Physical Sci .LIB. TN 24 C3 A3 NO. 179 c.3 i 7M24 A3 PHYSICAL SCIENCES LIBRARY UC DAVIS Geologic Reconnaissance 0£ t&e Tt&ttfan* (fawt ^cutyet and, California Division of Mines Bulletin 179 7960 GEOLOGIC RECONNAISSANCE OF THE NORTHERN COAST RANGES AND KLAMATH MOUNTAINS, CALIFORNIA, WITH A SUMMARY OF THE MINERAL RESOURCES By WILLIAM P. IRWIN U. S. Geological Survey Menlo Park, California Bulletin 179 CALIFORNIA DIVISION OF MINES FERRY BUILDING, SAN FRANCISCO, 1960 tar*!' Est Pres Aft j STATE OF CALIFORNIA EDMUND G. BROWN, Governor DEPARTMENT OF NATURAL RESOURCES DeWITT NELSON, Director DIVISION OF MINES IAN CAMPBELL, Chief Bulletin 179 Price $3.00 Prepared cooperatively by the U. S. GEOLOGICAL SURVEY Publication authorized by the Director, U. S. GEOLOGICAL SURVEY CONTENTS Abstract Introduction Extent of area Previous work Present u ork Vcknow ledgments < ieograph; Page 5 9 9 9 11 11 i: Paleozoic l>c-lt. Klamath ( leologu foj mations Sedimentarj and volcanic rocks I'll Jurassic rucks Formations of the east< i n Mountains I ndifferentiated Paleozoic formations i . iplej greenstone Kennett formation Bragdon formation Formations of the central metamorphic licit. Klamath Mountains Abrams and Salmon formations Formations of the western Paleozoic and Triassic belt, Klamath Mountains Previous work I itliologj Vge Hi the rocks Formations oi Jurassic .mil Cretaceous Rocks (it middle Late Jurassic age tains Galice formation South Fork Belt of Diller I L903a), of Hershey (1906), and Kerr Manning and Ogle i L950) Rocks of late Late Jurassic and ( retai ■ age Strata along the west side of the Sacramento Valley Knoxville formation Shasta series Upper Cretaceous Rucks of the northern ("oast Ranges of California Franciscan formation of the central bell Metamorphosed Franciscan(P) formation of the eastern belt Coast. il belt "I undifferentiated sedimentarj rocks Cactaceous rocks in the Klamath Mountains province Uppermost Cretaceous sir.ua Yager formation of Ogle (1953) igi , Klamath Moun- 14 14 16 16 16 is 18 19 20 :i 27 27 Weitchpec schist Ranch schist oi 28 SO ;: 33 5 5 34 54 54 4: 43 44 44 ( iualala series of Weave] (194 ( ',o\ eli i ilea Tertiary rocks Strata of I ocene age ( n\ i In area Shasta Vallej an., i Strata of ( HigO( i Si i ii. i of Miocene age Point Arena area Covelo area ( iarlierv illc area Petrolia area Winter formation oi Maxon Strata of Pliocene Igi Southern coastal area Wildcat group of Ogle I 1951 - I alor formation of Manning anil Ogle St. < ieorge formation Cache formation of \ndcrsoii (1936 Volcanic rocks oi I ertiarj age Quaternarj rocks Marine sedimentarj deposits Continental sedimentary deposits Glacial deposits Volcanic rocks Landslide deposits Intrusive rocks < iranitic rocks Page 44 45 46 46 46 46 46 47 47 47 4S ts 48 49 49 4" Ultramafic rocks Structure Mineral commodities Gold Platinum Chromite Copper Silver Quicksilver Manganese Miscellaneous metalliferous commodities Nonmetallic mineral commodities Gas and oil Coal References cited (1950)... 50 51 51 51 5: 52 52 54 55 56 56 56 56 58 64 64 67 67 69 71 71 71 71 75 75 78 78 i :; CONTENTS— Continued Illustrations Plate 1. Geologic map of northwestern California .... In pocket Figure 1. .Map showing the relation of the report area to the major geologic provinces of California 8 Index to topographic quadrangle maps of north- western California _ 10 J. Map of northwestern California and southwestern Oregon, showing distribution of lithic belts 1 5 4. Diagram showing comparison of nomenclature used by Hershey (1901, 1906, and 1911), Maxson (1933), Phot< and Hinds (1932), for rocks that are at least in part equivalent to the rocks of the so-called southwestern Devonian and Carboniferous belts of Diller (1903a) 21 5. Chart showing changes in concept of the Myrtle, Galice, and Dothan formations of Diller ( 1903b and 1907) of southwestern Oregon, and correlations with the Franciscan, Knoxville, Horsetown, and Paskenta formations of northern California _ 40 6. Graph showing trends of mineral production in northwestern California during the period 1880- 1953 63 7. Graph showing production of gold in northwestern California during the period 1903-1953 ._ 64 8. Map of northwestern California showing location of lode deposits of gold — 65 9. Map of northwestern California showing location of placer deposits of gold and platinum 66 10. Map of northwestern California showing location of deposits of chromite 68 1 1. Map of northwestern California showing location of deposits of copper ..._ - — ._ 70 L2. Map of northwestern California showing location of deposits of quicksilver 72 Page 13. Map of northwestern California showing location of deposits of manganese 73 14. Map of northwestern California showing location of deposits of miscellaneous mineral commodities _ 74 15. Map of northwestern California showing location of deposits of limestone _ 76 16. Map of northwestern California showing location of deposits of coal, and location of wells drilled for oil and gas (exclusive of the Sacramento Valley) ... 1. Aerial view, looking west from near the eastern boundary of the Klamath Mountains province. . 13 2. Aerial view, looking east toward the southern part of the Marble Mountains _. ._ _ 25 .3. Distant view of the Coast Ranges ... 31 4. Strike ridges of eastward-dipping strata of Jurassic and Cretaceous age 32 5. Thin bedded shale, sandstone, and conglomerate of the Knoxville formation _ _ __ 33 6. Quarry in eastward-dipping sandstone of Late Cre- taceous age 34 7. Folded chert of the Franciscan formation _ 36 8. Contorted greenschist of the metamorphosed Fran- ciscan(?) formation 39 9. Thick beds of graywacke of the coastal belt ... 42 10. Gualala series exposed in wave-cut cliff at Anchor Bay _ 45 11. Lignite interbedded with light colored clay, silt- stone, and sandstone of the Weavcrville formation 47 12. Anticline in strata of Miocene age . 13. Strata of Pleistocene age ... 48 _ 53 14. Aerial view of the Trinity Alps _ _ 55 15. Debris flow in area of Franciscan formation .. 56 (4) GEOLOGIC RECONNAISSANCE OF THE NORTHERN COAST RANGES AND KLAMATH MOUNTAINS, CALIFORNIA, WITH A SUMMARY OF THE MINERAL RESOURCES By WILLIAM P. IRWIN ABSTRACT This report describes the geology of northwestern California, an area of approxi- mately 19,000 square miles that includes most of the northern Coast Ranges and the Klamath Mountains geologic provinces in addition to the western part of the Sacramento Valley province. The text and maps are compilations of available published and un- published data, supplemented in large measure by reconnaissance during the period 1953-1957 by members of the U. S. Geological Survey. The geologic provinces of northwestern California differ markedly from the stand- point of topography, geologic history, and mineral deposits. The Klamath Mountains province is an area of rugged mountains, with many peaks reaching an altitude of more than 6,000 feet and a few nearly 9,000 feet. Accordant ridges are conspicuous features, most commonly below 6,000 feet, and evidence of former glaciation is widespread in the higher parts of the mountains. The Klamath Mountains province is drained chiefly by the Klamath River and its tributaries, and by the Smith River. The drainage in general is from east to west, and cuts across the lithic and structural grain of the province. In contrast, the northern Coast Ranges are lower in general altitude, and only along the main divide between the Coast Ranges and the Sacramento Valley drainage do a few peaks reach as high as 6,000 feet and show evidence of former glaciation. The principal rivers of the northern Coast Ranges are the Eel, Mad, Van Duzen, and Russian. The general course of the drainage is parallel to the structural and lithic grain of the province and, with exception of the Russian River, is northwestward. The Russian River flows southeastward for much of its length. In the northern Coast Ranges, as in the Klamath Mountains, accordant ridges are abundant, but are generally at lower altitudes. The chief basis for defining the two provinces lies in a natural grouping of the principal rock units of each province with regard to intrusion by granitic rocks. The principal rock units of the Klamath Mountains range from early Paleozoic to middle Late Jurassic in age, and are intruded by granitic rocks that range from hornblende diorite to true granite in composition. In the northern Coast Ranges the principal rocks range from late Late Jurassic to Cretaceous in age, and there is little evidence that they have been intruded by granitic rocks. The principal rocks of both provinces, however, are intruded by abundant mafic and ultramafic rocks. The Klamath Mountains comprise four concentric, arcuate belts that are concave to the east. From east to west the belts are (1) the eastern Paleozoic belt, (2) the central metamorphic belt, (3) the western Paleozoic and Triassic belt, and (4) the western Jurassic belt. The formations of the eastern belt are well known, with the exception of the oldest unit which includes Silurian and perhaps even Ordovician rocks. The other formations are chiefly the Copley greenstone of Devonian age, the Kennett formation of later Devonian age, and the Bragdon formation of Mississippian age. The meta- morphic rocks of the central belt are mainly quartz-mica and hornblende schists of the Abrams and Salmon formations, and generally have been considered the oldest rocks of northwestern California. The western Paleozoic and Triassic belt includes mildly metamorphosed shales, sandstones, cherts, greenstones, and limestones. They have been studied little, and have been referred to variously as the Lower Slate and Blue Chert series, the southwestern Devonian and Carboniferous belts, the Chanchelulla forma- tion, and the Grayback formation. The extension of the belt into southwestern Oregon includes the Applegate group. The western Jurassic belt includes the Galice formation of middle Late Jurassic age, and mica schists and greenschist. The schists include the Weitchpec and Kerr Ranch schists, and the schists of South Fork Mountain. These schists generally have been correlated with the Abrams mica schist of the central metamorphic belt, but herein are described as metamorphic equivalents of the Galice formation. The northern Coast Ranges are chiefly graywackes and shales that range in age from late Late Jurassic to Late Cretaceous. Along a northwest-trending central belt, the graywacke generally contains little or potassium feldspar and is interbedded at many places with cherts and greenstones. This assemblage of graywacke, chert, and greenstone is referred to as the Franciscan formation, as it is similar to the Franciscan formation of the type area on the San Francisco Peninsula. Along the northern part of the east side of the central belt, the Franciscan formation is faulted against schist of the western Jurassic belt of the Klamath Mountains province. Along the southern part it is bordered by a wedge of mildly metamorphosed rocks, at least some of which are equivalents of the Franciscan of the central belt. The mildly metamorphosed rocks are separated from the Sacramento Valley sequence by a north-trending band of serpentine. A coastal belt of graywacke and shale lies west of the central belt of the Franciscan formation. These rocks are not, as is generally thought, part of the Franciscan formation, as the graywackes generally contain appreciable quantities of potassium feldspar, and as chert and greenstones are rare. The Sacramento Valley sequence is an orderly pile of graywacke, shale, and con- glomerate that has been subdivided into the Knoxville formation of late Late Jurassic (middle Tithonian) age, the Shasta series of Early Cretaceous age, and Upper Cretaceous rocks. The strata of the Sacramento Valley sequence contain appreciable quantities of potassium feldspar, bulkwise, and the average content increases from the oldest to the youngest rocks. In general the strata dip eastward, away from the Coast Ranges, and form conspicuous strike ridges that trend northward along the west side of the Sacramento Valley. The age of the Franciscan with respect to the Sacramento Valley sequence is not clearly known. On a paleontologic basis, the Franciscan seems to range from late Late Jurassic to Late Cretaceous in age, and thus to be an equivalent of the Sacramento Valley sequence. On other evidence, however, some of the Franciscan appears to be Late Jurassic in age, and older than the oldest strata of the Sacramento Valley sequence. (6) Marine sedimentary rocks that probably range in age from latest Cretaceous to early Tertiary occur in the northern Coast Ranges. These include the Yager formation near Cape Mendocino, unnamed beds near Covelo, and the Gualala series along the coast southeastward from Pt. Arena. The Gualala series lies west of the San Andreas fault, forming a northwesterly extension of the fault block bounded by the San Andreas and Nacimiento faults. Sedimentary rocks of Tertiary age occur in both the northern Coast Ranges and Klamath Mountains, and cover an extensive area underlain by the Jurassic and Cre- taceous strata along the west side of the Sacramento Valley. They range in age from Eocene through Pliocene. In the Coast Ranges they are chiefly marine in origin, whereas in the Klamath Mountains and Sacramento Valley they are mainly continental. Volcanic rocks of Tertiary age occur sparsely near Clear Lake in the report area, but they cover large areas southward in the Coast Ranges and eastward in the Cascade Range. Rocks of Quaternary age cover only a small percent of the area of northwestern California. They include valley fill, coastal and river terrace deposits, landslide debris, glacial deposits, and beach and dune sands. Volcanic rocks of Quaternary age are abundant in the report area only at Clear Lake in the northern Coast Ranges. The structure of northwestern California is highly complex and poorly known. In both provinces the strata most commonly dip eastward. In the northern Coast Ranges the principal structures appear to be northwest-trending strike-slip faults of the San Andreas system, and subparallel folds. The boundary between the Coast Ranges and western Klamath Mountains is a high-angle reverse fault that for much of its length is nearly parallel to the faults of the San Andreas system. The southern boundary of the Klamath Mountains province is a transverse fault that is aligned with major trans- verse faults in the Sacramento Valley and the Coast Ranges, and may be related technically to the Gorda submarine escarpment. The arcuate arrangement of lithic belts in the Klamath Mountains province is interpreted as resulting from forces from the east, and the boundaries between the lithic belts are thought to be chiefly reverse faults that dip eastward. Mineral commodities having a total value of approximately $150 million have been produced from the area since the middle 1800's. During the early days the production was chiefly metallic minerals, especially gold, but during recent years the production of nonmetallic mineral commodities such as sand, gravel, crushed rock, and natural gas has exceeded the value of the metallic minerals. Large quantities of gold have been produced from both placer and lode deposits, essentially restricted to the Klamath Mountains province. Chromite has been mined from areas of ultramafic rock, and about two-thirds of the production has been from the Klamath Mountains. Copper occurs in complex sulfide ores, and all but one of the deposits with a record of significant production are in the Klamath Mountains. Important quantities of quicksilver have been produced from several deposits in the Coast Ranges, and from one deposit in the Klamath Mountains. Many deposits of manganese occur in both provinces, but most of the small production has come from deposits in chert members of the Franciscan formation in the northern Coast Ranges. The production of gas and oil from strata of Tertiary age is becoming of increasing importance in the northern Coast Ranges in western Humboldt County. I 7 I California Division of .Minks I Bull. 179 OREGON Eurekc ° 1 ° / <* , ° ! '-'"}\ ^> \ / \ r '£\ ^ t t« \ o San Francisco ME* 1C0 Figure 1. Map showing the relation of the report area to the major geologic provinces of California. I960 I Northern Coasi R \\(.i s \m> ki \m \ i n .Mm \ i w\s INTRODUCTION Extent of Area The area described in this report (herein referred to as northwestern California) borders the Pacific coast for a distance of 250 miles from near the mouth of the Rus- sian River to the Oregon State boundary, and has an average width of about 75 miles. It is bounded on the cast for much of its length by the Sacramento Valley (fig. 1). The area includes Mendocino, Humboldt, Trin- ity, and Del Norte Counties, and parts of Sonoma, Lake, Glenn, Colusa, Tehama, Shasta, and Siskiyou Counties. Ir includes most of two geologic provinces, the northern Coast Ranges and the Klamath Mountains, and a narrow strip of the west side of the Sacramento Valley. Previous Work Northwestern California is, geologically, one of the least known areas in the State, although geologists have worked sporadically in it since the late 1 sod's. I he east- ern parr of the area, where economic interest was great- est, where fossils are most abundant, and where suitable base maps were available for plotting geologic data, was studied most intensively during the early days. The early work was largely done by J. S. Diller and (). 1 1. I lusho . although other early workers such as H. W. Fairbanks, Charles Schuchert, and J. P. Smith made notable con- tributions. Diller, of the U. S. Geological Survey, began work- ing in northwestern California and southwestern Oregon in 1883, and during the succeeding three decades he studied much of the northern Coast Ranges and Kla- math .Mountains. One of his early papers, published in 1902, is a classic account of the physiographic develop- ment of the area, and provides the first clear definition of the two provinces. Perhaps his most important contri- bution, however, was a detailed study of the Redding 30-minutc quadrangle in the eastern Klamath Mountains, where he worked out the stratigraphy ami named many of the formations. Diller's strarigraphic column has with- stood the test of time well and has required only minor modifications in later years. Hershey was an economic geologist who began exam- ining mineral deposits in the Klamath .Mountains province about 1 S97. During his field excursions throughout the province he also studied the regional geology, and in 1901 he published the first comprehensive description of the geology of the Klamath .Mountains. In his report he named and described some of the principal formations. During the following decade, he published many papers expanding and modifying his earlier concepts. Between 1915 and World War II, reconnaissance map- ping was done at several places in the Klamath Moun- tains province. The geologic staff of the Southern Pacific Railroad mapped the area covered by the Etna and Vreka 30-minute quadrangles (see Averill, 1931). Hinds (1933) prepared a map of the Weaverville and part of the Red Bluff JO-minute quadrangles, and Maxson i 1933) mapped much of Del Norte and part of western Siskiyou Coun- ties (in reconnaissance scale. Considerable geologic work was done by the staff of the I". S. Geological Survey timing the strategic min- erals investigations of World War II. Most of the work- was under the supervision of 1'. (.',. Wells, and was aimed chiefly at working out the geology of many small min- eralized areas. However, the area! mapping of broader areas in the Klamath Mountains of southwestern Oregon by Wells and others has led to a better understanding of the regional geology of the Klamath .Mountains of California. Since World War II, major contributions to the arcal geology have been made in the Redding area bv A. R. Kinkel, Jr.. J. P. Albers, and W. E. Hall (1956)', and in the Gasquet quadrangle, Del Norte County, by F. W. Cater. Jr., and F. G.Wells (1954). Heyl and Walker (1949) studied the limestone deposits of an area near Gazelle in eastern Siskiyou County. The geology of a small area along the upper reaches of Coffee Creek in I rinity Count) was mapped bj T. E. Gay < 1949). The Helena quadrangle in north-central Trinity Count) was mapped in detailed reconnaissance by I). P. Cox (written communication, 1956), and the Marble Mountain area in Siskiyou County by W. P. Pratt (written communica- tion, 1957). The western and southern part of the report area, the northern Coast Ranges of California, has been studied even less than the Klamath .Mountains. Reconnaissance trips were made in the northern Coast Ranges as early as the 1880's by J. 1). Whitney, G. F. Becker, H. W. Fairbanks, A. C. Lawson, and J. S. Diller. However, little arcal mapping has been done and, even today, our knowl- edge of the area is based largely on analogy with the central and southern Coast Ranges, anil with the west side of the Sacramento Valley, where formations similar to those of the northern Coast Ranges have been studied more intensively. During the past few decades important contributions to the arcal geology of the northern Coast Ranges have been made by many geologists, but the work has been chiefly adjacent to the southeast part of the present re- port area. Within the report area, the principal published contributions to the areal geology have been by Ander- son (1936), Clark (1940), Weaver (1943), MacGinitie (1943), .Manning and Ogle (1950), and Ogle (1953). W. B. Meyers has mapped the Wilbur Springs area (writ- ten communication, 1956), S. J. Rice has made a recon- naissance map of the Eureka, Trinidad, Orick, Klamath, and Crescent City quadrangles i written communication, 1955), and C. G. Higgins has mapped the Pliocene rocks east of the San Andreas fault in northern Sonoma County (written communication, 1957). These previously un- published maps have been incorporated on the geologic- map of this report (plate 1). - T - ■n ~c vm i\n n Gaasr • _r\r. _ ~ ; -.-.-. ep orr and pr r~ t^ r ■ m-.'r 5Tr^V,> -,-.,— T1k ,,-j-jj- k nor M^ndr" " - -~ ~~ - r - - -------- -~ -~ rrz— - I — ;: ~ tri 'tc SDoiasc ----- — --- ' ~± _-; - r-. . .- ~ ~ . ares i . r^ ^ ^j . - _,.- . I^B^^rs- V -— — h 3_i -^». «c - - ? " "^ *■*" 7^—1-::.: - Nt — ; : — i_"i i— . -irx ~ -«^«" «* 1 * c «-»«" Mi*. m»5 4 f ^L^ -ajj t j. : i?»^ -M |L am, f-J- "-.■ ■IIP lnhMIL IMlJj fo*S5- ,_^ _ . _ . __ .._ _: : . . Vk sctje re I mci ecrszi — rfe i-i.i -~ _ ^- . — - _,_ - - ; - _ - -- --- reflkoco" " Ik ru_ - ~ t~ ;r~ - - 1_ - - - - - vicinal tuima.^ ;:s - --.- - :_ - - - "I - ■MB dan xrc incfekd z> x carcaseics ro n=ades isasc 11 llll III JMI iMIBMIIMl « , - - 7 - - ■*-T 12 California Division of Mines [Bull. 179 he and the writer jointly tested approximately 700 speci- mens of graywaeke from the northern Coast Ranges and Sacramento Valley for potassium feldspar content, and the results of the tests are used freely in this report. Pro- fessor H. E. Thalmann of Stanford University kindly ex- amined several thin sections of limestone for microfossils. The writer has also benefited through discussions with many other geologists, among them J. D. Frick of Humble Oil Co., G. Raydon and J. Floyd of Standard Oil Co., S. J. Rice of the California Division of Alines, D. Woods, D. M. Hill, and P. J. Lorens of the California Division of Water Resources, and J. E. Lawton and W. P. Pratt, graduate students of Stanford University. The writer has attempted to indicate faithfully the work of others at appropriate places in the text and on the map, but at some places may have failed where the overlap between map areas, or areas of thought, is indistinct. The field work was greatly facilitated by the friendly cooper- ation of the personnel of the U. S. Forest Service, espe- cially those stationed at Upper Lake Ranger Station. Geography Northwestern California has been divided into two provinces: the northern Coast Ranges in the southern and southwestern part, and the Klamath Mountains in the northeastern part (fig. 1). The boundary between the two provinces, as drawn by the writer, differs from the boundary originally drawn by Diller (1902, pi. 1). These provinces differ from one another in topography, in the character of the rocks, and to a large extent in the mineral resources. The northern Coast Ranges and Klam- ath Mountains constitute the major subject of this re- port, but parts of two other provinces are shown on the geologic map. A narrow strip of the Sacramento Valley along the east flank of the northern Coast Ranges is included because the geology along this strip is impor- tant to an understanding of the geology of the northern Coast Ranges. A part of the Cascade Range province is shown in the northeast part of the map. The Klamath Mountains province is an area of deeply trenched mountains in northwestern California and southwestern Oregon. In California, the province is drained by the Klamath and Smith Rivers. The Klamath River is the master stream of the province in California, and the Trinity, Salmon, and Scott Rivers are its major tributaries. The Trinity River, the largest tributary, drains the southern third of the area, and joins the Klam- ath River at Weitchpec near the middle of the western boundary of the province in California. The drainage pattern of the province is chiefly dendritic, and as most of the run-off is funneled into a single channel at Weitchpec, much of the drainage is transverse to the structural and lithic grain of the province. On the other hand, the structural and lithic grain of the province clearly controls certain parts of the major rivers in addi- tion to many tributary streams. The north-northwest trending lower part of the Trinity River and the South Fork of Trinity River are outstanding examples of such control, as are the Klamath River between Orleans and Happy Camp, and the South Fork of Smith River. The physiographic development of the Klamath Moun- tains and part of the northern Coast Ranges has been treated in detail by Diller (1894a, 1894b, 1902, and 1911). The following brief summary of Diller's views is given to provide the reader with a general impression of the phys- iography of the Klamath Mountains province, as well as to provide a convenient source of reference for later pages in this report. The altitude of many of the higher peaks in the Klam- ath Mountains is more than 6,000 feet, and a few peaks have an altitude of about 9,000 feet (photo 14). When viewed from a distance, the peaks are seen to project above even-crested and broad-topped ridges. The crest- lines of the ridges are accordant at two levels that range from about 500 to 1,000 feet apart, and they appear to be erosional remnants of two ancient land surfaces. The higher surface is known as the Klamath peneplain (Diller, 1902, p. 15), and is considered (Diller, 1911, p. 12) to be the result of the first cycle of erosion in the development of the present landscape. The lower surface is known as the Sherwood peneplain (Diller, 1902, p. 22), and has resulted from a second cycle of erosion (Diller, 1911, p. 12). The second cycle consisted of rejuvenation of the streams, with subsequent deepening and widening of the valleys until a broad plain, the Sherwood peneplain, was formed. The subdued character of the landscape presum- ably was broken only bv the ridges on which the Klam- ath peneplain is preserved and from which the higher peaks projected. During the third cycle of erosion that has continued to the present, the streams were again rejuvenated by uplift, and by forming deep terraced canyons they have reduced the Sherwood peneplain to a succession of accordant ridges. The remnants of the Klamath peneplain, (photo 1) are not all at the same altitude. A reconstructed surface based on the remnants of the Klamath peneplain would gradually rise from north to south and from west to east. This is well shown by a remarkable ridge that marks the western and southern boundary of the Klamath Moun- tains in California, and whose crest is thought to be a remnant of the Klamath peneplain. The ridge is nearly continuous from the California-Oregon boundary to the western edge of the Sacramento Valley, except at a few places where it has been notched by major streams. In central Del Norte Count\- the crest of the ridge is at an altitude of about 2,500 feet. It gradually increases in altitude southeasterly until it attains an altitude of about 6,000 feet in west-central Trinitv County where the ridge is known as South Fork Mountain. From the south end of the South Fork Mountains the ridge trends east-south- east, forming the southern boundary of the Klamath Mountains province, and along this part of the ridge the old surface in the vicinity of North Yolla Bolly Moun- tain is at an altitude of about 7,000 feet. Similar surfaces are found at an altitude of about 7,000 feet in the vicinity of the Trinity Alps north of Weaverville, but in the [9601 North i u\ < ihm Rvm.is v\i> Kiwi a hi Moi\ivi\s 13 Photo I. Aerial view, looking west from near the eastern boundary of the Klamath Mountains province .1 few miles southeast of Gazelle. Siskiyou County. U.S. Highway 99 trends northward in the foreground. In the middle of the photo, the rocks to the right of center are mainly undifferentiated Paleozoic formations, chiefly of Silurian age; bold outcrops of light-colored limestone can be distinguished at a few places. A large area of ultramafic rock is to the left oi center. Part of the Scott Valley can be seen farther to the west. Remnants of the Klamath peneplain constitute the horizon. Photo GS-OAD, 1-22, August 1953. north-centra] pare of the province remnants oi the Klam- ath peneplain are at lower altitudes. The crests of the principal ridges between the Trinity Alps to the east and the South Fork Mountains to the west are remnants of the Sherwood peneplain (see Diller. 1911, fig. 1 I. I he northern Coast Ranges province consists domi- nantly of northwest-trending ridges that are approxi- mately parallel to the structural and lithic grain of the area. The longest and highest ridge, however, trends nearly north, from near Wilbur Springs in western Co- lusa County to the south end of the Klamath Moun- tains province, and is the drainage divide between the Sacramento Valley and northern Coast Ranges. It is con- sidered to be a southern continuation of the old surface developed by Diller's first cycle of erosion, as the crest of much of the ridge is locally broad and is generally between 5,000 and 6.(i()() feet in altitude as far south as Snow Mountain east of Lake Pillsbury. In the northwest- trending central part of the Coast Ranges, other ridges whose crests are thought to be remnants of the first cycle of erosion, as well as ridge-crests of the second cycle, are seen, although they are at lower altitudes than com- parable surfaces nearby in the Klamath Mountains. In a licit along much of the coast the crests of the ridges are generally at a common level that ranges between 1,000 and 2,000 feet in altitude. The northern Coast Ranges are drained principal!) b) the Russian, Eel, Van Duzen, and Mad Rivers, as well as Redwood Creek and the extreme lower reaches of the Klamath and Smith Rivers. The drainage pattern is trel- lis, and although the major streams are chiefly parallel to the structural and lithic grain of the area, in some places thev are markedly transverse. The principal rivers drain northwestward. An exception is the Russian River which flows southeastward toward San Francisco I'.av for most of its length, but near Healdsburg it deviates sharply and flows southw estw ard, cutting across the grain of the Coast Ranges to discharge into the Pacific Ocean. The climate of northwestern California is determined mainly by westerly winds from the Pacific Ocean, and by the highland that includes the Klamath .Mountains and northeastern part of the ('oast Ranges. The average an- nual precipitation ranges from 30 inches in the southern parr of the area to more than 50 inches in much of the northern and western parts; locally it is as high as 100 inches. During the late fall and winter months of heavy precipitation, the rivers become enormously swollen and 14 California Division of Mines Hull. 179 often cause great damage to adjacent villages and trans- portation facilities. Rain is infrequent during the summer. The temperature along the coastal belt is moderate with small daily and annual ranges. Freezing is uncom- mon. The average annual humidity is greater than 70 percent, and it decreases gradually toward the east. East of the coastal belt the climate is more rigorous, and is characterized by greater daily and annual ranges in tem- perature. In the higher country, snow flurries may be expected in late October, and during the winter much of the area above 4,000 feet is covered by snow. Patches of snow remain in some high protected areas until the mid- dle of summer, but most of the high country is suffi- ciently free of snow to permit field work in late May. Vegetation is dense throughout most of the area, and is especially lush along the coastal belt, where remarkable stands of redwood are found principally north of latitude 40° N. Elsewhere, fir, spruce, pine, and cedar constitute the predominant forest cover. Brush and poison oak are abundant and are a deterrent to field work in much of the area. Lumbering is the principal industry throughout most of the area. The area contains about 40 percent of the State's water resources, but has only several percent of the State's irri- gable land. Most of the irrigable land is in the broad valleys near Eureka, Ukiah, Clear Lake, Willits, Covelo, and Potter Valley. Smaller openings in the forest cover found in the mountains, mainly in areas of landslide and solifluction along major shear zones, support a cover of natural grass for cattle grazing. Most of the land in the southern and coastal parts of the area is privately owned, except for a few State parks along the coast. Much of the land in the northern and eastern parts of the area, including Mendocino, Trinity, Six Rivers, and the Klamath National Forests, is Federally owned. Three large areas within the National Forests, the Marble Mountain, Salmon-Trinity Alps, and Yolla Holly-Middle Eel areas, have been designated officially as primitive areas. The principal highway through the area is U. S. Route 101. The only paved roads that cross the area eastward to U. S. Routes 99 and 99W in the Sacramento Valley are State Route 20 from Ukiah to Williams, and U. S. Route 299 from Areata to Redding. State Route 1 fol- lows the coastline in the southern part and is connected to U. S. Route 101 by State Route 28. Secondary public- roads are mainly gravel and dirt, and in general are wide!)' spaced and furnish poor coverage of the area. Private logging roads as well as jeep trails lend additional accessibility to some of the more remote areas, but many large areas, particularly the three wilderness areas, are inaccessible by vehicle. The central part of the northern Coast Ranges from the San Francisco Bay area to Eureka is serviced by the Northwestern Pacific Railroad. GEOLOGIC FORMATIONS The distribution of the major geologic units is shown on the geologic map (pi. 1). .Most of these units have been studied only briefly by various geologists, and our meager know ledge of them precludes detailed descrip- tion of lithology, thickness of section, age, and relations to adjacent rocks. Few type sections have been described in detail or specifically located. Correlations of the princi- pal units with better-known formations elsewhere, or even within the area, is uncertain. Hence, some map units may consist of two or more formations that are somewhat similar in lithology but differ in age, and may more ac- curately be considered lithic units rather than forma- tional units. The geologic units of northwestern California include sedimentary and volcanic rocks of Paleozoic, Mesozoic, and Ce'nozoic age. Certain schists have been considered bv some geologists to be as old as Precambrian. The old- est paleontologically dated rocks are Silurian in age, and these may be the oldest rocks in the area. The Paleozoic and some Mesozoic rocks are intruded by ultramafic and granitic rocks. The pre-Tertiary rocks are readily differentiated into two groups on the basis of age, distribution, and relation to granitic rocks. The most significant point of division is between the middle Kimmeridgian and middle Titho- nian stages of the Upper Jurassic. The rocks of middle Late Jurassic (middle Kimmeridgian) and older ages are the principal formations of the Klamath Mountains prov- ince, and they have been intruded by abundant granitic- rocks. Those that range from late Late Jurassic (middle Tithonian) to Late Cretaceous in age are the principal units of the northern Coast Ranges and Sacramento Valley, and there is little evidence that they are intruded by granitic rocks. Some formations of both age divisions are intruded by ultramafic rocks. Sedimentary and Volcanic Rocks The pre-Tertiary sedimentary rocks of the area are chiefly marine sandstones and shales, and the sandstones are mostly the graywacke type. Rhythmically thin- bedded chert is abundant in some formations. Limestone forms perhaps only 1 percent of the formations of pre- Jurassic age, and is even less common in the formations of Jurassic and Cretaceous ages. Volcanic rocks of both andesitic and basaltic composition are present and are thought to be submarine flows and pyroclastics. They are mostly altered to greenstone, but locally structures showing their origin are preserved. The older pre-Tertiary sedimentary and volcanic rocks of northwestern California range from middle Late Juras- sic (middle Kimmeridgian) to Silurian and perhaps older. These rocks crop out only in the Klamath Mountains province, except for two areas of schist in the northern Coast Ranges near the western boundary of the Klamath Mountains province. The outcrop pattern of the older pre-Tertiary sedimentary and volcanic rocks of the Klamath Mountains defines a broad arc that is concave to the east. Within the arc are four rudely concentric irregular belts underlain by different lithic units (fig. 3). The western belt, along the western boundary of the province, consists of rocks thought to be chiefly middle 19601 Northern Coast Ranges vnd Klamath Mountains 15 Figure J. M.ip of northwestern California and southwestern Oregon, showing distribution of lithic belts. Late Jurassic (late Oxfordian to middle Kimmeridgian) in aye. I he three belts to the cast consist chief!) ol for mations of pre-Jurassic ages. In the southern part of the Klamath Mountains, the trend of the lithic belts is northwest; in the northwestern pari it is nearly north, and in the northeastern part it is northeast. In the Klamath .Mountains oi southwestern Oregon the trend is also northeast. I his arcuate, concen- tric arrangement of the formations of the Klamath Moun- tains will he referred to as the Klamath Mountains arc. Sedimentary strata that range from late I. ate Jurassic (middle Tithonian) to late Cretaceous in age are well exposed in orderl) sequence across a licit that trends north along the west side of the Sacramento Valley from near Wilbur Springs to the south end of the Klamath Moun- tains province. The strata have been grouped into the Knoxville formation of late I. ate Jurassic (middle Titho- nian) age. the Shasta series of Earl) Cretaceous age, and an unnamed unit of I. ate Cretaceous age. They appear to represent a nearly continuous record of deposition from late 1 .ate Jurassic (middle Tithonian) through much of the Late Cretaceous, and arc referred to herein as the Sacramento Valle) sequence. Sedimentary and volcanic rocks that range from late Late Jurassic (middle Tithonian) to Late Cretaceous in age occupy most of the northern Coast Ranges, and the formations occur chiefly in northwest-trending belts. The Franciscan formation is the principal unit of the northern Coast Ranges. Man) geologists consider the Franciscan to be restricted in age to Late Jurassic, but paleontologic evidence indicates that it may range in age from late Late furassic (middle Tithonian) to early Late Cretaceous (Cenomanian) and that it may be at least in part a fades of the Sacramento Valley sequence. A wide belt of sedi- mentary rocks that extends northwest along the coast from near the mouth of the Russian River to near Cape Mendocino, southwest of the area of the Franciscan for- mation, has previously been considered part of the Fran- ciscan formation, but in this report it is considered a separate unit. The rocks of the coastal belt arc at least in parr Cretaceous (Late Albian) in age. Formations of sedimentary rocks that are thought to be chiefly late Late Cretaceous in age, but may range into the early Tertiary, occur at several places in the northern Coast Ranges and at least one place in the Klamath Mountains. In the Coast Ranges these rocks are known as: the Gualala series, southwest of the San Andreas fault between Fort Ross ami Point Arena; the Yager formation of western Humboldt County, which is likely of similar age; and unnamed beds southwest of Covelo in central Mendocino County. Along the east side of the Klamath Mountains province, north of Shasta Valley, sedimentary rocks of Late Cretaceous age overlie granitic and pre- Jurassic rocks of the province. They have long been re- ferred to as the Chico formation, but recently have been named the Hornbrook formation (Peck and others, 1956). 16 California Division of Minis [Bull. 179 The Cenozoic rocks consist chiefly of the erosion prod- ucts of the pre-Tertiary rocks, but volcanic rocks of Cenozoic age are found at a few places in the report area, mostly in the vicinity of Clear Lake. The Tertiary sedimentary rocks are largely marine deposits in the northern Coast Ranges, and chiefly continental deposits in the Klamath Mountains and along the west side of the Sacramento Yallev. The Quaternary sedimentary de- posits are chiefly fluvial and lacustrine in origin, with the exception of small areas of marine terrace deposits along the coast. Pre-Jurassic Rocks Pre-Jurassic rocks occur only in the Klamath Moun- tains province, where they form the three eastern lithic belts of the Klamath Mountains arc; the fourth and west- ernmost belt consists chiefly of rocks of Late Jurassic age. The easternmost of the belts of pre-Jurassic rocks will be referred to simply as the eastern Paleozoic belt; the next belt to the west will be referred to as the central metamorphic belt; the third belt will be referred to as the western Paleozoic and Triassic belt (fig. 3). The eastern Paleozoic belt occupies the eastern side of the Klamath Mountains province and extends northward from the west side of the Sacramento Valley near Red- ding to the west side of Shasta Valley as far north as Yreka. Midway between Redding and Yreka, however, the continuity of the belt is disrupted by intrusive rocks. The rocks in this belt have been studied in greater detail than those in the other two belts of pre-Jurassic rocks, and are particularly well known in the vicinity of Red- ding, east of the report area. They have been divided into formations that range from Silurian to Mississippian in age. Generally they have been metamorphosed only near contacts with granitic intrusive rocks. The central metamorphic belt extends about 90 miles northward from a point southwest of Redding to Yreka. It averages about 10 miles in width. Two large areas of rocks similar to those of the central belt lie in Siskiyou County and southwestern Oregon within the general boundaries of the western Paleozoic and Triassic belt. The rocks of the central metamorphic belt include the Abrams and Salmon formations, which have long been considered to be the most ancient rocks of the Klamath Mountains province. They have been variously consid- ered to be of pre-Devonian, pre-Silurian, or possible even of Precambrian age. However, the possibility that they may be a metamorphic facies of formations of the eastern Paleozoic and western Paleozoic and Triassic belts has not been thoroughly explored. The western Paleozoic and Triassic belt adjoins the central metamorphic belt to the east, and is bounded to the west by the western Jurassic belt of the Klamath Mountains arc. The southern end of the belt is at the west side of the Sacramento Valley in northern Tehama County, and from there the belt trends northwestward through western Shasta and Trinity Counties, northward through western Siski) ou County, and northeastward through southwestern Oregon to near Tiller in Douglas County— a total distance of 180 miles. The belt has an average width of about 20 miles. The rocks of the west- ern Paleozoic and Triassic belt are similar to those of the eastern Paleozoic belt, except that they have been meta- morphosed weakly and are structurally more complex. Fossils found in the western Paleozoic and Triassic belt by the early workers were considered to range from Devonian to Carboniferous. However, re-examination of some of the earlv collections has shown that some of the socalled Devonian fossils are Triassic in age, and that some of the socalled Carboniferous are Permian. Formations of the Eastern Paleozoic Belt, Klamath Mountains The principal rocks of the eastern Paleozoic belt range from Silurian, or perhaps even Ordovician, to .Mississip- pian in age. They are described in this report as undiffer- entiated Paleozoic formations of Silurian and perhaps Ordovician age, the Copley greenstone of Middle Devo- nian age, and the Bragdon formation of probable Mis- sissippian age. The Kennett formation of Middle or early Late Devonian age is not known in the report area (pi. 1 ) but is described in this report because it is intimately as- sociated with the Copley greenstone and is exposed to the east nearby. Undifferentiated Paleozoic Formations. A large area between Scott Valley and Shasta Valley consists chiefly of undifferentiated formations of Paleozoic age. The pre- dominant rocks are shale, sandstone, chert, and limestone similar in appearance to the Kennett formation of De- vonian age, with which they generally have been cor- related. Recent paleontologic work (C. \Y. Merriam, oral communication, 1957) has shown that in part of the area the rocks are largely Silurian in age, and some per- haps Ordovician, and therefore not correlative with the Kennett formation. The rocks over most of the area, however, are poorly known, and formations known else- where in the eastern Paleozoic belt may be present. The undifferentiated Paleozoic formations have been studied in most detail by Heyl and Walker (1949) and C. W. Merriam (oral communication, 1957) near Gazelle, and by Brewer ( 1954) in the China Mountain quadrangle a few miles to the southwest. According to Heyl and ^Yalker (1949, p. 517), the most prominent lithic unit in the Gazelle area is a fairly continuous thick-bedded limestone, about 200 feet thick, that forms bold cliffs (photo 1). The limestone is underlain by a sequence of somewhat slaty, gray and red shale, chert and sandstone, but in some places is separated from these rocks by con- glomerate containing abundant rounded pebbles of chert and quartz. The rocks that overlie the limestone are not well exposed, but are thought to be similar to the under- lying rocks. Strata similar to those of the Gazelle area are described by Brewer ( 1954, p. 10). The thickness of the stratigraphic section is not known. Heyl and Walker (1949, p. 517) state that ". . . in many places the bedding of the limestone is discordant with the strata immediately underlying it. Although this discordant contact might be interpreted as an erosional I960 Northern Coasi Ranges \\i> Klamath Mountains r unconformity, field evidence suggests that locally fault- ing between the competent limestone and underlying in- competent strata took place ;ir the time oi regional fold- ing." In the China Mountain quadrangle, however, the slates that underlie the limestone are tightly folded and are intruded and altered by many dikes oi gabbro and diorite porphyry, yet the overlying limestone is neirher intruded no]- altered (Brewer, 1954, p. 11). I he rocks of the area of undivided Paleozoic forma- tions were briefly mentioned l>\ I [ershe) ( 1901a, p. 2 '2 ) as a northeastward extension of the Lower Slate scries he described more fully in Trinity and southern Siskiyou Counties, anil presumably he considered the Kennett for- mation a part of the same series. Diller (1903a, p. $46) included the strata in the vicinity of Gazelle in his so- called Northeastern Devonian belt of limestone and shales, a belt that includes the Kennett formation. Simi- larly, Brewer ( 1954) correlates the slate, chert, and lime- stone in China Mountain quadrangle with the Kennett formation, based on supposed similarities of lithology and age. Although present knowledge ot these rocks is slight, it indicates that much of the literature is erroneous regard- ing correlation of the rocks of the Gazelle area with the Kennett formation. L'nril recent years, the strata of the Gazelle area were considered to be of Devonian age (Diller, lS94b; Stauffer, 1930). However, according to paleontologic studies by C. W. Merriam (oral communi- cation. 1957; Merriam, L940, p. 44-4S; Westman, 1947) man} of the strata are ot undoubted Silurian age. al- though some Devonian and perhaps even Ordovician Strata are present. If the Kennett formation is Middle Devonian, an aye designation recently strengthened by the work of Kinkel, Mall, and Ubers (1956), many of the srrara of the Gazelle area obviousl) are not correlative with the Kennett formation. Brewer's correlation of rocks in the China Mountain area with those of the Ken- nett formation was based on a paper by Stumm ( 1954, p. 223-224), who incorrectly assumed the Kennett forma- tion anil rocks of the Gazelle area to be correlatives and who redefined the age of the Kenncrt formation as Si- lurian on the basis ot tossils in rocks from the Gazelle urea. Copley Greenstone. The Copley greenstone is thought once to have overlain much or all of the area presently occupied b\ the Klamath Mountains (Hershey, 1901, p. 2.^2, and Minds, L932, p. >°4). Greenstones exposed widely throughout the eastern Paleozoic belt were named the Clear Creek formation by Hershey (190!, p. 226), and were later named Copley meta-andesite by Diller (1906). More recently, these rocks have been renamed Copley greenstone by Kinkel and Albcrs ( 1951, p. 4). The Copley greenstone consists of interlavcred spilitic volcanic flows, tuffs, and agglomerates that grade into rocks of andesitic and basaltic composition. Minor inter- beds of shale and chert are present. In the West Shasta district the formation is at least 3,700 feet thick, but the base is not exposed (Kinkel, Hall, and Albcrs, 1956). Elsewhere thicknesses of 1,200 and 1,500 feet have been reported (Hinds, 1933). last of the Sacramento River. beyond the report area, the Cople) is slightl) altered and sheared, bur it becomes progressively metamorphosed to the west, tow aril the Shasta Bally batholith. In tlie central "West Shasta district it is mostly altered to an albitc- chlorite rock, and farther west, where it is adjacent to the Shasta Bally batholith in the French Gulch quad- rangle, it is metamorphosed to amphibohte. epidote am- phibolite, hornblende gneiss, and migmatite over a width of as much as 4,000 feet | Kinkel. I [all, and Albcrs. 1956). The Coplej greenstone (Clear Creek formation) was first described bv Hershey (1901, p. 238) as Jurassic in age. owing to the intimate association of the greenstone with the overlying Bragdon formation, which he consid- ered equivalent in litholog) and age to the Mariposa slates of Jurassic age in the Sierra Nevada. Diller i 1906) assigned the Copley meta-andesite to the Devonian or older, for he found ir to be the oldest formation exposed in the Redding quadrangle and to be overlain by the Kennett formation of Middle Devonian age. In the Wesi Shasta district, according to Kinkel, Mall, and Albers (1956), "the Copley is believed to be Middle Devonian in aye, but no fossils have been found to accurately date it. It is conformable with the Balaklala rhyolite, and the upper part of the Balaklala has been dated as of Middle- Devonian age. 1 herefore, the main parr of the Copley is Middle Devonian or possibly slightly older." The Balaklala rhyolite occurs only locally, and conformably underlies the Kennett formation. The base ot rhe Coplev is not known in the eastern belt, rhe Copley is overlain conformably by the Balaklala rhyolite at a few places and at some places by the Kennett formation. .Most commonly, however, it is overlain by the Bragdon formation (Mississippian) with erosional unconformity (Kinkel, Mall, and Albers, 1956). Kennett Formation. The name Kennett formation was given by Smith ( 1 S94) for thin-bedded shale, sand- stone, chert, and limestone exposed along Backbone ('reek near the abandoned town of Kennett north of Redding, east ot rhe area shown on the geologic map (pi. 1). 1 he Kennett formation is missing from the strati- graphic section at many localities, and where present it ranges widely in thickness. Diller (1906) considered it to range from (I to 865 feet in thickness, and he attributed the marked range in thickness to uneven erosion of a for- merly continuous layer. Kinkel, Mall, and Albers i 1956) state that the maximum thickness is about 400 feet, and that rhe type section is thickened bv faulting. They at- tribute much of the uneven thickness of the Kennett to original variations in near-shore deposition of sediments against a. volcanic highland. Limestone of the Kennett formation occurs mainly as erosion remnants capping hills. Ir is fine grained, and ranges from thin to thick-bedded and light gray to bluish gray in color. According to Kinkel, Hall, and Albers i 1956) the limestone probably occurs at only one 18 California Division oi Minis Hull. 179 horizon in the West Shasta district, and is a maximum of about 2nd feet thick. It is discontinuous because of fault- ing and erosion. On the basis of an abundant fossil fauna found in the limestone and calcareous shales, the age of the Kennett has been well established as late Middle or early Late Devonian (Diller, 1906. p. 2; Stauffer, 1930. p. 95, 96; and Kinkel. Hall, and Albers, 1956). According to Kinkel, Hall, and Albers ( 1956) the Ken- nett formation grades into the underlying Balaklala rhyo- litc, and where the Balaklala is not present the bedding of the Kennett is conformable with the underlying Copley greenstone. However, Hinds ( 1933, p. 90) states that the Kennett overlies deformed and eroded Copley greenstone. /;, agdon Formation. The Bragdon formation is widelv exposed in the eastern Paleozoic belt, and occurs in several relatively small areas within the general bound- aries of the central metamorphic belt. It was named by Hershe) I 1901, p. 226, 1904). and described as a ". . . se- ries of alternating thin-bedded black slates and thick- bedded, blue quartzites . . ." of Jurassic age (1901, p. 2'S). Later it was studied in greater detail by Diller i 1903a, 1905, and 1906) and shown to be Paleozoic in age. The Bragdon consists of a monotonous sequence of interbedded shale, siltstone, sandstone, and conglomerate. Some of the sandstone shows graded bedding (Kinkel, Hall, and Albers. 1956). The sandstone grains consist chiefly of chert and quartz. Some of the sandstone is tufTaceous. The conglomerates are mostly pebbly, and the pebbles are mainly light-grav to black chert, shale, and vein iiu.ni/ i Kinkel. Hall, and Albers, 1956). Fragments of fossiliferous limestone are found in some of the coarser conglomerates, and these, as well as most of the Bragdon. are thought to have come from the Kennett formation (Diller, 1906). ["he thickness of the Bragdon formation is difficult to determine, owing to an abundance of small folds, but may be as great as 6.000 feet (Diller. 1906). Partial sec- tions 5,500 and 1.450 feet thick have been measured bj Kinkel. Hall, and Albers ( 1956). I he age of the Bragdon formation is based partly on paleontologic evidence, but few fossils have been found. fossils found by the early workers (Diller. 1906) were thought likely to be Mississippian in age. Recent studies indicate that the age of the Bragdon formation may range from Devonian to Mississippian | Kinkel, Hall, and Albers. 1956). The Bragdon sediments were deposited on the partly eroded Kennett formation of Middle or early Late Devonian age. but according to Kinkel. Hall, and Albers ( 1956) the contact between the Bragdon anil Kennett formations is sharp and conformable at most places. In places where the Kennett was not deposited, or has been eroded completely, the Bragdon rests on the Balaklala rhyolite or the Copley greenstone. In the northwestern part of the Weavcrville 15-minute quadrangle (tig. 2). the Bragdon formation underlies an area of several square miles within the central metamorphic belt. There it is in contact with the Abrams formation, and with rocks of the western Paleozoic and Triassic belt, but the contact relations are not known. Formations of the Central Metamorphic Belt, Klamath Mountains The rocks of the central metamorphic belt are prin- cipally quartz-mica schists and hornblende and chlorite schists. Crystalline limestone and quartzite or meta-chert occur at some places in the quartz-mica schist. In the southern part of the belt, these rocks were named Abrams formation anil Salmon formation for exposures in the upper Coffee Creek area and along the higher reaches of the Salmon River, respectively (Hershey, 1901. p. 226). The Abrams formation includes the quartz-mica schists and interlavered marble and quartzite or meta- chert. The Salmon formation includes the hornblende and chlorite schists, and commonly is considered to over- lie the Abrams formation conformably. Generally the two formations arc considered to be the oldest forma- tions of the Klamath .Mountains, and to be of pre-De- vonian, prc-Silurian, or possibly Precambrian age. How- ever, the ancient ages assigned to these formations seem to be based largely on the high metamorphic grade of these rocks relative to the lower metamorphic grade of the presumabl) younger rocks or adjacent belts. On the geologic map (pi. 1 ) the Abrams and Salmon formations are shown as a single unit. The most detailed descriptions of these formations are by Hershey (1901 ). Hinds ( 1932 and 1935). and Gay ( 1949). Rocks somewhat similar to the Abrams and Salmon formations crop out in the northern part of the central belt, and in a large area isolated within the general bound- aries of the western Paleozoic and I riassic belt in Cali- fornia and southern Oregon. They commonly are referred to the Abrams and Salmon formations although they arc not known with assurance to be correlative. The large isolated area is chiefly north of the Klamath River, and covers the four common corners of the Seiad and Yreka 30-minute quadrangles in California (fig. 2). and the Grants Pass and Vledford 30-minute quadrangles in southern Oregon. In the Seiad quadrangle the rocks have been referred to as "older metamorphic rocks" ( Rynear- son and Smith, 1940. p. 2X4). in the Yreka quadrangle as Abrams schist (see Averill, 1931. plate in pocket), and in the .Medford and Grants Pass quadrangles as "old schists'" (Wells and others, 1939 and 1940). The rocks of the large isolated area as a whole have been referred to as Salmon and Abrams schist by Wells and Cater (1950. p. si). In the Preston Peak quadrangle, isolated pendants of so-called Salmon formation have been re- ported by Maxson (1933, p. 12K). In the vicinity of Scott Valley, rocks previously mapped (see Averill. 1931, plate in pocket) as undivided sedimentary rocks and schists of early Paleozoic and possibly Precambrian age are considered to be Abrams and Salmon formations by Seymour .Mack (written communication. 1956). 19601 Northern Coasi Ranges vnd Kiwimh Mountains 19 I he schists ut' the South Fork Mountains and related ridges along the western boundary of the Klamath Moun- tains province generally have been correlated with the Abrams formation (see Diller, 1903a, p. 343; Maxson, 1933, p. 128; Jenkins. 1938; and faliaferro and Hudson, 1943, p. 219). but are herein correlated chiefly with the Galice formation. According to I liiuls i 1932, p. ^s" ), the Abrams and Salmon formations are exposed in rehama and Mendocino Counties, but cm the basis of the present reconnaissance, rocks of neither of these formations are thought tn lie exposed south of southern Shasta County where the) are overlapped by strata of the Sacramento Valley sequence. Abrams and Salmon Formations. The Abrams forma- tion consists principalis- of light to dark-graj quartz- mica schist. The schist is composed mostly of quartz, biotdte, and muscovite, with minor plagioclase and gar- net. According to Gaj (1949), the metamorphic grade of the schist is equivalent to ". . . the lower amphibolite facies and upper albite-epidote amphibolite facies "t re- gional metamorphism defined by Escola . . .". and to ". . . the almandine /one of regional metamorphism de- fined b) Barrow and Tilley in the Scottish Highlands." Other rocks included in the formation are micaceous quartzites, pure quartzites, meta-conglomerates, and mar- ble. Some of the quartzite maj be crystallized chert. Hinds (1933) believes, as did Hershe) (1901, p. 228), that the Abrams formation is dominantly metamorphosed sedimentary rock; the mica schist was formed from class and shal) sandstones, and the quartzites from quart/ sandstones. He attributes the considerable thicknesses of interlayered quartzite and mica schist exposed along the Stunt Fork of the Trinity River to the metamorphism of thinly interbedded chert and clay. In general, the schistosit) of' the mica schist parallels the bedding. Rx - nearson and Smith ( 1940; also see Wells. Smith. R\ near- son, and Livermore, 1949. p. 23) sr.ue that in the Seiad quadrangle ". . . thin bands of nearly pure quartzite, which also lie parallel to the schistositv. suggests that the mica schists were derived from sands argillaceous sediments." Although the Abrams formation is chiefly mica schist that appears to base been formed from detrital and chemical sediments, hornblende schist that mas- be formed from volcanic rocks occurs locally in zones ranging from a few inches to several hundred feet thick: some of the /ones ol hornblende schist are concordant. but others appear to transgress the original bedding of the Abrams sediments i Hinds. 1933). Hinds interprets these /ones to represent intrusive phases of later (Salmon) volcanic activity, but recognizes the possibility that the concordant zones mas' represent contemporaneous vol- canism. The Abrams formation is 1,000 feet thick at the type locality in the upper Coffee Creek area, according to Hershey (1901, p. 228). Hinds < 1933) reports an incom- plete section 2,500 feet thick on the Stuart Fork of the Trinity Riser in the Weaverville 30-minute quadrangle (tig. 2), and a probable thickness of more than 5,000 feet in the southern part of the same quadrangle. The latter estimate of thickness is uncertain, owing to isoclinal folding (Hinds. 1933). I he Salmon formation consists dominantly of dark green hornblende schist and subordinate chlorite schist, and in some places contains interbedded calcareous and quartzitic meta-sediments. I he metamorphic grade of the Salmon formation is similar to that of the Abrams forma- tion (Gay, 194''. p. 2~). The schists are thought to have been formed from volcanic rocks, predominantlj mafic (loss s and p\ roclastic rocks, possibl) including sills and dikes in the Abrams formation (Hinds. 1932). According to Hershey (1901) the Salmon formation probably is not less than 2,500 feet thick. Hinds (1933, p. 83) reports that the greatest thickness exposed prob- ably exceeds 5,000 feet, but he is uncertain of that thick- ness owing to structural complications. Along the Scott Riser a fess miles southwest of Scott Bar, the thickness of the Salmoni"-) formation appears to be several thou- sand feet. Actinolite-epidote schist of the Salmon formation forms a remarkably uniform zone about half a mile xside along the north-trending, western boundars of the cen- tral metamorphic belt in the Helena quadrangle (fig. _ i. according to D. P. (lux (oral communication. 1956). To the ssest the actinolite-epidote schist presumably is in fault contact with mildls- metamorphosed sediments ol the western Paleozoic and Triassic belt; to the east it grades into fine-grained hornblende schist, and tinalls into coarse-grained hornblende schist ss ithin a distance of two miles of the fault contact. The foliation of the actinolite-epidote schist dips eastward at a moderate angle, and is crudely parallel to the bedding of the so- called Chanchelulla formation and to the foliation of the hornblende schist. Many large bodies of granitic rocks intrude both the Abrams and Salmon formations, and locally near the granite, migmatite and gneiss are formed. Hinds (1933, p. 82 ) states that in some areas the intrusion of granitic rock has caused remetamorphism of the Abrams forma- tion. Serpentini/cd ultramafic rocks arc in contact xs ith the schists, mostly along the eastern boundars of the belt. They are assumed to have intruded the Abrams and Salmon formations, although their contacts generally are sheared or concealed. In the northern part of the Seiad quadrangle. Wells. Smith. Rynearson, and l.ivermore ( 1949) believe the serpentine to be essentially intrusise into the schists, and mention one small mass of coarsely recrs stallized schist enclosed in peridotite. Hershey < 1901 ) considered the Abrams formation to grade upxxard into the Salmon formation. Hinds i 1932, p. 390) agrees as to their relative stratigraphic positions. but contends that the rsso formations are separated by an erosional unconformity. Hossever. Gas i 1949. p. 27 states that in the Coffee Creek area, the Abrams forma- tion appears to be younger than the Salmon formation, but that the evidence is not conclusive. 20 (Mil ORN1 V Dl\ ISION 01 VllNES Bull. L79 The age of the Abrams and Salmon formations is un- known, us fossils have not been found in them, and as contact relations to strata of adjacent belts are obscure. 1 [ershey ( 1901 ) considered the rocks to lie pre-Devonian, probably Algonkian, in age; Hinds | 1933, p. s4) believes them to be pre-Silurian. probably Precambrian in age. Both writers believed that the Abrams :\nd Salmon for- mations were metamorphosed and subsequently overlain with angular unconformity by rocks of Devonian or pre- Devonian age. Both have noted the striking difference in degree of metamorphism between the rocks (if the west- ern Paleozoic ami Triassic belt and those of the central metamorphic belt. Hinds reports finding pebbles and boulders of rocks similar to those of the Abrams and Salmon formations in the Chanchelulla formation oi the western belt, and J. P. AJbers (oral communication, 1957) states that fragments of simili.ir schists are found rarely in the Copies greenstone in the west Shasta district. The Abrams and Salmon formations generally are con- sidered distinctl) older than other formations of north- western California, and thought to have been metamor- phosed to then' present grade prior to the deposition oi the rocks known to be Paleozoic in age. The basic rela- tions, however, are so poorly known that the possibility that the Abrams and Salmon formations ma) be meta- morphic facies of adjacent formations of Paleozoic age should not be disregarded. The sandstones, slates, cherts, and limestones of the eastern Paleozoic and western Paleozoic and Triassic belts, in some places interlayered or intruded by greenstone, are suggestively similar to the lithic prototypes that have been postulated for the Abrams formation. Similarly, metamorphism of the Copley greenstone apparent!) results in rocks like those of the Salmon formation. .Metamorphic rocks similar to those of the Salmon for- mation are known to have formed from the Cople) greenstone on the east side of the Shasta Ball) batholith in southern Shasta Count) . 1 he) are best seen on Brandy Creek in the French Gulch quadrangle (fig. 2). where according to Kinkel. Hall, and AJbers I 1956) the Cople) greenstone has been metamorphosed to amphibolitc. hornblende gneiss, anil migmatite along a /one as much as 4,0(10 feet wide adjacent to the batholith. 1 linds i 1933, p. 87-88) slates that "along shear /ones and near the con- tacts with the large subjacent intrusives. the Copley v ol- canics have been again re'crystallized to chlorite ,m^\ less commonly hornblende schists. Hie latter in man) places are difficult to distinguish from the Salmon schists pre- viously described and a careful study of the stratigraphy or tracing of the schists into normal Copley rocks is nec- essarv for their correct identification." Hornblende and chlorite schists w est of the Shasta Bally batholith. but separated from the batholith by a narrow band of ultra- mafic rock, are regarded as Salmon formation i Hinds. 1933, pi. 3) of ancient age. One may wonder, however, whether the schists on both sides of the batholith are not of the same w^q. I lershev i 1901, p. 239-243) discussed bi rejected the hypothesis that the Abrams and Salmon irmations arc more highlv metamorphic facies ot the so lied Devono- Carboniferous (lower Slate series), that rocks "t the western Paleozoic and [riassic belt. 1 be isative agents he discussed are intrusions of periodtit ir bodies of granitic rock, or the ". . . action ot a Lit magma of fluid granitic material underlying the whole tcrri- torv . . .". Kinkel. Hall and Albers (1 ( i) relate the metamorphism of the Cople) greenstone irectl) to the intrusion oi the batholithic rocks, but it questionable whether igneous intrusion can be the it to ac- count for the metamorphism ot the \br.u- and Salmon formations. The /ones of schist known . have been formed by metamorphism of Cople) ne occur as relatively narrow bands in a general art of nonmeta- morphosed rocks, whereas the \brams an Salmon for- mations form a belt 10 miles wide in w hb metamor- phism has been pervasive. I arge areas of itrusive rock are exposed along the central belt ot metamrphic rocks, and although one might postulate that the ire onl) the upward extension of ,\f\ enormous underlyig batholith. they do not satisfactoril) account for ti apparently rather uniform grade of metamorphism troughout the central metamorphic belt. \ stud) of the contact relations bei \br.mis anil Bragdon formations in the northwestei part of the Weaverville 15-minure quadrangle ma) prve of value in establishing a minimum age for the A bran formation. if the Bragdon formation proves to have ben deposited on the rocks of the central metamorphic be see pi. 1 ). Formations of the Western Paleozoic and Trissic Belt, Klamath Mountains The rocks of the western Paleozoic and riassic belt are chiclly slat) detrital sedimentary rocks, hert, lime- stone, and volcanic rocks. 1 he limestone is ist abund- ant and tonus discontinuous bodies along rue Iv -defined /ones within the western belt. 1 be trends i ones containing limestone bodies are roughl) pa] lei to the broad outlines of the western belt, and th trends, in addition to sparse paleontologic data, SUggfl that the structures .mA distribution of the formatias also are roughly parallel. I he rocks probablv const;. tc several straiigraphic units, some of which likely wil Move cor- relative with formations of the eastern Pa: zoic belt; however, they could not be divided into forrntions dur- ing the present brief reconnaissance, owing l part to their structural complexity. Their ages are porl) estab- lished, but they are least known to be rtlv late Paleozoic and Triassic in California, and parti) ["riassic in Oregon. In California the rocks of the wester Paleozoic and I riassic belt prcvioiislv have been descried as the Lower Slate series and Blue Chert series illcicv. [901 and 1906), the so-called southwestern Devnian and southwestern Carboniferous belts (Diller, 103a), the Chanchelulla formation (Hinds. 1932), and the Jrayback formation (Maxson, 1933); in southwestern ( gon the I960! Northern Coast Ranges and Klamath Mountains 21 Sout h astern man elt Southwestern Carboniferous belt g Blu Chert Lower Slate s es series of s-called of so-called man rDevono- Carboniferous ge oge 1 ft> •-< i G r v b a c k | ition | of - called | Deon i a n | ge | 1 2 a X VI O ID 1 1 Chanchelulla 1 formation of 1 so-called pre- 1 Copley greenstone (Devonian) age 1 X D a. in Figure 4. l)i;i .mi showing comparison of nomenclature used by Hershej 1906, and 1911). Maxson (1933), and Hinds (1932), for rockshat arc at least in part equivalent to the rocks of the so-called mthwestern Devonian and Carboniferous belts of Diller (19 rocks of the elt are known as the Applegate group (Wells, Hot/., id Cater, 1949) (fig. 4). Rocks near! equivalent in metamorphic grade to the Abranis and Simon formations occur in some areas of the northern : rt of the western Paleozoic and Triassic belt, and arc irerspersed with isolated areas of Abrams and Salmon f< mations. These are thought to be meta- morphic facie of the other rocks of the belt; in Oregon they are condered to be metamorphosed Applegate group (Wells 1955). Previous li rk. The first general description of the rocks of the stern Paleozoic and Triassic belt was by Hershey (19C). He proposed the name Lower Slate series for cm ures along the eastern part of the belt in western SI a, cistern Trinity, and southern Siskiyou Counties. He described the Lower Slate series (1901, p. 231-232 i a succession of black slates, quartzites, and limestones tin lie in a belt that is adjacent to the western edge of the cntral metamorphic belt and that extends from the \\ c side of the Sacramento Valley into Sis- kiyou Count ". . . it is traversed by the south fork of the Salmot River below Cecilville, where much of the country ovei width of ten or fifteen miles belongs to this series. Tfe belt averages about five miles in width." Continuing nrtheastward from the Salmon River, how- ever. Hershi included the rocks of the area of un- differentiate 'aleozoic formations with his Lower Slate series, that is le included rocks of the eastern Paleozoic belt that are parated from rocks of the western Paleo- zoic and Tn sic belt by metamorphic rocks of the cen- tral belt. In a later paper (1906, p. 59), Hershey applied the name Blue Chert series to "... a great series of black shales, limestones and blue cherts . . ." exposed on the western flank of Orleans Mountain a few miles east of Orleans in northeastern Humboldt County, and west of Hoopa Yallev "a great complex of intruded igneous ma- terial and of shales, bedded blue cherts and limestone identical in character with the Blue Chert series . . ." begins "... as a narrow belt and extends southward, gradually widening, to the border of the Sacramento Valley." On a reconnaissance map (1911), Hershey indi- cated a continuation of so-called Devonian (?) rocks, presumably the Blue Chert or Lower Slate series, north- w aid from near Orleans to the Oregon border of eastern Del Norte and western Siskiyou Counties. Hershey. strangely, does not mention the Lower Slate series in his paper of 1906, and owing to the coincidence of some areas vaguely described as the Lower Slate series in 1901 and as the Blue Chert series in 1906, (compare 1901, p. 232, and 1906, p. 60, 61), the relation between the Lower Slate series and Blue Chert series is not clear. However, the two series apparently included essentially all of the strata of the western Paleozoic and Triassic belt, with the exception of volcanic rocks that may be correlative with Copley greenstone. Hershey considered the Lower Slate series to be Devono-Carboniferous in age, and the Blue Chert series to be Devonian in age, based largely on paleontologic evidence gathered by Diller (1903a). Diller (1903a) collected fossils from widely-spaced bodies of limestone in the southern part of the western Paleozoic and Triassic belt, and briefly described the lithology at some of the localities. He concluded that the limestone bodies occur in two belts, referred to as the southwestern Devonian belt and the southwestern Car- boniferous belt (Diller, 1903a, p. 344, 348). Diller traced the so-called southwestern Devonian belt along the south- west side of the western Paleozoic and Triassic belt from near the west side of the Sacramento Valley to west of I Ioopa Valley. The so-called southwestern Carboniferous belt was traced through the central part of the western Paleozoic and Triassic belt to the northern half of the Ironside Mountain quadrangle (fig. 2) north of the Trinity River. Diller' s so-called southwestern Devonian belt apparently corresponds roughly to Hershey's Blue Chert series, and his so-called southwestern Carbonifer- ous belt is approximately equivalent to the Lower Slate series. In the extreme southeastern part of the western Paleo- zoic and Triassic belt. Hinds named the rocks the Chan- chelulla formation for ". . . excellent exposures on the slopes of a mountain of that name in the northwest cor- ner of . . ." the Chanchelulla Peak quadrangle (fig. 2) (Hinds, 1932, p. 392). "The base of the sequence is com- posed largely of thinly bedded gray or black cherts. which have suffered extensive recrystallization to quartz- ites. Interbedded with the cherts are micaceous and graphitic schists, quartzites, metaconglomerate and marble, some of which is graphitic. Toward the top of 22 California Division oi Minis Bull. 179 the formation, the proportion of metamorphosed elastics and limestone is considerably greater though chert con- tinues as an important element." The formation is de- scribed as forming a broad belt that extends northwest- w ard from the edge of the Sacramento Valley through the Weaverville and Big Bar quadrangles. Although Hinds (1932, p. 392) states that the rocks of the Chanchclulla formation have not been described in previous literature, they apparently had been included as part of the Lower Slate series by Hershey and the so-called southwestern Carboniferous belt by Diller. In western Siskiyou County the western Paleozoic and Triassic belt includes the Grayback formation named by Maxson (1933, p. 128) in the Preston Peak quadrangle. The Grayback formation consists of rocks formerly mapped as Devonian(r) by Hershey (1911), and pre- sumably considered a northward continuation of the so- called southwestern Devonian belt (Diller and Kay, 1909, p. 50, 51). In the Seiad quadrangle, the rocks of the west- ern Palezoic and Triassic belt have been referred to as "younger metamorphic rocks" by Rvnearson and Smith ('l 940,^-40). The western Paleozoic and Triassic belt has been studied mostly in southwestern Oregon. Diller made a reconnaissance of the area, and collected fossils from limestone localities (Diller and Kay, 1909). Later, the rocks of the belt in southwestern Oregon were mapped by Wells and others (1939, 1949), and by Wells, Hotz, and Cater ( 1949) who named them the Applegate group. Lithology. The western Paleozoic and Triassic belt consists dominantly of weakly metamorphosed detrital sedimentary rocks, chert, limestone, and volcanic rocks. The detrital sedimentary rocks are chiefly fine-grained and are altered to slate. Slate and chert constitute the bulk of the belt. Locally the volcanic rocks are abundant, and seem most abundant and diverse in the central and western pans of the belt. Generally they are altered to greenstone, and although some of the greenstone un- doubtedly is metamorphosed effusive volcanic rock in- terbedded with the slate and chert, some may be intru- sive. Most of the limestone is coarsely rccrystallized. Although limestone accounts for perhaps no more than 1 percent of the area of outcrop of rocks of the western Paleozoic and Triassic belt, it likely will prove of con- siderable importance to an understanding of the stratig- raphy and structure of the Klamath .Mountains. It is the only rock of the western belt in which diagnostic fossils have been found, and ultimately it may provide useful marker horizons. The slate is a dark gray, fine-grained foliated rock, and much of it more properly might be referred to as phyllite, as the surfaces of foliation have a slight sheen apparently caused by the development of fine-grained micaceous minerals. Locally the rock is schistose. Gen- erally the foliation of the slate is nearly parallel to the bedding. Medium- to coarse-grained detrital rocks are seen at relatively few places throughout the southern half of the belt, but in the northern part of the belt, particularly in Oregon, they are more abundant. Hershev (1901, p. 2.31) listed quartzitc, along with slate and limestone, as an im- portant constituent of the Low er Slate series, but he evi- dently referred to meta-chert rather than sandstone. Hinds (1932, p. 392) mentions quartzite and metacon- glomerate interbedded with chert, schist, and marble in the power part of the Canchelulla formation at the type locality, and states that the proportion of metamorphosed elastics is greater in the upper part. Cox (oral communi- cation, 1956) found no metaconglomerate in the Helena quadrangle (fig. 2), but found one small outcrop of gray medium-grained quartzite. The quartzite consists chiefly of quartz grains, with a few chert fragments and a few percent of microcline and plagioclase feldspar. Similiar light-grav quartzite was seen by the writer only as sparse float near the head of the East Fork of Horse Linto Creek in the northwestern part of the Ironside .Mountain quadrangle (fig. 2). Conglomerates were not seen by the writer in the southern half of the belt, except for chert- rich pebble conglomerates at a few places along the west edge of the belt, particularly in the northeastern part of the Pilot Creek quadrangle. Coarse-grained, poorly sorted clastic rocks of volcanic affiliation crop out in the central and western part of the belt. Conglomerate is more abundant in the northern part of the belt, judging from the description of the Applegate group by Wells, Hotz, and Cater (1949, p. 3). The peb- bles of the conglomerate are principally subangular frag- ments of gray or black chert. A few pebbles are fine- grained mica schist. Conglomerate, however, is not men- tioned in the description of the Seiad quadrangle (Rv- nearson and Smith, 1940), nor in Preston Peak quadrangle (fig. 2) (Maxson, 1933). Chert is the second most abundant sedimentary rock of the belt, but in some broad areas, particularly in the east- ern part of the belt, it appears even more abundant than slate. It is gray, green, or red, and most commonly forms beds about an inch thick that are interbedded rhythmi- cally with thinner beds of slate. At many places the inter- beds of slate are so thin as to be merely slaty partings, which may be so indistinct that the interlayers in sec- tions of chert many feet thick can be distinguished only by close examination. Much of the chert is recrvstallized, and has been referred to by some as quartzite. Cox (oral communication, 1956) states that the chert in the Helena quadrangle is completely recrvstallized and consists wholly of microcrystalline quartz and mica. Fossil radio- laria are locally abundant in some of the chert. The individual sections of rhythmically bedded chert most commonly range from a few feet to several tens of feet in thickness; a few, as in the central part of the Sawyers Bar quadrangle (fig. 2), appear to be several hundred feet thick. One of the thicker sections of chert is exposed along the Salmon River for about 10 miles west of Cecilville. In this area, Hershey ( 1906, p. 60) estimated the chert section to be 3,000 feet thick, but his estimate doubtless includes considerable interlavered I960 Northern Coasi Ranges \m> Klamath \1oi\ivi\s 23 slate and possibly volcanic rock. Uncommonh chick sec- tions of chert associated with volcanic rocks and slate are also exposed along the North Fork of Salmon River for a distance of lo miles northeast of Forks o( Salmon. On the west slope of Orleans Mountain, the thin-bedded chert forms sections ranging from SO feet to several hun- dred feet in thickness (Hershey, 1906, p. 59). In the Helena quadrangle, the Lower Slate series between the I ast Fork and the North Fork of the Trinity River is unusual!) uniform in width of outcrop and structure. I here, Cox (oral communication. 1956) estimates that the thin-bedded chert constitutes approximatel) so per- cent of a total section that is 2,000 to 4.000 feet thick. According to Hinds I 1932, p. 592) chert is most abun- dant in the lower parr of the Chanchelulla Peak section, but continues as an important element in the upper part. Limestone has been found at main scattered localities throughout the western heir. It occurs most commonly as lenses that range from a tew feet to several hundred feet in thickness, hut thicknesses as great as 1,000 feet are reported. Dining reconnaissance, no attempt was made to trace the limestone hodies along their strike, hut they generally seem highly discontinuous and even main of the thicker bodies probably arc less than a mile long. The limestone bodies of the southern half of the belt were described by Diller ( 1905a) as occurring discontin- uously along two well-defined parallel zones. I he western zone, the so-called southwestern Devonian belt of Diller i 1903a, p. 344), is generally within a mile or two of the western boundary of the western Paleozoic and Triassic belt, and can be traced about 60 miles from near the west side of the Sacramento Valley to near the west side of 1 loopa Valley. The eastern /one, the so-called south- western Carboniferous belt of Diller (1903a, p. 348), is about in the middle of the western Paleozoic and Triassic belt near the Sacramento Valley and from there it trends northwesterly "... to the Hall City mines and beyond by the base of Chanchelulla to Flay Fork and Bridge Creek, where one of the lenses forms a remarkable na- tural bridge. From Hayfork Valley the limestones extend up Baker ami Big Creeks and were not seen again until New River was reached near Patterson"s Ranch" (Diller, 1905a. (i. $48). Diller's (1903a) description of the distribution of the limestone seems somewhat oversimplified; during the present reconnaissance additional bodies of limestone were found, and although some of them occur along the general /ones described by Diller, others are between the two zones and are of unknown affiliation. The anomalous limestone bodies, however, ma) result from local struc- tural complexities, and in the southern part do not neces- sarilv invalidate Diller's concept of the general distribu- tion of the limestone bodies with regard to age. In the northern part of the area described by Diller (1903a). however, three rather than two zones of lime- stone bodies are present. The third is cast of the two described by Diller, and only a few miles west of the central metamorphic belt. It begins near Junction City in the Helena quadrangle and trends ninth to the Salmon River about 5 miles west of Cecilville, a distance of more than 20 miles. Limestone crops our at localities north of the area of the three zones just described, but the relation of the limestone at these localities with either the so-called southwestern Devonian belt or southwestern Carbonif- erous belt has not been established. In the Saw vers Bar 30-minute quadrangle, limestone occurs at several locali- ties north of the latitude of Cecilville. farther north, limestone has been reported at the Buzzard Hill mine and on the ridge between the Buzzard Hill mine and Titus Creek in the Ukonom Lake quadrangle (tig. 2). Other bodies of limestone have been found in the Dillon Mountain and Happy Camp quadrangles. In the northeastern part of the Seiad 30-minute quad- rangle, limestone has been described by Rynearson and Smith (1940. p. 285) as coarse-grained, grayish-white marble that forms lenses and layers, in some places nearly l.ooo feet thick; and on the west side of Orider Creek the marble forms cliffs more than 500 feet high. The limestone on the w est side of Grider Creek trends southward toward an unusually large and well exposed area of limestone in the Marble .Mountains, but has not been traced over a gap of nearly 10 miles. Lhe limestone on Grider Creek is massive and coarsely crystalline com- pared with that of the Marble Mountains area, which is relatively thin-bedded and granular, but speculation as to their correlation seems warranted because of the proximity and similar great thickness. In southwestern Oregon the limestone in the western Paleozoic and Triassic belt was described by Diller (Diller and Kay, 1909, p. 50, 51) as occurring in four northeast-trending zones containing about 50 masses, the largest outcrop being more than a third of a mile long and 200 feet thick. The limestone of the two western zones he considered to be of Devonian age; that of the two eastern zones he considered to be of probable Car- boniferous or Triassic age. In his description of the limestone deposits of southwestern Oregon, Diller did not mention the so-called southwestern Devonian belt ami southwestern Carboniferous belt of the southern Klamath Mountains in California, but the similarity of his descrip- tions of the two areas regarding the distribution of the limestone zones relative to age is notable. Volcanic rocks of the western belt range in compo- sition from andesitic to basaltic ami generally they are so altered to greenstone that original textures and struc- tures arc destroyed. At some localities, vesicles, pillow- structure, and agglomerate structure are seen in some of the greenstone, and these rocks are considered to be extrusive. Some of the greenstone appears to be in- trusive, and some is interbedded with the slate, chert and limestone. The relation of much of the greenstone to the other rocks was not determined, however, and some of it may be equivalent to the Copley greenstone of the eastern Paleozoic belt. 24 California Division of Minis Bull. 179 Dillcr (1903a) noted the common association of vol- canic rocks and chert with the limestone of both the so-called southwestern Devonian and southwestern Car- boniferous belts, but did not clearly state that he con- sidered the limestone and chert to be interbedded with the volcanic rocks. Neither Hershey (1901) nor Hinds (1932) considered the volcanic rocks to be interbedded with strata of the Lower Slate series or Chanchelulla formation, respectively, and Hershey (1906, p. 61) states that he saw no volcanic rocks interbedded with the Blue Chert series. Cox (oral communication, 1956), how- ever, noted flow breccia and pillow lava interbedded with the slate and chert in at least three places along the road from Helena to Hobo Gulch and at numerous other localities in the Helena quadrangle, but he esti- mates the volcanic rocks to amount to no more than 5 percent of the stratigraphic section. The extrusive volcanic rocks of the belt were con- sidered by Hershey (1901, p. 235) to be correlative with the Clear Creek formation, a name he applied to the Copley greenstone of Devonian age in the eastern Paleo- zoic belt (Hershey, 1901, p. 226, 233). However, he thought the Clear Creek formation to be of Mesozoic age, and to rest uncomformably on the Lower Slate series of Devonian to Carboniferous age (1901, p. 238). Her- shey interpreted the greenstone in the Lower Slate series to be intrusions related to a so-called Clear Creek (Cop- ley) stage of volcanism. Hinds (1932, p. 392) suggests a similar explanation for greenstone in the Chanchelulla formation, and states that the Chanchelulla formation is overlain by the Copley greenstone. In the northern part of the western Paleozoic and Triassic belt, volcanic rocks have been described as inter- bedded with the slate, chert, and limestone. Maxson (1933, p. 128) mentions flows of basalt interbedded with rocks of so-called Devonian age in the Preston Peak quadrangle. In the Seiad quadrangle, the volcanic rocks are basaltic and andesitic flows and sills with thin layers of sandstone, tuff, and shale, and some thick layers of limestone, hut most are altered to schists and gneisses (Ryncarson and Smith, 1940, p. 285). In southwestern Oregon, the Applegate group is dominantly extrusive volcanic rock with many thin but continuous lenses of tuffaceous sedimentary rocks, slate, quartzite, and chert, and stubby lenses of limestone (Wells, 1955). The rocks of some areas along the east side of the western Paleozoic and Triassic belt in central and north- ern Siskiyou County and southern Oregon are of a higher metamorphic grade than is common elsewhere in the belt. In southern Oregon, these rocks crop out over an area of approximately 40 square miles in the south- western part of the Medford quadrangle. They have been referred to as so-called younger metamorphic rocks by Wells and others (1939) and described as ". . . chiefly quartzites, quartz-mica schist, and quartz-amphibole schist, with lesser amounts of amphibolite and argillite and thin bands of marble. . . . They were probably de- rived for the most part from quartzose sediments with small interbeds of shale and limestone. The amphibolites were probably formed by metamorphosis of basic igne- ous rocks." The rocks were first considered to be older than the adjacent Applegate group of Triassic (?) age, but more recently they are thought to be a metamorphic facies of the Applegate group (Wells, Hotz, and Cater, 1949, p. 3, and Wells, 1955). In northwestern California, somewhat similar rocks were seen during the present reconnaissance in the Marble /Mountains area, and along the Scott River between Scott Valley and the mouth of Kelsey Creek. In the northern part of the Yreka 30-minute quadrangle (rig. 2), par- ticularly along the Klamath River, the rocks of certain areas have been described (Averill, 1931, p. 9) as in- cluding "... a great variety of metamorphic material, argillites, phyllites, quartzitic slates, very fine grained black schists, quartzites, talcose schists, pyroxene-horn- blende schists, limestone and marble." The general area of distribution of these metamorphic rocks is roughly contiguous with areas of the so-called younger meta- morphic rocks or metamorphosed Applegate group of southern Oregon, and perhaps the rocks of these areas are equivalent. In the Marble Mountains the rocks consist chiefly of thin-bedded amphibolite and chlorite schists, quartzite, and marble, and they appear to constitute a section that is more than 10,000 feet thick (W. P. Pratt, written com- munication, 1957). The marble is thin bedded and granu- lar, and is exposed for much of a distance of 5 miles along the north-trending ridge of the Marble Moun- tains. The strata along the ridge generally dip eastward at low angles, and along the southern part of the ridge the marble forms a dip-slope exposure more than a mile wide. The west face of the Marble Mountains is steep, and from a distance the strata that underlie the marble appear to be well exposed (photo 2). The total thickness of the sedimentary and volcanic strata deposited in the western Paleozoic and Triassic belt is not known. Estimates of thickness of the Lower Slate series, Blue Chert series, Chanchelulla formation, and Copley (?) greenstone have been made by others at several widely spaced localities, but owing to con- flicting references regarding order of superposition, cor- relation, and ages of the rocks, it is not feasible to add the individual estimates to arrive at a total thickness. Hershey (1901, p. 233) states ". . . the thickness of the [Lower Slate] series in any one section is not known to me. L T sually the succession of strata is repeated sev- eral times in a single area by faulting and folding . . . and an estimated average for the entire territory of 5,000 feet probably is sufficiently accurate for the present." Hershey, (1906, p. 60) estimated the Blue Chert series to be 5,000 feet thick in the central part of the Sawyers Bar quadrangle. The Chanchelulla formation exceeds 5,000 feet in thickness, and the additional thickness caused by abundant concordant bodies of greenstone, attributed by Hinds to intrusion of Copley greenstone, may be con- siderable, as some of the greenstone bodies are 500 feet thick (Hinds, 1932, p. 392). 19601 Northern Coasi Ranges \m> Kiwium \1oi\ivi\s 25 Photo -. Aerial view, looking cast coward the southern p.irr of tin Marble Mountains. I he light-colored outcrops along the crest of the ridge arc marble. A small part of the Scott Valley can be seen in the middle distance. Peaks of volcanic rocks oi the Cascade Range province, including Mount Shasta (wreathed in clouds), arc along the horizon. Photo GS-OAD, 1-101, September I9S3. The volcanic rocks (Copley? greenstone) exposed along Pearch Creek near Orleans, intrude and uncon- formably overlie the Blue Chert series, and are estimated to be 800 to 1,200 feet thick (Hershey, 1906, p. 60). The Cople\ ( : ) greenstone intrudes and unconformabl) oxer- lies the Chanchelulla formation, and two incomplete sec- tions measured in the Weaverville quadrangle arc 1,200 and 1,500 feet thick (Hinds, 1932, p. 394). The thickness of the volcanic section in the south-central part of the western Paleozoic and Triassic belt is not known. Age of the Rocks. Few paleontologic data are avail- able for assigning an age to the rocks of the western Paleozoic and Triassic belt. Fossils have been found only in the limestones, with the exception of radiolaria in some of the cherts. Generally the fossils are poorly pre- served, as most of the limestone is coarsely recrystallized. Dillcr ( 1903a) divided the rocks of the southern part of the western Paleozoic and Triassic belt into so-called southwestern Devonian and southwestern Carboniferous belts. The age assignments were based on fossils collected from limestone bodies at widely spaced intervals along the belts. In southwestern Oregon, Dillcr (Dillcr and Kay, 1909) described the limestone bodies of the western Paleozoic and Triassic belt as occurring in four parallel northeast-trending zones. Fossils identified as Devonian in age were found in the limestone of the two western zones, but only crinoid stems of indeterminate age were fount! in the two eastern /ones. The general absence of fossils other than crinoid stems in the two eastern /ones suggested to Dillcr an .v^i: different from Devonian, and he considered the limestone bodies likely to be Car- boniferous or Triassic in age. Partial re-examination of Diller's collection of fossils, in addition to a few newer discoveries of fossils, shows that at least some, and perhaps most, of Diller's age assignments of the limestones of the western Paleozoic and Triassic belt are in error. The limestone of the so- called southwestern Carboniferous belt seems to be Permian and perhaps Late Pennsylvanian in age and the limestone of at least one locality in the so-called south- western Devonian belt is Triassic in age. Diller's collection of fossils from his locality no. 705 (Oilier, 1903a. p. 344-345), sec. 30, T. 2S N., R. 10 W., near the south end of his so-called southwestern Devonian 26 California Division of Mines Bull. 179 belt, were re-examined by N. J. Silberling of the U.S. Geological Survey. According to Silberling (written communication, 1958): "These fossils were considered Devonian in age by Diller [1903a] (Am. Jour. Sci., 4th ser., v. 15, p. 345) who quotes Schu- chcrt as having recognized 'two species of Ammonoids of the family Prolecamtidae 1 in the collection. Accompanying the col- lection is an undated note signed by J. M. Clarke which reads 'Posidonia and [a] Goniatite— like Gastrioceras— [these] indicate Carbonic age and probably Coal Aleasures . . .' A more recent label (possibly prepared by A. K. Miller) reads 'Proarcests sp. etc. . . . Upper Triassic. . . .' "Several of the small fragmentary ammonites can be assigned to the genus Arcestes, sensn lato. These specimens have smooth involute globose shells with periodic constrictions of the whorls. In addition one of the specimens with these characters shows part of the suture which has numerous complexly crenulated elements. A more refined identification is not possible because the recognition of subgenera within the genus Arcestes depends on features of the body chamber and this part of the shell is not preserved. "Also present are three fragmentary impressions representing a coiled shell with finely-spaced strigate ornamentation. These are suggestive of the Upper Triassic ammonite genus Cladiscites. "The age of this collection is .Middle or Late Triassic, prob- ably Late Triassic." An ammonite collected from limestone in the so-called southwestern Carboniferous belt, in sec. 30, T. 30 N., R. 10 W., near Wildwood, was identified by J. P. Smith (Diller, 1903a. p. 350) as Permian in age. It has been re- examined and is thought to be Middle or Late Permian in age (Miller, Furnish, and Clark, 1957, p. 1062-1063). Each limestone body seen during the present recon- naissance was searched briefly for fossils, and although poorly preserved crinoid stems were seen in many of these, diagnostic fossils were found at only two localities. Abundant microfossils were collected by Cox at Hall City Caves (locality no. 17, p. 1) in SE'4 sec. 32, T. 30 N., R. 10 W., in the northeastern part of the Hoaglin quadrangle. The locality probably is the same as Diller's (1903a, p. 349) Hall City locality no. 702, and doubtless is part of the so-called southwestern Carboniferous belt. The fossils w ere examined by L. G. Henbest of the U. S. Geological Survey, who reports (written communication, June 29, 1956) the following: "The foraminifers in this sample consist of two or more species of Climacammina, primitive Miliolidae (?), a species of fusulin- ellid, and apparently two species that belong to Staffella, Ozaivai- nella, or possibly Eoverbeekina. Within certain limits, the strati- graphic range of each of the above listed genera in the Pacific and Asian realms is problematic. Poor preservation prevents a close determination of the fusulinids. The assemblage is not older than Middle Pennsylvanian nor younger than the middle part of the Permian. Permian rather than Pennsylvanian age seems most likely, but the evidence is vague." Fossiliferous limestone float was found by the writer near the center of the mutual boundary between the Hayfork and Weaverville 15-minute quadrangles (lo- cality no. IS, pi. 1). The locality is in center sec. 21, T. 32 N., R. 10 W., on a logging trail on the north side of a creek, and about 200 feet west of a sharp bend in the Douglas City-Hayfork road. The limestone seems to be broadly assignable to Diller's so-called southwestern Car- boniferous belt, although it is several miles east of the trace of the limestone bodies he used to define the belt, and only a mile west of the central metamorphic belt. The limestone was examined by L. G. Henbest, who re- ports (written communication, April 14, 1958) as fol- lows: "This altered limestone contains a considerable abundance of fusulinids. In the rock slices submitted, it was possible to recog- nize that most of the specimens belong to a peculiar species of Triticites whose features suggest early as well as late stages in the evolution of the genus. A few specimens even suggested a transitional stage into Pseudofusulina. A few of the fusulinids, seen only in odd sections, have some resemblance to Dmibari- nella. Two fragmentary specimens resembling the juvenarium of Schubertella or the microspheric generation of a larger fusulinid were also recognizable. Late Pennsylvanian or McCloud Permian, age seems to be as close a determination as can be made on the material at hand." Wells, Hotz, and Cater (1949, p. 3, 4) consider all of the rocks of the western Paleozoic and Triassic belt in southwestern Oregon to be of Triassic(P) age, because ". . . Reeside studied the collections of fossils made by the writer and re-examined the collections made by Diller. He pronounced them to be of Mesozoic age, probably Late Triassic." Formations of Jurassic and Cretaceous Ages The rocks of Jurassic and Cretaceous ases in the north- ern Coast Ranges and Klamath Mountains are subdivided into several formations that consist mainly of interbedded grayw acke and shale, but a few of these formations con- tain considerable thin-bedded chert and volcanic rocks. The ages of most of the formations are poorly known, as few diagnostic fossils have been found, and as some of the paleontologic data are not compatible with ap- parent structural relations. Formational designation has in some cases been based largely on geographic distribution, and many conflicting formational designations and strati- graphic interpretations have been made owing to the general similarity of the rocks and the scarcity of fossils, as well as to the structural disarrangement and generally poor exposures. Along the west side of the Sacramento Valley, however, the strata form an orderly sequence from Upper Jurassic to Upper Cretaceous. The formations are most conveniently discussed under three major headings; rocks of middle Late Jurassic age, rocks of late Late Jurassic and Cretaceous age, and rocks of late Late Cretaceous age. The rocks of middle Late Jurassic age form the westernmost belt of the Klamath .Mountains arc, and appear to have been deformed, lo- cally metamorphosed, and intruded by granitic rocks prior to deposition of the rocks of late Late Jurassic and younger ages. The rocks of late Late Jurassic and Cretaceous ages are the principal formations in the northern Coast Ranges of California and along the west side of the Sacramento Valley. A few relatively small patches of some of these formations lie with high angular unconformity on the rocks of the Klamath Mountains arc. In southwestern Oregon large areas of rocks of late Late Jurassic and Cretaceous ages have been included in the western part I will Northern Coasi Ranges \m> Kiwiuii Moisiuns 27 of the Klamath Mountains province as rlic outline <>t the province was drawn 1>> Diller I 1902, pi. 1 ). The rocks discussed as hue Late Cretaceous in age maj in fact range into early Tertiary. They probably were deposited \\ irh marked disconformitj on the rocks of early Late Cretaceous and older ages. In northwestern California they occur chiefly at three localities in the Coast Ranges. The largest area is in western Humboldt County. ;i second area is immediatel) west ol the San Vndreas fault in northwestern Sonoma and southwestern Mendocino Counties, and a third is near Covelo in north- central Mendocino County. Rocks of Middle Late Jurassic Age, Klamath Mountains I he Galice and Dothan formations are the oldest known Jurassic rocks in northwestern California and southwestern Oregon. The Galice formation previouslj had been mapped in southwestern Oregon and in north- ern Del Norte County, California. During the present reconnaissance, rocks thought to be of the Galice for- mation were traced southeastward along the western part of the Klamath Mountains province from Del Norte County, through northeastern I [umboldt County, to west-central Trinity County. Near Weitchpec in north- eastern Humboldt County, the rocks thought to he of the Galice formation appear to grade westward into schist. The schist forms a narrow heir along most of the western boundan of the Klamath Mountains province in California and is known variously at several different localities along the belt as the South Fork Mountain belt of Diller | 1903a), Weitchpec schist of Hershey I 1906), and Kerr Ranch schist of Manning and Ogle (1950). It generally has been considered to correlate with the Ab- rams formation of the central mctamorphic belt of the Klamath Mountains arc. and to be pre-Silurian or older in age, but in this report it is considered to be chiefly a mctamorphic facies of the Galice formation of middle Late Jurassic age. The Dothan formation has been studied mostly in southwestern Oregon. The only area of significant size in California that consists of rocks considered by some geologists to belong to the Dothan formation is an area chiefly ot graywacke and shale just west of the Klamath Mountains province in western Del Norte and northern 1 [umboldt Counties. The rocks of the same area are con- sidered b) the waiter and others to be part of the Fran- ciscan formation, although the Dothan and Franciscan genera Ih are not considered correlative. The age of the Galice formation is middle Late Jur- assic on the basis of paleontologic evidence, but the relative age of the Dothan formation, whether older or younger, has been in dispute since the two formations were named by Diller (1907). The Dothan is thought to grade upward into the Galice formation by Taliaferro ( 1942, p. 83), and Cater and Wells (1954, p. 85). Galice Formation. The Galice formation is the name applied b\ Diller (1907, p. 403) to slaty, dark to black, fine-grained sediments and subordinate sandstone and conglomerate exposed along Galice Creek in south- western Oregon. Wells. Mot/, and Cater (1949. p. 4) redefined the Galice formation to include a considerable quantity of intercalated volcanic rock. In northwestern California the Galice formation has been mapped in the northwestern parr of the Preston Peak 15-minute quad- rangle (Maxson, 1933, p. 129-130) and in the Gasquet quadrangle (fig. 2) (Cater and Wells. 1954, p. SY>- n 2>. In rhc adjacent parr of Oregon it crops out continuously for about so miles in a northeast-trending band along the west side of the western Paleozoic and Triassic belt. In the Gasquet quadrangle, the Galice formation has been described as consisting of a lower metavolcanic- rich section and an upper metasedimentary section (Cater and Wells, 1954, p. 86). The most abundant metavol- canic rocks are greenish meta-andesite flows and flow- breccias. Others include nierabasalf, spilite. metarhyo- lite(r), meta-andesite tuff, metarhyolite tuff and agglom- erate. A few lenses of black slate are intercalated with the volcanic rocks. The thickness of the metavolcanic- rich section is thought to be at least 7,000 feet, but in Oregon thicknesses of 10,000 and 15,000 feet have been estimated in the Kerby ami Galice quadrangles, respec- tively (Wells, Hot/, ami Cater. 1949, p. 7; and as the Rogue formation in Wells and Walker. 1953). The overlying section of metasedimentary rocks con- sists principally of slaty and ph) llitic shales w ith inter- bedded tuffaceous sandstones. Cater and Wells (1954, p. 91-92) found one small lens of gray marbleized lime- stone interbedded with slate and sandstone in the Gasquet quadrangle. Chert has not been reported in the literature as a constituent of the Calice formation, bur an excellent exposure of rhythmically thin-bedded chert was seen in the Galice formation in the northwestern parr of the Preston Peak 15-minute quadrangle during the present reconnaissance. The sandstones of the Galice formation are graywacke, generally tine to medium grained, and range from gray to green where unweathered, The) consist principalis of angular grains of plagioclase, quartz, augite, horn- blende, chlorite, epidote, micas, fragments of volcanic rocks, quartzite, and shale, shards of devitrificd glass, and minor amounts of carbonaceous and argillaceous ma- terial (Cater and Wells, 1954, p. 91 ). Graded bedding is present at some places. The graywacke is megascopic- ally similar to that of other formations of Jurassic and Cretaceous ages that are widely distributed throughout northwestern California and southwestern Oregon. The thickness of rhc metasedimentary section of the Galice formation has been estimated to be at least 3,000 feet (Cater and Wells, 1954, p. 84) in the Gasquet quad- rangle. Wells, Hotz, and Cater (1949, p. 7) estimate a thickness of at least 15,000 feet in the Kerby quadrangle, Oregon. In rhc Riddle quadrangle, Oregon, the thick- ness was estimated to be between 1,000 and 2,000 feet l.\ Diller (Diller and Kay, 1924, p. 2). The Galice formation is middle Late Jurassic in age, based on paleontologic evidence, and may be correlative with the Mariposa slate of the Sierra Nevada (Diller, 28 California Division or Minis I Bull. 179 1907, p. 404-405; Taliaferro, 1942. p. 77; and Cater and Wells, 1954, p. 92). The age and correlation is based principally on the occurrence of Bnchia erringtoni (Gabb) \ a species whose range in age, according to R. \Y. Imlay (written communication, Nov. 26, 1958), is late Oxfordian to middle Kimmeridgian, and which has been found also in the Mariposa slates. Slaty and phyllitic shales and sandstones throughout a large area in western Siskiyou, northeastern Humboldt. and western Trinity Counties appear to be a southeast- erly continuation of the rocks described as the Galice formation in northern Del Norte County, but they have a slightly higher metamorphic grade. They occur along the east side of the narrow belt of schist that forms most of the western boundary of the Klamath .Mountains in California, and are bounded to the east by plutonic rocks and the western Paleozoic and Triassic belt. The rocks are shales, sandstones, and minor conglom- erates, but are mostly converted to slate and phyllite. They have not been studied in thin section, but where the original character of the rocks has not been masked by metamorphism, the sandstones appear to be gray- wacke. Cleavage is well developed at most exposures, and generally is nearly parallel to the bedding. The strata are folded gently to moderately throughout most of the area, and dip most commonly to the northeast. Steep dips, however, are not rare. The thickness of the slate and phyllite appears to be at least several thousand feet, based on the topographic re- lief of areas uniformly underlain by these rocks. In the northeastern part of the Willow Creek quadrangle (fig. 2), the topographic relief between the Trinity River and Waterman Ridge several miles northeast is about 2,500 feet, and owing to the general northeast dip of the rocks it seems likely that the phyllite is considerably thicker. On the east side of Hoopa Valley, a logging road climbs the ridge along the north side of Hostler Creek to the Ironside Mountain batholith (pi. 1), a distance of about 5 miles across the strike of the phyllite and an altitude of 3,200 feet above the valley. The strata crossed by the road dip at an average of perhaps 25 degrees northwestward. They appear to constitute a stratigraphic section that is at least 10,000 feet thick unless 'serious error in measurement has been introduced by faulting or folding. Neither the top nor the bottom of the sec- tion has been recognized. Greenstone was found interlavered with the weakly metamorphosed sediments at only a few places. Phyllitic pyroclastic(r) rocks crop out in places along the road between Weitchpec and Orleans; near Red Cap Gulch, along the same road, some of the greenstone shows pillow structure. The Galice formation may be more widespread than is indicated on the geologic map (pi. 1), as some areas of volcanic rock, perhaps equivalent to the volcanic rocks 1 The name Buchia is used throughout this report instead of the synonym Aucella, except for quotations. of the Galice formation in Del Norte Count), may have been mapped as part of the western Paleozoic and Tri- assic belt in northeastern Humboldt and southwestern Trinity Counties. The outlines of the Galice formation shown on the geologic map were drawn chiefly on the basis of an abrupt change in the widespread, fairly uni- form tcrrane of slaty and phyllitic sandstones and shales. It is unlikely that relatively small areas of slates and phyllites, and possibly greenstones, of the Galice for- mation would have been distinguished from somewhat similar rocks of the western Paleozoic and Triassic belt during the present reconnaissance. The slaty and phyllitic shales and sandstones of north- eastern Humboldt and southwestern Trinity Counties are thought to be a southeasterly continuation of the Galice formation of northern Del Norte County. The correla- tion, however, is based only on lithology and geographic continuity, as no fossils were found. The shales and sandstones of the Galice formation in northern Del Norte County generally are slaty rather than phyllitic. In the northern part of the Orleans quadrangle, as one travels southward along the ridge that forms the boundary be- tween Del Norte and Siskiyou Counties, the slaty rocks appear to grade through a distance of several miles into the phyllitic rocks of the so-called Galice formation of Trinity County. Determination as to whether the slaty and phyllitic shales and sandstone in northeastern Humboldt and southwestern Trinity Counties are actually the Galice formation, or perhaps the Bragdon formation of pre- Jurassic age must await further study. They were first described by Hershey (1904, p. 349-354) as a western area of the Bragdon formation, and compared with the nonmetamorphosed Bragdon formation of the type area in the eastern Paleozoic belt. He considered the Bragdon formation to be Jurassic in age (Hershey, 1901 and 1904), principally owing to the lithologic similarity of the rocks of the so-called western area of the Bragdon formation to the Mariposa slate of the Sierra Nevada. Oilier (1903a and 1905), however, showed the Bragdon formation of the type area in the eastern Paleozoic belt to be largely Mississippian in age, an age Hershey (1906) was reluctant to accept. It is likely that Hershey later considered the rocks of the so-called western areas of the Bragdon formation to be equivalent to the Galice for- mation, as in 1911 he published a reconnaissance map of Del Norte and western Siskiyou Counties on which he shows a band of the Galice formation trending south- eastward across the northern boundary of Humboldt County. The band is in line and contiguous with areas of phyllite he previously described as western areas of the Bragdon formation. South Fork Mountain Belt of Diller, Weitchpec Schist of Hershey, and Kerr Ranch Schist of Manning and Ogle. Schists form a narrow selvage along nearlv the entire 1 50 mile length of the southern and western boun- dary of the Klamath .Mountains province in California, and occur also in two subparallel bands to the west in I960 I Nokiiiikn Cium Ranges \m> Kivmmii \lm\ni\s 29 the Coast Ranges area of northern Humboldi County. Diller (1903a, p. $43) referred to these schists synony- mous!) as the southwestern belt <>t schists and the South Fork Mountain belt of schists. They were named Weitchpec schist by Hershey ( 1906. p. 63; also see 1904. p. 357) for exposures near the settlement of Weitchpec at the confluence of the Trinity and Klamath Rivers in the northwestern part of the Hoopa quadrangle (fig. 2). Most recently they have been referred to ;is the Ken- Ranch schist for exposures near Kerr Ranch in the southwestern part of the Blue Lake quadrangle (tiy. 2) (.Manning and Ogle, 1950, p. 13). In Del Norte County, the schist has been described by Maxson (1933, p. 128) and Rice (1953, p. 2779). In southwestern Oregon, seemingly related rocks were named Colebrooke schist by Diller (1903b, p. 2). For convenience in further dis- cussion, the name South Fork .Mountain schist will be used in reference to the above-mentioned schists in California. The South Fork .Mountain schist underlies a continu- ous, even-crested ridge that marks the southern and most of the western boundary of the Klamath Mountains province in California. At the southern boundary of the Klamath Mountains province the ridge trends N. 70 W. for 30 miles, the higher points along the ridge being North Yolla Boll) and Black- Rock Mountains. The southwestern boundary of the province is the South Fork Mountains which trend V JO W. for about 50 miles along the west side of the South Fork of the Trinity River. The crest and northeast slope of the South Fork Mountains are underlain by schist. The southwestern slope is an area of abundant landslide and poor exposure, and small areas cither of schist or of graywacke of the Franciscan formation are found at short distances below the crest of the ridge and on the middle slopes. Near the north end of the South Fork Mountains, an en echelon ridge to the west. Redwood Mountain, begins and trends \. 25 W. for 4o miles at decreasing altitudes to the coast. The crest of this ridge also is schist, whereas the lower slopes arc dominantly rocks of the Franciscan formation. From the north end of the South Fork Mountains, the continuation of the province boundary ridge is some- what more irregular anil trends northward approximately 30 miles to near Weitchpec. where the Klamath River has cut a deep notch across the belt of schist. North of the Klamath River the schist continues a few miles along the western face of the ridge, the crest being underlain along most of the succeeding 40 miles to the southwest- ern part of the Gasquet quadrangle, by serpenrinized ultramafic rock. In the northern part of the Tectah Creek quadrangle (fig. 2). and northward, the rocks in the narrow belt along the west side of the ultramafic rocks are in general phyllitic or slaty, rather than schistose, and these rocks possibly belong to the Franciscan formation to the west rather than belonging to the South Fork Mountain schist. The schist consists dominantly ol quartz and sericite, but in some areas greenschist containing chlorite or epidote is abundant. According to Manning and Ogle (1950, p. L3) the Kerr Ranch schist includes metacon- glomerates, metacherts. and glaucophanc schists. During the present reconnaissance the diverse rock types in- cluded by Manning and Ogle were not seen, and it may be that they are most common to the Redwood Moun- tain belt. I he quartz-sericite schist is thinly foliated and gen- erally dark-gray. The folia consist principally of alter- nate layers of sericite and an aggregate of quartz and plagioclase. Most of the schist is crenulated, and the amp- litude of the crenulations commonly ranges from % to '/ 2 inch. Locally the schist is more highly deformed and contains abundant small lenses and irregular masses of quartz. The age and formational affiliation of the South Fork .Mountain schist is not entirely clear, but generally the schist has been considered to be pre-Devonian or perhaps Precambrian in age, and genetically unrelated to adjacent formations. The South Fork Mountain schist has most commonly been correlated with the Abrams formation of the central metamorphic belt of the Klamath .Moun- tains arc. However, more than one adjacent formation is at least in parr a lithologically suitable prototype for the schist, and one of these, the Galice formation, appears to grade into the schist near Weitchpec. The schist max represent a narrow zone of dynamic metamorphism, and although the metamorphism may have transgressed for- mational boundaries, most if not all of the schist is likely a metamorphic equivalent of the slaty and phyllitic rocks herein correlated with the Galice formation of middle Late Jurassic age. The contact between the Weitchpec schist and the slaty and phyllitic sandstones and shales of the Galice formation is generally abrupt, and at most places is prob- ably a fault. However, at a few places the slaty and phyllitic rocks of the Galice formation can be seen to grade into the Weitchpec schist. This gradation is best seen along the Klamath River near Weitchpec and along the Trinity River between Weitchpec and Hoopa Val- ley, where it was described by Hershey ( 1906, p. 63). On the west slope of the South Fork Mountains and northward to near Weitchpec, the schist is in contact with nonmetamorphic rocks of the Franciscan formation a short distance below the crest of the ridge. The contact relation is obscure, but owing to the uniform outline of the belt, to abundant landslides, and to the lack of grada- tional rocks, the contact appears likely to be a high-angle fault. The schist along Redwood Mountain appears similar to that of .the South Fork .Mountains, bur in general the schistosity is not as well developed and lenses of quartz are less abundant. The two belts are separated by a cor- ridor of nonmetamorphosed sandstones and shales of the Franciscan formation that narroxvs southeastw ard to ap- proximate! v a mile in width near the southeast end of the 30 California Division of Mines Bull. 179 Redwood Mountain belt. The contacts along both sides of the Redwood Mountain belt of schist appear to be thrust faults that dip northeast (Manning and Ogle, 1950, p. 2"; Rice, 1953, p. 2779). The schist in the small area west of the Redwood Mountain belt and near Trinidad Head is poorly exposed, but it is considered by S. J. Rice (oral communication, 1955) to be a remnant of a block that was thrust over rocks of the Franciscan formation. Although Hershey ( 1906, p. 63 ) recognized the grada- tional relation between the schist and the phyllitic sand- stones and shales adjacent to the east near YVeitchpec, he nevertheless stated that "... undoubted pre-Devonian schists occur in South Fork Mountain." He probably was reiving on reconnaissance observations by Oilier, who stated in connection with a description of the Cole- brooke schist of southwestern Oregon, that "... on South Fork of Trinity River a mica schist, probably of the same age as the Colebrooke schist, is overlain by strata containing Devonian fossils" ( Oilier, 1903b, p. 2). During the present reconnaissance this relation was not seen. Rocks of late Late Jurassic and Cretaceous age are not known to be in depositional contact with the South Fork Mountain schist in California. In southwestern Oregon, however, the younger Mesozoic rocks are in depositional contact with the Colebrooke schist, and as the Cole- brooke schist is considered correlative with the South Fork Mountain schist, a means is provided for closely dating the metamorphism of the Galice formation. The Colebrooke schist occurs in the Port Orford quad- rangle, southwestern Oregon, principally in two large areas surrounded mainly by sandstones and shales of the Myrtle formation of Oilier that ranges from late Late Jurassic to Cretaceous in age. It was described by Diller (1903b, p. 2) as sericite schists, phyllites and slates that were derived from sedimentary rocks, and he considered it equivalent to the schists along the South Fork of the Trinity River. On a geologic map of southw estern Ore- gon, Wells ( 1955) discarded the name Colebrooke schist, and showed those areas of rocks as having been derived from the Rogue formation, which consists of lava flows, tuff, agglomerate, and Mow breccia, mostly of dacitic and andesitic composition, and of Jurassic age. He de- scribed the rocks formerly named Colebrooke schist as banded crystalline rocks made up of dark hornblende- rich layers and light siliceous layers. Cater and Wells (1954, p. 86) correlate the Rogue formation with the lower, metavolcanic part of the Galice formation. The Colebrooke schist is overlain unconformablv by the Myrtle formation of Diller. Diller ( 1903b, p. 2) states that "... the Myrtle formation surrounds a number of small areas of Colebrooke schist, with which it is in con- tact, and the basal portion is a conglomerate containing many fragments of the schist. The conglomerate com- monly contains Aucella crassicollis." This species is common in the older part of the Shasta series of Early Cretaceous age along the west side of the Sacramento Valley. Elsewhere in the Myrtle formation of Diller, Buchia piochii (Gabb) of late Late Jurassic (middle Tithonian) age occurs, a species common to the Knox- ville formation along the west side of the Sacramento Valley. Although the strata containing Buchia piochii (Gabb) have not been found in depositional contact with the Colebrooke schist, it seems reasonable that they too were deposited after rnetamorphism of the Galice forma- tion of middle Late Jurrasic (late Oxfordian to middle Kimmeridgian) age. .Metamorphism of the Galice for- mation therefore seems likely to have occurred between the middle Kimmeridgian and middle Tithonian stages of the late Jurassic. Rocks of Late Jurassic and Cretaceous Age Formations that range from late Late Jurassic to Late Cretaceous in age are the principal rocks of the northern Coast Ranges and along the west side of the Sacramento Valley, and at some places overlie the rocks of the Klamath .Mountains arc. The formations consist chiefly of graywacke and shale, with exception of the Franciscan formation of the Coast Ranges which also includes con- siderable interbedded chert and volcanic rocks. The graywacke and shale along the west side of the Sacramento Valley are well exposed in a north-trending belt (photos 3 and 4), and locally contain abundant fossils. They form an essentially conformable sequence of strata that are subdivided into the Knoxville formation of late Late Jurassic (middle Tithonian) age, the Shasta series of Early Cretaceous age, and the Upper Creta- ceous rocks. Similar strata, although locally not the com- plete sequence, occur at some places in the Coast Ranges of California, some as far south as Santa Barbara County. A few small isolated patches of parts of the Sacramento Valley sequence occur southwest of Redding in the southern part of the Klamath .Mountains province in California, and overlie the rocks of the Klamath .Moun- tains arc with marked angular unconformity. In the northern part of the Klamath Mountains province, chiefly in southwestern Oregon, the rocks of the Klamath Moun- tains arc are unconformablv overlain by many patches of strata equivalent to the Sacramento Valley sequence. The area of deposition of the strata of the Sacramento Vallcv sequence appears to have increased during the Cretaceous. The Knoxville formation is found only along the west side of the Sacramento Valley, and as patches within the Coast Ranges of California and the western part of the Klamath Mountains province of Oregon. The Cretaceous strata are found in the same general areas as the Knoxville, but in addition they underlie a much greater area of the Sacramento Valley and were de- posited over much of the Klamath .Mountains province of both Oregon and California. The strata of the Sacra- mento Valley sequence were deposited after the develop- ment of the Klamath Mountains arc, after metamorphism of the Galice formation of middle Late Jurassic (late Oxfordian to middle Kimmeridgian) age, and after in- trusion of the granitic rocks that occupy large areas in the Klamath Mountains province. 19601 Northern Coasi Ranges v\i> kiwum Mountains 31 j>*». P o J. Distant view of the Coast Ranges, looking west from U, S. Highway 99 a few miles south of Willows in the Sacramento Valley. Strata of the Sacramento Vallej seouence form the low strike-ridges in rlu- middle distance, and generally dip ;it moderate angle toward the observer. Hie mountains beyond the low ridges arc of the Coast Ranges, and are chiefly metamorphosed Fran- ciscan i "- 1 formation. Rocks that commonly are referred r<> as the Franciscan formation occupj large areas in the northern and central ( !oasi Ranges of California and smaller areas in the south- ern Coast Ranges of California. Similar rocks in the Klamath Mountains of southwestern Oregon have been included in part of the Myrtle formation of Diller. The Franciscan formation consists largeh of graywackes and shales that arc megascopically similar to some of the Sacramento Vallc\ sequence. Manx of the sedimentary strata of the Franciscan formation, however, are inter- bedded with considerable quantities of chert and volcanic- rocks, and locallx the Franciscan includes limestone and glaucophane schist. In some areas the rocks of the Fran- ciscan formation have been metamorphosed weakly. ( icncrallv the chert, volcanic rocks, and limestone arc the features that serve to identify the Franciscan for- mation, although areas of rocks that are mapped as Fran- ciscan formation range from those that include large quantities of chert and volcanic rocks to those in which little or no chert or volcanic rock is present. In areas of little or no chert and volcanic rocks, obvious difficult) arises in distinguishing graywackes and shales of the Franciscan formation from megascopically similar rocks of the Sacramento Valley sequence, particularly in areas where the rocks are deeply weathered or poorl) exposed. 1 he age of the Franciscan formation and its relation to the strata of the Sacramento Valley sequence is not clear. I he Francisan formation appears likely to be older than most if not all of the strata of the Sacramento Valley sequence if one judges from the relatively greater de- formation, the general pattern of distribution, and cer- tain compositional differences of the Franciscan forma- tion with respect to the strata of the Sacramento Valley sequence. On the other hand, most of the few fossils found in rocks assigned to the Francisan formation are similar to those found in the various subdivisions of the Sacramento Valley sequence, ami they indicate that at least part of the Francisan formation spans a period of geologic time comparable to that of the Sacramento Valley sequence. Previous to the present reconnaissance, the northern Coast Ranges were generall) considered to be chiefly the Franciscan formation (for example see Taliaferro, 1943, p. 187 anil tig. 2). During the reconnaissance, however, the northern Coast Ranges were subdivided essentially into three northward-trending belts (tig. 3): a coastal belt that consists chiefly of graywacke ami shale; a cen- tral belt that includes chiefly graywacke, shale, chert, and volcanic rocks, and thus is like typical Franciscan formation; ami an eastern belt that consists of weakly metamorphosed rocks referred to as metamorphosed Franciscan formation. Within the central belt, areas solely of detrital rocks, as well as those of weakly metamor- phosed rocks, were outlined insofar as possible. The rocks of all three belts were indicated as Fran- ciscan group(?) on the preliminary geologic map (Pacific Southwest Field Committee, 1955, pi. 1), al- though it was recognized that onl) the interbedded graj wacke, shale, chert ami volcanic rocks of the central belt, might be referred to firmly as the Franciscan rocks. The rocks of the coastal belt of detrital sedimentary rocks, as well as the rocks of the smaller areas of detrital rocks within the central belt, were of questionable affilia- tion with the Franciscan. The rocks of all three belts previously (Taliaferro, 1943, p. 1S7, and fig. 2) had been considered Franciscan, and the writer had no firm basis for designating them otherw ise. Following completion of the interagency phase of the work, however, the graywackes of the three belts, and those of the Sacramento Valley sequence, were studied by Bailey and Irwin (1959) to determine whether the formational affiliation of the graywackes might be deter- 32 California Division of Minis I Bull. 179 'hoto 4. Strike ridges of eastward-dipping strata of Jurassic and Cretaceous age along the west side of the Sacramenti Valley. Aerial view looking northeast. mined by their content of potassium feldspar. The study showed that the gravwackes of the typical Franciscan of the central belt, as well as the metamorphosed Fran- ciscan of the eastern belt, generally contain little or no potassium feldspar. The gravwackes of the Sacramento Valley sequence, as well as those of the coastal belt and some isolated areas within the general boundaries of the central belt, generally contain significant quantities of potassium feldspar. On the basis of potassium feldspar content, and the general lack of interbedded chert and volcanic rocks, the strata of the coastal belt are not now considered to be part of the Franciscan formation. They appear to be more closely related to the Sacramento Valley sequence. Strata Along the West Side of the Sacramento Valley Strata exposed in a northerly trending belt along much of the west side of the Sacramento Valley represent a nearly continuous record of sedimentation from late Late Jurassic (middle Tithonian) to Late Cretaceous. The part of the belt shown on the geologic map (pi. 1) extends a distance of about 50 miles from near Wilbur Springs to a point southwest of Redding in southern Shasta County, and is less than 10 miles in average width of outcrop. Along the southern and central parts of the belt the strata are separated from the rocks of the northern Coast Ranges by a band of ultramafic rocks, but along; the northern part of the belt they unconformably overlie the rocks of the Klamath Mountains arc. Along the eastern side of the belt the strata dip under a mantle of Tertiary and Quaternary rocks. The strata consist of interbedded sandstone, shale, and conglomerate, and in general thev dip eastward (photo 4). Major folds in the strata generally are broad and are parallel to the northerly trend of the belt. The strata constitute a section that is about 35,000 feet thick. Be- neath the cover of younger sedimentary deposits of Sacramento Valley, the older parts of the section pinch out successively to the east, so that on the east side of the Sacramento Valley, a distance of about 35 miles, only strata of Late Cretaceous age are present. The strata of the Sacramento Valley sequence are fossiliferous at many places, and their orderly succession serves as a base with which to correlate the disarranged lithologic elements of the northern Coast Ranges and Klamath .Mountains which at a few places contain similar fossils. The section has been subdivided into three major units (see Anderson, 1933): the Knoxville formation of late Late Jurassic (middle Tithonian) age, the Shasta series of Fail) Cretaceous age, and the L T pper Cretaceous strata. The Shasta series has in turn been divided into lower and upper parts, the Paskenta and Horsetown formations, re- spectively. These divisions of the Sacramento Valley I960 I Northern Coast Ranges and Klamath Mot ntains ^•^■■■■■ir 33 &»*> 1 \ I Photo 5. Thin bedded shale, sandstone, and conglomerate of the Knoxville formation, dipping eastward near Stonj ford. sequence have been given group or formational status by various geologists and by the U. S. Geological Survey, but -with the possible exception of the Knoxville forma- tion they are differentiated chiefly on a fauna] rather than a lithologic basis. Knoxville Formation. Tbc Knoxville formation as exposed along the west side of the Sacramento Valley between Wilbur Springs and Paskenta is about 10,000 feet thick. The base is not known with certainty, as along most of the valley the lowest exposed beds are in fault contact with the band of ultramafic rocks. The outline of the Knoxville formation is inferred north of a fault zone that trends northwest across strata of the Sacra- mento Valley sequence at latitude 40 degrees north (pi. 1), and although the Cretaceous parts of the Sacramento Valley sequence arc known to be present north of Bee- gum Creek, it is not known with certainty that the Knoxville is represented. The northernmost exposure of rocks referred to the Knoxville by Anderson (1945, p. 926-927) is on the northeast slope of Tedoc Peak, at the southern boundary of the Chanchelulla Peak quadrangle, where he states that basal conglomerate of the Knoxville formation rests directly on the so-called Klamath com- plex. The Knoxville formation generally consists of a thick section of thin-bedded shales with thin lenses of lime- stone, but interbedded graywacke and conglomerate are locally abundant (photo 5). Fossils indicate that it is late Late Jurassic (middle Tithonian) in age, and one of its most characteristic and abundant species is Buchia piochii (Gabb). 2— 1S730 The contact between the Knoxville formation and the overlying Shasta series is marked by a fairly abrupt and complete change in fauna, by lenses of conglomerate at many places, and by broad structural conformity. Shasta Scries. The strata referred to the Shasta series have a higher ratio of graj wacke to shale than has the Knoxville formation. The average thickness is about 10,000 feet, divided about equally between lower and upper fauna! divisions, the Paskenta and Horsetown for- mations. The Shasta series contains a variety of mega- fossils (Anderson, 1938) as well as microfossils, and locally the fossils are abundant. One species characteristic of the Paskenta formation is Buchia crassicollis ( Key- serling), which represents the older Early Cretaceous (Valanginian). It is specifically mentioned as it also is found in some rocks of the northern Coast Ranges. The term Shasta series has generally been considered to include only Lower Cretaceous strata, but along much of the west side of the Sacramento Valley there has been little agreement as to where the contact between the Shasta series and Upper Cretaceous strata should be placed. This lack of agreement casts considerable doubt as to the validity of a hiatus many early workers have postulated between the Lower and Upper Cretaceous, and as noted by Kirby (1943, p. 289) there is no great structural' discordance or specific evidence of a great hiatus separating the Shasta series and the Upper Cre- taceous rocks of the Sacramento Valley area. Some geologists have placed the contact at the base of the Venado formation of Kirby (1943, p. 282, 287), as is shown on the geologic map (pi. 1), while others have 34 California Division of .Mines Bull. Photo 6. Quarry in eastward dipping sandstone of Late Cretaceous age, near Sites. Some thin interbeds of sandstone and shale pinch out, down dip. Man circled for scale near center of photo. placed it lower in the section at the base of a conglom- erate member. The conglomerate member and the Venado formation are separated by several thousand feet of shale. Lower Upper Cretaceous. Upper Cretaceous strata along the west side of the Sacramento Valley consist of sandstone and shales (photo 6) and are about 15,000 feet thick. They commonly have been referred to as the Chico formation (see Kirby, 1943, p. 281), although they range from the Cenomanian through the Campanian in age whereas the type Chico formation on the east side of the Saramento Valley ranges from the middle Conia- cian to the middle Campanian in age. Rocks of the Northern Coast Ranges of California The northern Coast Ranges of California consist chiefly of sedimentary and volcanic rocks that range from late Late Jurassic (middle Tithonian) to early Late Cretaceous (Cenomanian) in age. The area has been subdivided into three principal lithic belts that trend northwesterly; a central belt of sedimentary and volcanic rocks of the Franciscan formation, an eastern belt of weakly metamorphosed Franciscan formation (? ), and a coastal belt of undivided sedimentary rocks. Relatively small areas of rocks of the eastern and coastal belts occur within the central belt. Franciscan Formation of the Central Belt. The sedi- mentary and volcanic rocks of the central belt of the northern Coast Ranges of California appear similar to those exposed on the San Francisco Peninsula in the cen- tral Coast Ranges that were named the Franciscan series by Lawson (1895, p. 407). They also are similar to part of the Myrtle formation of Diller (1898) in the western part of the Klamath Mountains province of Oregon. The Franciscan formation is a eugeosynclinal accumu- lation of detrital sedimentary rocks, chemical sedimen- tary rocks, and volcanic rocks. The detrital sedimentary rocks are chiefly graywacke with interbedded shale and minor conglomerate. The chemical sedimentary rocks are rhythmically thin-bedded chert and minor foraminif- eral limestone. The volcanic rocks include flows and pyroclastics, largely of basaltic or spilitic composition, and are altered to greenstones. In addition, the Franciscan formation includes small masses of glaucophane-bearing • I960 Northern Coast Ranges wi> Kiwiwii Mountains J 5 schists. General]) the rucks of tlic Franciscan formation are sheared, deformed, and dislocated, and arc intruded widely by mafic and ultramafic rocks. Owing largely to its seemingly chaotic character, the Franciscan formation has defied satisfactory interpretation of its role in the geologic history of the Pacific Coast region. Graywacke is the dominant rock of the Franciscan formation. It is a fine- to coarse-grained, well indurated rock, and fresh specimens range in color from dark gray to greenish gray. The graj \\ acke weathers to shades of dark-brown to light-buff, and in some places where weathering has been particularly intense the rocks are friable. The grains that constitute the graywacke are mostl) angular and subangular, and arc mainly frag- ments of quartz, plagioclase feldspar, chert anil volcanic rocks. Some specimens contain a few grains, less than a tenth of a percent, of potassium feldspar, but most con- tain no potassium feldspar (Bailey and Irwin, 1959). A fine-grained matrix constitutes a small percentage of most specimens. Calcite is rarely present in the graywacke. The graywacke forms beds that range from a fraction of an inch to more than 10 feet in thickness, but most commonly the thickness is between 1 and 3 feet. Bedding planes generally are sharp. Most of the beds are even- grained, but at some places the sediments grade upward from coarse to fine grained. Dctrital shale fragments are seen in some beds of graywacke at most exposures throughout the northern Coast Ranges. They most com- monly occur in vaguely delineated zones in a bed of graywacke that perhaps otherwise is even-grained, but at other places appear to be randomly distributed. The shale fragments arc mostly flattened ellipsoids, but tabu- lar fragments that appear to have been transported only short distances do occur. The shale fragments are com- monly about a quarter of an inch in longest dimension. Fossils were found in the graywacke at locality no. 6 (pi. 1). The locality is in wV,NW'/ 4 sec. 10, T. 20 N., R. 12 \\\. about 100 feet east of a cattle guard at the south end of Eden Valley in central .Mendocino County. Only one of the fossils appeared sufficiently well pre- served to warrant being collected; the others were small fragments scattered abundantly throughout some of the graywacke. The best preserved specimen was examined by R. W. Imlay. who states (written communication. 1956) that it is an external mold of a right valve of an aucella, ami that it is too poorly preserved to be identi- fied specifically. The graywacke containing the fossil was tested by the staining method (Bailey and Irwin. 1959) and was found to contain no potassium feldspar. Shale is interbedded with graj w acke as layers that range from thin partings to beds several hundred feet thick. In places shale is rhythmically interbedded with fine-grained graywacke, and elsewhere with chert. The shale ranges from black to greenish gray. Fragments of fossil plants are locally abundant on bedding surfaces. particularly in shale partings between beds of gray- wacke, and in some shale the arenaceous tests of marine micro-organisms have been found. Conglomerates constitute only a small percentage of the bulk of the detrital rocks, but locally are abundant. The fragments range from fine pebbles to boulders as much as a foot in diameter, but pebbles and small cobbles are most common. The pebbles are dominantly rccrystal- lized chert, greenstone, and fine-grained porphyritic rocks. Most of the conglomerate beds are only a few 7 feet thick, particularly the finer pebble conglomerates, but some are several tens of feet thick. At a few places, sections of dctrital rock consisting largely of conglom- erate arc at least several hundred feet thick. Beds of boulder conglomerate seem most abundant in sections containing considerable chert and greenstone. The chert generally is abundant in the vicinity of vol- canic rocks. It is characteristically red-brown or green, and rhythmicall\ interbedded with thin shale layers. The individual chert beds range from a fraction of an inch to several inches in thickness. Some lenses of rhythmically bedded chert appear to be several hundred feet thick and more than a mile long, but most are considerably smaller. Distortion of manv chert sections is indicated by chevron folds with amplitudes that range from several inches to several feet (photo 7). Fossil radiolaria arc found in much of the chert, but well-preserved remains are not abun- dant. As the chert is nearly always close to volcanic rock, a genetic relation between the chert and the volcanics is probably r indicated. Limestone has been found in the northern Coast Ranges at few localities in areas of the Franciscan forma- tion. Some of the limestone lenses are similar to the Calera limestone member described by Lawson (1895 and 1914) as part of the Franciscan formation on the San Francisco Peninsula, and are likewise similar to the Whitsctt lime- stone described by Diller (1898) as part of the Myrtle formation in the Klamath Mountains of Oregon. These lenses of limestone characteristically arc thin-bedded and contain interbedded chert layers, volcanic debris, and locally abundant foraminifera. The best known locality of foraminifera] limestone in the northern Coast Ranges is near Laytonville, where it is exposed in several road cuts (locality no. 7, pi. 1) on Highway 101 about % mile north of the village. It is also exposed 2 miles north of Laytonville, about 200 feet northeast of Highway 101 where the limestone forms a prominent hillock in a grassland area (locality no. 8, pi. 1). These exposures have been referred to bv Diller (1902, p. 65-66), Thalmann (1943) and Taliaferro (1943. p. 193). The limestone near Laytonville is thought to be part of a stratigraphic section that includes chert and volcanic rocks as well as detrital sedimentary rocks, but the section is not clearly- exposed. The contact between the limestone and adjacent strata was seen at only* one place, and there the limestone is underlain by fine-grained graywacke. The limestone is thinly bedded, ranges from pink to pale red-brown in color, and contains many thin layers of reddish chert. At one place a minimum thick- ness of 12 feet of limestone is exposed, but exposures are such that the total thickness is not known. 36 California Division of Mines [Bull. 179 - ■ . b* ft* ■' *-i ? I-' 'If & -fit ( i ' 7 ; it %■ # v;- */ • >r / • '4 1 -^k^--* a- \ • t v-. # fJL. '/••*# i K ft* Photo 7. Folded clicrt of the Franciscan formation, between Dos Rios and Covelo. Similar foramini feral limestone crops out (locality no. 9, pi. 1) in SW l / 4 sec. 9, T. 3 S., R. 2 E., about 12 miles northwest of Garberville in southern Humboldt County. It is exposed as an isolated knob in a general area of sheared rocks of the Franciscan formation and serpentine (E. H. Bailey, oral communication, 1954). Abundant microfossils are found in the limestones near Laytonville and Garberville, as well as in bodies of similar limestone found elsewhere in the Franciscan formation and in the Myrtle formation (Thalmann, 1942 and 1943; Cushman and Todd, 1948; Walker, 1950; Church, 1952; Glaessner, 1949; Kiipper, 1955; and Thalmann, 1957, written communication). According to Taliaferro (1943, p. 193), radiolaria found in the chert associated with the foraminiferal limestone are the same type as those found in chert elsewhere in the Franciscan formation. Thalmann (1943) first considered the foraminiferal limestones of the Franciscan and Myrtle formations to be synchronous deposits of Turonian age. However, on the basis of later study he (Thalmann, written communi- cation, 1956) considers the Calera limestone member on the San Francisco Peninsula to be of Cenomanian age, and the limestones near Laytonville and Garberville to be slightly older, that is. Late Albian or possibly earliest Cenomanian in age (see Irwin, 1957, p. 2290). Limestone that differs from the foraminiferal lime- stones crops out (locality no. 5, pi. 1) about 3 miles south of Sheetiron Mountain and a quarter of a mile east of Bowery Flat in the northwestern part of the Stony- ford quadrangle (fig. 2). The limestone is finegrained and light-gray in color. It occurs as beds that range from Yi to 1 foot in thickness, and as nodules, interbedded with graywacke and shale. Pillow basalt nearby appears to be part of the stratigraphic section. Graywacke col- lected from the locality contains no potassium feldspar. Fossils were found at several places in the shale. They were referred to R. W. Imlay of the U. S. Geological Survey, who states (written communication, 1956) that they are Buchia crassicollis (Keyserling) of early Early Cretaceous (middle to late Valanginian) age (see Irwin, 1957, p. 2293). Limestone occurs (locality no. 4, pi. 1) at the north end of McLeod Ridge at the south shore of Lake Pills- burv, but it is questionable whether the limestone here is really a part of the Franciscan formation. The lime- stone is massive and is light-gray in color. It occurs as 1960] Northern Coast Ranges \\i> Imwiuh Mountains 37 beds that range from ' j to 1 toot in thickness in dark greenish gray shale. The rocks are sheared, and the lime- stone beds are broken into segments a tew feet long. Fossils are unusually abundant ami well preserved in both the limestone and the shale. They were submitted to R. \V. Imlav. wlm states (written communication, 1953) that they are Buchia piochii (Gabb) of bare Ju- rassic (middle Tithonian) age. Chert and volcanic rocks, generally considered characteristic of the Franciscan formation, were not seen to be interbedded with the nnks. ami the limestone and shale may belong to the Knoxville formation rather than to the Franciscan. Limestone has been found (locality no. 16, pi. 1) about miles east-northeast of Eureka, in sees. 13 and 14, T. 5 N., R. 1 E., on the northeast side of Jacoby Creek at an altitude of about 400 feet. It has been described by Aver- ill (1941, p. 516) and Rice (oral communication, 1955) as probably of the Franciscan formation, but the field relations apparently arc not clear. Most of the limestone is thought to be nonfossiliferous, but a specimen given to the writer by O. E. Bowen, Jr., of the California Divi- sion of Mines, contains abundant fossils. The specimen was examined by the late J. 1!. Reeside of the U. S. Geo- logical Survey, who reported as follows: "The fossils in this piece of rock appeal to be the comminuted fragments of one species of large pelecypod. Some of them bear fragments of the hinge and suggest very strongly a species of Glychneris or Idonearca. It would lie very difficulr to prove the age of the specimen, but I would guess it to be Upper Cretaceous. Ralph [mlay and David Nicol have examined the specimen also, and think this opinion not unreasonable." In the central part of the Alderpoint quadrangle, lime- stone is reported (Averill, 1941, p. 518) in sees. 20 and 29, T. 4 S., R. 5 I .. near Harris. It crops out as a cliff }5 feet long and 10 feet high, and smaller exposures are found at intervals for a quarter of a mile. Judging from its reported location, the limestone occurs in an area of the Franciscan formation. Manning and Ogle (1950. p. 21) mention only a few- small lenses of thoroughly recrystallized, dense, dark- gray limestone in the Franciscan formation in the Blue Lake quadrangle (\\ (Z X o >- z 2 }£ E *> 5C < o o < z * o or ^— uJ UJ a; o _j i _i Q a. 3 U. o O o or 0T —i —i e> CD > X z o z o a£ — Ul < CE t- _i f- a. a. < \- co =D 2 a: < or >- X o 2 CO a. o u. CE UJ — 1 —1 Ul _I o z H or or ul >- o _l 2 z < DILLARD inuJ OIE SERIES ZU1 (r UJ O < 1- co z or 5 UJ S Ul o _i i- Ul o (O _i tr Q K to o X - < o 2 H Z r- UJ < CO < 2 a. or o Ul u. _i ^ _i Ill o Ul 1- u > X o z _l DC * H M Ul 00 or - Q < 2 CE o < CO _l o _l z Q < or u. GALICE GROUP o 3 Q- o 5 ¥ D0THAN GROUP or UJ w _i £ •*- i Z a 5 o 1- Ul u. CO o or O X z 03 o — < h- l- z < Ul 2 CO or < 0. o u. E UJ ■*■ _i h- UJ _l rr _l >- > 2 X o z *: GALICE fm ROGUE fm D0THAN fm • * Interpreted by the writer on the basis that areas shown as Myrtle formation by Oilier are shown as Knoxville, Paskenta and Horsetown formations by Wells (1955). Relation of Rogue formation after Cater and Wells (1954). Figure 5. Chart showing changes in concept of the Myrtle, Galice ond Dothan formations of Diller (1903b and 1907) of southwestern Oregon and correlations with the Franciscan, Knoxville, Horsetown and Paskento formations of northern California. 1960] Northern Coast Ranges and Klamath Mm ntatns 41 increase in potassium feldspar content with decreasing age, the Late Jurassic ranging from to 4 percent potas- sium feldspar, the Early Cretaceous ranging from less than 0.1 to 25 percent, and the Late Cretaceous ranging from 0.5 ro 35 percent. This suggests that in- creasingh large areas of potassium feldspar-hearing plu- tonic rocks were being exposed to erosion at the source area during deposition of the Sacramento Valley se- quence. If the graywackes of the Franciscan formation are considered to have been derived from the same gen- eral source area as those of the Sacramento Valle) se- quence, they would appear to be older owing to the lack of potassium feldspar. This concept may apply to part ot the Franciscan formation, hut is nor consistent with the lack of potassium feldspar in some graywackes of the Franciscan formation where fossils equivalent in age to those of the Sacramento Valley sequence are found. Problems regarding the age and formational designation of rocks of the Franciscan and other formations of Juras- sic and Cretaceous ages in the Coast Ranges of California arc similar to those of the M\ rtle and Dothan formations of Oilier (fig. 5) in the western part of Klamath Moun- tains of Oregon. The formations of southwestern Oregon have not been examined extensively in the field by the writer, but judging chiefly from the literature the .Myrtle formation of Diller seems to be a northward continuation of the Franciscan formation plus associated strata equiva- lent to the Knoxville, Paskcnta, and Horsetown forma- tions of the Sacramento Valley. Diller (1907, p. 411) considered the Myrtle formation equivalent to strata that in the present report are referred to as Knoxville, Pas- kcnta. and Horsetown formations, and noted the presence of interbedded chert, volcanic rocks, and foraminifcral limestone (Whitsett limestone). Louderback i 1905, also see Diller 1907, p. 412-421) reinterpreted the .Myrtle formation, and subdivided it into so-called upper and lower series. The so-called lower series, named Dillard scries, included the detrital sediments with interbedded chert and foraminifcral limestone, and was considered equivalent to the Franciscan formation. The so-called upper series, named .Myrtle group, consisted wholly of detrital sediments that Louderback considered to be younger and less well indurated than those of the Dillard series and presumably equivalent to those of the Sacra- mento Valley sequence. Taliaferro ( 1942, p. 75-77) con- curred largely with Louderback's subdivision of the Myrtle formation, but grouped the Upper Jurassic part of the Myrtle group with the Dillard to conform with his concept regarding the relation between the Franciscan and Knoxville in the Coast Ranges of California. Areas mapped as Myrtle formation by Diller (1903b) in the Port Orford quadrangle, Oregon, were subdivided into two units, presumably on a faunal basis, by Wells (1955), but the connotation of his two units is signifi- cantly different from Louderback's subdivision. One unit has been named the Knoxville formation, and the other the Paskcnta and Horsetown formations. In all of the correlations of the Myrtle formation of Diller (fig. 5), the foraminifcral limestones (Whitsett limestone) have not been taken into proper account. According to Thalmann (1943) the foraminifcral lime- stones of the Myrtle formation of Diller are middle Cre- taceous in age. Thus they are younger, rather than older, than most of the Cretaceous rocks considered by Louder- back and Taliaferro to overlie them. Strata younger than the Sur scries ' and older than the oldest (middle Tithonian) paleontologically dated part of the Franciscan formation have not been recognized in the Coast Ranges of California. The w riter has no data that indicate the presence of such rocks, but points to the possibility of their existence and the probable diffi- cult \ of their recognition. The sedimentary strata of the Dothan, Galice, and Franciscan formations are similar, and arc interbedded, at least locally, with chert and volcanic rocks. All apparently contain little or no potas- sium feldspar, ami fossils are rare. Differences have been drawn between these formations on the basis of relative thickness of betiding, minor differences in degree of lithitication and slatiness, and whether small veinlets cut- ring the strata are siliceous or calcareous. None of these criteria is absolute, and indeed all are of highly question- able value, as the range in thickness of bedding, and degree of lithification and slatiness is as great within the formations as between them. The validity of the fore- going statements was partly recognized by Diller (1907, p. 411). who stated that ". . . on lithologic grounds, therefore, the Myrtle and Dothan arc not always easily distinguished . . . and ... it is only by means of fos- sils or definite stratigraphic data having references to fossiliferous horizons that affords a satisfactory basis for separating the Dothan and Myrtle in the held.' - One might well question how the Dothan, Galice, and Fran- siscan can be distinguished from one another if they intermingle in a structurally complex area. Historically, the various conflicting correlations that have been made with the Franciscan formation on a litho- logic basis do not indicate a unique lithology. Diller (1907, p. 420) and Wells, Hot/, and Cater (1949, p. 9) consider the Franciscan formation equivalent to the Dothan formation. Louderback (1905, p. 547-548) and Taliaferro (1942, p. 89) correlate the Franciscan forma- tion with the Dillard series, that is, part of the Myrtle formation of Diller. A large area of dominantly detrital strata in western Del Norte County has been assigned to the Franciscan by Taliaferro (1943, p. 123. fig. 2), Wells, Cater, and Rvnearson (1946, p. 6), and Rice (data incor- porated in pi. 1), and the rocks of the same area are assigned to the Dothan by Maxson (1933, pi. 4). Along the boundary between California and Oregon (see fig. 3), rocks assigned to the Franciscan in California are con- tiguous with rocks assigned (Wells, 1955) to the Dothan in Oregon. Judging from these conflicts, the several for- mations apparently are not different enough, lithologi- 1 Sux series is the name applied to quartzite, schist, and marble exposed in the Santa Lucia Range of the southern Coast Ranges of California. It gener- ally is considered to be pre-Franciscan, probably Paleozoic in age. 42 California Division of Mines [Bull. 179 cully, to permit accurate correlation or formational des- ignation on only a lithologic basis. Coastal Belt of Undifferentiated Sedimentary Rocks. Sedimentary rocks crop out in a belt that extends from near Petrolia in southwestern Humboldt County to the Russian River in Sonoma County, a distance of approxi- mately 150 miles, and probably continue southeastward. The belt ranges from about 10 miles to 25 miles in width. North of Point Arena it is bounded on the west by the Pacific Ocean. Southwestward from Point Arena it is bounded on the west by the San Andreas fault to a point a few miles north of the Russian River. The coastal belt is bounded to the east by the central belt of Franciscan rocks throughout most of Sonoma and Men- docino Counties, and in southern Humboldt County by the Yager formation of Ogle (1953). Rocks similar to those of the coastal belt underlie relatively small areas within the central belt of the Franciscan formation. The sedimentary rocks of th; coastal belt consist chiefly of graywacke, shale, and minor conglomerate (photo 9). Stain tests show (Bailey and Irwin, 1959) that most of the graywackes of the coastal belt contain ap- preciable quantities of potassium feldspar. In this respect the graywackes of the coastal belt are similar to the rocks of the Sacramento Valley sequence, but differ from tlv: graywackes of the Franciscan of the central belt and the metamorphosed Franciscan of the eastern belt. Volcanic rocks interbedded with graywacke and shale are found at a few places in the coastal belt and appar- ently are most abundant in the southern third of the belt. Small areas of pillow basalt, greenstone, and chert were seen at a few places along the Stewarts Point-Skaggs Spring road. Greenstone occurs over an area of 2 square miles east of Comptche in the southeastern part of the Glenblair quadrangle (fig. 2), and also 3 miles southeast of McDonald Ranch in the central part of the quad- rangle. Greenstone associated with small lenses of lime- stone 3 Vi miles northeast of Usal in the Piercy quadrangle is reported by Trask and others (1943, p. 80). Layers of pillow basalt are known in the west-central parts of the Point Delgada and Scotia quadrangles (fig. 2). Con- sidering the dense vegetation and poor exposure in the coastal belt, areas of volcanic rocks other than those seen are likely present, but the total quantity of volcanic rocks doubtless is very small compared with sedimentary rocks. Nevertheless, these few known areas of volcanic rocks apparently document volcanism contemporary with dep- osition of potassium feldspar-bearing graywacke. Limestone occurs at a few places in the coastal belt and in the smaller areas of similar rocks within the cen- Photo 9. Thick beds of ;raywacke of the coastal belt of undifferentiated sedimentary rocks, along U. S. Highway 101 about a mile west of Cummings. 1960] Northern 0>\m Ranges and Klamath Mountains 43 tral belt of the Franciscan formation. One of the most interesting occurrences of limestone (fossil locality no. 2. pi. 1 ) in the coastal belt is on the north bank of the Gualala River, opposite the YMCA Clamp in the cast- central part of the Annapolis quadrangle (fig. 2). The limestone is reddish in color and is lithologically similar to limestones of the Franciscan formation near Layton- villc and Garbcrville. It is a bed about 2 feet thick ad- jacent to greenstone in graj wacke and shale. Thin sec- tions of the limestone were examined by Professor H. E. Thalmann of Stanford University, who states (written communication, 1956) that the limestone contains micro- fossils that are the same as those in the limestones near Laytonvillc and Garberville, and that the fossils are Late Albian or basal Ccnomanian in age (see Irwin, 1957, p. 2290). About \y 2 miles southwest of the YMCA Camp, cobble conglomerate interbedded with graywacke and shale is well exposed (locality no. 1, pi. 1) on the banks of the Gualala River, and many of the cobbles are lime- stone. One of the limestone cobbles contained well-pre- served fossils that arc identified bv R. W. Imlay (written communication, 1956) as Buchia piochii (Gabb) of Late Jurassic (middle Tithonian) age. Limestone at Dugans Opening, about 3'/ 2 miles north- east of Usal in the central part of the Piercv quadrangle (fig. 2) is described by Trask (1950, p. 146-147). The limestone appears similar to the limestone near Layton- villc, and occurs in about 30 lenses interbedded with sand- stone and greenstone within an area of less than 3 square miles. The limestone is lithologically similar to the lime- stone of the Franciscan formation at Laytonville. Most of the lenses are less than 5 feet thick and 20 feet in length, but the largest is 50 feet thick and 150 feet in length. The greenstones consist of flows, tuffs and in- trusive rocks of approximately the composition of andc- site. Near the middle of the northern half of the Porno quadrangle (fig. 2), thin-bedded sandstone and shale is well exposed along the South Fork of the Eel River at the mouth of Tomki Creek, and a mile farther north where a bridge crosses the river. At the northern locality (lo- cality no. 3, pi. 1) a section more than 50 feet in thickness is exposed. The beds strike approximately N. 30° W. and dip at moderate angles to the northeast. Abundant worm- tube structures are seen in the beds, and at a few places lenticular nodules of limestone arc found. In one nodule, a large fragment of an inoceramus was found along xvith a few unidentified microfossils. A bed of light-gray limestone in shale and graywacke was seen in the northeast part of the Porno quadrangle, at an altitude of 1,900 feet along the east side of the road of Laleys Ranch and about l' : miles southwest of the ranch. A slab of similar limestone was found in a small creek that drains an area of dark greenish-gray shale a few hundred feet south of the Old Dashiel Place in the northeast quarter of the Porno quadrangle. Fossils xvere not found at either locality. Cretaceous Rocks in the Klamath Mountains Province Small isolated patches of sedimentary strata of Creta- ceous age overlie the plutonic rocks and pre-Jurassic strata in the southern part of the Klamath Mountains province. They are marine deposits of sandstone, shale, and conglomerate that likely are remnants of a mantle once continuous with the strata of the Sacramento Val- ley. The patches arc most abundant near the Sacramento Valley in the Chanchclulla Peak quadrangle, where they obviously overlie the pre-Jurassic rocks xvith sharp angu- lar and erosional discordance. The patches farther north and northwest are widely spaced, and most are associated with small areas of Tertiary strata. The patches of Cretaceous strata at Reading Creek about 10 miles south of Weaverville, at Rattlesnake Creek in the north-central part of the Hoaglin quadrangle, and at Big Bar in the northeastern part of the Hyampom quadrangle were studied by Dillcr (1908), Hinds (1933), MacGinitie (1937), and Anderson (1938). At Reading Creek 1,000 feet of Cretaceous strata is exposed (Hinds, 1933, p. 112), while at Big Bar the thickness is about 200 feet (Dillcr, 1908, p. 380). The fossils found in these strata indicate an Early Cretaceous age (Anderson, 1938, p. 49-50). Most of them are of the Hautcrivian stage, however, Buchia crassicollis (Keyserling) of the Valan- ginian stage was found (U. S. G. S. Mesozoic loc. no. 6627) at the Patterson mine near Big Bar (R. W. Imlay, xvritten communication, Dec. 1958). Se\ - eral less studied patches of Cretaceous strata occur in the southern part of the Klamath Mountains province. One is shown on the geologic map (pi. 1) 5 miles south- east of Hayfork, and another is on the east side of Hy- ampom Valley. The strata at both localities reportedly contain fossils of Late Cretaceous age. A small patch of pebble conglomerate perhaps 200 feet in width lies just west of a small area of Tertiary rock on the crest of the high ridge x\ est of Hoopa Valley, in the eastern part of the Coyote Peak quadrangle. The conglomerate probably is Cretaceous in age, but no fossils xvere found. A belt of Upper Cretaceous strata along the northeast margin of the Klamath .Mountains province north of Shasta Valley in California and Oregon has been de- scribed by F. M. Anderson (in Avcrill. 1931), Williams (1949, p. 16-18), and Feck. Imlay, and Popenoe (1956). The strata consist of buff-weathering sandstones and conglomerates that lie with angular unconformity on the plutonic rocks and pre-Jurassic strata of the Klamath Mountains province. The strata range widely in com- position, particularly the conglomerates, and reflect the nature of the adjacent bedrock. They constitute a section that is more than 2.673 feet thick (Feck, Imlay, and Popenoe. 1956, p. 1971). The beds dip northeastxvard at angles ranging between 10 and 30 degrees, and are thought to underlie the thin veneer of alluvium in Shasta Valley and perhaps continue northeastward under the lavas of the Cascade Range. They commonly have been referred to as the Chico formation, but recently (Peck, Imlay, and Popenoe, 1956) have been named the Horn- 44 California Division of Mines [Bull. 179 brook formation. Anderson (in Averill, 1931) considered them to range from Late Turonian to Early Senonian in age, but according to Peck, Imlay, and Popenoe (1956, p. 1978-1982) the strata range at least from Cenomanian to middle or late Campanian in age, and include one unconformity. Uppermost Cretaceous Strata Three principal areas of strata of probable late Late Cretaceous age are shown on the geologic map (pi. 1). One area is chiefly in west-central Humboldt County, and includes the Yager formation. The second area lies west of the San Andreas fault from Point Arena south- ward to Fort Ross, and includes the Gualala series of Weaver (1943). The third is a small area of strata near Covelo in central Mendocino County. Yager Formation of Ogle. The Yager formation is the name applied by Ogle (1953, p. 16-22) to a section of detrital sedimentary strata typically exposed along Yager Creek in the Fortuna quadrangle. The total thick- ness of the formation is not known, but is thought to be more than 2,500 feet. The formation consists of inter- bedded shale, gravwacke, and conglomerate, with thin- bedded shale as the predominant rock. Specimens of gravwacke from five different localities contained from 3 to 35 percent potassium feldspar, and averaged about 15 percent. In reconnaissance mapping, the characteris- tics used to distinguish the Yager formation from adjacent rocks of the Franciscan formation and coastal belt of sedimentary rocks were the relative abundance of thin- bedded shale, the general lack of interbedded chert and volcanic rocks, and the relatively mild deformation of the Yager strata. As mapped, the Yager formation is nearly restricted to southwestern Humboldt County; small areas, however, may well have been overlooked at other localities in the Coast Ranges, particularly in the coastal belt. Conversely, some of the area shown as uppermost Cretaceous on the geologic map (pi. 1) may include detrital rock of other stratigraphic units. South of the area of Tertiary rocks in the Eel River Valley area, a westerly trending zone described as the False Cape shear zone by Ogle (1953, p. 22-24) has been included in the area shown as upper- most Cretaceous although other formations are reported to be found in that zone. The age of the Yager formation and its relation to the Franciscan formation and formations of the Sacramento Valley sequence is poorly known. Index fossils have not been found, but a small gastropod that has been found elsewhere in California in the Markley sandstone of Eocene age was noted by Ogle (1953, p. 20). Microfossils found in the finer-grained sediments are reported (Ogle, 1953, p. 19) to suggest that the formation is at least as young as Cretaceous. Foraminifera recovered from shale samples collected from widespread localities during the present reconnaissance are chiefly agglutinated arena- ceous forms and are not satisfactory for age determina- tion. Ogle (1953, p. 21) assigned the Yager formation to the Upper Jurassic and Cretaceous, the Upper Jurassic assignment being based on a lithologic correlation of the thin-bedded shales with the Knoxville formation, and the Cretaceous assignment presumably being based on the presence of microfossils. Judging from the average amount of potassium feld- spar in the few samples that were tested, the Yager for- mation is as young or younger than the Upper Creta- ceous rocks of the Sacramento Valley sequence; and judging from the relatively mild deformation of many areas of Yager formation, it may even range into the Tertiary. The original extent of deposition of the Yager formation is not known, but its present distribution ap- pears to be controlled by downwarping and faulting. The downwarping is more clearly shown in the overlying late Teritary strata of the Eel River Valley area. The strata of the Yager formation generally dip at gentle to moderate angles, and over many areas have been dis- turbed only moderately by faulting. In contrast, the strata of the Franciscan formation most commonly dip at moderate to high angles, and have been highly sheared and faulted. The area of the Yager formation lies partly athwart the northwest-trending central belt of the Franciscan for- mation, and the Yager probably overlies the Franciscan. In the southwestern part of the Garberville quadrangle the Yager strata appear to overlie conformably the strata of the coastal belt, and the contact was mapped on the basis of relative abundance of shale and gravwacke (E. H. Bailey, oral communication, 1954). Northwesterly through central Garberville quadrangle the Yager for- mation is in fault contact with the Franciscan formation, largely along zones containing abundant serpentine. In the [aqua Buttes quadrangle (fig. 2) the contact between the Yager formation and the Franciscan rocks of the central belt is a fault. Gualala Series of Weaver. Detrital sedimentary rocks of the Gualala series form the narrow belt of land along the southwest side of the San Andreas fault between Fort Ross and Point Arena. They were named for exposures near the village of Gualala that were examined by G. F. Becker (White, 1885, p. 7), and were described in greater detail and mapped by Weaver (1943, p. 629, fig. 280). The Gualala series consists of interbedded gravwacke, shale, and conglomerate (photo 10). Samples of gray- wacke that were tested ranged from to 35 percent potassium feldspar. Pillow basalt appears to be inter- bedded with the detrital rocks approximately a mile north of Black Point in the Stewarts Point quadrangle. According to Weaver (1943, p. 629) the aggregate thick- ness of the Gualala series is 21,600 feet, but neither the base nor the top of the section is accurately known. The Gualala rocks of the report area form a north- westerly extension of the San Andreas-Nacimiento fault block of the central and southern Coast Ranges of Cali- fornia. They are not surely known, however, to be con- fined to the southwest side of the San Andreas fault. 19601 Northern Coast Ranges and Klamath .Mountains 45 -te^ i Photo 10. Gualala series exposed in wave-cut cliff at Anchor Bay, about 3 miles northwest of Gualala. Most of the sandstones of the Gualala series arc similar in hand specimen to the graywackes of the coastal belt, the Franciscan, and parts of the Sacramento Valley se- quence. Some, however, are cleaner and better sorted than those most commonly found northeast of the fault. In this respect, as well as perhaps a slightly lesser degree of induration, some of the sandstones more closely re- semble some of the Late Cretaceous formations found elsewhere. Conglomerates containing cobbles of quartz diorite occur in the Gualala series, but none was seen in the coastal belt northeast of the San Andreas fault. Sand- stone, however, similar to the cleaner sandstone most distinctive of the Gualala series was seen northeast of the San Andreas fault, about a mile southeast of lint Russ School along the road to Cazadero. The age of the Gualala series is not accurately known. In the vicinity of Point Arena, the Gualala is overlain b\ Miocene strata, but strata older than the Gualala are not known southwest of the San Andreas fault in the report area. White (1885, p. 7) considered the Gualala series to occupy a stratigraphic position between the Shasta series and the Chico formation, but Weaver (1943, p. 630) assigned it more broadly to the Cretaceous. If the Gua- lala strata arc younger than the strata generally found on the northeast side of the San Andreas fault, they prob- ably are Late Cretaceous or early Tertiary in age, as some of the strata on the northeast side of the fault are late Early Cretaceous (Late Albian) in age. According to Durham and Kirk (1950, p. 1537), fossils found in the Gualala strata indicate that some of the strata are probably Late Cretaceous (Maestrichtian) in age, and some may be Paleocenc or Eocene. Covelo Area. Detrital rocks of Late Cretaceous age that occur in several small areas southwest of Covelo in north-central .Mendocino County were mapped by Clark (1940). The rocks consist of brown- to buff- weathering sandstones, shales, and minor conglomerates, and are less well-indurated and sheared than the detrital rocks of the Franciscan formation of the central belt with which they are in fault contact. According to Clark (1940, p. 124) they consist of sediments derived mainly from the Fran- ciscan formation, and arc not lithologically distinctive from strata of Eocene age that are found in the same general area. Fossils found at several localities by Clark were examined by F. M. Anderson (Clark, 1940, p. 124). and were considered Late Cretaceous in age and younger 46 California Division of Mines [Bull. 179 than the Chico formation. Clark states that the section is 4,000 feet thick, and that it is conformable with the overlying Eocene strata but separated by a depositional hiatus. Tertiary Rocks Rocks of Tertiary age occur in both the northern Coast Ranges and Klamath Mountains of California, and form a nearly continuous blanket over most of the Upper Jurassic and Cretaceous rocks of the Sacramento Valley. Included are rocks that range in age from Eocene into the early Quaternary. They are chiefly detrital strata, but volcanic rocks occur at a few widely spaced localities. The areas of rocks of Tertiary age in the northern Coast Ranges and Klamath Mountains are few in number, and generally are small and widely separated. The Terti- ary rocks of the northern Coast Ranges and the north- western part of the Klamath Mountains are dominantly marine in origin, while those of the central part of the Klamath Mountains are chiefly continental in origin. Strata of Eocene Age Covelo Area. Marine sedimentary strata of Eocene age are associated with the uppermost Cretaceous strata west of Covelo in north-central Mendocino County. Here, as elsewhere in northwestern California, several post-Franciscan formations occur together in a restricted area and have been preserved by down-faulting. On a paleontologic basis the Eocene strata have been correlated by Clark (1940) with the Martinez, A4eganos and Capay formations of central California. The rocks consist of fine- to medium-grained sandstone with minor interbedded shale and conglomerate. They are light brown to buff colored in weathered outcrops, but where fresh rock is exposed in deep, newly made roadcuts, the rock is seen to be light bluish gray in color, similar to most sedimentary rocks of Tertiary age elsewhere in northern California. The sandstones differ in this respect from the pre-Tertiary sandstones which generally are greenish and darker gray in color. In general, the Eocene strata in the Covelo area dip steeply northeastward. They were distinguished from the uppermost Cretaceous strata, and from each other, only on a paleontologic basis (Clark, 1940, p. 128). The strata assigned to the Martinez formation in the Covelo area total approximately 1 30 feet in thickness, and judging from the paleontologic evidence and similarity of structure they overlie the late Upper Cretaceous strata disconformably (Clark, 1940). The strata assigned to the Meganos formation are about 300 feet in thickness. Their structural attitude is similar to that of the underlying Martinez and overlying Capay formations. The overly- ing strata assigned to the Capay formation total about 1,500 feet in thickness. Shasta Valley Area. Sedimentary rocks of Eocene age crop out in a narrow belt on the northeast flank of the Klamath .Mountains province. The belt trends north- west from the north end of Shasta Valley into southern Oregon, and similar rocks are thought to underlie Shasta Valley. The rocks have been described in most detail by Williams (1949), from whom much of the following description is taken. The Eocene rocks are known as the Umpqua forma- tion and consist of sandstone, shale, and conglomerate that laterally range widely in composition, and locally are interbedded with coal and tuffaceous material. Gen- erally the sandstone constitutes the lower part of the section, and is separated from an upper shaly part by a bed of coal that is a maximum of 6 feet thick. Some of the sandstone is seamed with limonite, and at one place a sandstone bed grades into a bed composed almost en- tirely of limonite and magnetite. The coal beds, and cross-bedding, and carbonized logs in some of the sand- stone, indicate a nonmarine origin. However, northward in Oregon the Umpqua formation is of marine origin. The thickness of the Umpqua formation ranges from 800 to about 2,000 feet. The formation rests disconform- ably on the Hornbrook formation, and is overlain with angular discordance by Tertiary volcanic rocks. Strata of Oligocene(?) Age Several small areas of continental sedimentary deposits of Oligocene(P) age occur in the southern part of the Klamath Mountains province. The deposits were de- scribed by Diller (1894b, 1902, 1911, and 1914a) and named Weaverville formation by Hinds (1933, p. 115). The most detailed work, particularly with regard to a fossil flora found in the rocks, has been done by Mac- Ginitie (1937). The principal areas of exposure of the Weaverville for- mation are at Weaverville, Reading Creek, Hayfork and Hyampom Valleys, and Big Bar. In addition to these, several small patches of Tertiary deposits that are pos- sibly related were found during the present reconnais- sance at Corral Bottom, Clark Creek, and Buckhorn Creek in the northern part of the Hyampom quadrangle (fig. 2), and northwest of Hoopa Valley. The areas of Weaverville formation are small blocks that have been preserved by being faulted into the older rocks of the southern part of the Klamath Mountains province. At several of these areas of Tertiary rocks, small areas of strata that range from Early to Late Cre- taceous in age are similarly preserved, as at Reading Creek, Big Bar, Hvampom Valley and possibly at Hoopa Valley. The Weaverville formation consists of fine-grained sandstone, shaly sandstone, sandy shale, fine-grained lake beds, lignitic shale, lignite, tuff, and conglomerate (Hinds, 1933, p. 115), that are thought to have been deposited on a flood-plain with widespread swampy lakes (Mac- Ginitie, 1937, p. 102). Some may be estuarine (Diller, 1902, p. 43). The lignite has been mined on a small scale at several localities (photo 11). At Hyampom Valley a lignite bed ranges from 10 to 16 feet in thickness (Mac- Ginitie, 1937, p. 96). A thick section of lignite is well exposed on the northeast bank of the South Fork of the Trinity River, where a bridge on the county road spans the river about one-quarter mile west of Hyampom. 1960| Northern Coast Ranges vnd Kj vmath Mot ntains 47 ^' ? Photo 11. Lignite inte coal roedded with light colored clay, siltstone, and sandstone of the Weaverville formation at Reese Brothers mine, near Browns Creek in the central p.irt of the Weaverville 15-minute quadrangle. I he Weaverville strata at m:>st places ilip gently to mod- erately, lint at a few localities where they are in fault contact with adjacent older rocks they dip steeply. The thickness of the Weaverville formation is 1,900 feet at Reading (.'reek, probably not less than 2,000 feet at Hay- fork Valley, and about 1,100 feet at Hyampom; ar J5ig Bar it is a little less than 500 feet but neither the top nor the bottom of the section is exposed (MacGinitie, 1937). \n abundant fossil flora is found in some of the shaly beds of the Weaverville formation. The flora was first considered to indicate a Miocene age (I)iller, 1902, p. 41- 45), and later thought to be chiefly Eocene (Hinds, 1933, p. 79, 114-116; Jenkins, 1938). According to MacGinitie (1937, p. 129), however, the flora is Oligocene in age. The Weaverville formation was considered by Dillcr I 1902, p. 12) to be associated with the development of the Sherwood peneplain, that is, the so-called second cycle of erosion. If MacGinitie's (1937) assignment of the formation to the Oligocene is correct, however, the \\ eavcrvillc formation is older than even Diller's Klamath peneplain. Strata of Miocene Age Marine sedimentary deposits of Miocene age occur at Point Arena, and near Covelo, Garberville, Petrolia, and along the Bear River. Deposits in western Del Norte County that commonly are referred to as Miocene in age are discussed with strata of Pliocene age in this report. Point Arena Area. At Point Arena, along the coast of southern Mendocino County, marine sedimentary de- posits are exposed over an area of about 1 1 square miles, and constitute the largest area of exposure of Miocene rocks in northwestern California. Thev have been mapped and described by Weaver ( 1943, p. 630-631, and fig. 280), who separated the strata into lower and upper units. The lower unit, the Gallaway beds, consists of dark- gray and brown argillaceous shale, mudstone and me- dium-grained sandstone, interlaycrcd with thick beds of brownish-gray sandy shales and foraminiferal shales. The upper unit, the Point Arena beds, consists of interbedded gray-brown clay shales, diatomaceous and foraminiferal shales, and cherty shales. Sandstone beds nearly 50 feet thick occur at intervals in the upper unit, and two of these contain abundant petroleum residues. Some vul- canic ash is found in the upper unit. The Miocene age of the strata is based on study of the foraminiferal fauna. The Gallaway beds are 2,075 feet thick, and the Point Arena beds are 3,355 feet thick. They have been folded moderately into several small anticlines and synclincs that trend northwest, parallel to the San Andreas fault, and rest with angular unconformity on the strata of the Gualala series. The folded Miocene strata are beveled (photo 12), and are overlain with marked angular uncon- formity by marine sedimentary deposits of Pleistocene age. Covelo Area. Several small areas of sedimentary de- posits of Miocene age occur west of Covelo near small areas of rocks of late Late Cretaceous and Eocene age. Thev occur in separate fault blocks, however, and with the exception of one place where they are in fault contact with strata of late Late Cretaceous age, they are every- where in fault contact with rocks of the Franciscan for- mation. The deposits have been described by Clark (1940, p. 131-138), who correlated them with the Temblor formation (middle Miocene) of central California. 48 California Division of Mines (Bull. 179 Photo 12. Anticline in strata of Miocene age, near Point Arena. The strata of Miocene age consist mainly of sandstone and conglomerate, with some interbedded shale and a few beds of coal. Conglomerate is much more abundant than in the nearby areas of older Tertiary strata. Some of the coal has been mined on a small scale. In general the strata dip gently northeastward, and attain a thickness of more than 2,200 feet. A marine molluscan fauna of Miocene age is fairly abundant. According to Clark (1940, p. 134) the source of the sediment was partly the Franciscan group, and he interprets the strata to have been deposited under shallow-water, near-shore marine or estuarine conditions. Garberville Area. Marine deposits of Miocene and Pliocene age have been mapped as two elongate areas near Garberville by MacGinitie ( 1943, fig. 282) and Bailey (see pi. 1 ), and one near Piercv. Those of Miocene age have not been differentiated on the map (pi. 1) from the associated deposits of Pliocene age, but according to E. H. Bailey (oral communication, 1954) the Miocene deposits occur principally in the western of the two areas near Garberville. The strata of Miocene age consist of diatomaceous mudstone with interbeds of medium- grained sandstone, and are 900 to 1,200 feet thick. Ac- cording to MacGinitie they are correlative with the Santa Margarita formation of Late Miocene age (1943, p. 633). The Tertiary rocks of the Garberville area have been warped into northwest-trending synclines, and are in contact with rocks of the Franciscan formation and Yager formation along northwest-trending faults. The relation between the Miocene and Pliocene rocks is not known. Petrolia Area. Limestone float containing megafossils was found (locality no. 10, pi. 1; U. S. G. S. Cenozoic loc. no. 19054) at the mouth of LaRue Gulch in W'/ 2 sec. 6, T. 2 S., R. 2 W., about 3% miles west of Petrolia. The fossils were examined by the late Ralph Stewart and E. J. Trumbull of the U. S. Geological Survey who re- ported as follows: "Gastropods: Bathybembix? sp. cf. B.? Washingtoniana (Dall) Amauropsis? sp. cf. A. oregonensis (Dall) "Pelecypod: Volsella sp. V. cf. modiolus (Linne) "The gastropods were both originally described from the Em- pire formation (Pliocene?) at Coos Bay, Oregon. Volsella modi- olus is a circumboreal bivalve which has been found living as far south as San Pedro (Dall, W. H., 1921, U. S. Nat. Mus. Bull. 112, p. 21 as Modiolus modiolus). "Age: Miocene or Pliocene (?): No positive age determina- tion could be made on the basis of the fossils submitted. The fauna may belong to the Wildcat formation and may be in- dicative of a moderately deep-water (5-50 fathoms) environ- ment." Winter Formation of Maxson (1933). A few small, thin, patches of marine sediments occur at an altitude of approximately 2,000 feet on the western margin of the Klamath Mountains province in western Del Norte County. They occur at the general level of a dissected old-land surface, the Klamath peneplain, and are consid- ered by Diller (1902, p. 30, 32) to have been deposited during development of the Klamath peneplain. The rocks were named Wymer beds by Diller (1902, p. 32-33), and have since been re-named Wimer formation by Max- son (1933, p. 134, see Wilmarth, 1938, p. 2347). The formation consists of friable shales, sandstones and con- glomerates that weather yellowish and reddish in color. Maxson states that the beds are flat-lying and that the formation is a maximum of 150 feet in thickness (1933, p. 134). Imprints of mollusks and plants are abundant locally in the beds, and according to F. H. Knowlton (in Diller, 1902, p. 33) and Maxson (1933, p. 135) the fossils indicate that the deposits are late Aliocene in age. Diller considered the Wymer beds to be eastern ero- sional remnants of marine deposits exposed 10 to 15 miles westward at Point St. George (1902, p. 32); how- ever, the beds at Point St. George are now thought to be Pliocene in age (Allen and Baldwin, 1944). I960] Northern Coast Ranges and Klamath Mountains 49 In the Gasquet quadrangle. Cater and Wells (1954, p. 104-105) describe deposits of gravel that occur only at the same general altitude as the Wimer formation, and that till channels that have been cur into the Wimer and older formations. The gravels are poorly sorted, and include clay as well as boulders. Some of the pebbles and boulders arc fresh and hard, while others arc thoroughly weathered and crumble easily. Cater and Wells (1954) believe the gravels to have been deposited shortly after emergence of the Wimer formation, and that the gravels probably are late Miocene or early Pliocene in age. Gravels that arc similar to those described by Cater and Wells ( 1954) occur for 2 l / 2 miles along the broad crest of French Camp Ridge, about 8 miles northwest of Hoopa Valley, and at an altitude of approximately 3,000 feet. They are poorly sorted anil contain both fresh and thoroughly weathered cobbles. Diller (1902, p. 52-54) considered these gravels to have been deposited in an ancient bed of the Klamath River. Strata of Pliocene Age Marine sedimentary deposits of Pliocene age are widely distributed in the northern Coast Ranges, and form the greatest total area of exposure of Tertiary rocks. None is found in the Klamath Mountains province except for a few small patches along the extreme western margin in western Del Norte Count). Continental deposits of Plio- cene age, principally the Tehama formation, are wide- spread along the west side of Sacramento Valley, but as they are somewhat beyond the scope of this report the reader is referred to Anderson and Russell ( 1940). Southern Coastal Area. In southwestern Mendocino and northwestern Sonoma Counties, marine scdimentar\ deposits of Pliocene age (Peck, 1957) occur in a north- west-trending belt about 20 miles long and 4 miles wide along the east side of the San Andreas fault. C. G. Hig- gins has mapped these deposits (data incorporated in geologic map, pi. I) and described them (Higgins, 1957). The outcrops are erosional remnants of a formerly con- tinuous blanket that overlay much of the coastal belt of undivided sedimentary rocks with high angular un- conformity, and that has since been dissected by the South Fork of Ciualala River and its tributaries. The Pliocene strata consist dominantly of weakly consoli- dated, light-colored sandstones, with some conglomeratic and finer grained sediments, and a few thin layers of white tuff. The strata are as much as 200 feet in thick- ness, and have been only mildly warped and faulted. They appear to have been deposited on a shallow sub- marine terrace, and have since been uplifted to altitudes ranging from 500 to 1,700 feet above sea level (Higgins, 1957). A fossil molluscan fauna of Pliocene age indicates that the deposits are equivalent in age to the lowermost Merced formation of the San Francisco Peninsula or the upper Purisima formation of the Santa Cruz quadrangle (Peck, 1957). Wildcat Group of Ogle (1951). The name Wildcat series was given by Lawson (1894) to marine sedimen- tary deposits of Tertiary age in the Eel River Valley area of western Humboldt County. Ogle (1951) called it the Wildcat group. The deposits have been studied by manv geologists, and for a review ol the previous literature the reader is referred to Stewart and Stewart ( 1949, p. 174-185). The deposits were mapped and de- scribed in derail by Ogle (1953). Ogle's Wildcat group consists of weakly consolidated mudstone, siltstone, sandstone and conglomerate, and minor intcrbeds of limestone, tuff, and lignite. In the southern parr of the Fel River Valley area, the group has been subdivided into five formational units by Ogle (1953, p. 26-39), from oldest to youngest, the Pullen, Eel River, Rio Del, Scotia Bluffs and Carlotta formations. The three oldest formations consist dominantly of fine- grained sediments, whereas the two youngest formations consist dominantly of coarse-grained clastic sediments. In the Eel River Valley area the Wildcat strata arc a total of 12,000 feet thick. They dip gently to moderately, and in over-all view the structure is thought to be a broad syncline whose axis trends west-northwest. Minor anticlines on the limbs of the syncline plunge westerly (Ogle, 1953, p. 64). The base of the Wildcat group has not been seen, but it is thought to rest with marked angular unconformity on the Yager formation (Ogle, 1953, p. 26). Abundant fossils of a molluscan and foraminifcral fauna indicate the Wildcat group to be dominantly ma- rine deposits of Pliocene age. However, the oldest unit, the Pullen formation, may range in age to Late Miocene (Mohnian), and the youngest unit, the Carlotta forma- tion, is dominantly non-marine and may be as young as early Pleistocene (Ogle, 1953, p. 28, 38). The Wildcat group likely is of considerable submarine extent west of the Humboldt Bay area, judging from the westward ami northwestward structural trends of the formation and the bounding faults, and from the results of dredging off the coast. Hanna (1952, p. 333, 342, and 358, fig. 2) reports that numerous fragments of Wildcat strata containing fossils were dredged from depths of 80 to 120 fathoms as far as 30 miles out to sea west of Humboldt Bay, and that similar fossiliferous rocks w ere found southwest of Trinidad Head at 96 fathoms. It should be noted, however, that the 30-mile distance ap- pears erroneous, as the continental slope at a distance of 30 miles offshore from Humboldt Bay is at depths rang- ing from 400 to more than 1.00(1 fathoms according to the map of California, editon of 1953, U. S. Geological Survey. Depths of 120 fathoms or less appear to be no further than approximately 12 miles offshore from Hum- boldt Bay. During the present reconnaissance, mapping of the Eel River Valley area of the Wildcat group was extended southeastward into the Weott quadrangle (fig. 2). In addition, four small areas of Tertiary rocks that likely are correlative with the Wildcat group were found. Two of these arc in the Weott quadrangle. The other two are along the boundary between the Alderpoint and Hoaglin 50 California Division of .Mines [Bull. 179 quadrangles, but are too small to be shown on the geo- logic map (pi. 1 ). In the extended area of the Wildcat group fossils were collected (locality no. 14, pi. 1; U. S. G. S. Cenozoic loc. no. 19053) along Highway U. S. 101 in NW14 sec. 32, T. 1 N., R. 2 E., about l'/ 2 miles south of Pep- perwood in the northwestern part of the Weott quad- rangle. The fossils are from moderately dipping, friable mudstone that is thought to be of the Wildcat group. They were studied by E. J. Trumbull of the U. S. Geo- logical Survey, who reports as follows: "Gastropods: Ncptunea? sp. Gyrineum sp. cf. G. scotiaensis (Martin) "Pelecypod: Yoldia? sp. "Age: Pliocene (?). No positive age determination could be made on the basis of the fossils submitted. The fauna may belong to the Wildcat formation and may be indicative of a moderately deep-water (5-50 fathoms) environment." In the northeastern part of the Weott quadrangle, Tertiary sediments are exposed over an area of half a square mile along the county road between Bridgeville and Blocksburg in W'/ 2 sec. 30, T. 1 N., R. 4 E., and E'A sec. 25, T. 1 N., R. 3 W. The rocks are dominantly friable, medium-grained sandstones that are light bluish gray in color where unweathered. Fossils are abundant near the eastern limit of the area. Specimens collected from that locality (locality no. 15, pi. 1; U. S. G. S. Cenozoic loc. no. 19052) were studied by E. J. Trumbull, who reports as follows: "Gastropods: Cryptonatica sp. cf. C. clausa (Broderip and Sowerby) Unidentified naticids Nassarius? sp. "Pelecypods: Crvptomva? sp. cf. C. californica (Conrad) Volselh?'sp. Macoma? sp. cf. M. nasuta (Conrad) Chione (Securella) securis (Shumard) Solen? sp. Unidentified pelecypod "Age: Pliocene (?). No positive age determination could be made on the basis of the fossils submitted, but they may belong to the Wildcat formation and may indicate a moder- ately shallow-water (less than 5 fathoms) environment." The other small area of Tertiary rocks in the Weott quadrangle covers about a square mile on the northeast side of the Eel River east of AlcCann. It consists of mud- stone, sandstone and conglomerate, much of which has been sheared. The Tertiary rocks are surrounded by the Yager formation, and the contacts between the two seem likely to be faults. Fossils in pebblv sandstone collected in SE'/4NW l / 4 sec. 3, T. 2 S., R. 3 E. (locality no. 11, pi. 1; U. S. G. S. Cenozoic loc. no. 19051) were studied by E. J. Trumbull, who reports the following: "Gastropods: Calliostoma? sp. Unidentified trochid Unidentified calyptrid Thais? sp. Unidentified gastropod "Scaphopod: Ucntalium sp. "Pelecypods: Patinopecten? sp. Vertipecten? sp. Unidentified cardid "Age: Pliocene? No positive age determination could be made on the basis of the fossils submitted. The fauna may belong to the Wildcat formation, and may be indicative of a moder- ately deep-water (5-50 fathoms) environment." One of the two localities of Tertiary rock along the boundary between the Hoaglin and Alderpoint quad- rangles is approximately in EVz sec. 4, T. 4 S., R. 6 E., on the road from Kettenpom Peak to Blocksburg Ranger Station. The general area is one of highly sheared rocks of the Franciscan formation and small bodies of serpen- tinized ultramafic rock. The Tertiary rocks are exposed discontinuously in shallow road cuts for about 400 feet. They consist chiefly of weakly consolidated sandstones and conglomerate. The sandstones are light-buff where weathered, but are light-cream or pale bluish-gray where fresh. Bedding is obscure, but the strata appear to dip about 45 degrees to the southeast. Fossils were not found, but in general comparison with rocks seen elsewhere, the strata seem likely to be of Pliocene age. The other locality is about 4 miles north of the previ- ously described locality, and is along the road between Zenia and Alderpoint. It consists of several isolated areas of Tertiary strata that are exposed for widths of a few hundred feet at intervals between points 54 to 1 mile southwest of Zenia. The areas of Tertiary rocks appear to be fault blocks in a general area of sheared rocks of the Franciscan formation, and at one place the contact between the two is a nearly vertical fault. The Tertiary rocks consist of friable mudstone, sandstone and con- glomerate. The sandstones generally are light-buff where weathered, but pale bluish-gray or greenish-gray where fresh. The beds dip at low to moderate angles, generally eastward. Abundant fossil mollusks were seen at one exposure but were too poorly preserved to be specifi- cally identified. The fine-grained sediments (locality no. 12, pi. 1) contain radiolaria, sponge spicules, and diatoms of Pliocene age, similar to those found in samples from the Wildcat group in the northwestern part of the Weott quadrangle. Falor Formation of Manning and Ogle (1950). In the Blue Lake quadrangle (fig. 2) along the lower reaches of the Mad River, Tertiary rocks occur as a northwest- trending fault block in Franciscan rocks. The Tertiary rocks have been described as the Falor formation by Manning and Ogle (1950, p. 22-25), and are thought to be equivalent to part of Ogle's Wildcat group. They are chiefly marine detrital deposits, consisting mostly of gray- to buff-colored sandstone, shale and conglomerate, with a few interbeds of limestone and lignite. The strata range from 750 feet thick near Korbel, to 2,460 feet thick elsewhere. The upper 200 feet of the section near Korbel consists of red-brown clays and gravels that may be continental deposits. The beds of the Falor formation 1960] Northern Coasi Ranges and Klamath Mountains 51 dip about 20 degrees northeast. Fossil mollusks are abundant locally, and the) indicate the formation prob- ably is upper lower Pliocene and extends into lower middle Pliocene (Manning and Ogle, L950, p. 20-23). The detrital sediments are thought to have been derived from areas of the Franciscan formation and Kerr Ranch schist nearby. St. George Formation. In western Del Norte County, marine sedimentary deposits of Tertiary age were de- scribed by Oilier (1902, p. 31-35) as the Point St. George beds and the Crescent ( itv beds. They have since been included under the name St. George formation by Maxson (1933, p. 135). The St. George formation is exposed in a few small areas along the coast in the vicinity of Point St. George and Crescent City. It probably underlies much of the low, broad coastal terrace at the mouth of the Smith River, but is concealed by a thin veneer of Pleistocene and Recent deposits. The formation consists of weakly consolidated marine deposits, chiefly light gray and buff- colored sandstones and shales. The beds dip northeast- ward at low to moderate angles. A thickness of about 100 feet of the strata are exposed, but the maximum thickness of the formation is thought to be considerably greater (Maxson, 1933, p. 135). Some of the beds are abundantly fossiliferous. Oilier (1902, p. 32) considered the Point St. George beds to be Miocene in age and correlative with the Fmpire for- mation of coastal Oregon, based on faunal studies by W. II. Oall (in Oilier, 1902). On the same basis the Crescent City beds were thought to be largely Miocene, but in part Pliocene in age. The Empire formation has since been called Pliocene in age (Allen and Baldwin, 1944, p. 29-31), and on this basis the St. George forma- tion seems likely to be of Pliocene age as designated by Maxson (1933, p. 135). Cache Formation of Anderson (1936). Lacustrine and fluvial deposits crop out over an area of approxi- mately 40 square miles in the Coast Ranges east of Clear Lake. They were first described by Becker (1888, p. 219) as the Cache Lake beds, but later were renamed the Cache formation by Anderson ( 1936, p. 633). The de- posits are not thought to represent a former extension of present-day Clear Lake ( Anderson, 1936, p. 638). The most detailed studies of the Cache formation have been by Anderson (1938, p. 632-639) and Brice (1953, p. 30-34), and the following description is chiefly a sum- mary of their work. The Cache formation consists of a thick series of beds of weakly consolidated gravels, sands and silts. Some of the beds are calcareous, and thin beds of tuff arc found locally. Layers of basalt that form conspicuous tablelands in the area are considered to be interbedded with sedi- mentary rocks of the upper part of the Cache formation. The formation is remarkably thick, considering its mode of origin and seemingly small basin of deposition. Anderson (1936, p. 633) estimates a maximum thickness of at least 1,700 feet. Brice < 1953, p. 33) estimates a maxi- mum thickness of 6,500 feet, and states that at some localities he presumes to be near the edges of the basin of deposition, the formation is only a few hundred feet thick. Anderson (1936, p. 638) states that "the surface on which the Cache formation accumulated must have had considerable relief, judging from the marked differ- ences in thickness of the rocks underneath the inter- bedded basalt flow . . . ", thicknesses ranging from 100 feet to at least 1,700 feet. 1 he strata of the Cache formation have been folded mildly and generally dip at angles of less than 25 degrees. Within the map area the formation may be entirely in fault contact with older rocks, but nearby to the south it lies with marked angular unconformity on rocks of Eocene and older ages. Subsequent to folding and fault- ing, the formation was overlain by Recent lava flows in the map area, and by volcanic rocks of Pleistocene age in areas near Lower Lake to the south. The age of the formation is not accurately known. In- conclusive evidence of a late Pliocene or early Pleistocene age, based on freshwater invertebrate and fragmentary vertebrate fossils, has been summarized by Anderson (1936, p. 639). He tentatively regards the Cache forma- tion as early Pleistocene in age, but notes the marked lithologic similarity to the Tehama formation of late Pliocene age (Anderson, 1936, p. 639). The nearest ex- posures of the Tehama formation are in the Sacramento Valley approximately 10 miles east of the Cache for- mation. Volcanic Rocks of Tertiary Age Few areas of volcanic rocks of Tertiary age, other than those previously mentioned in association with chiefly sedimentary formations of Tertiary age, are found in the portion of the northern Coast Ranges and Klamath Mountains shown on the geologic map (pi. 1). In ad- jacent areas, however, volcanic rocks of 1 erriary age are relatively abundant. Some of these, principally the rocks of the Cascade Range east of Shasta Valley, are shown on the geologic map (pi. 1) as a matter of convenience in outlining the report area; they will not be described in detail. Basalt crops out in a small wedge-shaped area at the coast a few miles south of Point Arena, at the contact between the Gualala series and the Gallaway beds. The basalt has been mapped, and named Skooner Gulch basalt by Weaver (1943, p. 629-630, fig. 280). As described by Weaver, the basalt is 900 feet thick. Some of it shows flow and pillow structures, and some contains lens-like masses of tuffaceous sandstone. He interprets the basalt to be a submarine flow that lies unconformably on de- formed strata of the Gualala series, and as older than the adjacent. Gallaway beds. It is not clear whether Weaver (1943, compare the stratigraphic column, p. 630, with fig. 280, p. 631) considered the basalt to be entirely Ter- tiary in age or in part Cretaceous in age. If the strati- graphic relations described by Weaver are correct, and if, as suggested by Durham and Kirk (1950, p. 1537), 52 California Division of Mines [Bull. 179 the Gualala series is in part as young as Eocene, all of the Skooner Gulch basalt must be Tertiary in age. Volcanic rocks crop out approximately 1,000 feet along Rockpile Road in a general area of Franciscan rocks in the north-central part of the Skaggs Spring quadrangle, in E'/ 2 sec. 10, T. 10 N., R. 11 W. The area is too small to be shown on the geologic map (pi. 1). The rock is chiefly basalt with vesicles and pillow struc- ture, and may be an isolated remnant of the Sonoma group (Dickerson, 1922) of late Pliocene age. The Sonoma group has not been found north or west of this locality, but beyond the map area, to the east in the Healdsburg quadrangle (Gealey, 1951), and to the south- east nearly to San Francisco Bay (Weaver, 1949, and others), it covers large parts of Sonoma and Napa Counties. Quaternary Rocks Sedimentary and volcanic rocks of Quaternary age cover only a small percent of the northern Coast Ranges and Klamath Mountains area, although deposits of similar age are extensive in the provinces adjacent to the east. The older rocks, of Pleistocene age, are marine and con- tinental in origin and are chiefly exposed in terraces. The younger rocks, of Recent age, are continental in origin except for small areas of beach and dune sands along the coast. Volcanic rocks of both Pleistocene and Recent ages are prominent near Clear Lake in the northern Coast Ranges, but none are found in the Klamath Mountains. The pattern of distribution of the rocks of various origin indicates that the general configuration of the coastline has changed little since early Quaternary time. Marine Sedimentary Deposits. Marine deposits of sand and gravel of Pleistocene age occur in a narrow belt along the coast as a thin capping on wave-cut terraces. Since their deposition they have been elevated far above present-dav sea level and have been dissected deeply by Recent streams. Many of the remnants of these deposits are too small to be shown on the geologic map (pi. 1 ). The terraces occur at several different altitudes and usually are less than 3 miles distant from the coast. Along the coast of Sonoma and Mendocino Counties the terrace deposits appear to occur chiefly within two ranges in alti- tude, from 50 to 100 feet, and from 250 to 500 feet. East of the narrow belt of terrace gravels prominent flat sur- faces were seen on many of the principal ridges, mainly at altitudes ranging approximately from 1,000 to 2,000 feet, but these appeared generally devoid of Quaternary deposits. Lawson (1894, p. 246-247), however, studied the terraces in the vicinity of Fort Ross at the south end of the map area (pi. 1) in some detail; he states that wave- cut terraces occur at altitudes of 280, 350, 760, 1,1 SO, and 1,400 feet. The highest terrace on which he found evi- dence of wave action is 2 ! A miles east of Fort Ross at an altitude of 1,520 feet. Beach sands and gravels also were found at some of the highest of these altitudes. Lawson (1894, p. 246) considered a flat-topped ridge at an alti- tude of 1,600 feet east of Fort Ross, to be an erosional remnant of a widespread coastal plateau. The age rela- tions are not clear among the higher terrace deposits, the so-called plateau surfaces, and the mildly deformed blanket of marine sedimentary rocks of Pliocene age described by Higgins (1957). Further north, near the mouth of the Fel River, marine terrace gravels are found at an altitude of 900 feet, and may be equivalent in age to the Hookton formation; other terraces are numerous in the area, but they are capped by floodplain deposits of the Rohnerville and Hookton formations of Pleistocene age (Ogle, 1953, p. 63-64). The broad coastal plain in the vicinity of Cresent City is at an altitude of about 50 feet. It is an emerged marine terrace that appears to have been cut chiefly on deformed rocks of the St. George formation of Pliocene age. It is overlain by a thin veneer of the Battery formation (Max- son, 1933, p. 136), by beach and dune sands, and by alluvial debris from the Smith River. The Battery forma- tion consists of unconsolidated strata of Pleistocene age that are exposed on the southern part of the terrace. Olmsted (1956, p. 20-21) states that the formation con- sists of ". . . fine sand, silt and clay, and a basal 1-foot bed of pebble gravel. The thickness of the Battery aver- ages about 35 feet but locally is as much as 60 feet." Recent deposits of beach and dune sand are sparse. Most of the rugged coastline is faced by steep cliffs, and the beaches that fringe the cliffs arc narrow and short. Beach sands and associated dune sands are most abundant near the mouths of the principal rivers. Some of these deposits are of minor economic interest as a source for special purpose sands, for their heavy-mineral content such as chromite (Wells, Cater, and Rynearson, 1946, p. 74-76) and, to a lesser degree, gold and platinum (Maxson, 1933, p. 143) along the coast of Del Norte and northern Humboldt Counties. Continental Sedimentary Deposits. Fluvial and la- custrine deposits that range from Pleistocene to Recent in age occur chiefly in the few broad intermountain val- levs and along the coast of northern Humboldt County near the mouths of the Eel and Mad Rivers and Red- wood Creek. The older deposits are very mildly de- formed, and are exposed chiefly in terraces that have been cut by recent streams. They have been studied in most detail by Ogle (1953, p. 57-63) near the mouth of the Eel River where they are known as the Rohner- ville and Hookton fotmations. Fluvial deposits occur also on relatively small terraces that are perched along the courses of the major streams, at elevations ranging from a few feet to several hundred feet above the present streams. They are broadly correlative in age with the fluvial deposits of the intermountain valleys and coastal areas. Along the upper reaches of the Trinity River they include the auriferous gravels that have been referred to as gravels of the third cycle by Diller (1911, p. 26-28). Recent deposits of sand and gravel are sparse along many of the upper reaches of the streams, however, owing to the rampageous discharge and flushing action of the 19601 Northern Coasi Ranges vnd Klamath Mountains S3 ' i V ', • . > A * .' j ■,< t t y ■■-{-■ \f /./. Www* W-Mmik n h\ , s i j ( PHOTO 15. Strata of Pleistocene age exposed m .1 road cut on Route 2u cast of Calpclla. 1 he str.ir.i consist of silr, sandstone, .unl conglomerate, and dip 1_ NW. Note the erosional disconformity between the conglomerate and beds of silt and sandstone. streams during the rainy season. Glacial deposits have been found in some parts of the Klamath .Mountains, and to a smaller extent in the northern ("oast Ranges. The 1 lookton formation, as described by Ogle (1953, p. 57-63), consists of orange- or yellow-brown colored gravel, sand, silt, and clay, and may be as thick as 420 feet. The rocks arc mainly nonmarine, hut some may be cstuarine. The Rohnerville formation is similar in color to the Hookton, hut is mainly floodplain gravels and ranges from 10 to only 2> feet in thickness. Both forma- tions were deposited unconformably on the Wildcat group of Pliocene and earl) Pleistocene (?) age. The Hookton formation probably is middle and late Pleisto- cene. The Rohnerville formation is thought to be late Pleistocene, but younger in age than the Hookton. Both formations have been gently folded along the old struc- tural axes of the more highly deformed Wildcat group. Similar deposits near the mouth of Redwood Creek in the central part of the Orick quadrangle (fig. 2) have been mentioned by Rice ( 1953, p. 2779). The principal intermountain valleys that arc filled with appreciable quantities of sedimentary rocks of Quaternary age are in the northern Coast Ranges. The older of these rocks are herein considered to be of prob- able Pleistocene age, as they are exposed chiefly in high terraces, are weakly consolidated, and are mildly de- formed and faulted. However, fossils diagnostic of their age have not been found, and the possibility of a late Pliocene age for some of the rocks should not be dis- regarded. The strata consist mainly of gravel and sand, but include silt and clay, and appear to he fluvial and lacustrine' in origin (see Davis, 1933, p. 195). The higher terrace deposits generally arc remnants of a formerly more extensive and deeper valley fill. Along the Russian River, east of Ukiah, and between the East Fork of the Russian River and Redwood Valley 54 California Division of Mines [Bull. 179 east of Calpella (photo 13), the principal high terrace underlain by deposits of Quaternary age is at an altitude of 1,000 feet above sea level, and has been entrenched to a depth of about 400 feet. Deposits in Potter Valley are at a similar altitude but are entrenched less deeply. In- vestigations of the Coyote Dam site on the East Fork of the Russian River indicate the older valley fill to have been 1,000 feet thick (Treasher, 1955, p. 1666), that is, the old valley floor is 1,000 feet below the terrace level. The old valley floor must therefore be about at present- day sea level. Southeast of Willits in Little Lake Valley a thickness of more than 200 feet of sediments is exposed between the valley floor and the terrace level at an altitude of about 1,700 feet. According to Olmsted (1956, p. 86-87) the deposits that underlie the terrace consist of clay, diatomaceous shale, silt, sand, gravel, and conglomerate, with an estimated thickness of several thousand feet. The south end of Round Valley, near Covelo, has been cut to a depth of about 200 feet in mildly deformed beds of gravel, sand, and clay that are exposed at an altitude similar to those of Little Lake Valley, and the total depth of the valley fill is estimated by Olmsted (1956, p. 83) to exceed 1,000 feet. A widespread terrace at a general altitude of 1,500 feet along the west side of Clear Lake is underlain by uncon- solidated sands and gravels. The terrace level is about 200 feet higher than the recent valley fill and artificial level of Clear Lake. Nearby, about 4 miles southwest of Kel- seyville, deformed beds of weakly consolidated fine- grained sediments underlie a somewhat higher old-land surface, and may be older than the sediments that underlie the 1,500-foot terrace. An ancient valley surface appears to have developed at an altitude of about 2,300 feet in the vicinity of Lake Pillsbury. On the east side of the lake, weakly consolidated sands and gravels are exposed from the artificial 1,800-foot level of the lake to as high as 2,300 feet above sea level; on the west side of the lake the gravels cap a ridge, and the base of the terrace gravels is about 200 feet above the lake. Old alluvium covers much of an old-land surface west of Laytonville Valley. Bedrock crops out within the area of the old surface as low, subdued hills, and according to Olmsted (1956, p. 79) the alluvial cover between the hills probably is less than 50 feet thick in most places. A mile or two north of this old surface, a terrace at nearly the same altitude covers about two square miles along the southwest side of Tenmile Creek. It is underlain by unconsolidated sedi- ments, and has been entrenched to a depth of 200 feet by the creek and its tributaries. Recent alluvium covers most of Laytonville Vallev and is as much as 150 feet thick (Olmsted, 1956, p. 79). In the Klamath .Mountains province, areas of valley fill of Quaternary age generally are relatively small. The exceptions are Scott Valley, where alluvial fan deposits attain a probable thickness of 400 feet (Olmsted, 1956, p. 28-29), and Shasta Valley, adjacent on the east of the province, where broad areas are covered by glacial and alluvial deposits. The only other valleys of significant size in the Klamath Mountains are Weaverville, Hayfork, Hyampom, and Hoopa Valleys. Weaverville, Hayfork, and Hyampom Valleys are chiefly areas of rocks that are Tertiary in age, and alluvium of Quaternary age occurs only locally and as a thin veneer. Hoopa Valley is rela- tively narrow and consists chiefly of unconsolidated sands and gravels that underlie terraces at a succession of several levels; the principal high terrace is at an alti- tude of about 500 feet, approximately 200 feet above the Trinity River. According to Olmsted (1956, p. 56) individual terrace deposits along Hoopa Valley range in thickness from a thin edge to more than 35 feet. The bulk of the deposits of Quaternary age in the Klamath Mountains, with the exception of Scott Valley, occur as terraces in the valleys and on the canyon walls along the courses of the Smith, Klamath and Trinity Rivers and their tributaries, and as deposits in the stream beds. Some of the terrace deposits are as high as 400 feet above the present streams, and more than 100 feet thick. During the early days the terrace and stream gravels were mined extensively for placer gold. Owing to their economic interest they were studied along the upper reaches of the Trinity River by Diller (1911 and 1914a), who referred to them as auriferous gravels of the third cycle of erosion (Diller, 1911, p. 26-28). One deposit described by Diller (1911, p. 26-27) is a few miles south of Weaverville. It underlies a terrace 175 feet above the Trinity River. The upper 1 1 5 feet of the deposit is red- dish, poorly stratified clay, sand, and gravel. It is under- lain by 19 feet of blue gravels, sand, and clay, with a thin carbonaceous layer near the base. Fossil bones and shells are associated with the carbonaceous layer, and indicate a Pleistocene age. The bones are of mammoths, deer, and ground sloths, while the shells are similar to those of living fresh-water species (Diller, 1911, p. 27). Terrace deposits along the South Fork of the Salmon River have been described in detail by Hershey (1903d) in an at- tempt to relate the deposits to several glacial stages. Those along the Smith River have been described by Cater and Wells, (1954, p. 105-106, 124). Glacial Deposits. Alpine glaciers formed at many places in the Klamath Mountains and in an adjacent small area of the northern Coast Ranges, but none is now present. Evidence of the former presence of glaciers is at most places topographic, but deposits of glacial debris are found at some places. In many of the higher moun- tains, cirques, bedrock basins, marshy meadows, and U-shaped vallevs are common features of the landscape (photo 14) (see Davis, 1933, p. 215, figs. 19, 20; Hinds, 1952, p. 139-142, fig. 100). Small lakes associated with these features are abundant, generally at altitudes above 6,000 feet in the eastern part of the province, and at altitudes above 5,000 feet along the boundary between Siskiyou and Del Norte Counties in the western part. Diller (1902, p. 58) notes that on the northeast slopes of both North Yolla Bolly Mountain at the south end of the Klamath Mountains, and South Yolla Bollv Moun- 1960] Northern Coast Ranges and Klamath Mountains 55 Photo 14. Aerial view of the Trinity Alps, looking northwest toward the glaciated, upper reaches of Canyon Creek in the northeastern part of the Helena quadrangle. Arrow points to Thompson Peak (altitude 9,002 feet), rlie highest point in the Klamath Mountains province. Photo GS-OAD, S-SO, September 19S3. tain nearby in the northern Coast Ranges, ". . . there were formerly glaciers a number of miles in extent which have left well-defined records in striated and polished nicks and ground moraines, with small lakes and mead- ows above terminal embankments." Southward along the high divide to near Anthony Peak, marshy meadows and vague cirque-like features suggestive of former glaciation were seen during the present reconnaissance. According to Holway (1914), evidence of former glaciation, such as striae on bedrock, small cirques, and moraines, is seen as far south as Snow Mountain along the high divide east of Lake Pillsburj . Detailed descriptions of some of the glacial features of the eastern part of Klamath Mountains have been given by Hcrshey (190(1, 1903a, 1903c, 1903d), The glaciers ranged from 2 to 15 miles in length, from one-fourth to a mile in width, and from 500 to 1,500 feet in thickness (Hershev, 1900, p. 45-49). He considered the latest stage of glaciation to be Wisconsin in age, an intermediate stage to be low an, and the earliest to be at least as old as lllinoian and perhaps as old as Kansan, the three stages corresponding to high, intermediate and low terrace de- posits along the South Fork of Salmon River (Hershev, 1903d, p. 453-454). At one locality, Hershev (1903a, p. 140) found fossil tusks of a mammoth embedded in an old soil formed at the surface of a glacial till. Volcanic Rocks. Volcanic flows, tuff beds, and cones arc conspicuous features in the vicinity of Clear Lake in the northern Coast Ranges, and have been described by Becker (1888), Anderson (1936), and Brice (1953). None have been found in the Klamath Mountains, al- though they are abundant in the Cascade Ranges adja- cent to the east. During the present reconnaissance the volcanic rocks of the Clear Lake area were not studied, and the following brief description is based on detailed work by Anderson (1936). .Mount Konocti, the principal volcanic landmark of the area, is an eroded multiple volcano on the west side of Clear Lake, and rises to an altitude of 2,800 feet above the level of the lake. It consists chiefly of a series of rhyo- dacitic flows that is underlain by rhyolitic pyfoclastic rocks. South and southeast of Mount Konocti, dacite and rhyolitic obsidian that are somewhat older cover an area of about 12 square miles. They probably are middle or late Pleistocene in age if the Cache formation is as young as early Pleistocene, judging from the absence of frag- ments of these rocks in the Cache formation, and from their stagjc of erosion. East of Clear Lake, rhyodacite that may be related to that of Mount Konocti, although per- haps nor extruded from the same vent, rests on deformed Cache formation. Recent lava flows and cinder cones, perhaps no older than a few thousand years, occur principally on the east 56 California Division of Mines Bull. 179 Photo 15. Debris flow in area of Franciscan formation. View looking southwest from near Mendocino Pass, about 3 miles south of Anthony Peak. side of Clear Lake. They are largely andesites and basalts. At some places, notably Sulphur Bank, they have been altered greatly by solfataric action, and have been ex- ploited for their sulfur and quicksilver content. Landslide Deposits. Landslides are striking and abun- dant features in much of northwestern California, partic- ularly in the Coast Ranges. They are most common and widespread throughout the central belt of Franciscan formation where they are perhaps the foremost mode of degradation of the landscape. Although many of the landslides are measurable in terms of square miles, few are shown on the geologic map (pi. 1). Most of the landslides of the central belt of Franciscan formation appear to be debris flows (photo 15) rather than rotational slump blocks, and the debris generally consists of sheared and jumbled masses of graywacke, shale, greenstone, chert, glaucophane schist and serpen- tine. Many of these debris flows are characterized by grassy slopes that are nearly devoid of trees and brush. At places they occur along broad northwest-trending belts, and some of these belts can be traced many miles by means of the grassy slopes through terrain which otherwise is covered by brush and trees. These belts seem likely to be the traces of broad shear zones, owing to their linearity, the generally sheared character of the debris, and the presence of glaucophane schist and ser- pentine. Intrusive Rocks Granitic Rocks The term granitic rocks is used in this report as a con- venience in referring to plutonic crystalline rocks that range chiefly from diorite to granodiorite in composi- tion; true granite occurs at relatively few places. The granitic rocks are exposed over many hundreds of square miles in the Klamath Mountains province. In the north- ern Coast Ranges, granitic rocks are known only in two small areas a few acres in extent, but in the central and southern Coast Ranges granitic rocks crop out over large areas. Both areas of granitic rocks in the northern Coast Ranges are too small to be shown on the geologic map (pl. 1). In the Klamath Mountains of California the granitic rocks are widely distributed, and are found within all of the principal areas of stratified rocks of pre-Cretaceous age. In the southern half of the province the granitic rocks occur in two rudely defined belts that reflect the Klamath Mountains arc. The eastern belt of granitic rocks includes the Shasta Bally batholith at the southern end as well as other batholiths and smaller plutons northward along the central metamorphic belt, the eastern Paleozoic belt, and areas of ultramafic intrusives. The western belt of granitic rocks is chiefly in the western Paleozoic and Triassic belt. The largest body of granitic rocks of the western belt extends northwesterly from Hayfork Valley about 50 miles, and is herein referred to as the Ironside Mountain batholith for its exposure on a mountain of that name in the southwestern part of the Ironside Moun- tain quadrangle (fig. 2). The Ironside Mountain batho- lith is remarkably elongate and is the largest single area of granitic rocks exposed in the Klamath Mountains province. Other bodies of granitic rock included in the I960] Nor i in kn C< Ranges vnd Klamath Mountains ^ _ w estern belt are several plutons southeast of Hayfork Valley, as well as several relatively small elongate plutons to the west along the east side of the belt of South Fork Mountain schist. The granitic rocks of the western belt are chiefly hornblende diorite, whereas those of the eastern belt arc chiefly quartz diorite and granodiorite. The rocks of the western belt have not been described in the literature. but those of the eastern belt have been described in some detail bv Hinds ( 1934, p. 182-192, and 1935, p. 336-354), Kinkel, Hall, and Albers I 1956), and Gay (1949). In the northern half of the Klamath Mountains of Cali- fornia the granitic rocks are not amenable to subdivi- sion into two belts. Maxson (1933, p. 128-129, 131-134, and pi. 4) described the principal areas of granitic rocks in eastern Del Xortc and western Siskiyou Counties as the Siskiyou granodiorite and the subordinate Preston hornblende diorite. The name Wooley Creek batholith is herein applied to the area of granitic rock that is drained largely by Wooley Creek and that covers much of the Marble Mountains wilderness area in southwestern Siskiyou County. This batholith consists largelj of quartz diorite that is rich in hornblende and biotite. Many large boulders of an unusual garnet-bearing facies of the quartz diorite were seen along Elk Creek in E'/2 sec. 32, T. 15 N., R. 8 I-".. The boulders consist of medium-grained, hornblende-biotite-rich diorirc with euhedral crystals of reddish-brown garnet approximately one inch in diam- eter distributed throughout. On the geologic map (pi. 1) the Wooley Creek batholith is shown as a solid mass of granitic rocks, and it appears to be nearly as large as the Ironside Mountain batholith. However, much of the cen- tral area of the batholith was not traversed timing the reconnaissance, and the outline of the batholith, particu- larly near the upper reaches of Wooley Creek, is poorly known. In the northeastern part of the Seiad 30-minute quadrangle the granitic rocks arc quartz diorite and gran- odiorite (Ryncarson and Smith, 1940, p. 285-286, 287). Further east, in the northern part of the Yrcka 30-minute quadrangle, the prevailing granitic rocks were mapped as diorite and granodiorite (Avcrill, 1931, plate in pocket). Granodiorite intrudes diorite at several widespread lo- calities in the Klamath Mountains province. This relation, in addition to other admittedly inconclusive data, has been considered by Hinds (1932, p. 406-407, and 1934, p. 186) and Maxson (1933, p. 128-129) to indicate two distinct and w idely spaced periods of intrusion of gra- nitic rocks, the diorirc being emplaced during the Late Paleozoic, and the quartz diorite and granodiorite during the Late Jurassic. They describe exposures where the granodiorite or related rocks intrude diorite, and accord- ing to Hinds the diorite does not intrude rocks younger than the Bragdon formation of Mississippian age. How- ever, in other parts of the Klamath Mountains province, in Oregon as well as in California, thorite intrudes rocks as young as the Applcgate group of Triassic(r) age (Wells, 1955) and the Galice formation of Late Jurassic- age (Cater and Wells, 1954, p. 99; Wells, Hotz, and Cater, 1949). "Hie diorite presumably was emplaced dur- ing the same general period as the more fclsic intrusive rocks, during Late Jurassic or Cretaceous time. The age of the quartz diorite and the related more fclsic rocks has been argued by many geologists, w ith respect both to field relations observed in the Klamath Mountains province and by comparison to the Sierra Nevada batholith with which the granitic rocks of the Klamath region have commonly been related through broad speculation. The principal arguments have been summarized by Hinds (1934, p. 182-184). The lower age limit of the so-called younger granitic rocks of the Klamath Mountains province has been based previously (Hinds, 19H, p. 189) on intrusion of the Potem formation of Middle Jurassic age (Diller, 1906). How ever, it appears that the lower limit can be placed in the Late Jurassic on the basis of relations observed elsewhere in the province. In the Gasquet quadrangle, according to Cater and Wells (1954, p. 92-104), the Galice formation of middle Late Jurassic (late Oxfordian to middle Kimmeridgian) age is intruded by ultramafic rocks that in turn arc intruded by diorite, as well as by dikes of quartz thorite that are ". . . thought to be highly silicic differentiate of the main hornblende diorite body . . .". In the Kerby quadrangle, Oregon, the Calice and Dothan formations are intruded by a large body of hornblende diorite and related but more felsic rocks (Wells, Hotz, and Cater, 1949). Granitic rocks are overlain by gently-dipping strata of Cretaceous age at two general localities along the eastern border of the Klamath Mountains province. In Califor- nia and Oregon, near their common boundary north of Shasta Valley, the Hornbrook formation (Peck, Imlay, and Popenoe, 1956) of Late Cretaceous age lies on the stripped and eroded surface of a quartz diorite batholith. Strata of Early Cretaceous age lie similarly on the Shasta Ball) batholith southwest of Redding, and with high angular unconformity on the strata of pre-Latc Jurassic (middle Tithonian) age that are intruded by the granitic rocks. The strata that overlie the Shasta Bally batholith are reported to range from Valanginian to Hauterivian in age (Hinds, 1934, p. 189-190), and pebbles of quartz diorite thought to be derived from the Shasta Bally batholith or similar intrusive bodies are found in nearby strata as old as basal Paskenta (Hinds, 1934, p. 190). However, doubt has been cast that the Shasta Bally batholith is overlain by strata older than lowermost Horsetown (see Murphy, 1956. p. 2102-2105. fig. 4). The Knoxvillc formation is critical in dating precisely the emplacement of the Shasta Bally batholith. Hinds (1934, p. 191) notes the likelihood of the period of granitic intrusion being pre-Knoxville formation in aye if Knoxvillc strata overlie the strata of the Klamath Mountains province. This relation is reported by Ander- son (1945, p. 926-927). Viewed more broadly, however, the emplacement of the Shasta Bally batholith must in- deed pre-date the Knoxville formation, as strata of the Shasta series overlie the .Shasta Bally batholith vv ith ero- 58 California Division of Mines [Bull. 179 sional unconformity, and as the Shasta series is generally conformable with the Knoxville in a long belt that ex- tends from near latitude 40 degrees southward to near Wilbur Springs. The writer would expect to find a marked angular unconformity between the Knoxville formation and the Shasta series, if the Shasta Bally batho- lith had been emplaced after the deposition of the Knox- ville formation. If the granitic rocks of the Klamath Mountains province be considered to have been emplaced during a single period, the period would seem most likely to be post-Galice formation (late Oxfordian to middle Kimmeridgian) and pre-Knoxville formation (middle Tithonian). The two known localities of granitic rocks in the northern Coast Ranges are not shown on the geologic map (pi. 1), as neither of them appear to be more than a few acres in extent. One of the localities is in the northern part of the Eureka quadrangle, in SE'/jNW 1 / sec. 8, T. 6 N., R. 1 E., about a quarter of a mile north of the Mad River and a few hundred feet east of High- way 101, where large blocks of medium-grained syenite occur on a brush-covered hillside. The blocks are as much as 15 feet long, and once were quarried on a small scale for tombstones. Higher on the hillside, weakly con- solidated mudstone, sandstone, and conglomerate are ex- posed in a small area, and the conglomerate contains abundant pebbles and cobbles of granitic rock. It is not clear whether the large blocks of syenite came from an intrusive body nearby, or whether they are unusually large blocks from the weakly consolidated conglomerate. Ultramafic Rocks Ultramafic rocks are abundant in the northern Coast Ranges and Klamath Mountains provinces. Peridotite is the prevailing type of ultramafic rock, but dunite is im- portant locally. Pyroxenite and hornblendite are rela- tively uncommon. Small bodies of gabbroic and diabasic rocks are widely associated with the ultramafic rocks, and are generally thought to be related genetically. Most of the ultramafic rock has been altered to serpentine to a considerable extent, and indeed is commonly referred to as "serpentine" by field geologist and human alike. The peridotite ranges in color from green to nearly black where fresh, and brown where weathered. It com- monly is coarse grained, and the coarse-grained texture remains evident even in many areas where the rock has been altered almost completely to serpentine. Soil de- rived from the peridotite and other ultramafic rocks commonly is red-brown in color, and generally supports only brush and a sparse growth of timber. The ultramafic rocks generally occur as rudely tabu- lar bodies. Some have been considered to be sills, whereas others occur along fault zones. Generally they are highly sheared. Some are thought to have intruded in a molten state, but others, according to some geologists, may have been emplaced by so-called cold or plastic intrusion (see Taliaferro, 1943, p. 202-206). Commonly the contact between the ultramafic and adjacent rock is not exposed sufficiently to permit direct observation as to whether it is one of intrusion or faulting. Because of probable structural dislocation of many of the bodies of ultramafic rock, the age or ages of intrusion are not readily apparent. The ultramafic rocks of the Klamath Mountains may be of a different age from those of the Coast Ranges, and even those within a single prov- ince may not be all of one general age. In the Klamath Mountains, ultramafic rock occurs as sill-like bodies in the Applegate group, and intrudes the Galice formation (Wells and Cater, 1950, p. 81). Maxson (1933, p. 131 and fig. 7) notes that the ultramafic rock intrudes the Galice formation, and is in turn intruded by, and occurs as xenoliths in, Siskiyou granodiorite. Southwest of Red- ding, strata of the Horsetown formation of late Early Cretaceous age overlie a belt of ultramafic rocks ad- jacent to the west side of the Shasta Bally batholith. Owing to the broadly conformable relation of the Knox- ville and Horsetown formations, the ultramafic rock overlain by the Horsetown would seem most likely to be pre-Knoxville in age. Thus, if the ultramafic rocks southwest of Redding are the same age as those that in- trude the Galice, thev must have been emplaced between the middle Kimmeridgian and middle Tithonian stages of the Late Jurassic. The available data suggest that the ultramafic and granitic rocks of the Klamath Mountains were emplaced during the same general interval of time, the ultramafic rocks preceding the granitic rocks. In the northern Coast Ranges, ultramafic rocks are widespread throughout the Franciscan rocks of the cen- tral belt. At most places their relation to adjacent rocks has not been proved, but at some places they doubtless are intrusive. As the Franciscan rocks, however, may be restricted to the Late Jurassic in age, or may range from Late Jurassic to early Late Cretaceous, the age of the ultramafic intrusion is not closely known. Near Wilbur Springs and Knoxville, thick stubby lenses of sedimentary serpentine occur in the Knoxville and Paskenta forma- tions (Averitt, 1945, p. 73-74, and fig. 2; Taliaferro, 1943, p. 206-207); these presumably represent submarine land- slides from nearby serpentine bodies that were exposed during the Late Jurassic and earliest Cretaceous. Ac- cording to Taliaferro (1943, p. 202-205) the Knoxville formation is intruded by ultramafic rocks. STRUCTURE The structure of northwestern California is complex, and is not amenable to detailed description and interpre- tation on the basis of brief reconnaissance such as the present study. Undoubtedly the area has been mobile throughout much of the time from the Paleozoic to the present. Owing to the resulting structural complexities and to the close lithologic similarities and generally poor exposures of many of the formational units, the broad structural relations are not accurately known even in those few quadrangles that have been studied in com- parative detail by other workers. The situation is similar in adjacent areas from which data might be extrapolated, such as the northern continuation of the Klamath Moun- I960! Northern Coast Ranges and Klamath Mountains 59 tains in southwestern Oregon and the southern continu- ation dt' the northern Coast Ranges to the San Francisco Bay area. The pattern of the lifliic units shown on the geologic map (pi. 1) may he a clue to the structure of the area, hut a clear knowledge of the structure of north- western California must await painstaking study in the field. In both provinces, the strata most commonly dip east- ward. Faults in the northern Coast Ranges are generally at a high angle and are part of the northwest-trending San Andreas system of dominantly strike-slip and high- angle faults. Some of these faults, however, doubtless have a significant vertical component, as shown by ver- tical offset of Tertiary ami Pleistocene strata, and may be chief!) dip-slip. The dominant structural elements of the Klamath .Mountains province appear to be a scries of concentric moderate to high-angle reverse faults over which the rocks of the province were thrust southwest- ward. The boundaries between the Klamath .Mountains and the Coast Ranges, and between the Coast Ranges and the Sacramento Valley, doubtless are major tectonic features of the Pacific Coast region, but they have been given only scant attention by geologists. A small segment of the San Andreas fault, another tectonic feature of great magnitude, is in the southwestern part of the map area, beyond which to the northwest it is covered by coastal water. It is better known than the province boundary structures, as it has been studied much in central and southern California. The province boundary between the Klamath .Moun- tains and the Coast Ranges was first drawn by Oilier (1894b, pi. 40), and later was modified (Diller, 1921, lig. 1). Diller (1902, p. 9-10) defined the boundary on the basis that the Klamath Mountains ". . . are composed largely of sedimentary and igneous rocks, similar to those of the Sierra Nevada. . . ." and that the drainage of the Klamath .Mountains, in contrast to the Coast Ranges, is transverse rather than in general parallel to the strike of the rocks. However, the two features that form a basis for drawing a boundary do not coincide exactly, and Diller appears rather clearly to have drawn much of the boundary in favor of lithology and geomorphic history rather than drainage. Along the South Pork Mountains, for example, Diller drew the boundary on the southwest side to include the South Fork Mountain schist in the Klamath Mountains province, despite the fact that the South Pork of the Trinity River on the northeast side of the ridge is parallel not only to the strike of the rocks bur to the principal rivers of the Coast Ranges. On the other hand, in the western parr of the Klamath .Moun- tains of Oregon Diller included large areas of rocks equivalent to those of the Sacramento Valley sequence, that is, rocks that are not common to the Sierra Nevada. Northwesterly from the South fork Mountains, the boundary line of Diller (1921, fig. 1) is along Redwood Creek, and thereby includes in the Coast Ranges the Red- wood Mountain belt of schist although it is similar to the Si Miih I'oik Mountain schist of the Klamath Mountains. Along the same interval it includes in the Klamath Moun- tains a belt of rocks that appear to be related to the Franciscan formation rather than to the Galice or older formations of the Klamath .Mountains. Some geologists (for example see Taliaferro and Hudson, 1943, p. 219) consider the boundary to intersect the coastline about 6 miles southwest of Orick, thus including the Redwood Mountain belt of schist within the Klamath Mountains province, but excluding the smaller area of schist to the west. The southern extremity of the Klamath Mountains province of Diller is a lobe that extends southward slightly beyond the latitude of Paskenta. The boundary here may have been drawn to include within the Klamath Mountains province several high peaks such as Ovenlid, South Yolla Polly, Harvey, Sugarloaf, Hammerhorn, and Anthony, some above 7,000 feet in altitude, rather than on the basis of lithology. Or perhaps Diller did not con- sider that the rocks, south of the southeast-trending belt of schists that underlie North Yolla Bolly Mountain, are Franciscan rather than formations that are generally con- sidered to constitute the Klamath Mountains. The boundary line between the Klamath Mountains and the Coast Ranges as drawn by the writer (see fig. 1) more consistently outlines the two major groups of for- mational units of northwestern California. In addition it more clearly reflects the structural and lithic grain of the Klamath Mountains arc. The boundary excludes from the Klamath Mountains the two areas of schist that are isolated in an area w hich otherwise is characteristic of the Coast Ranges. The boundary is along the southwest- ern slope of a prominent high ridge that is nearly con- tinuous from the Oregon border to the Sacramento Val- ley, a distance of approximately 150 miles. The ridge has been notched deeply by the Klamath and Smith Rivers on their courses to the sea. Names applied to various intervals from northwest to southeast along the ridge include, among others, Rattlesnake Mountain, Red Mountain, Blue Creek Mountain Ridge, Pine Ridge, In- dian Field Ridge, South Fork Mountains, North Yolla Bolly Mountain, ami Tomhead .Mountain. North of the notch cut by the Klamath River, much of the ridge is a belt of ultramalic rock, but south of the Klamath River the ridge is chiefly schist. As the boundary is drawn, the formational units of the Klamath Mountains province are of late Jurassic (Kimmcridgian) and older ages, with the exception of a few small patches of younger rocks, and, with the same exception, have been intruded by sig- nificant quantities of granitic rocks. The formational units of the northern (oast Ranges of California, with the exception of two isolated areas of schist that may be related to the schist of South Fork Mountain, are all thought to be younger than Kimmcridgian in age, and generally arc not intruded by granitic rocks. The boundary between the Klamath Mountains prov- ince and the Coast Ranges has long been considered to be a fault along which the schists of South Fork .Mountain 60 California Division of Mines [Bull. 179 have been thrust southwestward over the rocks of the Coast Ranges. The origin of this concept has been attrib- uted to O. H. Hershey and others by Diller (1915, p. 52), and although the concept has gained wide recogni- tion (Fenneman, 1931, p. 469-470; King and others, 1944) the writer can find little record of its having been substantiated by conclusive data. Taliaferro and Hudson (1943, p. 219), however, state that the boundary is a thrust fault that dips northeast 40° to 45° near the south- east end of the South Fork Mountains. During the pres- ent reconnaissance, nearly the entire length of the boundary along the southwest slope of the South Fork Mountains and related ridges was seen to be mantled by landslide debris, and the contact between the rocks of the two provinces generally is concealed. Marked large- scale irregularities in the contact were not seen at the various notches along the ridge where one might expect them to be if the contact is a low-angle reverse fault. The fault seems most likely to be steep, judging from the apparent uniformity of the trend of the boundary for a distance of more than 100 miles from south-central Trin- ity County to near the Oregon border. The two belts of schist west of the boundary of the Klamath Mountains, isolated from the Klamath Moun- tains by presumably younger rocks of the Coast Ranges, are most readily explained by means of a series of alter- nate normal and reverse faults that trend nearly parallel to the boundary fault. The western boundary of each belt of schist appears to be a reverse fault, the schist being thrust westward over adjacent rocks of the Fran- ciscan formation. Taliaferro and Hudson (1943, p. 219) consider the western contact of the principal isolated belt of schist to be a northward continuation of the boundary thrust of the South Fork Mountains, and to dip steeply to the northeast. According to S. J. Rice (oral communi- cation, 1955) the contact between the principal belt of schist and the Franciscan formation to the west is well exposed in the east-central part of the Trinidad quad- rangle (fig. 2), and is a fault that dips about 60° NE. He considers the small area of schist near Trinidad to be thrust westward over the Franciscan formation, but to be in contact with the upthrown Franciscan formation to the east along a normal fault. Although the pattern of distribution of the belts of schist bounded on the west by reverse faults is most easily explained if the eastern boundaries of the schist belts are considered to be normal faults. Manning and Ogle (1950, p. 27) state that in the Blue Lake quadrangle the Franciscan rocks have been thrust westward over schist along the east side of the Redwood Mountain belt. The southern boundary of the Klamath Mountains province is along the base of the southern slope of a bold ridge of schist that includes North Yolla Bolly Mountain and Tomhead Mountain. The ridge trends about N. 65° W., diverging sharply from the N. 30° W. trend of the South Fork Mountains. The boundary was crossed at only two places during the present reconnaissance, as the area is remote and access is difficult. Judging largely from inspection of aerial photographs, the boundary seems most likely to be a vertical or high-angle fault. Transverse faults in adjacent provinces are aligned with the southern boundary of the Klamath Mountains. One is nearby to the east in the Sacramento Valley province, where strata of Late Jurassic and Cretaceous ages are offset with an apparent left-lateral displacement of several miles. To the northwest, in the Eel River Valley area of western Humboldt County, the faults chiefly trend nearly west, and according to Ogle (1953, pi. 2) they are high-angle reverse faults. The area south of the Eel River Valley area, to the Mattole River, is one of considerable structural complexity. The northern part of this area has been described by Ogle (1953, p. 22-24) as the False Cape shear zone. On the geologic map (pi. 1 ) the area is shown as chiefly uppermost Cretaceous rocks, but, as noted by Ogle (1953, p. 22-24), it includes complexly in-folded and in-faulted blocks of Franciscan and Tertiary rocks. The axes of at least some of the in- folds trend westward (Hoots, 1928) parallel to the structural axes of the Eel River Valley area. Thrust faults likely are present, as a hole drilled for oil is re- ported to have intersected rocks of Tertiary age after penetrating older rocks to a depth of 4,000 feet. The Gorda submarine escarpment (pi. 1) is another transverse structure, and although it is somewhat south of the line of the southern boundary of the Klamath Mountains province, it appears likely to be related. The Gorda escarpment is a north-facing scarp that extends west from Cape Mendocino. Here the base of the steep continental slope ranges approximately between 1,000 and 1,600 fathoms, and along the escarpment it is offset in a manner that might be ascribed to right-lateral faulting with an apparent displacement of several tens of miles. The structure continues due west for at least 1,400 miles, and has been referred to as the Mendocino escarpment (Menard, 1955). West of the westernmost projection of the continental slope, however, the escarp- ment faces south rather than north. It ranges from 3,300 to 10,500 feet high, and north of the escarpment ". . . the sea floor for hundreds of thousands of square miles is about half a mile higher than the floor to the south." (Menard, 1955, p. 36-37.) The strata of the northern Coast Ranges have been folded and faulted, and as the resulting structure is of a complexity that does not lend itself to solution by re- connaissance, the writer can add little to the knowledge of the structure of the area. The province includes a great abundance of faults that in general trend northwest. Near the latitude of Cape Mendocino the northwest trend is intersected by more westerly, transverse struc- tures that have already been described. Folds in the strata appear fairly broad, and at the few places where the trends of the axes of the folds are known, the trends generally are nearly parallel to the trend of the faults. Some of the fold axes in the Gualala series west of the San Andreas fault trend westward at a large angle to the fault. The strata most commonly dip gently to 19601 Northern Coasi Ranges \m> Klamath Mountains 61 steeplv northeast, but it is oversimplification to state that the structure of the northern Coast Ranges is merely one of fault blocks that are tilted northeast. Only the most important faults are shown on the geo logic map (pi. 1). Faults are abundant, however, par- ticularly in the central belt areas of interbedded detrital sedimentary rocks, chert, and volcanic rocks. Not only are these rocks sheared and dislocated, hut small bodies oi glaucophane schist and highly sheared lenses ol serpen- tine occur in them along fault lines. Additional evidence of faulting that is particularly common within the Fran- ciscan formation of the central belt is the abundance of so-called faultline ridges, saddles, valleys, sag ponds, and landslides. All of the major intermountain valleys ol the northern Coast Ranges are cither entirely or partly within areas of the Franciscan formation, and they have been formed at least partly by faulting. A fault extending N. 3~ W. from Fort Ross to a point 5 miles northeast of Point Arena is the northernmost ex- posed segment of the San Andreas fault. Northward the fault continues to sea. Southward the fault also is covered by coastal water, but the same fault, presumably, has been projected across narrow exposures of land near Bodega Head and Tomalcs Bay and thence projected to the west coast of the San Francisco Peninsula. Southward from the San Francisco Peninsula the San Andreas fault has been traced approximately 600 miles, and con- sidered to be a right-lateral fault with perhaps great strike-slip displacement. Along the central and southern Coast Ranges of California it is a boundary between the Franciscan formation to the east, and granitic and meta- morphic rocks to the west. Tertiary rocks also are abundant west of the fault. The presence of granitic rocks west of the fault at Bodega Head and Tomalcs Bay, as well as at Cordell Bank about 20 miles offshore from Point Rexes (Hanna, 1952, p. 364; Chesterman, 1952, p. 360-361 ). suggests that the fault projected to near Point Arena is indeed the northern continuation of the San Andreas fault, even though granitic rocks are not found west of the fault between Fort Ross and Point Arena. The fault between Fort Ross and Point Arena separates the Gualala series of late Fate Cretaceous and early Tertiary ages to the west, from strata to the east that arc of early Fare Cretaceous and perhaps older ages. Shortly after the well-known San Francisco earth- quake of 1906, scarps and other evidence of movement along the San Andreas fault could be traced southward from Point Arena to Fort Ross, across Bodega I lead and at the southeast end of Tomales Bay, and on the San Francisco Peninsula and southward (Lawson and others, 1908, p. 53-151). Similar effects of movement along a fault were seen at Point Delgada and northwest toward Petrolia, and these xvere considered to indicate the con- tinuation of the San Andreas fault beyond Point Arena (Lawson and others, 1908, Atlas, map no. 1; King and others, 1944). The fault thus projected beyond Point Arena would deviate markedly from its otherwise re- markably uniform northwestward trend where it is ac- curately known south of Point Arena, and would follow the coastline in a northerly direction in order to resume a northwestward trend from Point Delgada toward Petrolia. Shepard and Emen I 1941, p. 38-39, and fig. 1m conclude that from Point Arena, the San \ndrcas fault closel) follows the coastline even beyond Point Delgada. curving westward to sea to continue as the Mendocino fracture /one along the Gorda escarpment. In projecting the San Andreas fault beyond Point \rena. the fact that the Coast Ranges arc a broad zone ot northwest-trending fault blocks should he considered, and although the San Andreas fault may he the master fault of the system, some other faults of the system also are of major magnitude. It also is significant that the Franciscan formation, including greenstone, chert, and gra) wacke, crops out west of the fault at Point Delgada; elsewhere in the Coast Ranges, to the southeastward be- yond the report area, the Franciscan rocks rarely occur in the Nacimiento-San Andreas fault block west of the San Andreas fault. As noted by Shepard and Emery I 1941, p. 38-39), the coastline in the vicinity of Point Delgada appears to he controlled by a fault. The coast- line for a distance of 20 miles in either direction from Point Delgada trends northwest, nearly parallel to the general trend of the faults of the system, and is aligned with an apparently major fault that trends northwest along the east side of the coastal belt of sedimentary rocks near YVillits. It seems likely that although the fault at Point Delgada is probably parallel to the San Andreas fault, it is several miles to the northeast, and that beyond Point Arena the San \ndrcas fault continues seaward along its regular northwest trend. Differences of opinion exist as to xvhether the San Andreas fault continues northwestward beyond the Men- docino fracture zone. As previously mentioned, Shepard and Emery ( 1941, p. 38-39) consider the San Andreas fault to continue west along the .Mendocino escarpment, and ask, "What could be more likely than that one of the greatest of all land faults should extend out to sea as one of the most remarkable of all submarine escarp- ments?" However, if the submarine configuration of the San Andreas fault in the vicinity of the Mendocino frac- ture /one is analogous to its configuration along the Transverse Ranges of southern California where it is intersected by the Murray fracture /one (Menard, 1955, fig. 2), it might he expected to curve westward and then resume its regular northwestward trend northward beyond the fracture zone. Menard (1955, p. 1193) con- siders the San Andreas fault to cross the .Mendocino frac- ture zone, ami. based on the location of epicenters, to continue to a point some distance west of the coast of Oregon. Whether these epicenters arc along the San Andreas fault, or are along another fault of the same system, probably will remain an academic question. Nevertheless it seems likely, as stated by Menard (1955, p. 1193), that "Perhaps the San Andreas and related faults mark a great fracture zone produced b\" the same 62 California Division of Mines [Bull. 179 stress as the submarine fracture zones and complementary to them." The boundary between the northern Coast Ranges and the Sacramento Valley, from near Wilbur Springs to the southern tip of the Klamath Mountains province, is an apparently continuous belt of serpentinized ultramafic rock. The ultramafic rock is sheared, and at some places encloses small lenses of strata that appear to be fault slices. The shear planes of the ultramafic rock are most commonly north-trending and steep, as is the foliation of the slaty rocks adjacent to the west. The eastward dip of the strata of the Sacramento Valley sequence steepens toward the belt of ultramafic rock, and in some places near the belt of ultramafic rock the strata are overturned. Although the structure is not clearly under- stood, the ultramafic rock appears to be in a zone of high-angle faulting along which the slaty rocks of the Coast Ranges to the west are in juxtaposition with the Sacramento Valley sequence of generally only mildly deformed rocks to the east. Taliaferro (1943, p. 209) states that the contact between the ultramafic rock and the Sacramento Valley sequence is a high-angle thrust fault that dips 60° to 65° W. in northern Glenn County, and a vertical fault in central Colusa County, but that at Redbank Creek, the contact is clearly intrusive. In essence, Taliaferro (1943, p. 210) considers the ultra- mafic rock to be a sill that ". . . intrudes the upper part of the Franciscan and the lower part of the Knoxville, but in some places it is wholly within either Knoxville or Franciscan." In the North Elder Creek area of Tehama County, the ultramafic mass where mapped by Rynearson (1946) is thought to be a dike inclined steeply westward, perhaps intruded along a pre-existing fault that separated east- ward-dipping strata of the Franciscan formation from similarly dipping strata of the Knoxville formation (Ry- nearson, 1946, p. 199). Although the overall trend of the belt of ultramafic rocks is slightly west of north, it consists of a series of alternate northerly and northwesterly trends. The north- erly trends are roughly parallel to the long axis of the Sacramento Valley, whereas the northwesterly trends are parallel to, and probably related to, the Coast Ranges system of faults. At three "hooks" in the belt of ultra- mafic rocks, one near Paskenta, another near Stonyford, and a third near Wilbur Springs, the local structure of the Knoxville formation is more complicated by folding and faulting than is usual. Near Wilbur Springs, the ultramafic rocks and strata of the Sacramento Valley sequence have been folded into an anticline that plunges gently southeastward. The belt of ultramafic rocks ends on the southwest flank of the anticline, to again continue a few miles south of the map area, but the strata of the Sacramento Valley sequence on the southwest flank of the anticline have been warped into a parallel syncline. These northwest-trending folds in the strata of the Sacramento Valley sequence near Wilbur Springs are in line with a major shear zone, marked in part by a narrow belt of ultramafic rocks, that trends northwestward to Lake Pillsbury and perhaps beyond. The trends of structures and lithic belts of the Kla- math Mountains form an arc that is convex westward (see fig. 3). In general, the south- and southeast-trending segment of the Klamath Mountains arc is in California, and the northeast-trending segment is in southern Ore- gon. As noted by Hershey (1903b), and elaborated by Diller (1915, p. 51-52), the structural trends in the north- ern part of the Klamath Mountains are aligned with the Blue Mountains of Oregon to the northeast, and those of the southern part are aligned with the structural trend of the northern part of the Sierra Nevada to the south- east. The Klamath Mountains thereby give the impression of a tectonic bulge in which the rocks have been pushed westward, and this seems to be supported by the few facts and inferences that can be drawn regarding the broad structure of the province. As previously described, the western boundary of the province appears to be a high-angle reverse fault that dips eastward. West of the boundary, similar faults are thought to occur along the west sides of outlying belts of schist similar to the schist of the South Fork Mountains. Hershey (1903b) was the first to give an hypothesis relating to the broad structure of the Klamath Mountains province. He considered the province to consist of two parallel synclinoria, one on each side of the belt of schist that includes the Abrams and Salmon formations. His hy- pothesis, at least with regard to the more westerly of these so-called synclinoria, seems to have been based largely on his correlation of the schist of the South Fork Mountains with the Abrams formation. He considered the schist to be continuous from the South Fork Moun- tains to the central metamorphic belt of Abrams and Salmon schists, the schists being overlain in the trough of the synclinorium by presumably younger rocks of Paleozoic age. His hypothesis appears erroneous, how- ever, as the South Fork Mountain schist is more likely correlative with the Galice formation of late Jurassic (late Oxfordian to middle Kimmeridgian) age, rather than with the Abrams formation. The Galice formation is found only along the western edge of the province, and it is unlikely on both stratigraphic and structural grounds that its schistose facies, the South Fork Moun- tain schist, underlies the broad belt of Paleozoic and Triassic rocks to the east and is continuous with the Abrams schist as was hypothesized by Hershey. In ad- dition, the strata immediately west of the central meta- morphic belt most commonly dip eastward; one would expect the adjacent strata to the west of the central metamorphic belt to dip westward if they are on the east limb of a synclinorium, unless they are overturned on a large scale. The principal faults appear to be chiefly along the boundaries between the lithic belts as shown on the geologic map (pi. 1), although at only a few places were these boundaries seen to be faults by field observation. Thev are somewhat similar in position to features de- 1960] Northern Coast Ranges and Klamath Mot ntains 63 scribed briefly as major faults by Hershey (1903b, 1906, p. 58-59; also sec Lawson and others, 1908, Atlas, map no. 1). Two of the major faults postulated on the basis of the present reconnaissance of the Klamath Mountains prov- ince are rudely parallel to the western boundary of the province. One is along the w est side of the central meta- morphic belt, and extends from the Jurassic ami Cre- taceous overlap southwest of Redding northwestward to the Salmon River. Along much of its length the foli- ation of the strata on either side dips moderately to steeply northeastward, and the boundary seems likely to be a reverse fault whose attitude is nearly parallel to the foliation. Beyond the Salmon River the lithic grain is northeastward toward Scott Valley and Vreka, but whether the fault continues to or beyond Scott Valley is not clear. Another major fault appears to form much of the boundary between rocks of the w estern Jurassic belt that are intruded by relatively small quantities of granitic- rocks, anil strata of the western Paleozoic and Triassic belt that are intruded by abundant granitic rocks. In Trinity County, the fault for much of its length north of the Trinity River is along the contact between the ( ialice formation and the west side of the Ironside Moun- tain batholith. Bodies oi sheared serpentine occur at each place the fault was crossed during reconnaissance, al- thought generally they are too small to show on the geologic map (pi. 1 ). Foliation ami bedding in the Galice formation near the fault generally dip eastward. The general dip of the fault most likely is steeply eastward. Southward from the Trinit) River the fault probablv continues along the west side of the Ironside Mountain batholith to the west end of Hayfork Valley, and from there may continue southeast forming a boundary be- tween an area of abundant ultramatic rock to the west and areas of granitic rocks to the east. In Siskiyou County the northward continuation of the fault is marked by a belt of ultramahc and mafic rock that, for about half the distance to Happy Camp, is along the cast side of the Klamath River. The fault has not been traced north of 1 lappv Camp. Maxson (1933, p. 136-138, and pi. 4) described three faults in Del Norte County. One he referred to as the Orleans fault after Hershey (1906, p. 58; also see Law- son and others, 1908, Atlas, map no. 1). It trends north- east nearly parallel to and a few miles west of the eastern boundary of Del Norte County, and is the contact be- tween the ( Ialice formation to the west ami a complex of ultramalic and granitic rocks to the cast. According to Maxson (1933, p. 136-137) it is a steep reverse fault, presumably dipping southeast, with a throw of several thousand feet. In the Gasquet quadrangle, where the reconnaissance of Maxson | 19V?) is superseded b\ more derailed mapping by Carer ami Wells (1954, pi. 11 ), the so-called Orleans fault is not shown, but it might well trend along a belt of ultramafic rock. A second fault referred to by Maxson (1933, p. 137, and pi. 4) is along the west side of the serpentine ridge that marks the western limit of the Klamath .Mountains province south of the Smith River in the Crescent City quadrangle. It was considered to be a possible continua- 1950 1880 1890 1900 1910 1920 1930 1940 From Pacific Southwest Field Committee (1955). Figure 6. Graph showing trends of mineral production in northwestern California during the period 1880-1953 64 California Division of Mines [Bull. 179 tion of the faults along Redwood Mountain, along the largest belt of schist that lies west of the Klamath Moun- tains province. As shown on the geologic map (pi. 1), however, the southeastward continuation of the fault along the serpentine ridge is east of the faults that bound the Redwood Mountain belt of schist. Maxson (193 3, p. 137) states that the rocks on the east side of the fault have been uplifted 400 feet relative to those on the west. It is likely that the estimate of the magnitude of uplift was based on physiographic data. Maxson (1933, p. 137) postulated a third fault to outline the area of Cenozoic rocks of the Crescent City platform. Cater and Wells (1954, p. 106) state that in the Gasquet quadrangle the structure is one of " . . . close overturned folds and high-angle reverse faults. The axial planes of the folds and the associated faults are roughly parallel, trend north-northeast, and dip steeply eastward. Other faults, some trending northeastward and others northwestward, postdate the folds and reverse faults but probably belong in general to the same period of deformation." They consider that this deformation resulted from the Nevadan disturbance at the close of the Jurassic period, but that differential vertical movements and gentle tilting probably began in late Miocene and are still continuing. o 80 / \ Combined lode ond plocer gold \t.\ :i 'I n / i Lode gold '(! Placer gold 1900 1910 1920 1930 1940 1950 From Pocific Southwest Field Committee (1955) Figure 7. Graph showing production of gold in northwestern California during the period 1903-1953. MINERAL COMMODITIES Mining activity began in the report area during the middle 1800's and by 1958 mineral products having a total value of approximately $150,000,000 had been pro- duced. The chief interest in the early days was the gold- bearing placers along the Klamath River and its tributar- ies, but as prospecting diversified, significant quantities of other metallic mineral commodities such as chromite, quicksilver, copper, and manganese ores were produced. As the population of the area increased, production of nonmetallic mineral commodities such as sand and gravel increased to a point where their value exceeds that of the metallic mineral commodities. The combined produc- tion of metallic and nonmetallic mineral commodities has fluctuated markedly owing to various economic condi- tions (fig. 6). Although the total production of mineral commodities is small as compared to many areas of com- parable size in the western United States, it has con- tributed significantly to the development and economy of northwestern California. Gold Nearly all of the gold deposits in northwestern Cali- fornia are in the Klamath Mountains province, and this province ranks second only to the Sierra Nevada in gold production in California. The gold has come from both placer and lode deposits; placer deposits have been by far the most productive (fig. 7). Gold was the first metal diligently sought in the area. It is said to have been dis- covered by a Major Reading in 1848, in a placer deposit along the Trinity River near Douglas City. Within a few years, lode deposits of gold also were discovered. Most of the richer placer and lode deposits of gold had been found by the late 1800's. Production of gold from northwestern California dur- ing the period 1880-1952 totaled 3,852,800 fine ounces valued at $90,803,000 and during the year 1953 was 9,579 fine ounces valued at $335,265. Production figures re- lated to type of deposit are not available prior to 1903, but during the period 1903-1952 approximately 1,602,000 fine ounces of gold was produced from placer deposits, compared to 383,300 fine ounces of gold produced from lode deposits during the same period. In 1953 the gold production was 5,806 ounces from placer deposits, com- pared to 3,773 ounces from lode deposits during the same year. According to the report of the Pacific Southwest Field Committee (1955, p. 19-20), "Gold production reached its peak during the period 1937 through 1942, prior to interruption of mining during World War II. An increase in the price of gold from $20.67 to $35.00 per ounce in 1934 greatly stimulated the gold mining industry in [northwestern California]. By 1943, however, the rising tendency of wages, the movement of miners into defense industries and the armed forces, shortages of equipment and supplies, plus Government restrictions including War Production Board Order L-208, forced most of the gold mines to close, although some of the larger placer mines were able to continue working. In July 1945, Gov- ernment restrictions on nonessential industries, including gold mining, were lifted; but most of the machinery and equipment used in placer mining had been transferred to war industries, underground workings had deteriorated, and operating costs had risen. Contributing to the decline l'M()| 124' Northern (ihm Ranges \m> Klamath Mountains 123° 65 Area of granitic rocks LODE GOLD DEPOSITS @) More than 1500,000 production ® 8100,000 to 8 500,000 production • Less than 8 100,000 production o No recorded production PRINCIPAL PRODUCERS No 1 MINE Hazel Production 8 800,000 2 Golden Eagle (Sheba) 1,000,000 3 Dewey 900,000 4 Highland 1 500,000 5 Block Bear 3,000,000 6 Klamath 600,000 7 Cummings (Oro Grande) 500,000 8 Gilta (Gold H II) 1,000,000 9 Headlight 500,000 10 Trinity Bonanza K ng 1,250,000 1 1 Enterprise 500,000 12 Alaska group 600,000 13 Fair view 5,000,000 14 Brown Bear 10,000,000 15 Venecia 500,000 16 Midas 3,500,000 17 Siskon not re ported SA Modified after Pacific Sout Field Committee (1955 ) 40 MILES Figure 8. Map of northwestern California showing location of lode deposits of gold. 3 — 18730 66 California Division of Mines [Bull. 179 Area of granitic rock • Placer gold deposit O Placer platinum and gold deposit Modified after Pocific Southwest Field Committee (19551 Figure 9. Map of northwestern California showing location of placer deposits of gold and platinum. I960] \ [-hern Coasi Ranges wd Klamath Mountains 67 in gold production was the depletion of some important placer areas and deposits of high grade ore". Lode deposits of gold I Eg. 8) occur in all of the prin- cipal formations of middle Late Jurassic and older ages in the Klamath Mountains province. Granitic rocks of Late furassic age intrude all of these formations, and the gold probably is related to them although few of the deposits are iii granitic rocks. The rocks of the northern Coast Ranges are younger than the granitic rocks of the Klamath Mountains, and lode deposits of gold in them are rare. Production of gold from lode deposits has come chiefly from the pre-Jurassic rocks of the Klamath Mountains arc; quartz veins containing native gold in the Bragdon formation have been the most important source. Seven- teen mines have produced more than S500.000 in gold, and several have produced more than f 1,000,000 in gold. The greatest production has been from the Brown Bear mine, where gold valued at as much as $10,000,000 is said to have been produced (Averill. 1933, p. L3). Many of the mines have been described by Ferguson (1914), Tucker (1922a), Averill (1931, 1933), Maxson (1933), and others. The placer deposits of gold (fig. 9) arc the products of erosion, transportation and gravitational concentration of the gold of the lode deposits of the Klamath Moun- tains province. Detrital gold occurs in most of the sedi- mentary formations of Tertiary and Quaternary ages in the Klamath Mountains, as the placer gold ultimately was derived from the rocks of Late Jurassic and older ages that contained the gold-bearing lode deposits. The richer placer deposits of gold, however, arc those of Quaternary age. that is. the gravels in the terraces and stream beds along the courses of the present streams. In general, this is the result of repeated re-concentration of detrital gold from volumes of sedimentary rocks of Tertiary and Quaternary ages as they were eroded, but also added to each cycle was gold derived directly from the erosion of gold-bearing lodes. The placer deposits arc greatest in number in the areas of most abundant lode deposits of gold and along the courses of the major streams that drain those areas (com- pare figs, s and 9). Thus the placer deposits are more widespread than the related lode deposits, and although most ot them are in the Klamath Mountains province, a few occur in the northern Coast Ranges. In addition, sediments that reached the ocean have been winnowed to form deposits in beach sands along the coast of northern Humboldt and Del Norte Counties. Much of the gold in the beach sands probably was derived from erosion of sedimentary rocks of Tertian- and Quaternary ages that occur nearby. The gold in the beach sands, however, is finely divided, and in general is of little economic in- terest. The occurrence of gold-bearing gravels in the Trinitv River basin is described by Dillcr (1911 and 1914a) with regard to several cycles of erosion, and the distribution of the principal areas of gold-bearing gravels along the major streams of northwestern California is described in detail bj Halej (1923, p. 82-101). Attempts to mine the beach deposits are described b\ Logan ( L919, p. 41-43). In the northern Coast Ranges of California, lode and stream placer deposits of gold have been found at a few- places, but they have been of slight economic interest. Small quantities of gold are associated with cinnabar at some quicksilver mines and in detrital deposits nearby (E. H. Bailey, oral communication, 1956). Panning in several streams in the northern Coast Ranges has yielded traces of gold, but important concentrations have not been found. Logan (1919, p. 44-48) describes two inter- esting localities in Mendocino County, one near I Iopland and the other near Capclla, where small quantities of detrital gold associated with platinum and cinnabar were produced. Gold-bearing stringers of quart/ in metamor- phosed rocks of the Franciscan formation(?) arc noted by O'Brien (1953, p. 359-360). Platinum Detrital platinum occurs in many of the gold-bearing placer deposits in northwestern California (U Klamath Mountains 73 124 123° MANGANESE DEPOSITS ® Production more than 1000 tons • Production less than 1000 tons o No recorded production SONOMA Modified chiefly after Economic Mineral Map Number 5 (Manganese) California Div. of Mines, Bull 125,1943 40 MILES Figure 13. Map of northwestern California showing location of deposits of manganese. "4 California Division of Mines 123° [Bull. 179 EXPLANATION .a. Antimony A Arsenic A Asbestos C Clay G Graphite • Iron 9 Lead-silver M Magnesite ■ Molybdenum n Nickel (D Ocher o Soapstone, talc ▼ Tin MA " Tungsten A Volcanic ash Modified after Pacific Southwest Field Committee 1955 Figure 14. Map of northwestern California showing location of deposits of miscellaneous mineral commodities. I960 Northern Coasi Ranges vnd Klamath Mountains 75 indication that production of these metals will prove im- portant to the economy <>t the area. Significant quantities of nickel ore currently are being mined in southwestern Oregon, in areas where old-hind surfaces are formed on bodies of ultramafic rocks. On these old surfaces, which arc presumably parts of the Klamath peneplain of Diller, lateritic 'soil has been formed, and where the soil is formed on bodies ot ultra- malic rocks, both the soil and underl) ing weathered rock is enriched with nickel. Similar old-land surfaces also are formed on ultramafic rocks in northwestern Cali- fornia, chiefly in Del Norte County, and several major metal-mining companies were investigating the nickel- producing potential of the area in 1957. Nonmetallic Mineral Commodities The dollar value of nonmetallic mineral commodities produced in the northern Coast Ranges is many times greater than that of metallic commodities, but in the Klamath Mountains it is only a third that of metallic commodities. The nonmetallic commodities generally are of low unit value compared to metallic commodities, ami with the exception of the mineral fuels, they are used chiefly for construction purposes. In most cases the source of supply must of necessity be near the consumer. Miscellaneous stone, including sand, gravel, crushed rock, rubble, and riprap, is by far the most important nonmetallic mineral commodity. During 1953 it consti- tuted nearly half of the dollar value of the total mineral production of northwestern California. Its production, transportation, and use in roads, ballast, fills, and con- crete construction have resulted in the employment of such substantial numbers of persons as to be of great economic importance to the area. Sand and gravel arc obtained from river, terrace, and beach deposits, and the resources of such material are large. Greenstone and chert are widely used as road metal on secondary roads, particularly in the Coast Range, and deposits of these rocks arc so abundant and widespread in areas of the Franciscan formation as to be practically inexhaustible. Blocks of graywacke com- monly have been used as riprap, but glaucophane schist is becoming of increasing interest for this use. Although production of miscellaneous stone may vary consider- ably over periods of time, a steady increase in population, industrial expansion, road and dam construction, and many other factors will doubtless result in increased pro- duction. Deposits of limestone occur at many places in north- western California (fig. 15), but the most important from an economic standpoint are the larger of the Paleozoic and Triassic deposits in the Klamath .Mountains. The foraminiferal limestone of the Franciscan formation in the northern Coast Ranges generally occurs as deposits too small to be of economic interest. Many of the lime- stone deposits of northwestern California have been tabu- lated and described briefly' by Logan (1947) and others, and those near Gazelle in Siskiyou County have been studied in detail by Heyl and Walker (1949). Several of the deposits have had a small production, mainl) for agricultural uses and the manufacture of quicklime, and a small quantity of recrystallized limestone has been quarried as marble for dimension stone; some are thought to be suitable for the manufacture of cement. The last recorded production of limestone in the area was in L945, and significant future production probably will await increased population and industrial expansion. Many other nonmetallic commodities haw been mined, but have not yet proved of great importance to the economy of the area. Clay has been mined, principally in the vicinit) of Eureka, for the manufacture ot brick and tile, and other deposits having small production are near Scott Valley. The total recorded production of Clay has amounted to about $337,000. Dimension stone. including sandstone and granite, has been mined, but little has been produced during the past few decades. Deposits of asbestos occur at some places in areas of ultra- mafic rocks, but none has had appreciable production. Other nonmetallic mineral commodities that have been produced in small quantities in northwestern California include volcanic rocks for use as light-weight construc- tion aggregate, pebbles for use in grinding nulls, mag- nesite, sulfur, ami semiprecious gem stones. Gas and Oil Wells have been drilled for gas and oil in the northern Coast Ranges, chiefly in the Point Arena, Mattole River, Bear River, and Tompkins Hill areas (see fig. 16). A few of the wells have yielded significant quantities of gas but none has yielded more than minor amounts of oil. In general, the results of the drilling have been disap- pointing, but several oil companies were continuing ex- ploration in 1956. 1 he only production of gas and oil has been from western Humboldt Countv. A minor quantity of gas was withdrawn for local consumption near Bnceland during the period 1909-1938, but the greatest production has been from the Tompkins Hill field near Fortuna. A small quantity of oil was produced near Petrolia in 1953, the first recorded production of oil in the area. According to a report of the Pacific Southwest field Committee < 1955, p. 35), "The value of petroleum and natural gas produced in [northwestern California! has been about 1 percent of the total value of the basin's mineral production. The production of oil and gas in | northwestern Californial. however, has been fairly re- cent, and the combined values of petroleum and natural gas extracted in 1953 amounted to 12 percent of the value of [northwestern California! mineral production of that year. For the years 1909 through 1952 the annual average volume of natural gas withdrawn and utilized was about 41 v 100,000 cubic feet, compared with the withdrawal of 1,768,197,000 cubic feet in 1953. The trend of the natural gas production in the area since 1939 has been one of gradual ascendancy". In the northern Coast Ranges the rocks of principal interest from the standpoint of gas and oil production are Miocene and Pliocene in age, and of these the rocks 76 California Division ok Mines [Bull. 179 LIMESTONE DEPOSITS • Smoll recorded production o No recorded production Modified after Pacific Southwest Field Committee (1955) 40 MILES Figure 15. Map of northwestern California showing location of deposits of limestone. 1960| 124 Northern Coast Ranges vnd Klamath Mountains 123° 77 EXPLANATION Principol oreos underlain by monne sedimentary rocks of Tertiary age. COAL DEPOSITS Small production • No recorded production o Exploratory well drilled for oil and gas, exclusive of the Sacramento Volley Location of coat deposits modified otter Pacific Southwest Field Committee (1955) Location of exploratory wells after Jennings and Hart (19561 40 MILES 1 Figure 16. Map of northwestern California showirg location of deposits of coal, and location of wells drilled for oil and gas (exclusive of the Sacramento Valley). 78 California Division of Minis Bull. 179 of Pliocene age have been the most productive. The larg- est and most productive area of rocks of Pliocene age is the Eel River Valley in west-central Humboldt County where west-trending folds provide structural traps for the accumulation of gas and oil. Westerly structural trends, in addition to meager data resulting from marine dred^ino-, suggest that offshore from some of the coastal areas^ rocks of interest from the standpoint of gas and oil may be of considerable extent. According to a report of the Pacific Southwest Field Committee (1955, p. 36), "The Tompkins Hill gas held near Fortuna was discovered in 1937, and is the only commercially productive area at present. Nine wells were completed to the end of 1953. During 1953 about 1 768 197 000 cubic feet of gas was produced. The total production of the field to the end of 1953 was 12,703,- 000 000 cubic feet of gas. The California Department of Natural Resources, Division of Oil and Gas, estimated die reserve of this field to be about 20,000,000,000 cubic feet of "as as of July 1, 1954. The field is on a small anti- cline on the northeast limb of the Eel River synclme. The gas is produced from sands of Pliocene age at a depth" of approximately 5,000 feet". Coal Small quantities of coal have been mined at several localities in northwestern California (see fig. 16), chiefly from strata of Tertiary age. The coal ranges from lignite to sub-bituminous in rank. The recorded production of coal during the period 1880-1952 was approximately 4 000 tons," and most of the production was prior to 1925. Production was chiefly from deposits near Dos Rios in Mendocino Countv, and at Big Bar and Browns Creek (photo 11) in Trinity County. Coal is not now produced. REFERENCES CITED Mien I F., and Baldwin. E. M., 1944, Geology and coal resources ' of the Coos Bay quadrangle. Oregon: Oreg. Dept. Geol. and Min. Industries, Bull. 27, 154 p. \nderson C A 1936, Volcanic history of the Clear Lake area, ' California: Geol. Soc. America Bull., v. 47, no. 5, p. 629-644. Anderson, C. A., and Russell, R. D., 1940. Ternary formations of northern Sacramento Valley, in 35th report of the State Miner- alogist: California Div. Mines, v. 35, no. 3, p. 219-2*3 Anderson F. 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A., 1946, Chromite deposits of the North Elder Creek area, Tehama County, California: U. S. Geol. Survey Bull. 945-G, p. 191-210. Rynearson, G. A., and Smith, C. T., 1940, Chromite deposits of the Seiad quadrangle, Siskiyou County, California: U. S. Geol. Survey Bull. 922-J, p. 281-306. Shepard, F. P., and Emery, K. O., 1941, Submarine topography of the California coast; canyons and tectonic interpretation: Geol. Soc. America Special Paper 31, 171 p. Smith, J. P., 1894, The metamorphic series of Shasta County, Cali- fornia: Jour. Geology, v. 2, p. 588-612. Stauffer, C. R., 1930, The Devonian of California: California Univ. Dept. Geol. Sci. Bull., v. 19, no. 4, p. 81-188. Stewart, R. E., and Stewart, K. C, 1949, Local relationships of the Mollusca of the Wildcat Coast section, Humboldt County, California: Oreg. Dept. Geol. and Min. Industries, Bull. 36, pt. 8, p. 166-208. Stinson, M. C, 1957, Geology of the Island Mountain copper mine, Trinity County, California: California Jour. 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D., 1950, Geologic description of the manganese de- posits of California: California Div. Mines Bull. 152 (Suppl. to Bull. 125), 378 p. Trask, P. D., Wilson, I. F., and Simons, F. S., 1943, Manganese deposits of California, a summary report in Manganese in Cali- fornia: California Div. Mines Bull. 125, p. 51-215. Treasher, R. C, 1955, Areal geology of the Coyote dam site, Mendocino County, California (abs.): Geol. Soc. America Bull., v. 66, no. 12, pt. 2, p. 1666-1667. Tucker, W. B., 1922a, Gold lodes of the East Fork mining district, Trinity County, to 18th report of the State Mineralogist: Cali- fornia State Mining Bur., v. 18, chap. 6, p. 270-273. — , 1922b, Silver lodes of the South Fork mining district, Shasta County, in 18th report of the State Mineralogist: Cali- fornia State Mining Bur., v. 18, chap. 7, p. 313-321. Walker, G. W., 1950, The Calera limestone in San Mateo and Santa Clara Counties, California: California Div. Mines Special Rept. 1-B, 7 p. Weaver, C. E., 1943, Point Arena-Fort Ross region, in Geologic formations and economic development of oil and gas fields of California: California Div. Mines Bull. 118, pt. 3, p. 628-632. Weaver, C. E., 1949, Geology of the Coast Ranges immediately north of the San Francisco Bay region, California: Geol. Soc. America Mem. 35, 242 p. Wells, F. G., 1955, Preliminary geologic map of southwestern Oregon: U. S. Geol. Survey Mineral Inv. Map MF 38. Wells, F. G, and Cater, F. W., Jr., 1950, Chromite deposits of Siskiyou County, California: California Div. Mines Bull. 134. pt. 1, chap. 2, p. 77-127. Wells, F. G., Cater, F. W., Jr., and Rynearson, G. A., 1946, Chromite deposits of Del Norte County, California: California Div. Mines Bull. 134, pt. 1, chap. 1, 76 p. Wells, F. G, Hotz, P. E., and Cater, F. W., Jr., 1949, Preliminary description of the geology of the Kerby quadrangle, Oregon: Oreg. Dept. Geol. and Min. Industries, Bull. 40, 23 p. Wells, F. G, Smith, C. T., Rynearson, G. A., and Livermore, J. S., 1949, Chromite deposits near Seiad and McGuffy Creeks, Siskiyou County, California: U. S. Geol. Survey Bull. 948-B, p. 19-62. Wells, F. G, and Walker, G. W., 1953, Geology of the Galice quadrangle, Oregon: U. S. Geol. Survey Geol. Quad. Map [GQ 25]. Wells, F. G, and others, 1939, Preliminary geologic map of the Medford quadrangle, Oregon: Oreg. Dept. Geol. and Min. Industries. — , 1940, Preliminary geologic map of the Grants Pass quad- rangle, Oregon: Oreg. Dept. Geol. and Min. Industries. Westman, B. J., 1947, Silurian of the Klamath .Mountain province (abs.): Geol. Soc. America Bull., v. 58, no. 12, pt. 2, p. 1263. White, C. A., 1885, On new Cretaceous fossils from California: U. S. Geol. Survey Bull. 22, p. 7-25. Williams, Howel, 1949, Geology of the Macdoel quadrangle, Cali- fornia: California Div. Mines Bull. 151, 78 p. Wilmarth, M. G., 1938, Lexicon of geologic names of the United States: U. S. Geol. Survey Bull. 896, pt. 1 and 2, 2396 p. Iv7::u "-CO 3,500 printed in CALIFORNIA STATE PRINTING OFFICE — COLLATE : PIECES 80 California Division of Mines [Bull. 179 Ogle, B. A., 1951, Wildcat group in the Eel River area, Hum- boldt County, California (abs.) : Geol. Soc. American Bull., vol. 62, no. 12, pt. 2, p. 1510. Ogle, B. A., 1953, Geology of Eel River Valley area, Humboldt County, California: California Div. Mines Bull. 164, 128 p. Olmsted, F. H., 1956, Summary of ground-water conditions in northwestern California, in Water resources, Appendix to Natural resources of northwestern California: U. S. Dept. In- terior, Pacific Southwest Field Committee, 93 p. Pacific Southwest Field Committee, 1955, Geology, mineral re- sources, and mineral industry. Appendix to Natural resources of northwestern California: U. S. Dept. Interior, 40 p. Peck, D. L., Imlay, R. W., and Popenoe, W. P., 1956, Upper Cretaceous rocks of parts of southwestern Oregon and northern California: Am. Assoc. Petroleum Geologists Bull., v. 40, no. 8, p. 1968-1984. Peck, J. H., Jr., 1957, Marine Pliocene fauna in northwestern Sonoma County, California (abs.): Geol. Soc. America Bull., v. 68, no. 12, pt. 2, p. 1840-1841. Ransome, A. L., and Kellogg, J. L., 1939, Quicksilver resources of California, in 35th report of the State Mineralogist: California Div. Mines, v. 35, no. 4, p. 353-486. Rice, S. J., 1953, Reconnaissance geology of the California coastal area north of Eureka (abs.) : Am. Assoc. Petroleum Geologists Bull., v. 37, no. 12, p. 2779. Rynearson, G. A., 1946, Chromite deposits of the North Elder Creek area, Tehama County, California: U. S. Geol. Survey Bull. 945-G, p. 191-210. Rynearson, G. A., and Smith, C. T., 1940, Chromite deposits of the Seiad quadrangle, Siskiyou County, California: U. S. Geol. Survey Bull. 922-J, p. 281-306. Shepard, F. P., and Emery, K. O., 1941, Submarine topography of the California coast; canyons and tectonic interpretation: Geol. Soc. America Special Paper 31, 171 p. Smith, J. P., 1894, The metamorphic series of Shasta County, Cali- fornia: Jour. Geology, v. 2, p. 588-612. Stauffer, C. R., 1930, The Devonian of California: California Univ. Dept. Geol. Sci. Bull., v. 19, no. 4, p. 81-188. Stewart, R. E., and Stewart, K. C, 1949, Local relationships of the Mollusca of the Wildcat Coast section, Humboldt County, California: Oreg. Dept. Geol. and Min. Industries, Bull. 36, pt. 8, p. 166-208. Stinson, M. C, 1957, Geology of the Island Mountain copper mine, Trinity County, California: California Jour. Mines and Geology, v. 53, nos. 1, 2, p. 9-33. Stumm, E. C, 1954, A Devonian species of Heliolites from Nevada: Michigan Univ. Mus. Paleontology Contr., v. 11, no. 12, p. 223-228. Taliaferro, N. L., 1942, Geologic history and correlation of the Jurassic of southwestern Oregon and California: Geol. Soc. America Bull., v. 53, no. 1, p. 71-112. — , 1943, Franciscan-Knoxville problem: Am. Assoc. Petro- leum Geologists Bull., v. 27, no. 2, p. 109-219. Taliaferro, N. L., and Hudson, F. S., 1943, Genesis of the man- ganese deposits of the Coast Ranges of California: California Div. Mines Bull. 125, p. 217-275. Thalmann, H. E., 1942, Qlobotruncana in the Franciscan lime- stone, Santa Clara County, California (abs.): Geol. Soc. America Bull., v. 53, no. 12, pt. 2, p. 1838. Thalmann, H. E., 1943, Upper Cretaceous age of the "Franciscan" limestone near Laytonville, Mendocino County, California (abs.): Geol. Soc. America Bull., v. 54, no. 12, p. 1827. Trask, P. D., 1950, Geologic description of the manganese de- posits of California: California Div. Mines Bull. 152 (Suppl. to Bull. 125), 378 p. Trask, P. D., Wilson, I. F., and Simons, F. S., 1943, Manganese deposits of California, a summary report in Manganese in Cali- fornia: California Diy. Mines Bull. 125, p. 51-215. Treasher, R. C, 1955, Areal geology of the Coyote dam site, Mendocino County, California (abs.): Geol. Soc. America Bull., v. 66, no. 12, pt. 2, p. 1666-1667. Tucker, W. B., 1922a, Gold lodes of the East Fork mining district, Trinity County, hi 18th report of the State Mineralogist: Cali- fornia State Mining Bur., v. 18, chap. 6, p. 270-273. , 1922b, Silver lodes of the South Fork mining district, Shasta County, in 18th report of the State Mineralogist: Cali- fornia State Alining Bur., v. 18, chap. 7, p. 313-321. Walker, G. W., 1950, The Calera limestone in San Mateo and Santa Clara Counties, California: California Div. Alines Special Rept. 1-B, 7 p. Weaver, C. E., 1943, Point Arena-Fort Ross region, in Geologic formations and economic development of oil and gas fields of California: California Div. Alines Bull. 118, pt. 3, p. 628-632. Weaver, C. E., 1949, Geology of the Coast Ranges immediately north of the San Francisco Bay region, California: Geol. Soc. America Mem. 35, 242 p. Wells, F. G., 1955, Preliminary geologic map of southwestern Oregon: U. S. Geol. Survey Mineral Inv. Map AIF 38. Wells, F. G., and Cater, F. W., Jr., 1950, Chromite deposits of Siskiyou County, California: California Div. Alines Bull. 134, pt. 1, chap. 2, p. 77-127. Wells, F. G., Cater, F. W., Jr., and Rynearson, G. A., 1946, Chromite deposits of Del Norte County, California: California Div. Alines Bull. 134, pt. 1, chap. 1, 76 p. Wells, F. G., Hotz, P. E., and Cater, F. W., Jr., 1949, Preliminary description of the geology of the Kerby quadrangle, Oregon: Oreg. Dept. Geol. and Alin. Industries, Bull. 40, 23 p. Wells, F. G., Smith, C. T., Rynearson, G. A., and Livermore, J. S., 1949, Chromite deposits near Seiad and AIcGuffy Creeks, Siskiyou County, California: U. S. Geol. Survey Bull. 948-B, p. 19-62. Wells, F. G., and Walker, G. W., 195 3, Geology of the Galice quadrangle, Oregon: U. S. Geol. Survey Geol. Quad. A lap [GQ 25]. Wells, F. G., and others, 1939, Preliminary geologic map of the Medford quadrangle, Oregon: Oreg. Dept. Geol. and Alin. Industries. — , 1940, Preliminary geologic map of the Grants Pass quad- rangle, Oregon: Oreg. Dept. Geol. and Alin. Industries. Westman, B. J., 1947, Silurian of the Klamath Mountain province (abs.): Geol. Soc. America Bull., v. 58, no. 12, pt. 2, p. 1263. White, C. A., 1885, On new Cretaceous fossils from California: U. S. Geol. Survey Bull. 22, p. 7-25. Williams, Howel, 1949, Geology of the Alacdoel quadrangle, Cali- fornia: California Div. Alines Bull. 151, 78 p. Wilmarth, Al. G., 1938, Lexicon of geologic names of the United States: U. S. Geol. Survey Bull. 896, pt. 1 and 2, 2396 p. 1S730 -60 3,500 ttiled in CALIFORN A STATE PRINTING OFf ICE t Foldout too large for digitization May be added at a later date