad l^aneh, are situated on the fault limiting the Yellow Butte horst on the east. Along the edges of Shasta Valley nmnerous small springs issue from layers of tuffaeeous clay between the lavas of the Western Cascade series. Springs are also common close to the contact between these lavas and the overlying flows of the High Cascade series. In the High Cascades themselves springs are found especially under the following conditions: some issue from the flanks of the shield vol- canoes, flowing from the porous tops and bottoms of flows or from joints in the lava, as at Spannus and Grouse Springs on the Eagle Kock volcano ; others issue from the rims of depressions between adjacent shields, like those that supply Grass Lake, Bull Meadows, and the meadows near Kuck's Cabin; still others are located along faults cutting the lavas, as along the margins of Butte Valley ; and finally, some springs gush from tubes in basaltic flows, like those on the Granada Ranch and near Mount Shasta Woods, which pour out of the Butte Creek basalt. in Butte Valley, ground water is found everywhere close to the surface, so that it is seldom necessary to drill wells below 10 to 20 feet. The water table rises westward, intersecting the surface among the marshes around ]\Ieiss Lake. A description of the Beswick Hot Springs has already been given by Waring.-" They occur in alluvial flats along the banks of the Klamath River, and formerly they fed hot-mud and clear- water baths at a popular health and fishing resort. The hottest spring then had a temperature of 152° F., and several others were only slightly cooler. Analyses of the water are notable particularly for their high content of sodium chloride and for the presence of borates. Presumably the chlorine comes from deeply buried marine beds of the Chico formation, and probably th^^ borates are derived from the overlying lavas. There is no evidence that the heat is of volcanic origin, for the closest lavas of Recent age lie 7 miles downstream, near the Copco Dam. Nor is there evidence that the springs lie on a major fault, although their position may be related to minor fractures along which there has been little displacement. Indeed such fractures may be partly responsible for the long, straight canyon of Shovel Creek at the mouth of which the Beswick Springs occur. Since the springs issue from the Western Cascade series and this dips eastward throtighont a belt that stretches for many miles to the west, it seems likely that the water is forced to the surface from great depth. Certainly that must be so if the chlorine is derived from the Chico beds, since those must lie at least 10,000 feet below. ■" Warinp, O. A., Springs of CaUfornia : U. S. Geol. Survey Water-Suppl.v I aper 338, pp. 120-121, 1915. 56 MACDOEL QUADRANGLE [Bull. 151 "Waring ^^ has also described two clusters of carbonated springs, popularly known as Soda Springs, one near Bogus School and the other near Table K(jck. The largest group, the Bogus Springs, includes at least eleven, although at the time of "Waring 's visit there were only six. Each has built a low mound of calcareous tufa, the biggest measuring 30 feet in height and 30 yards in width. Gas bubbles from all of them. In "War- ing 's report, the temperature range is given as 72° to 76° F. A quali- tative analysis made in 1047 by J. D. Howard of Klamath Falls ^^ showed the presence of sodium chloride, magnesium and calcium carbonate, sodium ]ihosphate, silica, iron, and traces of lithium and hydrogen sul- phide. It is presumed that here also the chlorine originates from Chico sandstones at great depth. The other group of carbonated springs, near Table Rock, has been discussed by "Wearing in the report mentioned above. An analysis of water from one of the springs on the north side of Table Rock, in sec. 20, T. 4-') X., R. 4 "W., formerly bottled as a carbonated mineral water by the Yreka Coca Cola Bottling "Works, is cited by O'Brien.^'' It is notable on account of the high content of calcium and sodium bicarbonate and of sodium chloride. On the ]\Iartin Ranch, the active "soda spring" issues about 75 yards west of a tufa mound 10 feet high, which was formerly the principal outlet. The presence of this mound and of much tufa cementing the gravels along the banks of the adjacent stream suggest that the waters may formerly have been hotter than at present. Geologic mapping does not indicate the occurrence of any major faults near either the Bogus or Table Rock Springs, but probalily they lie on fractures of small dis- placement. BESWICK "CRATERS" In view of the widespread interest that they have aroused, brief mention should be made of the so-calleil "Beswick Craters" which lie on a spur approximately 350 feet above the Klamath River near its con- fluence with Shovel Creek. More precisely, they are located a quarter of a mile east of the old Hessig Ranch. The "craters" consist of a cluster of closely spaced, circular pits from a few feet to 10 feet deep, and from a few feet to about 10 yards in diameter. The.y are distributed over an area of aproximately an acre, witliiu a hummocky pile of boulders, most of which measure a foot or so across, though a few exceed 3 feet in nuiximum dimension. These boulders are renuiaiits of one of the intra-canyon flows of High Cascade lava perched on a bench cut in rhyolite belonging to the "Western Cascade series. Most of the "craters" are funnel-shaped, but some of the smaller ones are almost cylindrical. Generally tliey are to be found on the tops of block-mouiuls. Occasionally, small pits occur on the rims of larger ones. By some, these features are regarded as products of volcanic explo- sions, a snjiposition fostered no doubt by the presence of the Beswick Hot Springs not far away. Indeed, it has been reported that in 1046 a "blow-out" took place at the "craters" and that bushes were uprooted and killed. I^ut close inspection reveals no signs of solfataric or fumarolic activity within the area and no evidences of heat. Exjilosions powerful »* Op. cit., 1)11. L' 17-220. 3* Oral coniiminiration. » O'Urien, .1. C, Mine.s and mineral resourco.<5 of Si.'jkiyuu County, California : Cali- fornia Jour. Mines and Cleolopy, vol. 43, pp. 413-462, 1947. 1949] GKOLOGY 57 oiiou<::]i to produco lariro pits in such coarse, l)oiil(lci\\' material would surely have hlown liner ejecta to <;reat distances, but there is no hint of such debris. The conclusion is inescapable: the "craters" are not vol- canic. Probably one is confronted liere with tlie dismembered relics of a basaltic flow, with a field of residual blocks the huiiiinocky surface of which results either from unequal erosioji of the underlying rliyolite or from deposition on an uneven surface. Currents of cold air issue from the bottoms of some of the "craters," su{rp:estinn: the presence of subter- ranean channels. Doubtless the shapes of some of the "craters" have been modified by "pot hunters" and perhaps some of the pits were formerly utilized by Indians, many of whom used to camp along the Klamath River and Shovel Creek. ECONOMIC GEOLOGY Coal Thin beds of lignite and sub-bituminous coal have been found at several localities along the edge of Shasta Valley within the T^mpqua for- mation. The principal workings are at the Ager coal mine on the llage- dorn Ranch, approximateh^ 5 miles south of Ager, ad.ioining the Ager- Montague road on the west. According to Averill,^' the main seam reaches a thickness of 6 feet, but the best part varies between 14 inches and 4 feet, averaging 2 feet. The seam pinches and swells rapidly and it includes and is underlain by thin layers of carbonaceous shale. The beds dip to the northeast at 18° for the most part, but at higher angles where they are cut by small, normal faults. An incline has been driven down the dip for 700 feet, and from this three drifts run north for a maximum distance of 500 feet and south for a maximum distance of 400 feet. A pro- duction of 100 tons, valued at $500, was reported, in 1914 by the Yreka Development Company, then lessee.^^ Averill states that numerous prospect holes have been drilled near this mine on the Herr, Cooley, and Denny Ranches. On the Cooley Ranch, a hole was bored to a depth of 130 feet by C. B. Kay, on the strike of the Ager seam, passing through 11 feet of coal at a depth of 118 feet. Another hole, 106 feet deep, is said to have struck 20 inches of coal at a depth of 95 feet. Averill also records the occurrence of small streaks and spots of soft coal and a seam up to 2 inches thick near Hornbrook. There can be little doubt that these are also in the Umpqua formation, and that they lie on about the same horizon as the more extensive coals found near Ashland and Talent in Oregon.^^ Thin beds of coal are also present near the base of the Umpqua for- mation in the hills east of Yreka. These do not appear to have been exploited commercially. A bed of lignite and lignitic shale occurs between the volcanic rocks of the Western Cascade series on Glenn "Williams' ranch in sec. T, 44 N., R. 4 "W. Its extent and thickness are not known. Other coal deposits, on approximately the same horizon, are reported to be present on the northern flank of Bogus jNIountain, but these were not located. ST Aver in, C. V., Mines and mineral resources of Sisltiyou County: California Div. Mines Rept 31, pp. 255-338, 1935. 3-s O'Brien, J. C, op. cit., p. 423. ™L)iIler. .1. S., The Rogue River Vallev coal field, Oregon : U. S. Oeol. Survey Hull. 341, pp. 401-405, 1907. 58 MACDOEL QUADRAXfiLE [Bull. 151 Copper and Molybdenum The Yellow Butte mine, comprising approximately 318 acres of patented land in the W I sec. 25, T. 43 N., R. 4 AY., lies on the northeast slope of YclloAv Butte. It is assessed to the Lone Hill Mining Company.^^ The workings oL-eur in a hody of coarse-grained hornblende-biotite quartz monzonite close to its contact with Paleozoic ( ?) quartzites and siliceous schists. Averill ^^ stated that an inclined shaft, about 300 feet deep, had recently beo)i retiiiib(M-e(l for 35 or 40 feet, but in 1948 the shaft was caved 10 feet from tlie collar. The plutonic rock here is cut by shear planes and stringers of quai'tz that strike in general N. 25° E. and dip 70° NW. No ore was seen in place, but specimens of vein quartz on the adjacent dump carry pja-ite, molybdenite, chalcopyrite, and chrysocolla. Produc- tion has been small but exact figures are not available. Several pi-ospect pits have been driven into the quartzites close to the monzonite, and others may be seen in the metamorphic rocks on the western side of Yellow Butte, but all appear to be barren of ore. In view of the fact that Yellow Butte is a narrow horst bounded by north-trending faults of great throw, the limits of practicable mining are much restricted. Building Stone and Crushed Rock Sandstone. Tlie massive Cliico sandstones forming the outlier approximately 2 miles northeast of Yreka, have been quarried for build- ing stone."*- Similar rocks have also been worked on a small scale in the vicinity of Cam]) Lowe and Ilornbrook. Lava. An immense supply of lava is available both for building stone and road metal. To date only the lavas of the Western Cascade series in Shasta Valley have been utilized, although many of those forming the High Cascade volcanoes ai-e equally satisfactory. The Western Cascade andesites are particularly useful for criishcd rock where they are cut by closely spaced, platy joints and break with a hackly fracture. Much andesite of this kind is to be found among the hillocks in the western half of Shasta Valley, but only at one locality, in see. 25. T. 45 X., K. (I W., has it been quarried on a large scale. The nuitei-ial hci-(> proved satisfactoiy for surfacing the Siskiyou County Air- i)()rt. lilock-y jindesite has been quarried for road metal in sec. 36. T. 45 N., R. 5 AV., and in sec. 29, T. 44 N., R. 5 W., but no use seems to have been made of the massively jointed, dense andesite widespread along tlie south- west margin of Shasta Valley. Rliyolitic Java has also been quarried for the surfacing of roads. The two principal localities are as follows: on Drop-off, in sec. l(i. T. 44 N., R. 5 W., whei-e the long slides of talus below the sunnnit-cliffs have been worked on a small scale; and on Ceineterv Knoll, near Little Shasta, in sec. 3(i, T. 45 N., R. 5 W. The Pinto's Cave basaltic lava, owing to the ease with which its jointed crns! breaks into cnboidal blocks, has b(>cn widely utilized by ratichei-s for const iMiction of stone fences. lihifnlih TkJJ. Because most of the rhyolite tail's of the I'egion are friab'e and pnlvcrize easily into line dust, little use has been made of them. *" O'Rili'n, .1. <'., op. (it., p. 428. «> Op. oit., I!i:!.'). pp. 27;!-274. *- Averill, ('. v., op. oit., 193."., p. 3:'.7. 1949] OKOLOfiY .in But locally, as in sec. 7. T. 47 N., 11. 4 W., close to the Ajrer-Beswick road, the firmer, wehlcd types have been excavated for road metal. ()tli( r Volcanic Ixocks. A lar«re quarry in sec. 7, T. 45 N., H. 5 W., was oj)eii(vl up recently for materials to surface the Siskiyou County Aii-- port. It occurs in mudllow (lahar) deposits of the ^Vestern Cascades series that consist of large boulders of andesite, rhyolite, and quartzite set in a matrix of red, tuffaceous clay. Owiny; to the nature of the fine con- stituents, the material proved to be unsatisfactory. Basaltic cinders have been utilized extensively in the surfacinj^ of hieko / NATIONAL MON. / X ^•-LEAF AREA / Uy^HASTA VALLEY AREA ^^ ^^^^^^ Xweed Y iOunsmuir i^Adin ' ^ ^y — ^» / ^^c'l striictiMis in the St. Klias l{an!,-i', YuUim Toiritory : Jour. C.eomorpl.nlnKy.,v^^^^^^^^ Hango. US ,„... Auburn. Maine, Merrills Weber Co.. l'J32. 1949] CIRCULAR SOIL STRUCTURES The Concentration of Clay 65 Due to initial lieterojroncity in the distribution of clay in the soil, certain areas near the surface hold more water than otlun-s. Clay-rich areas, since they can hold more water, will upon saturation and freezing exi)and in relation to the surrounding soil. Conrad ^ states that a satur- ated cube consisting of 70 percent soil and 30 percent water expands on Initiol distribution of cloy ond stones. Upfreezing Kos produced stone povement and clay has begun to concentrate in center. '■c:i . O. a Doming hos begun ond povement in center of dome tios started to work outword. L-?. O o_ Mature dome structure with stone-filled ring trenches ond stone— free center. Not to sccle. Fig. 3. Diagiani.s showing origin of circular soil fitructure.«!. 8 Conrad, V., Polygon nets and their physical development : Am. .lour. Sci., \i>l. 2 14, no. 4, pp. 277-296, 1946. 5—9172 66 MACDOEL QUADRANGLE [BuU. 151 its edge by a factor of 0.01 upon freezing, and that the increase in radius of a saturated spot will be 0.01 times the radius of the spot. When adjacent clay patches touch during this expansion and then contract as a result of mutual adhesion of the clay-sized particles during thawing and drying, part of the smaller patch may be drawn into the larger one. By repeated expansion and contraction, a clay patch may thus grow in size at the expense of the surrounding soil until a large, slightly domed concentration of clay-rich soil is formed. Upfreezing of Buried Stones This process depends upon the principle that freezing begins at the surface, the frozen zone thickening downward; thawing also begins at the surface, the thawed zone thickening downward. When freezing begins, the top of a large stone is firmly held by the surface ice sheet. Freezing below this level forces both the sheet and stone upward by expansion of newly forming ice. Since the bottom of the stone is held only by unfrozen soil, it is easily lifted with the surface sheet, the effect being more pronounced the larger the stone fragment. It is also probable that the void below the lifted stone is filled by inflow of saturated soil so that the sinking of the stone to its original level during thawing is prevented. During thawing the top soil layers contract and settle do-svn relative to the stone which is still held fast by ice at its base. When this ice melts the stone settles but by an amount smaller than the initial uplift. In this manner buried stones are eventually deposited on the surface. This process undoubtedly plays a large part in the formation of the loose stone pavements commonly observed in alpine regions. Radial Movement The radial displacement of stones to the rings and polygons prob- ably results from a combination of several mechanisms. As soon as the doming of the clay mass has been accomplished, the radial direction becomes also a downhill direction. Two processes may then become active. One is the well-known frost-heave action by which stones are lifted perpendicular to the sloping surface during freezing but drop vertically during thawing so that there is a downslope movement by repeated short steps. The other process is simple .-liding caused by almost frictionless shear planes developed between ice layers during thawing. Conrad states that the radial expansion of the freezing clay patches is the most important factor in the outward movement of stones on the surface. Expansion carries the stone outward but thawing does not cause a return to the initial position because the soft, saturated soil has not the consistence to carry large stones and because this movement would be uphill. Therefore, after each thaw the clay particles are drawn back b}^ adhesion while the larger fragments are left in displaced posi- tions because they are not affected by adhesive forces. In this manner the growing clay patches simultaneously purge themselves of the larger sizes and add to themselves by the force of adhesion between colloid and clay size. Experimental Evidence In order to test the applicability of these three processes in the Siskiyou County mounds a closer examination was made of several of the more perfectly formed rings at Leaf. 194;)J CIRCULAR SOIL STRUCTURES 67 A trench Avas dug- from several feet outside a ring to a point several feet inside the enclosed mound. The observed cross-section is shown in figure 3. Outside tlie ring the surface pavement is superficial; below it is a soil layer 8 to 10 inches deep which is nearly free from stones. Below this depth, stones are again abundant and keyed in a soil matrix so that digging is very difficult. The ring itself was 3 feet wide and 6 to 9 inches deep in the center, and stones in it were clean and free from soil ; in other words, the trench had not been filled at the bottom to any great extent. The surface pavement stops at the ring but the lower stone surface continues uninterruptedly beneath the mound. One important feature of this cross-section is the presence of the stone-free stratum immediately below the surface. Here is good evidence that the upfreezing process has been operative. Apparently the mechan- ism is effective only to a depth of 10 or 12 inches ; that is, to the depth of the soil laj-er. Since the proportion of large sizes to the soil matrix is high in this formation, it is possible that below a poorly consolidated top layer a foot or so thick the stones are too well keyed to be raised by the freezing process. A series of experiments by Taber ■* suggests another possible explana- tion. He found that frost heaving in almost pure clays was due to the formation of pure ice layers between bands of clay, the vertical thrust- ing being due to the growth of these layers rather than to the volume increase of frozen, saturated soil. AVater to form the layers was drawn from below by surface tension in the minute intergranular openings of the cla3^ Therefore, the depth to which heaving occurred was dependent upon the amount of water supplied from below. This amount was depend- ent upon the depth from which water could be made to rise, which was in turn dependent upon the grain size and consequent capillarity of the sediment. The extent to which this phenomenon occurs, therefore, is con- trolled b}'' the clay content of the soil, there being no effect in sandy, clay- free soil and perfect layering in pure clays. This mechanism causes much greater vertical movement than simple volume expansion and offers a better explanation for upfreezing. In addition, it provides a possible reason for the thinness of the superficial stone-free soil band, since the size-composition of the soil limits the depth to which heaving can operate. Two readily observable features suggest that concentration of clay into mounds has occurred. In many places the vegetation within the rings is notably different from that covering most of the terrace surface. Out- side the rings, the cover is sparse grass and scattered low bushes, but on the mounds the grass and brush are thicker and grow to much larger size. Occasional small juniper trees are also limited to the mounds and several of the straight ridges have lines of trees down their centers. This differ- ence is probably due both to the greater retention of water by the clay and the greater rapidity of the chemical destruction of these finely divided minerals. This feature is not apparent in the Shasta Valley mounds because the area is used for grazing. A second noteworthy feature is the limitation of most of the single rings to a maximum diameter of about 85 feet. This condition suggests that some control prevents further growth of the mounds and rings. Probably this control is the proportion of clay in the soil. It seems rea- * Taber, Stephen. The mechanics of frost heaving: Jour. Geolog-y, vol. 38, pp. SOS- SIT, 1930. 68 MACDOEL QUADRANGLE .^>' /s ., .... „ ... _ . ... ^ .. _ 1- iG. I. I'fiail orone of the bordering rings. Thi- iiK>uiided side is on the right. sonable to assume that when a mound has grown to some maximum size by concentration of clay from the surrounding soil, a stage is reached in which the mound is encircled by a band of clay-free soil too wide to allow capture of additional clay from the outside. In an effort to test this hypothesis a series of soil samples was taken from each of four mounds, three from the Butte Creek area and one from Sliasta ^'alloy. These samples were screened down to about minus 0.03 inches and small grab-samples were taken by ecpial volume. These samples were placed in test tubes and water was added to the same height in each. After thorough agitation, the suspended samples were allowed to stand undistur])ed. According to Stoke 's Law, the velocity with which a particle falls through a liquid is largely dependent upon the size of the particle, the smallest particles falling most slowly. Therefore, after a given time all particles remaining in suspension above a given ilopth will be less than a certain size which may be conqjuted by Stoke 's Law. The samples from each series were run together so that they could be observed side by side during the settling process. In general, suspen- sions of those saini)les from the immediate vii-inity of the rings were the least dense after settling from 2 to 120 hours. Sami)lcs from within the mounds were the most dense, with the exception of No. (i. and those from presumably unatl'ected soil varied between tliese extremes. These observa- tions seem to i)rove that concenti'ation of day in the mounds takes place at the exjiense of the surrounding soil. For a more complete comparison of the samj)les, the transmission of light by the suspensions was measured. This metlunl was necessary because ecpiipment for the usual type of wet mechanical soil analysis was not available. A strong beam of light was ]iassed through the suspensions at a depth of "> centimeters and at timed intervals the intensity of this beam was measured with a pliotoelectric light-meter. Since the intensity of passed light varies inversely with the amount of material in susp<>n- ]!>4!)| ciiuTi.AK son. sTiu'cTrRKs 69 sion. these readinjrs were inverted by dividinp; tlieni into the maximum intensity reatliufr for clear water. The loj^arithms of the values thus obtained were plotted a;jrainst FI.if.21.2S. 20. .-.!) Agor. !», 11.17, IS. 1!). •22. 24. r>7 -Hoswick road. 24, ft!) ('o:vl mine, 57 -MontajT'ie road, 10 Alaska. 2.-.. l!4 Alder Crook, 14, .'50, 40, 4('.. 47. .',1 i)asalt, 4«> AiiKiuropsin oriformis flal>i). 17 Andorson. F.M., citod, 17 Antovs. Kriist. citod, (!4 Ashland, 1!>, 57 Averill, C.V., cited, 15, 17, 2,3, 27, 57, 58 Ball Mountain, 35, 36, 30, 40 liarroisiceras kniphtcni Anderson, 17 .'«wfr///o(/c'M«/.'* Anderson, 17 Bear Valley, 18 Bedford Ridge, 15 Be.swick. 11, 25 Hot Springs, 17, 55. 5(5 "Beswick Craters," 50 P.ig Si)rings. 32. 43, 53 Black Butte, .30 Black Mountain, 16, 18, 19, 25 Blackbutte-Elkhead-Nonpareil, 32 Bogus Creek. .36, 37 Mountain, 21, 22. 23, 24. 57. 50 School. 17, 24, 32. 36, 5G Soda Springs. 22 Springs, 56 Bolam, 41 glacier, 51 Bray, 45 Brown, Hcrrick C. 62 Brush Creek, 21,23 Bull Meadows. .55 Butte Creek, 11, 14, 39. 40. 45, 46, 48, 51, 64, 68 ha.salt, 45, 46. 47, 55 Canyon, 63, 71 Valley, 64 Valley, 9, 11, 12, 13, 14, 35, 36, 39, 44, 45, 46, 54, 55, 62 basalt, 44, 45, 48 California, 20, 33, 35, 64 Archaeological Survey. 61 State Tish Hatchery," 28. 29 . T'niversity of. l.'! Callaghan, Eugene, cited, 13. 20 Camel. 31 Camp Leaf. 63 Lowe, 16, 19, 58 Canada, 64 Cascade Range, 11, 13, 14, 17. 20, 28, 29, 33, 35, 51, 52 Cedar Lake, 27, 31 Cedarville beds. 20 Cemetery Knoll, .58 Chanev. R.W.. cited, 19, 33 Chi CO beds, 18 formation, 13, 16, 17, 18. 19 20, 55, 56, 58, 59 (73) MACDOEL QUADRANGLE [Bull. 151 Chione varians Gabb, 17 Clanio formation, 20 Coast Ranges, 13 Columbia River basalt, 20 Conrad, V., cited. 65, 00 Rancb, 52, 53, 55 Cooley Rancb, 32, 57 Copco basalt, 48 Dam, 11, 14, 28, 29, 35, 46, 47, 55, 59 Lake, 47, 59 road, 29 Cottonwood Creek, 16, 18, 19 Valley, 18 Crater Lake, 52 Cretaceous, 13, 15. 17. 20. 53 conglomerate. 31 pre-, 14, 18, 25 Upper, 13, 10 CucuUaea dcciirtata Gabb, 17 Davis Gulch, 21, 27, 48 l>cfr .Muuiitain, 14, 41 Denny Ranch, 57 Dcsmocvras klamathae n. sp., 17 yoloeiise n. sp., 17 Dewey Gulch, 25,30 Dlller, .I.S., cited, 19,57 Duriis. 9, 54 Doul)le Spring, 39 Dn.i> nff Peak. 20, 27, 28, 30. 44, 58 Dry Creek. 21. 25, 30 Dwinnell Dam, 40. 51, .59, 64 Reservoir, 11, 43, 49, 50, 54 Eagle Rock Mountain. 11, 13. 14, 32, 35, 39 volcano, '.I't, 36, 55 Edgcwood, 51 Eocene epoch, 12. l-'.. 10, IT. 19. 20. 32, 35 sediments, 18 upper, 33, 51 Europe, 64 Fall River Mills, 02, 71 Fenenga, Franklin, 61 (Jazelle, 9 Clen Williams' Ranch. 27. 5J (Uycytnvrh vcntvlii (;alii), 17 Goosenest Mountain. 11, 14, 20, 34, 35, 36 volcano, 3S. 41,48, 49 Granada Ranch, .".O, 46, 51, 55 Grass Lake. 25, 55 (Jreat Hasin, 12 (Jregory Mountain, 31 Gren.ola. 15. 1(5. IS. 25 (inmse Springs, .55 (li/rodtH fJixnisii (J.iiib, 17 Ilagedorn Ranch, 57. 59 Il.iiglit Mnnntaiii. :'.9. I(>. .5(1. 51. 71 Hart Ranch. 41 llavsl.Mck Rulte. II. 12, 59 Henley. 18 Herd Peak, 46 Herr Ranch, .57 llessig Ranch, 52, 56 imn] i\i)i;x 75 IIif;h Ciisnul.-s. 11. 1L». 20. 2:5. 2(;. :!4. 3.".. 30. 3S, -IC. ."O. .-.1. .VJ. :. 1. .V.> s:',. -,-,, 56, r>s iiiit. 1(1. 1.;. i(t. IS, lit, 32 I lorniinx.k. J>. 13, 1<>. IT, IS. 27, .'VJ. :;:'.. ,"7, 58 llorsrlliicf l?u(te, 42 1 lotliiiu ,i;l;ici(M-. 51 Ilow.inl. .1.1).. 5(> llust'iiiaii. K.r.. oitod. 17 lUrslVak. 35 Iiidijui.s, (51, (54 IiiiH' forin.-itioii. 20 .I<'r(iii!('.44 .luliii l>iiy fortiiafioii, 20 .luiiiiu'r Lodijc. 45 .lurassio porioil, 13, 14. 15. 10 Kay, C.B.. 13. 43. 57, 5!) K<'KK cono, 42, 50 Klamath Falls. 0. 12. 35. .37, 5(5 kiver. 11. 12,^13, 14, 15, 16. 17. 10, 23, 24, 25, 28, 29, 32, 36, 37, 46, 47, 48, 52, 55, 57 -Siskiyou Mountains, 12, 16, 17, 19, 33, 35, 52, 54 Klaiuathon, 27 Knowkon, — , cited. 10 Kuck's Cabin, 55 Lassen County, 62 Peak, 27, 40 Leaf, 62. 66, 71 area. 64, 69 Little Bogus Creek, 24 Deer Mountain, 14, 42. 45. 50, 59 Shasta. 23. 27. 28. 30, 31 , 34, 58 River. 24, 48 Valley, 27, 43, 55 Lone Hill Mining Company, 58 Low Wood School, 32 Lower Klamath Lake, 62, 71 .McfJavin Peak, 35, 37 Macdoel, 9, 12, 54 area, 13 quadrangle. 9, 10, 11. 13, 14. 16. 18, 20, 21, 31. 33, 35, 39, 40. 42, 44. 15. 4S, 49, 50, 51, 52 shields, 36 Martin Ranch, 56 Mary Peak, 31, 32 Mascall formation, 20 Medford, 9, 32 qu.ndrangle. 13, 15, 16. 18. 19. 24, 25, 32, 35, 51 region, 18, 32 Meiss Lake, 11, 54, 55 Ranch, 54 Merriam. Richard, cited, 32 Mesozoic. pre-, 1.5 Mexico, 47 Michigan. 33 Miller Mountain, 11, 13, 14, IS, 25, 26. 27, 32, 34, 35, 36, 40, .54 shield. 36 volcano. 37 Miocene ejioch, 12, 13, 14, 32, 33, 35, 51, 52, .54 , late, 33 Modoc Count.v, 62 Montague, 9, 11 , 12, 13. 16, 17, 31, 59 76 MACDOEL QUADRAXGLE [BuU. 151 Mortonirerns crenulatum Andorson. 17 Mount Hebron. 0. 11, 36. 4.", Station, 44, .">4 JpfFerson, r»2 Mnzania. 40 Hainipr, 40 Shasta. 11, 13. 14. liO. 21. r^.O. 40. 41. 43, 40, .10. TA, •".".. 63. 64. 71 Woods, 4."!. 46. ."il, .0.") Nichols, R.L., cited, 44 OTlricn. .T.C.. cited. .".6. .".7. 58 0;ikl;in.l.62 Ohio, :!;{ OliRoceno. 12, 33 OreRon. 12. 13. 19, 20, 21. 27, 32, 3.5, 52. 57 -California state line. 0. 1(>. IS, 10. 20. 25. 51. .59 Orr Lail sik.vcI Ci-fck, •_'."•, ;>«), ."{T, r»r). no. r>7 Siskiyou County, «.», (51. C2, ()4. GG Airport, r>S, ")'.( Muiiiitiiins, 11. 13, 14 Smitli. AHiimI. citod, 12 Snuwiliin. !•, .">1, r)2, r>4 Sciiool, IG. IS, 32 Station, 2."{ Soda Spriiifis. 17, HG Solomon's T»'in])lt'. 2.~>, .">G, 3S Soule lianch, 45, 51, (>.'> cone, 42, Hi) Sonthorn Pacific Railroad. 0. IT. 27. 41, 43. 59 Spannns Sprinj;, .55 Spriuy Creek, 55 School, 54 Stoke's Law, 08 Taber, Stephen, cited. 67 Table Rock, 17. 21. 25. 27. 2S. 3(!. 37, 54. 5G Springs. 5G Talent. ID. 57 Temple Rock, 38 Tertiary period, 13. 20, 33 Terwiliger rid^e. 23 I'hayer, T.P., cited, 52 The Caves, 43 "The Camel," 34 Trigonid. 17 cninsana Meek, 17 Turonian. 17 I'nipqiia beds. 10 formation, ^3, 16, 17, 18, 25, 32, 33, 51, 52, 53, 57 River, 12 sandstone, 20 sediments, 16, 18, 20, 31, 32, 51, 53 United States, 64 Valley of Ten Thousand Smokes, 25 Wallbridse Gulch, 27, 48 Wank. M.E., cited. 12 Wariiij,', (;.A., cited, 55, 56 AVaruer Range, 20 Washington, 20 Waters, A.C., cited. 32 Watson, f].P.., cited, 12 Weed, 0. 10, 20, 25, 50, 51 Wells, F.G., cited, 15, 18, 19, 25, 32 , H.L., cited, 17, 43, 49 Western Cascade series, 13, 14. 20, 21. 22. 23. 25. 26, .30, 32, 33, 35, 36, 38, 40. 4S, .50. 51. 52, 53, 54, 55, 56, 57, 58, 59 Whaleback basalt cone, 34 Mountain. 11, 14 volcano, 42 Whitnev glacier, 49, 51 Williams, Ilowel. cited. 14, 32, 49, 50, 52 Willow Creek, 23, 24, 27, 54 Mountain, 13, 26, 34, 35, 36, 38, 40 Valley, 54 School, 32 Wisconsin stage, 40, 41, 50 78 MACDOKL QUADRANGLE [BuU. 151 Yellow Butte, 13, 14, 15, 40, 41, 51, 52, 53, 55 mine, 58 Yirka. t), 12. 13, 15, 10. 20. 32, 57, 58 (^)f•a ('i)la liottliiif; Works. ."><; I)(>vi'lopiinMit ("uiiipaiiy, ."d -Mi)nta;;uf road, 15 quadran^'lc. K'., 15, 10, 18. '24, 25, 32, 51 9172 .O-IU 2M \ THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW BOOKS REQUESTED BY ANOTHER BORROWER ARE SUBJECT TO IMMEDIATE RECALL RECEIVED NOV 2 8 19g(? PHYSSC! I IBOAR m G 1990 LIBRARY, UNIVERSITY OF CALIFORNIA, DAVIS Book Slip-Series 458 COLLATE f ?7 !i?0 [Jalifomia. Division of *4ines, GEOLOG) Call Number: TN2U C3 A3 A \ G7420 3 1175 00496 8833 E g c 1 3 ll F^ -3 il "^. ^" ' o 3 s C S" ='j s ^ 1 cj: ;^i'' 1° o 1 '?■ . ^ " y. : :'■ £!■ tUfMJJ pVD »UJJO}tlil,l a * A ^ - t Sr ■ '■ i[ ^ 5 l2- 1 K ■■^ % ^ 1 1 • i ^1 Ai 1 f- L 5 S «-3 e5 o K %. S" ■? -/ l§ 2 a- ■""■w.'ff-' U303 I \ ^1 O < 15 ii s I - ij s I I I a |1 5 I '4 :1 ■■;.■? Is s Si; 1^ if F = i I' t'i s. c 1 O'^ »^ — iinn^ = H ^lAi \| y \ii fir I O' „ 5 .a s" *-& I I ^ II ri*wj/ puf fi"^f}tijij h / ;2 O a ' hJ o ' "n^ ^ ■ < S K S ^ - Q -< *fl t^ (T c H -^ ' ii J 1-) J it 1 w is 1 i o U i" " ^ ^ Is nH o ►r" £ ^ << >) > ,^* »*< w : w " "^ H hB &M o " Ph <1 a o c ( o y •=. e « »-3 Ss s a £ * S _ DIVISION OF MINES OL AF P JENKINS, CHIE F SNOWDON HORST STAT E OF C ALl FORNl A DEPARTMENT OF NATURAL RESOURCES BULLETIN 151 PLATE 3 EXPLANATION Olivine basalt iQbvyiB Whaleback basalts GOOSENEST Qbl MT. HEBRON I sss"' B GEOLOGIC SECTIONS ACROSS THE MACDOEL QUADRANGLE BY HOWEL WILLIAMS Qm 3'o o n ono' ^'" oc Andesite Moraines zrid^ Dacites and old ondesites Older olivine basalt |tp-^ Necks II I'M » mTu ^ Western Cascade series Unnpqua formation Kc Chico series 1+ + + +Ja-'- + Monzonite \\\ Schist SCALE I 2 I I 3 4 5 Miles I I I 151 PLATE 1 LEGEND Oal I Is