V c» STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES GEOLOGY AND MINERAL DEPOSITS OF THE ANGELS CAMP AND SONORA QUADRANGLES CALAVERAS AND TUOLUMNE COUNTIES CALIFORNIA SPECIAL REPORT 41 UN.VwKali^ 0^ CALIFORNIA UAVIS At;-: 9 R ■?" DIVISION OF MINES FERRY BUILDING, SAN FRANCISCO SPECIAL REPORTS ISSUED BY THE DIVISION OF MINES l-A. Sierra Blanca limestone in Santa Barbara County, Cali- fornia, by George W. Walker. 1950. 5 pp., 1 pi. Price 25*. 1-B. The Calera limestone, San Mateo and Santa Clara Counties, California, by George W. Walker. 1950. 8 pp., 1 pi., 6 figs. Price 25 *. 2. Geology of part of the Delta-Mendota Canal near Tracy, Cali- fornia, by Parry Reiche. 1950. 12 pp., 5 figs. Price 25tf. 3. Commercial "black granite" of San Diego County, California, by Richard A. Hoppin and L. A. Norman, Jr. 1950. 19 pp., 18 figs. Price 25*. 4. Geology of the San Dieguito pyrophyllite area, San Diego County, California, by Richard H. Jahns and John F. Lance. 1950. 32 pp., 2 pis., 21 figs. Price 50*. 5. Geology of the Jurupa Mountains, San Bernardino and River- side Counties, California, by Edward M. MacKevett. 1951. 14 pp., 1 pi., 14 figs. Price 25*. 6. Geology of Bitterwater Creek area, Kern County, California, by Henry H. Heikkila and George M. MacLeod. 1951. 21 pp., 2 pis., 15 figs. Price 35tf. 7-A. Gem- and lithium-bearing pegmatites of the Pala district, San Diego County, California, by Richard H. Jahns and Lauren A. Wright. 1951. 72 pp., 13 pis., 35 figs. Price $2.50. 7-B. Economic geology of the Rincon pegmatites, San Diego County, California, by John B. Hanley. 1951. 24 pp., 1 pi., 5 figs. Price 35tf. 8. Talc deposits of steatite grade, Inyo County, California, by Ben M. Page. 1951. 35 pp., 11 pis., 25 figs. Price 85tf. 9. Type Moreno formation and overlying Eocene strata on the west side of the San Joaquin Valley, Fresno and Merced Counties, California, by Max B. Payne. 1951. 29 pp., 5 pis., 11 figs. Price 60*. 10-A. Nephrite jade and associated rocks of the Cape San Martin region, Monterey County, California, by Richard A. Crippen, Jr. 2d printing. 1951. 14 pp., 14 figs. Price 25*. 10-B. Nephrite in Marin County, California, by Charles W. Chester- man. 1951. 11 pp., 16 figs. Price 25*. 10-C. Jadeite of San Benito County, California, by H. S. Yoder and C. W. Chesterman. 1951. 8 pp., 6 figs. Price 25tf. 11. Guide to the geology of Pfeiffer-Big Sur State Park, Monterey County, California, by Gordon B. Oakeshott. 1951. 16 pp., 1 pi., 28 figs. Price 25tf. 12. Hydraulic filling in metal mines, by William E. Lightfoot. 1951. 28 pp., 15 figs. Price 50*. 13. Geology of the saline deposits of Bristol Dry Lake, San Ber- nardino County, California, by Hoyt S. Gale. 1951. 24 pp., 1 pi., 2 figs. Price 35*. 14. Geology of the massive sulfide deposits at Iron Mountain, Shasta County, California, by A. R. Kinkel, Jr., and J. P. Albers. 1951. 19 pp., 6 pis., 6 figs. Price 75*. 15. Photogeologic interpretation using photogrammetric dip cal- culations, by D. H. Elliott. 1952. 21 pp., 9 figs. Price 50tf. 16. Geology of the Shasta King mine, Shasta County, California, by A. R. Kinkel, Jr., and Wayne E. Hall. 1951. 11 pp., 3 pis., 4 figs. Price 50*. 17. Suggestions for exploration at New Almaden quicksilver mine, California, by Edgar H. Bailey. 1952. 4 pp., 1 pi. Price 25*. 18. Geology of the Whittier-La Habra area, Los Angeles County, California, by Charles J. Kundert. 1952. 22 pp., 3 pis., 19 figs. Price 50*. 19. Geology and ceramic properties of the lone formation, Buena Vista area, Amador County, California, by Joseph A. Pask and Mort D. Turner. 1952. 39 pp., 4 pis., 24 figs. Price 75tf. 20. Geology of the Superior talc area, Death Valley, California, by Lauren A. Wright. 1952. 22 pp., 1 pi., 15 figs. Price 50tf. 21. Geology of Burruel Ridge, northwestern Santa Ana Moun- tains, California, by James F. Richmond. 1952. 1 pi., 11 figs. Price 50*. 22. Geology of Las Trampas Ridge, Berkeley Hills, California, by Cornelius K. Ham. 1952. 26 pp., 2 pis., 20 figs. Price 75*. 23. Exploratory wells drilled outside of oil and gas fields in Cali- fornia to December 31, 1950, by Gordon B. Oakeshott, Lewis T. Braun, Charles W. Jennings, and Ruth Wells. 1952. 77 pp., 1 pi., map. Price, map and report, $1.25 ; map alone, $1. 24. Geology of the Lebec quadrangle, California, by John C. Crowell. 1952. 23 pp., 2 pis., 10 figs. Price 75tf. 25. Rocks and structure of the Quartz Spring area, northern Panamint Range, California, by James F. McAllister. 1952. 38 pp., 3 pis., 13 figs. Price 75tf. 26. Geology of the southern Ridge Basin, Los Angeles County California, by Peter Dehlinger. 1952. 11 pp., 1 pi., 7 figi Price 50*. 27. Alkali-aggregate reaction in California concrete aggregat by Richard Merriam. 1953. 10 pp., 12 figs. Price 35tf. 28. Geology of the Mammoth mine, Shasta County, California, b; A. R. Kinkel, Jr., and Wayne E. Hall. 1952. 15 pp., 9 pis., figs. Price 75*. 29. Geology and ore deposits of the Afterthought mine, Shasta County, California, by John P. Albers. 1953. 18 pp., 6 pis., 9 figs. Price 75*. 30. Geology of the southern part of the QuaU quadrangle, Cali- fornia, by Charles W. Jennings. 1953. 18 pp., 2 pis., 16 figs. Price 75tf. 31. Geology of the Johnston Grade area, San Bernardino County, California, by Robert Barton Guillou. 1953. 18 pp., 1 pi., 19 figs. Price 75*. 32. Geological investigations of strontium deposits in southern California, by Cordell Durrell. 1953. 48 pp., 9 pis., 12 figs. Price $1.25. 33. Geology of the Griffith Park area, Los Angeles County, Cali- fornia, by George J. Neuerberg. 1953. 29 pp., 1 pi., 15 figs. Price 50?. 34. Geology of the Santa Rosa lead mine, Inyo County, Califor- nia, by Edward M. Mackevett. 1953. 9 pp., 2 pis., 3 figs. Price 50*. 35. Tungsten deposits of Madera, Fresno, and Tulare Counties, California, by Konrad B. Krauskopf. 1953. 83 pp., 4 pis., 52 figs. Price $1.25. 36. Geology of the Palen Mountains gypsum deposit, Riverside County, California, by Richard A. Hoppin. 1954. 25 pp., 1 pi., 32 figs., frontis. Price 75* 37. Rosamond uranium prospect, Kern County, California, by George W. Walker. 1953. 8 pp., 5 figs. Price 25* 38. Geology of the Silver Lake talc deposits, San Bernardino County, California, by Lauren A. Wright. 1954. 4 pis., 18 figs. Price $1.00. 39. Barite deposits near Barstow, San Bernardino County, California, by Cordell Durrell. 1954. 8 pp., 4 pis., 1 fig. Price 50*. 40. Geology and mineral deposits of the Calaveritas quadrangle, Calaveras County, California, by Lorin D. Clark. 1954. 23 pp., 2 pis., 6 figs. Price $1.75. 41. Geology and mineral deposits of the Angels Camp and So- nora quadrangles, Calaveras and Tuolumne Counties, Cali fornia, by John H. Eric, Arvid A. Stromquist, and C. Melvin Swinney. 1955. 55 pp., 4 pis., 21 figs. Price $3.75. STATE OF CALIFORNIA GOODWIN J. KNIGHT. Governor DEPARTMENT OF NATURAL RESOURCES DeWITT NELSON. Director DIVISION OF MINES FERRY BUILDING. SAN FRANCISCO 11 OLAF P. JENKHJS. Chief ;AN FRANCISCO SPECIAL REPORT 41 JANUARY 1955 GEOLOGY AND MINERAL DEPOSITS OF THE ANGELS CAMP AND SONORA QUADRANGLES CALAVERAS AND TUOLUMNE COUNTIES CALIFORNIA By JOHN H. ERIC, ARVID A. STROMQUIST, and C. MELVIN SWINNEY Geological Survey, U. S. Department of the Interior Price $3.75 GEOLOGY AND MINERAL DEPOSITS OF THE ANGELS CAMP AND SONORA QUADRANGLES CALAVERAS AND TUOLUMNE COUNTIES, CALIFORNIA* By John H. Eric, Arvid A. Stromquist, and C. Melvin Swinney t OUTLINE OF REPORT Page Abstract 3 [ntroduction 5 General geology 7 Stratigraphy 7 Calaveras formation of Paleozoic age 7 Mesozoic rocks 9 Cosumnes formation 10 Logtown Ridge formation 11 Mariposa formation 12 Pre-Cretaceous rocks of uncertain age 15 Tertiary rocks 16 River gravel of Eocene ( ?) age 16 Valley Springs formation 16 Merhten formation 18 Latite of Table Mountain 19 Some problems of correlation 19 Correlation of marble and interbedded rocks 19 Tentative correlation of phyllite, stretched conglomerate, and related rocks 20 Tentative correlation of the green schist and related rocks 20 Intrusive rocks 20 Serpentine 21 Gabbro and diorite 21 Hornblendite 21 Porphyritic diabase 22 Diabase 22 Hornblende lamprophyre 22 Altered quartz-bearing intrusive rocks 22 Age 22 Structure 22 Folds 22 Major folds 22 Minor folds 23 Faults 23 Mother Lode fault system 23 Zone of intense faulting 23 Evidence for faults ! 26 Faults outside the Mother Lode system 26 Displacement on faults 27 Periods of faulting 27 Age of faulting 27 Cleavage and schistosity 27 Joints 29 Lineation 29 Stretched pebbles - nd fragments 29 Intersections and crenulations 29 Lineations on faults and quartz veins 29 Petrology and metamorphism 30 Rocks of the chlorite 1 subzone 30 Quartzose and argillaceous rocks 31 Mafic volcanic rocks 32 Mafic and ultramafic intrusive rocks 33 Rocks of the chlorite 2 subzone 36 Quartzose and argillaceous rocks 36 Sericite schist derived from felsic tuff 38 Amphibole crystal tuff and tuffaceous sandstone 38 Albite-actinolite schist 39 Hornblende andesite 39 Plagioclase-chlorite-zoisite schist ^ 39 Albite-chlorite-epidote schist 39 Lenses of greenstone within the green schist 39 Marble 40 Intrusive rocks 40 Economic geology 40 Gold 41 History and production 41 Placer gold deposits 42 Quaternary placer gold deposits 42 Tertiary placer gold deposits 42 * Publication authorized by the Director, U. S. Geological Survey. Manuscript submitted for publication April 1954. t Geologists, U. S. Geological Survey. Page Vein gold deposits 43 The Mother Lode belt 43 Hydrothermal alteration 44 Suggestions for exploration 45 Other mineral commodities 45 Chromite, manganese, and copper 45 Talc and soapstone, magnesite, and asbestos 45 Limestone or marble, building stone, road metal, and riprap 46 References 46 Tables of mines and prospects 48 Illustrations Plate 1. Geologic map of the Angels Camp quadrangle, California In pocket 2. Geologic map of the Sonora quadrangle, California In pocket 3. Mines and prospects, Angels Camp quadrangle, California In pocket 4. Mines and prospects, Sonora quadrangle, California In pocket Figure 1. Index map showing the location of the Mother Lode belt, Tertiary river channels, and distribution of quadrangles 6 2. Photo of tectonic breccia in the highly sheared Calaveras (?) formation 8 3. Photo of marble lenses, white rock, in faulted zone, 10 4. Photo of San Domingo hydraulic pit 17 5. Photo of a latite lava flow of Table Mountain 17 6. Photo of stretched conglomerate containing marble pebbles 17 7. Structure map of the Angels Camp quadrangle 24 8. Structure map of the Sonora quadrangle 25 9. Geologic map of accessible part of Melones adit 28 10. Photomicrograph of grit member from the Mari- posa formation 30 11. Photomicrograph of graywacke from the Mariposa formation 32 12. Photomicrograph of lapilli tuff of the Logtown Ridge formation 33 13. Photo of altered anorthosite dike in gabbro 35 14. Photomicrograph of phyllonite 36 15. Photomicrograph of stretched conglomerate 36 16. Photomicrograph of quartz-muscovite schist 37 17. Photomicrograph of quartz-mica schist (X27) 37 18. Photomicrograph of chiastolite schist 38 19. Photomicrograph of albite-actinolite schist 40 20. Photomicrograph of relatively unsheared lens of greenstone within the green schist 41 21. Photomicrograph of relatively unsheared pod from within the green schist 42 ABSTRACT The 7^-minute quadrangles Angels Camp and So- nora — in Calaveras and Tuolumne Counties, California — are approximately at the geographic center of the Mother Lode gold belt. This area is underlain chiefly by steeply dipping metamorphosed sedimentary and vol- canic rocks of Mesozoic and Paleozoic age, and by meta- morphosed intrusive rocks of Mesozoic age. These rocks are covered in places by nearly flat-lying sedimentary and volcanic rocks of Tertiary age. About 500 mines and prospects in the area are listed. Gold leads the minerals in value and quantity, with some 20 mines each having a recorded production of more than $200,000. The Calaveras formation, of Paleozoic age, occurs in three belts. It is chiefly marble and schist, in part inter- bedded. Discontinuous strips of sheared rocks consisting (3) Special Report 41 of tectonic breccia, marble lenses, schists, and phyllitic material have been mapped as probable Calaveras for- mation. These sheared rocks are confined to strongly faulted zones. The Cosumnes formation, of Middle or Late Jurassic age, is exposed in a small part of the mapped area. This formation consists of thin-bedded tuff, slate, tuffaceous sandstone and siltstone, and chert. Overlying the Co- sumnes is the Logtown Ridge formation, also of Middle or Late Jurassic age. This formation consists dominantly of rocks derived from coarse-grained, generally mafic, pyroclastics, as well as from tuff and flows. One of the most characteristic and consistent units within the Log- town Ridge formation is a green massive augite-albite- epidote greenstone derived chiefly from basalt and andesite breccia and agglomerate. The Cosumnes and Logtown Ridge formations make up the Amador group. The youngest pre-Cretaceous sedimentary formation in the mapped area is the Mariposa slate, for which the more appropriate name Mariposa formation is proposed. This unit is of Late Jurassic age and is unconformably above the Logtown Ridge formation. The lithologic units are interbedded slate, graywacke, sandy and silty tuff, tuffaceous sandstone, and pebble conglomerate. Part of the mapped area is underlain by phyllite and conglomerate containing stretched pebbles and part by green schist, of uncertain, pre-Cretaceous age. In general these rocks have been somewhat more metamorphosed and deformed than the rocks of known Jurassic age, and in the past most of them have been assigned to, or asso- ciated with, the Calaveras formation. Inasmuch as no valid evidence has been found for the age of these rocks, in this report they have not been assigned an age. How- ever, in places some of them resemble rocks of the Co- sumnes and Logtown Ridge formations, suggesting a possible tentative correlation with these formations. Four formations of Tertiary age have been mapped. The oldest of these is river gravel of Eocene ( ?) age, containing pebbles and cobbles of pre-Tertiary bedrock. This gravel, which we believe to be approximately con- temporaneous with the clay, sand, and lignite of the lone formation farther west, is of great economic im- portance, for much gold has been mined from it. Uncon- formably overlying the river gravel is the Valley Springs formation, which consists of interbedded rhyolite tuff and gravel that contains pebbles and cobbles of bedrock. The Valley Springs formation may be of Miocene age. Unconformably overlying the Valley Springs is the Mehrten formation of Miocene and Pliocene age, a unit that is dominantly andesitic or basaltic and consists chiefly of volcanic conglomerate and mud flows, agglom- erate, breccia, and tuff ; the fragments are mainly of Ter- tiary rocks, a distinct contrast to the bedrock fragments found in the river gravel of Eocene ( ?) age and Valley Springs formation. Unconformably overlying the Mehr- ten is a latite lava flow that occupies an old channel. Intrusive rocks underlie only a small part of the Angels Camp quadrangle, whereas they underlie about a fourth of the Sonora quadrangle. They are represented chiefly by stocks of gabbro and related rocks, chiefly diorite and serpentine. The serpentine rock generally is massive, but along major faults has been intensely sheared. Locally the serpentine contains viens of chryso- tile, and some asbestos has been mined ; elsewhere in the serpentine are small chromite prospects. The gabbro gen- erally is medium- to coarse-grained and consists essen- tially of saussuritized plagioclase and amphibole. It is massive except near faults. Other intrusive rocks include mafic dikes of several types and quartz-bearing plutonic rocks. The major structure of the mapped area is character- ized by steep dips of beds and foliation; overturned, nearly isoclinal folds ; and reverse faults. Most of the major folds plunge gently, whereas their axial planes dip steeply. In addition to these folds, formed by hori- zontal compression, some major folds apparently were formed by the intrusion of some of the larger stocks. Minor folds generally plunge steeply; most of them are probably drag folds associated with some of the faults and regional shear zones. The Mother Lode fault system is a zone of anasto mosing reverse faults and shears extending across the mapped area from northwest to southeast. The fault zone in this area ranges in width from about 1,000 feet to about 3 miles. In general the faults dip more gently than beds or cleavage, so that in places younger rocks have been thrust over older rocks. Some of the faults have been mineralized along part of their extent, and it is in such places that the larger or more productive vein mines are situated. Locally, within the Mother Lode fault system, rocks of the Amador group and fault- bounded lenses of serpentine, have been brought by? faulting into close association with lenses of marble thati are assumed to belong to the Calaveras formation. At least four periods of faulting have occurred in the< mapped area, for longitudinal faults have been offsel along transverse faults and these in turn have been offset along longitudinal faults; late normal movement has taken place along some of the older reverse faults. Most of the pre-Tertiary rocks in the mapped area are foliated ; nonfoliated rocks are the more massive in-l trusive rocks and the coarse volcanic breccia of the Logtown Ridge formation. Except on the noses of plung- ing folds, schistosity and bedding are approximately parallel. In parts of the mapped area a late shear cleav- age has been superimposed on the regional schistosity. Shear cleavage is approximately parallel to the axial planes of minor folds, whereas schistosity is approxi- mately parallel to the axial planes of major folds. The linear elements in the mapped area include (1)J fold axes, (2) long axes of stretched fragments, both in clastic and in pyroclastic rocks, (3) intersections of< planes, chiefly bedding, schistosity, and shear cleavage, (4) crenulations due to minute displacements along planes of shear cleavage, and (5) slickensides and mul- lions on faults and quartz veins. Nearly all the pre-Tertiary rocks in the mapped area are of dynamothermal types that belong to the chlorite zone of metamorphism. Only the rocks of Tertiary age have not been metamorphosed. The pre-Tertiary rocks of the chlorite zone have been subdivided, on a struc- tural and mineralogic basis, into two subzones. The rocks lying to the west of one of the major Mother Lode faults, which forms the metamorphic boundary or isograd be- tween the subzones, are only slightly altered and have been assigned to the chlorite 1 subzone. Their original textures and structures, and some of their original min- erals, are largely retained. To the east of the metamor- Geology of the Angels Camp and Sonora Quadrangles phic boundary the rocks have been considerably more altered and schistose structures have developed. These rocks have been assigned to the chlorite 2 subzone ; they are largely reconstituted mineralogically, and only a few relict minerals remain. About 180 mines and prospects have been identified by name on the accompanying maps. Gold is the most important mineral commodity in the area, both in quan- tity of ore produced and in dollar value. Gold has been recovered from quartz veins, mineralized schist, and river gravels of Tertiary and Quaternary age. In addition to gold, the following commodities are reported to have been prospected or produced in the mapped area : asbestos, building stone, chromite, copper, limestone and marble, magnesite, manganese, road metal and riprap, roofing granules, and talc and soapstone. Silver and copper have been recovered as byproducts from the gold ore. In many of the mines that have been large gold pro- ducers, fault zones near contacts between rocks of dif- ferent types have been favorable locales for ore deposi- tion. Ankeritization has been the most widespread hydrothermal alteration, and in places ankerite is a good indicator of the presence of gold ore. The fault system of the Mother Lode belt rather than the host rock probably was the chief controlling factor in ore deposition. Most of the mines with large production are alined along a narrow part of the Mother Lode fault system. Along this linear belt three areas have been especially productive : Angels Camp-Altaville, Carson Hill, and the area west and southwest of Jamestown. Probably most of the gold near the surface has been recovered, but undoubtedly much gold remains. Some of the areas between the three most productive ones are favorable for more intensive exploration than has been done to date. Likewise, the fault zones 1£ miles west of Angels Camp and the one just west of Sonora merit further exploration. Unexplored areas also exist in the Tertiary river gravels, specifically in the Ceneral Hill Channel. INTRODUCTION Location and Topography. The area described com- prises two 7^-minute quadrangles : the southeast quarter of the San Andreas 15-minute quadrangle (Angels Camp quadrangle) and the Sonora quadrangle. Figure 1 shows the location of the area. The Angels Camp quadrangle is bounded by latitudes 37°07'30" and 38° N. and by longitudes 120°30' and 120°37'30" W. ; the Sonora quadrangle by latitudes 38° and 37°52'30" N. and by longitudes 120°22'30" and 120°30' W. Most of the Angels Camp quadrangle is in Calaveras County, whereas the Sonora quadrangle is almost entirely in Tuolumne County, California. Angels Camp, Sonora, and Jamestown are the principal towns in the mapped area. The region is one of moderate relief, as the lowest altitude is about 735 feet at Melones Reservoir on the Stanislaus River and along Woods Creek, and the high- est is 2,895 feet at the summit of Bear Mountain ; the average altitude is about 1,500 feet. Bear Mountain, in the Angels Camp quadrangle, is a monadnock whose relief must be inherited from at least early Tertiary time, for apparently it deflected one of the principal early Tertiary streams of the region. Another conspicu- ous topographic feature is Table Mountain, a flat-topped, steepsided elongate and sinuous hill that extends across the Sonora quadrangle from northeast to southwest with gradually decreasing altitude. It is held up by the rem- nants of a lava flow that in late Tertiary or early Quaternary time streamed down and filled one of the major river channels then draining the region. The country supports a growth of grass, oaks, and pines ; chaparral grows on many of the hills. The climate is hot and dry in summer, cool and rainy in winter; snow is uncommon. Purpose and Scope of Field Work. The area was mapped by the U. S. Geological Survey under a coop- erative program with the California State Division of Mines. The purpose of the work was to prepare detailed geologic maps of parts of the Mother Lode region. Parts of the area have been mapped twice before by the Geo- logical Survey, first by Turner and Ransome (Turner, 1894; Turner and Ransome, 1897) and later by Ran- some (1900). The present survey attempts to solve some of the stratigraphic and structural problems of the area. During the present survey the geology was mapped on aerial photographs, issued by the U. S. Forest Service, on a scale of about 1 : 20,000 ; for compilation, topo- graphic maps on a scale of 1:24,000 (2,000 feet to the inch) were used. These scales are considerably larger than those heretofore used by the Geological Survey in regional geologic mapping in the Mother Lode region, and the resulting more detailed geologic maps afford a basis for new interpretations of the stratigraphy and structure. Rock units as narrow as 50 feet have been mapped, as have the major faults, quartz veins, and alteration zones. Because of inaccessibility of the mines, field work has been confined almost entirely to surface mapping. Field Work and Acknowledgments. Field work was begun by John H. Eric and George R. Heyl in May 1946 ; Arvid A. Stromquist joined the party in Septem- ber of the same year. In June 1947 C. Melvin Swinney was assigned to the project, and in September of the same year John H. Wiese joined the party. Swinney worked with the group on a part time basis. Heyl and Wiese were associated with the project for 14 and 10 months respectively. Mapping of the Angels Camp quad- rangle was finished in November 1947 and of the Sonora quadrangle in August 1948. The authors of this report are indebted to F. C. Cal- kins of the Geological Survey, who examined about 150 thin sections of rocks from the area. Many of the petro- graphic descriptions in this report are based on his notes. Shirley Huddleston of the Geological Survey assisted in the compilation of the data on mines and prospects in the area; officials of Calaveras County in San An- dreas, of Tuolumne County in Sonora, and of the Cali- fornia State Division of Mines in San Francisco and Sacramento also were helpful in this work. Several resi- dents of the mapped area aided the authors in finding and identifying by name some of the mines that have long been abandoned. Walter Lyman Brown, of the Car- son Hill Gold Mining Corp., allowed us to map the Melones adit. Special Report 41 Figure 1. Index map showing the location of the Mother Lode belt, Tertiary river channels, and distribution of quadrangles referred to in the report. Geology of the Angels Camp and Sonora Quadrangles Professor N. L. Taliaferro spent several days with the survey party in the field and his knowledge of the geology of the Sierra Nevada proved highly beneficial. GENERAL GEOLOGY The Mother Lode belt extends from the vicinity of Georgetown, El Dorado County, to the vicinity of Mari- posa, Mariposa County, a distance of about 120 miles (Knopf, 1929, p. 1). The mapped area (fig. 1) is approxi- mately at the geographic center of the belt. The Mother Lode fault system is a narrow fault zone about 1,000 feet wide at the south edge of the Sonora quadrangle, but to the northwest it branches and forms a zone 2 to 3 miles wide. Some of the individual faults and shear zones have been mineralized. The Mother Lode fault system traverses a great variety of rocks. In the mapped area these rocks include marble, tectonic breccia, schist, and phyllitic material of probable Paleozoic age; phyllite, conglomerate, mica schist, and a green schist of uncertain but pre-Creta- ceous age; and sedimentary, volcanic, and instrusive rocks of Jurassic age. The marble has been assigned to the Calaveras forma- tion of probable carboniferous age. Some of the sedi- mentary and volcanic rocks have been assigned to the Amador group, of Late or Middle Jurassic age, and to the Mariposa formation, 1 of Late Jurassic age. In this area the Amador group consists of a lower unit, the Cosumnes formation, made up largely of thin-bedded tuff and slate, sandstone, tuffaceous sandstone, and conglom- erate ; and an upper unit, the Logtown Ridge forma- tion, which consists chiefly of coarse- to fine-grained metamorphosed pyroclastics. The Mariposa formation overlies the Amador group and consists chiefly of inter- bedded dark-gray slate, and metamorphosed siltstone, grit, graywacke, tuffaceous graywacke, and pebble con- glomerate. The intrusive rocks of the mapped area range from ultramafic to felsic, but the commonest ones are serpentine and gabbro. Unaltered intrusive rocks, which are characteristic of the core of the Sierra Nevada, are absent in the mapped area. The pre-Cretaceous rocks were dynamo-metamorphosed (Turner, 1948, p. 5) during the Nevadan orogeny in Late Jurassic time, and in many places no original con- stituents can be recognized. Despite this fact the grade of metamorphism generally is low, and most of the rocks are in the chlorite zone of metamorphism. Like most of the Paleozoic and Mesozoic rocks of the western Sierra Nevada, the rocks in the mapped area have been folded and faulted. Open and isoclinal folds have been mapped. In general the dip of beds ranges from vertical to about 50° NE. Faults are present not only within the Mother Lode fault system but also in other parts of the area, and highly crushed, sheared rocks are commonplace. Schistosity is well developed over a wide area, and many of the rocks exhibit linear elements such as intersections of planes, long axes of stretched fragments, axes of minor folds, and striations on fault surfaces. Quartz has been introduced along some of the faults. The quartz veins range in thickness from about 100 feet 1 The accepted name for this formation is the Mariposa slate, but inasmuch as the lithology varies considerably within the mapped area, and in places slate actually is a minor constituent, the name Mariposa formation is proposed. down to minute stringers measurable in fractions of an inch. The more conspicuous veins, known as "bull" quartz veins, are composed largely of milky quartz that contains very little gold ; most of the gold ore shoots are in the mineralized wall rocks. Some of the quartz veins can be traced along their strikes for about a mile, but in general the veins occupy only short stretches along the faults in which they occur. Unconformably overlying the pre-Cretaceous rocks described above are nearly flat-lying rocks of Tertiary age. These rocks include gravel ; rhyolite tuff, andesite tuff, volcanic conglomerate, and siltstone ; and a latite lava flow. The oldest of these rocks is a river gravel that has yielded sizable accumulations of placer gold. STRATIGRAPHY The rocks of the map-area are of two major categories, namely, a younger non-metamorphosed flat-lying series, and an older metamorphosed, steeply-dipping bedrock series. The explanations accompanying plates 1 and 2 describe and give the stratigraphic order of these rocks. The flat-lying series consist of river gravel, often gold- bearing, the Valley Springs formation, Mehrten forma- tion, and a latite lava flow of Table Mountain. The bed- rock series comprise rock units of Calaveras, Cosumnes, Logtown Ridge, and Mariposa formations, and various intrusive masses and dikes. In addition, green schists and related rocks, phyllites, and conglomerates of undeter- mined age have been mapped. However, in the geologic cross-sections these rock units have been tentatively correlated with the other formations present. The cor- relation has been based on lithologic similarities and geologic relations as far as possible. Calaveras Formation of Paleozoic Age Turner (1893) named the Calaveras formation from a belt of fossiliferous marble outcrops of Paleozoic age that lie along the west flank of the Bear Mountains in Cala- veras County. Within the mapped area the rocks that have been assigned to the Calaveras formation are repre- sented chiefly by marble, schist, and a tectonic breccia. Three discontinuous belts of Calaveras formation have been mapped. Western and Central Belts. The western belt lies about a mile southwest of Bear Mountain and is repre- sented in the mapped area by a single lens of marble along a fault zone in the southwest part of the Angels Camp quadrangle ; however, other small lenses occur along this fault zone outside the mapped area. Marble lenses of the central belt are distributed along, or adjacent to, faults and shear zones of the Mother Lode system and crop out along a narrow strip where they usually are associated with tectonic breccia or crush conglomerate. The largest of the marble lenses in this belt is about a mile long and has a maximum width of 600 feet. The marble in the lenses of the western and central belts is fine- to medium-grained, crystalline, and pale blue-gray in color. It is commonly banded with fine- grained dark carbonaceous layers a fraction of an inch thick, and weathers light gray to brownish gray. Cylin- drical crinoid columnals have been found in some of the marble lenses, and some of these fossils suggest a possible Paleozoic age; therefore, the marble and the tectonic 8 Special Report 41 breccia with which it is usually associated have been mapped as part of the Calaveras formation. The tectonic breccia associated with the marble lenses has fragments that range from a fraction of an inch in diameter up to several feet in length. Other components of the tectonic breccia, in addition to marble, are frag- ments of chert, sandstone, quartzite, and quartz. Most of the fragments are rounded by attrition, but many are angular, especially those of quartzite. All are embedded in a very fine-grained matrix of crushed rock debris. Fine-grained quartz-mica schist and phyllite or phyllo- nite are locally closely associated and interfingered with the tectonic breccia. These rocks may represent original strata of fine-grained argillites, or possibly they are merely zones of more complete shearing along faults. Locally, thin, discontinuous, sharply crumpled beds of quartzite may be observed. In such areas, small boudins of quartzite occur where the strata have been pulled apart by intense shearing. Figure 2. Tectonic breccia in the highly sheared Calaveras ( ?) formation. "Pebbles" consist chiefly of marble (M), chert (C), quartzite (Q). Mormon Creek, Sonora quadrangle. Probably the original sequence of strata consisted of interbedded limestone, sandstone, shale, and chert, which, after intense shearing and metamorphism, is now repre- sented by lenses of marble, tectonic breccia, schist, and phyllite or phyllonite. "We believe, therefore, that in the central belt, as well as in the western belt, the Calaveras formation occupies a zone of major faulting. Figure 2 shows details of the tectonic breccia exposed along Mor- mon Creek in the Sonora quadrangle. In this area the Calaveras formation is about 2,000 feet wide. In figure 3 some of the highly sheared material commonly as- sociated with the marble is shown cropping out between the light-colored marble exposures. It has been suggested that in the western and central belts the marble lenses, many of which exhibit sharp minor folds in the banding, are the result of the plastic injection of the marble along fault zones; thus the marble lenses are not necessarily of the same age as the rocks immediately surrounding them (Heyl, 1947; Eric and Stromquist, 1948). Inasmuch as fossils have been found only in the marble lenses there is no positive way of correlating the age of the highly sheared surrounding rocks with that of the marble. Near the lower part of Woods Creek in the southeast part of the Sonora quadrangle and northeast part of the adjacent Chinese Camp quadrangle, as well as to the north, just beyond the northwest corner of the Sonora quadrangle, a variety of rocks has been brought into juxtaposition along this control belt of major faulting. These rocks include marble, tectonic breccia, conglom- erate, tuff, volcanic breccia, and gabbro and serpentine, of differing ages and stratigraphic positions. Eastern Belt. The eastern belt of the Calaveras for- mation is represented in part, by the relatively large body of marble near the city of Sonora. Unlike the smaller discontinuous areas of Calaveras formation in the central and western belts, this larger body is not con- fined to a fault zone, but apparently is interbedded with quartzose rocks, chiefly micaceous quartzite, quartz-mus- covite schist, and quartz-actinolite albite schist. The marble of the eastern belt is massive, fine- to medium-grained, jointed, and shows only vague bedding or banding. It is gray and weathers to a very light gray. The noncalcareous rocks with which the marble appears to be interbedded are dark gray, finely crystalline, re- sistant rocks that consist of beds of slightly micaceous but nearly pure quartzite up to 3 feet thick interbedded with more argillaceous material, chiefly quartz-muscovite schist, and quartz-actinolite-albite schist. The sequence of marble and quartzose rocks has been assigned to the Calaveras formation, chiefly because the marble is litho- logically similar to marble that has been mapped as Cala- veras formation in other places. No diagnostic fossils have been found in the rocks, although structures of possible organic origin have been observed in the marble. Black quartz-mica schist, locally graphitic and well bedded, that occurs in the northeast corner of the Angels Camp quadrangle has been assigned to the Calaveras formation. Farther north in the Calaveritas quadrangle quartz-mica schist is interbedded with limestone. Age. The fossils discovered during the present sur- vey do not permit an age assignment closer than Paleo- zoic for the Calaveras formation in this report. Recognizable fossils were collected from several locali- ties in small marble lenses in the Sonora quadrangle. One of these localities is about 4,500 feet southeast of Mormon Creek and 2,000 feet west of French Flat; ac- cording to Reeside, 2 "The only fossils that have sur- vived recrystallization are crinoid stems. . . . These reach a large size and are of a type said to be most common in Mississippian rocks, but not confined to them." Con- cerning crinoid columnals found in marble in the same belt but only 1,500 feet southeast of Mormon Creek, Reeside 3 states that "Dr. Edwin Kirk, a crinoid special- ist, expresses the opinion that the crinoid remains are of later Paleozoic age rather than Mesozoic, but no closer assignment can be made." Crinoid stems found in other marble lenses in the mapped area and in a marble lens in the canyon of the 2 Reeside, J. B., Jr., personal communication, June 27, 1947. 3 Reeside, J. B., Jr., personal communication, November 22, 1946. Geology of the Angels Camp and Sonora Quadrangles 9 lower part of Coyote Creek, Columbia quadrangle, do age is unknown or uncertain, or some or all of the rocks not permit an age determination. that ' ' look older ' ' by reason of their greater metamor- „,. . , , J7 „ , , „ „ 7 -r, ,. phism and deformation. Relation of Age to the Catchall Calaveras Formation. Rockg that simply are more metamorphosed or de- The wide age span for the so-called catchall Calaveras f orme d than nearby known Jurassic rocks should not formation is a direct result of the fact that no descnp- necessarily be included in the Calaveras formation, be- tion exists for a type section of the Calaveras formation. eauge grade of me tamorphism and amount of deforma- Consequently, many different types of rocks have been ti(m are funetions of tectonic history and environment, mapped as Calaveras formation by various geologists in and not necess arily of age. Therefore, in the mapped different areas. However, in this report the term Cala- area; we haye exelude d from the Calaveras formation veras formation includes those rocks only that we be- cert ain rocks previously assigned to the Calaveras for- heve to be Paleozoic in age because of paleontologic and mat i n because no valid evidence of Paleozoic age has geologic evidence. been found The term Calaveras formation was introduced by In tbig report we uge the term Calaveras formation Turner (1893), who first defined it as including all of ag it wag originally defined by Turner, i.e., it includes the Paleozoic sedimentary rocks of the Sierra Nevada. aU rocks that are ghown to be p a i e0 zoic in age on the Rocks of volcanic origin were excluded. Shortly there- bagig of pa i e ontologic or geologic evidence, after he excluded certain formations in the northern . Sierra Nevada that later were described by Diller esozoic oc (1908), namely, Silurian rocks and the Robinson forma- So far as is known, all of the Mesozoic rocks in the tion of Pennsylvanian age, and therebv seemingly re- mapped area are of Jurassic age; the oldest of these stricted the Calaveras to the Devonian and Mississippian. roeks > the Cosumnes formation, is probably Middle or Of the rocks previously assigned to the Calaveras for- J^ate Jurassic in age ; the youngest the Mariposa forma- e -i tT -u * j * -i i tion, is of Late Jurassic age. The following Jurassic mation, tossils have been round, so tar as is known, only „ ' . , , ° , . ., , ° , _ . „ . ,, ' ,, T • -, zionn o\ + + +i, + +„• formations have been mapped in the two quadrangles in the marbles. Lmdgren (1900, p. 2) states that certain , , , , ,. a ■,-., i • j ? +• „ \- fossils found in the Calaveras formation near Colfax and correlated > ehiefl y on lithologic and stratigraphic lussns iouiiu in tiie \^*ii1t i ii n ,i Agglomerate and volcanic breccia 400 zoic sedimentary rocks ot the Sierra Nevada; all or the Pillow lava . 35 Paleozoic sedimentary rocks of the Sierra Nevada except Agglomerate and volcanic breccia 875 those of Silurian and Upper Carboniferous age ; and the Tuff 85 pre-Mesozoic bedrock of the Sierra Nevada south of the Agglomerate and volcanic breccia.. 490 Taylorsville region. Some geologists apparently have Pillow lava 40-85 used the term Calaveras to include all the rocks whose Agglomerate and volcanic breccia 900 10 Special Report 41 Table 1. Generalized section of the Amador group, Cosumnes River, Amador and El Dorado Counties — Continued. Formation and lithology Apparent thickness (feet) Cosumnes formation 5,100 Bedded tuff and fine-drained volcanic breccia 1,000 Bedded tuff, sandstone, siltstone, slate, and thin conglomerate 2,000 Dark blue-gray to black slate with consider- able sandstone 600 Coarse- and fine-grained conglomerate with many argillaceous interbeds 1,500 Amador group, total thickness 8,000±50 Cosumnes Formation Lithology, Distribution, and Thickness. The Co- sumnes formation was first described by Taliaferro (1943, p. 283). The rocks assigned to the Cosumnes for- mation, in the southwest part of the Angels Camp quad- rangle, consist dominantly of dark-gray to black slate feet of thin-bedded tuff that is very similar to the tuff southwest of Bear Mountain. The total exposed thickness of the rocks assigned to the Cosumnes formation is about 1,500 feet in the mapped area, but inasmuch as the base of the formation is not exposed the total thickness is greater. In the Sonora quadrangle, near Quartz Mountain, the Cosumnes formation consists of black slate, tuff, and minor chert and conglomerate beds. Total thickness of the formation in this area is about 1,200 feet. Age. The Cosumnes formation is considered to be of Late or Middle Jurassic age. Jurassic fossils have been found in the Amador group at several localities and according to Taliaferro (1943, p. 284) indicate an age older than the Oxfordian. Taliaferro believes that the **V ■ w W* it< Figure 3. Marble lenses, white rock, in faulted zone. Highly sheared phyllitic rocks, dark exposures, are associated with the marble. North bank of Stanislaus River. and associated tuffaceous siltstone and sandstone, and of greenish-gray thin-bedded tuff. Southwest of Bear Mountain the rocks are chiefly tuff in beds that range in thickness from a fraction of an inch to 3 inches. These rocks underlie the much coarser, poorly bedded pyro- clastics of the Logtown Ridge formation. Thin-bedded gray to reddish-brown chert is an abundant constituent in parts of the Cosumnes formation of this area. It oc- curs as thin lens-shaped bodies in the volcanic rocks. A few of the chert bodies are as much as 20 feet wide and 50 feet long but commonly they are much smaller. Phyl- litic slate occurs in a few places, generally in beds 10 to 20 feet thick near the contact with the overlying Log- town Ridge formation. Northwest and north of Bear Mountain dark-gray slate, about 750 feet thick, with interbedded sandy and tuffaceous layers, underlies the Logtown Ridge formation ; below the slate is about 750 age of the Amador group extends "from the upper Middle to the lower Upper Jurassic, ' ' although earlier he (1942) expressed doubt that the Amador actually does extend into the Middle Jurassic. During the present investigation an ammonite was found in thin-bedded tuff of the Cosumnes formation, about 2,000 feet west of the contact between the Cosum- nes formation and the overlying Logtown Ridge for- mation, on the north bank of the Cosumnes River about 2 miles below Huse Bridge (State Highway 49), and about 1,850 feet east of the west boundary of the Piddletown quadrangle, El Dorado County. Imlay 4 states that this fossil "is a perisphinctid ammonite, but generic determination is not possible. As the perisphinc- tids first appeared in early Middle Jurassic time, the beds containing this ammonite cannot be as old as the 4 Imlay, R. W., personal communication, January 17, 1950. Geology op the Angels Camp and Sonora Quadrangles II Lower Jurassic. . . . Perisphinctids similar to this am- monite are more common in the early Upper Jurassic than in older beds." Logtown Ridge Formation In the mapped area the Logtown Ridge formation, the upper unit of the Amador group, consists predomi- nantly of metamorphic rocks derived from coarse- grained, generally mafic, pyroclastics ; mafic tuff ; mafic flows ; a little f elsic tuff ; and a few thin beds of tuf- faceous shale. All of these rocks have undergone low- grade metamorphism. The formation was described by Taliaferro (1943, p. 283). One of the most characteristic and consistent units within the Logtown Ridge forma- tion is a coarse-grained volcanic breccia and agglomerate composed chiefly of augite basalt and andesite fragments. Augite Basalt and Andesite Breccia and Agglomerate. Volcanic breccia and agglomerate made up largely of augite basalt and augite andesite, and identical with the Logtown Ridge formation at the type locality on the Cosumnes River, occurs in several areas in the western and central parts of the two mapped quadrangles. The largest of these areas is that occupied by Bear Mountain, in the southwest quarter of the Angels Camp quad- rangle. The coarse-grained fragmental nature of the rock can be observed conveniently in road cuts along State Highway 4 about 1,800 feet east of the west edge of the quadrangle, as well as along the road to the top of Bear Mountain. The breccia and agglomerate are dark green, greenish gray, or gray. The maximum diameter of the blocks is slightly more than a foot, but most of the larger frag- ments have diameters that range from 1 inch to 3 inches. The fragments may be closely spaced, or separated from one another by a considerable amount of tuffaceous matrix. They may be angular or rounded. Most of the fragments are porphyritic ; the phenocrysts commonly are crystals of augite, most of which are 1 to 4 mm in diameter but some are an inch across. Phenocrysts of saussuritized plagioclase are common. The tuffaceous matrix generally is of the same mineralogical composi- tion as the larger fragments. Light-gray glassy-looking fragments that appear to have been derived largely from dacite are also rather common. The sparse phenocrysts are quartz, augite, and highly saussuritized albite. Some of these fragments may be keratophyric rocks, as described by Knopf (1929, p. 16). Amygdaloidal fragments also are common in the coarser-grained pyroclastics of the Logtown Ridge for- mation. Generally they are among the best rounded of the fragments. Many of these fragments are distinctly scoriaceous and appear to have been bombs ; others are more angular and nonscoriaceous and contain only scat- tered amygdules. The amygdules are albite, calcite, chlo- rite, epidote, a green mica, and quartz ; usually several different kinds of amygdules are associated, even in a single thin section. Some of the amygdules consist of two minerals, for example interiors of calcite and rims of albite. The agglomerate and volcanic breccia of the Logtown Ridge formation also occur in other parts of the mapped area besides Bear Mountain. Good exposures of these rocks may be seen on Peoria Mountain, in the west part of the Sonora quadrangle ; in the Angels Camp quad- rangle, just east of the main belt of Mariposa formation; and in a small body, faulted along the east side, at the west boundary of the Sonora quadrangle north of the north arm of Melones Reservoir. Tuff. Pine-grained volcanic rocks of the Logtown Ridge formation are exposed south of Table Mountain, and from there they extend in a strip nearly to the south edge of the Sonora quadrangle. In the Angels Camp quadrangle bedded tuff occurs in the belt of Log- town Ridge formation just west of Texas Charley Gulch, and in the belt just east of the main band of Mariposa formation. Particularly good exposures of bedded tuff showing graded bedding (top to the east) can be seen in road cuts just southwest of the road junction in see. 15, T. 2 N., R. 13 E., about 3 miles south of Angels Camp. In general the rocks of these areas are fine-grained dense dark gray-green tuffs with a few layers of coarser- grained tuff that contain fragments of volcanic rocks up to 3 or 4 cm in diameter. The tuff appears to have been originally andesitic or basaltic in composition, though much of the plagioclase has been completely altered, and all of it has been at least partly altered (as has practically all the plagioclase in- the Mother Lode region). Conglomerate and Slate. Small lenses of conglom- erate have been mapped along the contact between the Logtown Ridge and Cosumnes formations at four places in the southwest part of the Angels Camp quadrangle. The pebbles in this conglomerate are rounded to sub- angular, generally a quarter of an inch to an inch in diameter, and consist of vein quartz, intrusive rocks, dark fine-grained tuff, slate, phyllite, and mica schist. The conglomerate has been assigned arbitrarily to the Logtown Ridge rather than to the Cosumnes formation on the theory that it is basal and occupies local channels in the Cosumnes. A small belt of dark-gray slate has been mapped in the southeast part of the Angels Camp quadrangle. This belt of slate is surrounded by volcanic rocks of the Log- town Ridge formation, and is here interpreted as part of that formation, although other plausible hypotheses are that the slate represents the Mariposa formation ex- posed in the trough of a syncline or, somewhat less likely, the Cosumnes formation exposed in the crest of an anti- cline. Thickness. The thickness of the Logtown Ridge for- mation differs from place to place, which is to be ex- pected in dominantly coarse-grained volcanic rocks. The formation is about 2,700 feet thick 5 (Taliaferro, 1943, p. 283) at the type locality on the Cosumnes River, west of Huse Bridge, whereas on Bear Mountain, near the headwaters of Brower Creek in the Angels Camp quad- rangle, the thickness is about 1,500 feet ; near the top of the mountain the thickness is at least 2,600 feet. In the Sonora quadrangle much of the Logtown Ridge forma- tion has been cut out by intrusive bodies and faults, and consequently its thickness cannot be determined. Age. The Logtown Ridge formation is of Middle or Late Jurassic age. Fossils, found by E. T. MeKnight of the Geological Survey, were collected from the Logtown Ridge formation in the SE^ sec. 20, T. 1 N., R. 14 E., 5 Taliaferro, N. L. 12 Special Report 41 just northwest of the junction of State Highway 49 and the road to Montezuma, in the Sonora quadrangle. The fossils occur in tuffs about 65 feet below the top of the formation. Referring to these fossils, Imlay" says "The collection contains Lima cf. L. dilleri Hyatt, Camptonectes sp., and a Tellina-like pelecypod. These fossils cannot be defi- nitely identified with species in our collections, but the Lima and Camptonectes closely resemble species in the Mormon sandstone of Middle Jurassic age in the Tay- lorsville region." However, if the underlying Cosumnes formation is early Late Jurassic in age at the type local- ity, it is unlikely that the Logtown Ridge formation is Middle Jurassic in age 50 miles away. Concerning peris- phinctid ammonite from the type locality of the Logtown Ridge formation. Imlay 7 reports that the fossil "shows features that are more common among Kimmeridgian than among upper Oxfordian ammonites. ' ' Mariposa Formation The youngest pre-Cretaceous sedimentary formation in the mapped area is the Mariposa formation. The ac- cepted name of this unit is the Mariposa slate (Wil- marth, 1938, p. 130), but inasmuch as the lithology varies considerably within the mapped area and in places slate actually is a minor constituent, the name Mariposa for- mation is proposed. Moreover, the proposed name is one that has been used generally by geologists, including Survey geologists. "Mariposa beds" was the name first applied by Becker (1885, p. 18) to the formation; no type locality has been described. Distribution and Lithology. The Mariposa formation is exposed, in the mapped area, in a partly fault-bounded northwest-trending belt that lies just west of the Mother Lode fault system. Near the south edge of the Sonora quadrangle this belt is about 3,000 feet wide; near the south boundary of the Angels Camp quadrangle the belt is about 12,000 feet wide ; and near the west edge of the Angels Camp quadrangle the belt is about 7,000 feet wide. A short distance south of the Angels Camp quad- rangle this main belt splits, and a much narrower belt of Mariposa formation, 250 to 1,500 feet wide, is exposed just west of Bear Mountain ; the narrow belt is a syn- cline, and it is interesting to note that Turner (1894a, p. 457), in a cross section, long ago showed the synclinal structure of the belt. In the Sonora quadrangle about two-thirds of the rocks assigned to the Mariposa formation are dark-gray to black slates, and the rest are metamorphosed fine- to coarse-grained sandstone and grit, graywacke, pebble conglomerate, tuffaceous sandstone, and sandy to silty tuff. Slate is exposed in the Sonora quadrangle along Highway 49 where it crosses Slate Creek ; and about half a mile to the cast thin grit and conglomerate beds occur in the slates that crop out just northwest of the high- way. In this same area thin dark-gray, fine-grained tuf- faceous sandstone overlies the slate. The Mariposa formation is thought to have a deposi- tional contact with the Logtown Ridge formation along the east flank of Peoria Mountain and along parts of the 6 Imlay, R, W., personal communication, May 20, 1947. 7 Imlay, R. W., personal communication, March 9, 1950. flanks of Bear Mountain. In these areas the Mariposa consists chiefly of dark lead-gray slate with minor layers of grit and pebble conglomerate. Toward the east, near Peoria Mountain, tuffaceous and graywacke interbeds become common, although slate predominates. The east- ern part of the Mariposa formation is cut off by faults of the Mother Lode fault system. In the mapped area the proportion of volcanic material increases toward the northwest, and in the western part of the Angels Camp quadrangle about 70 percent of the rocks assigned to the Mariposa formation is volcanic or partly volcanic in origin and consists chiefly of schistose sandy tuff and tuffaceous graywacke. The possibility has been suggested that practically all the rocks of the Mariposa formation are essentially vol- canic in origin. Such a hypothesis demands that the slates actually are merely a fine-grained facies (dust- tuff) of the volcanic rocks, and that they are not derived from detrital clay. Because of the fineness of grain, and the metamorphism that these rocks have undergone, evi- dence in the mapped area is inconclusive. However, the fact that in places the slate is composed largely of minute fragments of quartz suggests that some of the slate, at least, may be derived neither from detrital clay nor from dust-tuff, but rather from fine-grained silt. A rather smooth cleavage is developed in most of the rocks of the Mariposa formation. In the fine-grained slates it is nearly perfect, and even in the sandy layers cleavage is good. In the grit, conglomerate, and gray- wacke layers cleavage generally is incipient or lacking, but even these rocks have been sheared in places and have developed a cleavage. Some of the tuffaceous layers have an irregular, primary schistosity, which is described below. Considerable local crumpling and sharp minor folds in beds are common in parts of the Mariposa for- mation, particularly in the slate units in the Sonora quadrangle. The axes of these minor folds generally plunge steeply, and they appear to be the result either of local drag along faults or of shearing with a strong horizontal component. In places quartz veins and pockets are associated with these minor fold axes. Subdivisions. In the vicinity of Colfax, Placer County, the Mariposa formation has been subdivided by Smith (1910, charts opp. pp. 217, 222; 1916, pp. 30-31) into a lower formation, the "Mariposa slates," made up of dark slate containing Aucella erringtoni Gabb and Cardioceras alternans, (von Buch) [equals Amoeboceras Dubium (Hyatt) ] and an upper unit, the "Colfax for- mation," composed principally of tuffaceous material and containing Perisphinctes colfaxi Gabb. Goranson (1924, p. 162) similarly divided the Mariposa formation. South of the Merced River, Taliaferro (1933, p. 149) has used the name "Mariposa group" to include two for- mations : a lower formation, the ' ' Indian Gulch agglom- erates, tuffs, sandstones, and conglomerates," and an upper formation, the "Mariposa slates." Although evidence for such a twofold stratigraphic di- vision of the Mariposa formation has not been found in the Sonora quadrangle, a division is possible in the Angels Camp quadrangle. In the southwest part of that area, particularly on parts of the southern and eastern flanks of Bear Mountain, the Mariposa formation lies with depositional contact upon metavolcanic rocks of the Geology of the Angels Camp and Sonora Quadrangles 13 Logtown Ridge formation and here the basal part of the Mariposa consists almost entirely of dark lead-gray slate with subordinate sandy and pebbly layers. Apparently overlying the slate to the east, although separated by a fault, are interbedded slate and tuffaceous rocks that may correspond to the Colfax formation of Smith. Tuffaceous Sandstone. The sandstone of the Mariposa formation is chiefly graywacke as the term is defined by Pettijohn (1949, p. 227). It is composed of fragments of volcanic rocks, slate, phyllite, chert, augite, saussuritized plagioclase, and, in places, quartz, in a matrix of ex- tremely fine-grained slaty and phyllitic material. The fragments are angular to subrounded and generally are less than 4 mm in diameter, and average 1 to 2 mm. Interbedded with these essentially volcanic rocks are dark slates which, in the Angels Camp quadrangle, occupy an area only a fraction as large as the total area underlain by the volcanic rocks. Along the main belt of the Mariposa formation, east of Bear Mountain (pi. 1), the geology has been generalized ; that is, thin slaty bands occur within the units mapped as volcanics, and, con- versely, a few thin bands of volcanics occur within the units mapped as slate. A detailed section across the Mariposa formation, measured along parts of Bower Creek and Angels Creek in the south-central part of the Angels Camp quadrangle, is shown in table 2. As shown in the measured section, there are a few massive tuffaceous sandstone units, within the schistose tuffaceous rocks of the Mariposa formation that possibly could be assigned to the Logtown Ridge formation; these massive units, however, do not closely resemble any rocks known to belong to the Logtown Ridge for- mation in the mapped area; in particular they do not resemble the nearby augite porphyry greenstone breccia of Bear Mountain. The tuffaceous sandstones and tuffs, here assigned to the Mariposa formation, bear no megascopic resemblance to rocks known to belong to the Logtown Ridge forma- tion in the mapped area. Under the microscope, frag- ments of augite and of augitic greenstone can be seen; such fragments, it is true, do resemble those in the Log- town Ridge formation, but their presence is to be ex- pected in rocks that overlie and presumably were de- rived in part from the Logtown Ridge formation ; in other words, these augitic fragments are thought to represent merely the debris of the underlying formation. If the tuffaceous sandstones and siltstones are assigned to the Logtown Ridge formation, it is necessary to postu- late, for this section, the existence of a great many small isoclinal folds, in which tuffaceous rocks (Logtown Ridge formation) occupy anticlines and slaty rocks (Mariposa formation) occupy synclines. Bedding is well shown in the excellent exposures along Brower Creek, but no folds are visible. The few graded beddings observed in the section all show tops to the east. Thickness. The major structure of the main belt of the Mariposa formation, east of Bear Mountain, in the Angels Camp quadrangle, is not sufficiently known to warrant a measurement of thicknesses of the Mariposa formation. In the southern part of the Sonora quadrangle and adjacent parts of the adjoining Chinese Camp quad- rangle, graded bedding is unusually well developed in the Mariposa formation, and shows that the top of the section is toward the east. The Mariposa formation here is about 3,000 feet thick. To the west the Mariposa for- mation unconformably overlies the Logtown Ridge for- mation ; to the east it is cut off by the Mother Lode fault zone, so that the top of the formation is not seen. According to Taliaferro (1933, p. 149) the Mariposa consists of more than 3,000 feet of acid and intermediate volcanics, sandstones, and cherts, and 2,000 to 2,500 feet of slates, making the total exposed thickness in this general region about 5,000 to 5,500 feet. Age. The Mariposa formation is of Late Jurassic age. Three fossil localities were discovered in the Mari- posa formation. Two of these are in the Sonora quad- rangle, and one is to the south in the adjoining Chinese Camp quadrangle. Also, the well-known Texas Ranch locality is only a few hundred feet south of the south boundary of the Angels Camp quadrangle. The fossils found in Long Gulch, about a mile south of Melones Reservoir, are poorly preserved and are not diagnostic, for they have been so crushed and distorted that species are not recognizable. However, Belemnites sp., Aucella sp., and fragments of ammonites can be identified, along with carbonized plant remains. Concerning fossils found on the crest of a ridge about 1^ miles northwest of Jacksonville, Chinese Camp quad- rangle, Imlay 8 says ' ' The fossils in the fine-grained conglomerate . . . consist mainly of an Aucella with fine radial striations that has commonly been called Aucella erringtoni Gabb and is characteristic of the Mariposa formation. ..." Fossils also were found in the canyon of Woods Creek about 1,500 feet north of the south border of the Sonora quadrangle. Imlay 9 states that the fossils are Aucella erringtoni Gabb and Lamellaptychus sp. He adds, " La- mellaptychus occurs in the Middle and Upper Jurassic and the Neocomian and represents the apertural cover- ing of such ammonites as Haploceras, Lissoceras, Oppelia, and similar comparatively smooth forms. Aucella erring- toni is rather common in collections from the Mariposa slate." The Late Jurassic age of the Mariposa formation has been known for many years, but paleontologists have been unable to agree on the proper stage to which the Mariposa should be assigned. Some say upper Oxfordian, and others say Kimmeridgian (Reeside, 1919, p. 10). Concerning the occurrence of Aucella erringtoni in the Mariposa formation, Imlay 10 says ' ' Finely striate Au- cellas, such as this species, occur commonly in the Pacific northwest and in the Arctic regions in beds of Kim- meridgian age and are rare in the upper Oxfordian. The age of at least the lower part of the Mariposa formation has been fixed by the occurrence of Amoeboceras (Amoe- bites) dubium Hyatt, as the subgenus Amoebites has been found consistently elsewhere only in beds of lower Kimmeridgian age." If the lower part of the Mariposa is Kimmeridgian, none of the formation can be Ox- fordian. Smith (1916, p. 30) thought that the Mariposa formation was Kimmeridgian and Portlandian in age. 8 Imlay, R. W., personal communication, October 14, 1946. " Imiay, R. W., personal communication, March 5, 1947. 10 Imlay, R. W., personal communication, March 5, 1947. 14 Special Report 41 Table 2. — Section across Mariposa formation, measured along Broiler Creek, and Angels Creek, Calaveras County, California * SW. Logtown Ridge formation Fault Thickness Mariposa formation (in feet) Not exposed 125 Dark-gray slate 40 Dark-gray tuffaeeous siltstone, beds about 2 in. thick 45 Alternating coarser gray, finer dark-gray tuffaeeous siltstone 90 Not exposed 55 Thin-bedded fissile tuffaeeous siltstone 30 Dark-gray slate and fine gray tuffaeeous siltstone, quartz stringers 25 Dark-gray slate and fine gray tuffaeeous siltstone 30 Dark-gray slate 50 Dark-gray tuffaeeous siltstone 30 Dark-gray slate 5 Dark-gray tuffaeeous siltstone to 2 ft. thick, interbedded dark-gray slate to 3 in. thick 35 Dark-gray slate, interbedded tuffaeeous siltstone 10 Dark-gray tuffaeeous siltstone 20 ft. 85 10 GO 20 15 Dark-gray slate, quartz stringers Dark-gray tuffaeeous siltstone, beds about 1 thick '___ Gray tuffaeeous siltstone, beds 2 to 3 ft. thick- Not exposed Dark-gray slate, a little tuffaeeous siltstone Gray tuffaeeous sandstone, fragments to 2 mm. Not exposed 15 Tuffaeeous siltstone, a little slate 30 Tuffaeeous grit, fragments to 5 mm 50 Tuffaeeous siltstone 50 Tuffaeeous siltstone, quartz stringers 5 Gray tuffaeeous sandstone, with fissile silty layers up to 5 ft. thick 195 Tuffaeeous grit, fragments up to 5 mm 50 Gray tuffaeeous sandstone 70 Tuffaeeous siltstone and dark-gray slate (50-50) 25 Tuffaeeous sandstone , 25 Dark-gray slate with tuffaeeous siltstone 20 Tuffaeeous sandstone 20 Tuffaeeous siltstone and dark-gray slate 80 Not exposed 35 Dark-gray slate and tuffaeeous siltstone 30 Tuffaeeous sandstone, fragments up to 1 mm 100 Tuffaeeous sandstone with lenses of black "shale" up to 14 in. long and 1 in. wide 5 Tuffaeeous sandstone with a few 1-in. beds of dark-gray slate 40 Tuffaeeous sandstone, fragments up to 2 mm 10 Tuffaeeous sandstone, fragments up to 1 mm 40 Tuffaeeous sandstone with scattered 2-in. layers of tuffaeeous siltstone 20 Tuffaeeous siltstone and dark-gray slate 30 Tuffaeeous siltstone, a little tuffaeeous sandstone 40 Tuffaeeous siltstone, quartz stringers 10 Tuffaeeous siltstone, beds 1 to 6 in. thick 15 Dary-gray slate and tuffaeeous siltstone 30 Tuffaeeous siltstone 235 Dark-gray slate 10 Tuffaeeous siltstone 10 Milky quartz vein 5 Massive tuff (Logtown Ridge?) 40 Tuffaeeous siltstone, scattered beds of tuffaeeous sandstone 175 Dark-gray slate _ 20 (feet) 125 165 210 300 355 385 410 440 490 520 525 560 570 590 595 680 690 750 770 785 800 830 880 930 935 1130 1180 1250 1275 1300 1320 1340 1420 1455 1485 1585 1590 1630 1640 1680 1700 1730 1770 1780 1795 1825 2060 2070 2080 2085 2125 2300 2320 Thickness (in feet) (feet) Slaty tuffaeeous siltstone 150 2470 Tuffaeeous siltstone 80 2550 Massive tuff (Logtown Ridge?) 50 20(10 Tuffaeeous sandstone, fragments up to 2 mm.__ 130 2730 Tuffaeeous grit, milky quartz pebbles, a few 1-ft. beds of slate and tuffaeeous siltstone 120 2850 Fine-grained tuffaeeous sandstone 75 2925 Tuffaeeous grit 30 2955 Slate and tuffaeeous siltstone 30 2985 Tuffaeeous grit 35 3020 Tuffaeeous siltstone 45 3065 Dark-gray slate and tuffaeeous siltstone 75 3140 Dark-gray slate and tuffaeeous siltstone, quartz stringers 20 3160 Tuffaeeous siltstone 120 3280 Dark-gray slate, minor amounts of slaty tuff 30 3310 Tuffaeeous siltstone 60 3370 Dark-gray slate, minor amounts of tuffaeeous siltstone 100 3470 Tuffaeeous siltstone, minor amounts of dark-gray slate 230 3700 Tuffaeeous siltstone (approx. junction of Brower and Angels Creeks) 20 3720 Tuffaeeous sandstone 30 3750 Tuffaeeous siltstone 10 3760 Fine-grained tuffaeeous sandstone 10 3770 Tuffaeeous siltstone, minor amounts of fine- grained tuffaeeous sandstone 30 3800 Tuffaeeous sandstone, some silty 20 3820 Tuffaeeous siltstone, some sandy 20 3840 Fine-grained tuffaeeous siltstone and dark-gray slate 30 3870 Fissile tuffaeeous siltstone, a few beds of slate_. 40 3910 Tuffaeeous siltstone, a few thin sandy beds 180 4090 Tuffaeeous slate-siltstone 35 4125 Tuffaeeous sandstone 5 4130 Fissile tuffaeeous siltstone 80 4210 Dark-gray slate with tuffaeeous siltstone inter- beds. Exposures poor, float abundant 350 4560 Tuffaeeous siltstone, minor amounts of slate 25 4585 Dark-gray slate, minor amounts of tuffaeeous siltstone 145 4730 Not exposed 185 4915 Dark-gray slate, minor amounts of tuffaeeous siltstone 105 5020 Tuffaeeous siltstone 5 5025 Tuffaeeous sandstone 10 5035 Tuffaeeous grit, quartz pebbles 10 5045 Tuffaeeous sandstone 35 5080 Tuffaeeous siltstone 160 5240 Dark-gray slate, minor amounts of tuffaeeous siltstone 60 5300 Not exposed 145 5445 Dark-gray slate 55 5500 Not exposed : 35 5535 Fissile tuffaeeous slate, tuffaeeous siltstone, and dark-gray slate 45 5580 Dark-gray slate 60 5040 Not exposed 60 5700 Not exposed, slate float 210 5010 Dark-gray slate 240 6150 Fault Logtown Ridge formation NE. * This section may not be a stratigraphic section, as several major folds may be present ; "thickness" therefore is not necessarily true thick- ness. In this section "siltstone" means that the rock is coarser than slate but most of the individual grains are barely visible to the unaided eye; "sandstone" means that the grains are easily visible but generally are less than 2 mm. in diameter: "grit" means that the grains in general are 2 to 4 mm. in diameter. In the table, graywacke is included under the term "sandstone." The section was measured by J. H. Eric, A. A. Stromquist, G. W. Walker, and F. G. Wells, on May 1 and 2, 1948. Geology of the Angels Camp and Sonora Quadrangles 15 Pre-Cretaceous Rocks of Uncertain Age An area underlain chiefly by phyllite, stretched con- glomerate, and green schist of undetermined, pre- Cretaceous age lies in general northeast of one of the main faults of the Mother Lode system. These rocks have not been assigned to any formation, although they have been tentatively correlated in part with the Co- sumnes and Logtown Ridge formations. We believe they represent a more schistose and slightly more meta- morphosed facies of those formations. Evidence per- taining to the tentative correlation of these rocks is discussed elsewhere in this report, under "Some prob- lems of correlation." Phyllite, Stretched Conglomerate, and Related Rocks. In the northeast part of the Angels Camp quadrangle the rocks have been more intensely metamorphosed than elsewhere in the quadrangle. Phyllite, quartz-mica schist, phyllonite, and conglomerate are the common sedimentary rock types in this part of the mapped area. Pebbles in the conglomerate have been stretched. Ratios of diameters of the pebbles are commonly in the order Of 1 : 2 : 4 to 1 : 2 : 8. Conglomerates and phyllites, derived from slates and thin-bedded tuffs, are well exposed near the southeast corner of the Angels Camp quadrangle. The conglom- erate is an important mapping unit in this area because some of the layers are excellent markers and can be traced several miles. Although some of the conglomerate beds have been faulted into their present positions, prob- ably they do not all represent faulted or folded parts of a single conglomerate bed. The conglomerates and phyllites in the northwest part of the Sonora quadrangle, like those in adjacent parts of the Angels Camp quadrangle, are only slightly meta- morphosed and consist of pebble conglomerate with in- terbeds of sandstone, slate, siltstone, and bedded tuff. The conglomerate contains pebbles of a great variety of rocks, including volcanic rocks, slate, schist, chert, mafic intrusives, quartz, quartzite, and marble. The marble in the pebbles bears a close resemblance to the marble that is assumed to belong to the Calaveras formation, but no fossils have been found in the pebbles. Many of the pebbles have been stretched, and ratios of the pebble diameters are in the order of 1 : 2 : 4. Adjacent to the pebble conglomerate in the northwest part of the Sonora quadrangle are dark-gray siltstone and slate that contain minor amounts of sandstone, thin conglomerate beds, and bedded tuff and tuffaceous sand- stone. These rocks have all been mapped as phyllite ; in places they appear to grade into the pebble conglom- erate. Their total exposed thickness in this area, includ- ing the conglomerate, is about 2,500 feet, but they are cut off by faults both to the northeast and to the south- west. Phyllite, phyllonite, and fine-grained quartz-muscovite schist occur along the north edge of the Sonora quadran- gle, near the city of Sonora, and in the vicinity of Raw- hide Flat, Jamestown, and Stent. These rocks bear a close resemblance to rocks typical of the Cosumnes for- mation though they are of slightly higher metamorphic grade. Some beds, intercalated with phyllite and schist, contain pebbles that are much more distorted than those in the northwest part of the Sonora quadrangle ; gener- ally the pebble layers have been completely crushed and recrystallized to phyllonite. These rocks are dark gray- green, nearly black where fresh, but rusty gray-brown where weathered. In the core of the major north-plunging anticline, southeast of Jamestown, the predominant rock type is dark-gray slate that contains layers of phyllite, sandy layers showing a phyllitic luster, and scattered con- glomerate layers with stretched pebbles. Green Schist and Related Rocks. A large area under- lain by green schist lies in general to the east of one of the main faults of the Mother Lode system. Most of the rocks of the green schist have not been assigned to any formation on the geologic maps (pis. 1 and 2), but some have been tentatively correlated with the Logtown Ridge formation and are believed to represent a more schistose facies of that formation. Evidence pertaining to the cor- relation of these rocks is discussed elsewhere in this re- port under ' ' Some problems of correlation. ' ' In the southwest part of the Angels Camp quadrangle several small areas of green schist have been mapped; because of more certain correlation, the green schist in these areas has been assigned to the Logtown Ridge formation. In the Sonora quadrangle the green schist is well ex- posed along the road to Jacksonville in the southeast part of the quadrangle ; along State Highway 49 be- tween Jamestown and Sonora ; and along the same high- way north of Table Mountain, especially near Tuttle- town. In the Angels Camp quadrangle the green schist covers wide areas and is exposed along Highway 49 for almost the entire distance through the quadrangle. Most of the rocks of the green schist are dark green to brownish green and gray on weathered surfaces, but where fresh the schist generally is bright green to gray- green. Schistosity is well developed although locally it is absent in lens-shaped areas in which are preserved the original textures and structures of the pyroclastic rocks. Part of the green schist in the mapped area is clearly derived from coarse-grained agglomerate and voteanic breccia ; the original texture can be well seen in the large area underlain by the green schist northeast of Altaville, especially on Brunner Hill. The coarse fragmental na- ture of the original rock can also be seen clearly in the area just north of Tuttletown. Bedded tuffs are less abundant than coarse pyroclastic rocks in the green schist. However, bedded tuffs are well exposed along San Domingo Creek, east of Highway 49 in the north part of the Angels Camp quadrangle, and in parts of a narrow belt of the green schist extending from Carson Hill to Altaville. In hand specimen the tuff of this belt appears to be almost identical with non- schistose bedded tuff in the Logtown Ridge formation east of the main band of the Mariposa formation ; the only difference is that the abundant dark-green augite crystals have been replaced by uralitic hornblende and actinolite crystals. Plow rocks make up a small percentage of the green schist. Locally the flows show pillow structure ; and in all cases observed, the tops of the pillows are to the east. These features can be observed along Sullivan Creek, es- pecially where the road between Campo Seco and Algerine crosses the creek. Three volcanic units within the mapped area are suffi- ciently distinctive to warrant their being mapped sepa- 16 Special Report 41 rately from the other volcanic rocks lumped into the green schist. One map unit is fine- to medium-grained well-bedded amphibole crystal tuff with minor flows of interbedded hornblende andesite. The tuff is light gray to gray-green ; the flows are dark green to nearly black. These rocks are best exposed along Sullivan Creek near the east edge of the Sonora quadrangle and on State Highway 49 just south of the city of Sonora. Near Sonora the rock is fairly massive, well jointed, and somewhat coarser- grained than elsewhere, and was originally mapped by Turner and Ransome (1897) as diorite. The second map unit is a felsic, possibly rhyolitic, tuff, much of which has been metamorphosed to sericite schist. This rock is well-exposed in the Sonora quadrangle along Highway 49 between Sonora and Jamestown, and stands out in sharp contrast to the more typical green schist because it is lustrous white where fresh and rusty buff where weathered. To the south this unit becomes less schistose, contains less sericite, and grades into a fine- grained gray, slightly schistose tuff. Toward the north, near Altaville, rhyolitic tuff have been mapped but they are not extensive in area. The third unit is hornblende andesite. This unit oc- cupies two areas in the Angels Camp quadrangle, one just west of State Highway 49 between Carson Hill and Angels Camp, and one just south of the northwest corner of the quadrangle ; it can be seen conveniently along the hillside half a mile due west of Frogtown. The rocks of this unit are chiefly metamorphosed massive flows and flow breccias ; agglomerate may be present in a few places. The hornblende andesite is porphyritic and has small but conspicuous phenocrysts of euhedral green hornblende in a light greenish-gray fine-grained ground- mass. In a few places quartz is an important constituent, and the rock is hornblende dacite, but these small areas have not been mapped separately from the main bodies of hornblende andesite. The stratigraphic relations of the bedded amphibole crystal tuff, the sericite schist, and the hornblende andes- ite units have not been established. Tertiary Rocks Essentially flat-lying rocks of Tertiary age occupy parts of the mapped area. Their distribution, shown on the geologic maps (pis. 1 and 2), indicates that they occupied ancient valleys. Owing to their resistance to erosion, some of these rocks now stand as hills above the surrounding landscape. Three formations and one lava unit of Tertiary age have been mapped. These are : river gravel of Eocene (?) age; Valley Springs formation (interbedded rhyolite tuff and gravel) ; Mehrten forma- tion (conglomerate, mudflows, agglomerate, breccia, and tuff that are essentiaally andesitic or basaltic through- out) ; and latite of Table Mountain. River Gravel of Eocene (?) Age The oldest rocks of Tertiary age within the mapped area consist of gravel and conglomerate with interbedded sand and sandstone. These rocks are exposed chiefly in parts of the Tertiary Calaveras River in the northern part of the Angels Camp quadrangle, where they are overlain by rhyolites and andesites ; and also in the southern part of the Sonora quadrangle, where they are overlain by andesites. The gravels are well exposed in the hydraulic pit of the San Domingo mine (fig. 4), where their thickness is more than 100 feet. The larger fragments are pebbles, cobbles, and boulders of many kinds of bedrock and include pebbles of white vein quartz. The lowest part of the formation has yielded much gold. On the early maps of the Mother Lode district, the "auriferous gravels," along with the other rocks of Ter- tiary age, were assigned to the Neocene, a term formerly used to designate Miocene and Pliocene. It is now known that not all the Tertiary rocks are of Miocene and Plio- cene age. In fact, Lindgren and Knowlton (Knowlton, 1911, p. 57) recognized the deep gravel as probably Eocene in age. The exact age of the auriferous gravel in the mapped area has not been established, as no fossils have been reported from it. Similar deposits farther north, however, Chaney (1932, pp. 229-302) has called Eocene. Allen (1929) believes that these early gravels were deposited contemporaneously with the lone forma- tion of Eocene age a few miles to the west, and MacGinitie (1941) has referred to similar river gravels as "lone gravels" and "lone formation." We are un- certain of the age relations of the river gravel to the deposits of clay, sand, and lignite in the lone formation farther west. In some areas, such as parts of the Sonora quadrangle and the northwest part of the Angels Camp quadrangle, where auriferous gravel locally does not underlie younger deposits, there may have been some reworking of the river gravel in Pleistocene time. Valley Springs Formation Unconformably overlying the auriferous river gravel of Eocene ( ?) age are rocks that have been mapped as the Valley Springs formation (Piper, et al., 1939, pp. 71-80). These rocks consist of interbedded rhyolite tuff and gravel. The gravel is identical with the underlying river gravel of Eocene ( ?) age from which it very likely was derived, so that, in this area, the presence or absence of rhyolite tuff was the sole means used to distinguish the two formations ; the contact was arbitrarily placed at the base of the lowest observed layer of rhyolite tuff. In the mapped area the Valley Springs formation is exposed only in the Tertiary Calaveras River, where it has a maximum thickness of about 200 feet, although rhyolitic lake beds have been reported (Bowen and Crip- pen, 1948, p. 50) in an old tunnel under Table Mountain near Jamestown. The Valley Springs formation is well exposed at only a few places, but at such places rhyolite tuff exceeds gravel in abundance. The tuff is white to light gray, compact, and fine-grained. Under the micro- scope it is seen to consist essentially of shards of glass with scattered crystals of sanidine, up to 3 mm in diam- eter, and of quartz, some of which is embayed. In a few places the tuff contains clear crystals of quartz up to 5 mm in diameter ; one of these places is on the lower north slope of a hill half a mile east of Altaville, just east of the pipe line. In other places some of the tuff appears to be poor in quartz, and may be trachyte. In addition to the interbedded rhyolite tuff and gravel, which comprise the greater part of the Valley Springs formation in this area, there are a few isolated hills composed of rhyolite tuff without gravel (pi. 1). These areas stand topographically higher than the rest of the formation, and therefore the nongravelly rhyolite tuff is Geology op the Angels Camp and Sonora Quadrangles 17 K a a o o V ,£= 2 fl "5 i) T3 a 3 o oq 0> J3 T3 •*-> fl B 4) ,° 0) ■" » fl S B ra .2 £ ■SI'S a a v-i B O B o> w ■w ft .B (-. Cv O S fl & J o Oj to s M a- t» _a a -t-j CM a •rt u cs << a a iffl ru +J a o a £ M 18 Special Report 41 assumed to occur in the upper part of the formation. One of these hills rests directly on bedrock, suggesting that the rhyolite tuff may once have been more extensive than the gravels and tuffs of the lower part of the forma- tion, which were confined -to the channel. The nongrav- elly rhyolite tuff may be remnants of one bed, although Julihn and Horton (1938, p. 45) write of "two distinct periods in which heavy blankets of rhyolite tuffs were laid down." The age of the Valley Springs formation has not been established definitely, but it is probably Miocene. Piper, Gale, Thomas, and Robinson (1939, pp. 79-80) suggest that it may be correlated tentatively with the middle Miocene Salinas shale of the Coast Ranges. Miocene leaves were reported by Knowlton (1911, pp. 57-64) either from gravel just below the lowest beds of rhyolite tuff or from the lowest rhyolite tuff, in Placer and Nevada Counties, but studies by Chaney (1932, pp. 229-302) have suggested that these fossils are Eocene. Inasmuch as the fossils may have come from below the lowest rhyolite tuff, however, they may not be from the Valley Springs formation or its representative in Nevada County; another possibility is that there may be differ- ent ages of rhyolite tuff in the Sierra Nevada. For exam- ple, Jenkins (1935, p. 196) suggests that deposition of rhyolite ash began in Oligocene time. Mehrten Formation Unconformably overlying the Valley Springs forma- tion is the Mehrten formation (Piper, et al., 1939, pp. 61- 71). This formation is exposed in the northeast part of the Angels Camp quadrangle, where it attains a maxi- mum thickness of about 300 feet and occupies essentially the same system of channels as the older Tertiary rocks. It is also exposed near Table Mountain in the Sonora quadrangle. In the mapped area the Mehrten formation is essentially andesitic or basaltic throughout, and con- sists of conglomerate, mudflows, agglomerate, breccia, and tuff, composed chiefly of hornblende andesite. The matrix of the pyroclastic rocks is similar in composition to the fragments. Fragments of andesite as much as 4 feet in diameter have been observed. Some of the con- glomerate and agglomerate layers are so thoroughly in- durated that they stand out as ledges and small cliffs as shown in figure 5. The rocks are bedded, although at many places the bedding is not readily apparent. In the vicinity of Table Mountain, laminated clay, siltstone, and ash are abundant. In some places, such as about 1^ miles northwest of the Calaveras Central mine, frag- ments of rhyolite tuff and pebbles of bedrock from the underlying Valley Springs formation have been incor- porated in the basal parts of the Mehrten. This makes it difficult to establish the contact between the two forma- tions ; however, the presence of fragments- of andesite or basalt generally distinguishes the Mehrten from the underlying rocks. Although andesite in the form of frag- ments is by far the most common rock type in the Mehr- ten formation, fragments of other rocks are locally abundant. Boulders of granitic rocks, some as much as 5 feet in diameter, have been observed within the Mehrten formation. Two principal types of andesite or basalt are present : one is dull red, the other white to light gray. Both types contain easily visible phenocrysts of plagioclase and am- phibole, and in both types the plagioclase is shown, by measurement of refractive indices, to have a composition of approximately An 4 r., although maximum extinction angles suggest that some of the plagioclase may have a composition closer to An G o- The plagioclase in the red variety is faintly zoned, whereas much of that in the white kind is well zoned. The red rock contains highly pleochroic basaltic hornblende, with a small extinction angle, as well as augite, hypersthene, and magnetite. The white andesite contains common hornblende, a little magnetite, and apatite ; pyroxene is less common. Fossils were found in laminated clay and siltstone below andesitic volcanics in the Pulpit Rock adit, about half a mile northwest of Jamestown. According to Brown n the collection represents the so-called Table Mountain flora, and contains the following fossils: Quercus convexa Lesquereux Carya iyphinoides (Lesquereux) Condit Persea coalingensis (Dorf) Axelrod Cercocarpus antiquus Lesquereux Ilex opacoides Condit Mahonia sp. Ribes or Crataegus sp. According to Condit (1944, p. 74) the Table Mountain flora, which is from deposits near Columbia, California, indicates "a transitional Mio-Pliocene age." However, some uncertainty seems to exist as to the formation, and even the nature of the rocks, from which the fossils were collected. "We have assigned the laminated clay, siltstone, and ash of the Pulpit Rock adit and other places under Table Mountain to the andesitic Mehrten formation. Knowlton (1911, p. 57) says that the leaves collected at the Columbia locality are from the upper part of the andesite. Chaney (1932, p. 299) says that they were found in "tuffaceous shale." Louderback (1934, p. 12) says that they came from "andesitic sediments." Jen- kins (1935, p. 193, fig. 31) in a cross section of Table Mountain, shows the fossil locality as " 'pipe clay' [rhy- olitic ash] lake-bed silt," below the lowest andesite Piper, Gale, Thomas, and Robinson (1939, p. 70) state that the fossils came from "andesitic sediments that are presumed to be equivalent to the lower part of the Mehrten formation." Condit (1944, pp. 59, 73) says that the fossils came from "andesitic sediments." The laminated clays, siltstones, and ashes that are pre dominantly andesitic probably are correctly assigned to the Mehrten formation; if any are chiefly rhyolitic they may belong to the underlying Valley Springs formation. Study of four thin sections from the mapped area, one of thin-bedded white laminated siltstone and the others of pale-gray ash, shows that these rocks are predominantly andesitic in composition. Unlike the rhyolite tuff of th Valley Springs formation, this ash and siltstone contain only minor amounts of potash feldspar, quartz, and glass, but large amounts of basaltic hornblende and augite ; and measurement of maximum extinction angles shows that the feldspar is about An- >() in composition, and some may be even more calcic. Such a mineral composi- tion suggests that the laminated clay, siltstone, and ash of the mapped area, though chiefly andesitic in composi- tion, have been contaminated by fragments of older rhyolitic rocks and that they are properly assigned to the Mehrten formation, and not to the Valley Springs forma- tion. 11 Brown, R. W., personal communication, January 2, 1947. Geology of the Angels Camp and Sonora Quadrangles 19 Latite of Table Mountain The most prominent topographic feature in the Sonora quadrangle, though not the highest eminence, is Table Mountain, a flat-topped, steep-sided, elongate and sinu- ous hill that extends across the quadrangle from north- east to southwest with a gentle southwesterly slope. The hill is formed by a resistant cap of latite, the remnant of a lava flow that in late Tertiary or early Quaternary time streamed down and filled one of the major river channels then draining the region. The maximum thick- ness of the latite cap is about 200 feet, and in the mapped area the latite-capped hill now forms the divide between tlie drainage basins of the Tuolumne and Stanislaus Rivers. The latite has been described in detail in a paper by Ransome (1898), where the term "latite" was first used. A chemical analysis of the rock, made for Turner (1894, p. 491) and quoted by Ransome (1898, p. 58), from samples taken near Shaws Flat, just north of the Sonora quadrangle, is given below. Ransome says (1898, p. 10), "the distinctive chemical feature of these rocks is a rather high percentage of total alkalies, with the total potash somewhat in excess of soda. Chemically they stand between typical andesites and typical trachytes, and belong to a general chemical group of the effusive rocks which it seems necessary to classify under a new name." Accordingly, Ransome (1898, p. 64) proposed the name latite, from the Italian province of Latium, where similar rocks are abundant, for the extrusive equivalent of monzonite. Chemical analysis of latite of Tahle Mountain, near Shaics Flat. (Turner, 11. W., U. 8. Geol. Survey U,th Ann. Rept., p. 491. W. F. Hillebrand, analyst.) Si0 2 56.19 TiOi .69 A1 2 3 16.76 Fe 2 3 3.05 FeO 4.18 MnO .10 M R 3.79 CaO 6.53 BaO .19 Na 2 U 2.53 K a O 4.46 P 2 ()5 .55 IPO above 100° C. .66 H 2 Q below 100° C. .34 SrO tr. Li 2 tr. Total 100.02 In the Sonora quadrangle the rock is augite latite porphyry. The phenocrysts consist of labradorite, some as calcic as AN 58 and up to 15 mm long ; dark-green to pale greenish-brown to colorless augite ; and brown oli- vine. The groundmass consists of labradorite, augite, olivine, magnetite, apatite, and glass. In places the rock contains andesine instead of labradorite. Potash feldspar has not been detected. Ransome (1898, p. 58) points out that some of the analyses of latites from the Sierra Ne- vada show "as much as 5 percent of potash, which, if it were present in the form of orthoclase, would make up nearly 30 percent of the rock." Ransome believed that the potash occurs in the glass of the groundmass. How- ever, the latite in the mapped area seems to contain an insufficient amount of glass to account for the reported potash. The rock was studied with the aid of a universal stage, and it was noted that the plotted position of the poles of twinning axes of plagioclase phenocrysts con- sistently lie to the left of the standard curves of Duparc and Reinhard (1924) and Nikitin (1936). Possibly this departure might be due to the presence of orthoclase in solid solution in the plagioclase. Departures from the standard curves have been discussed by Turner (1947), who noted that Barber (1936) "dismissed variation in potash content" as one of the causes. However, Turner (1947) believes that such departures might be caused by a chemical influence. The possibility that potassium, in solid solution in the plagioclase, has an effect on the position of the twin axes should not be overlooked. More- over, the standard curves were based on study of plu- tonic rocks ; therefore, they need not necessarily apply to volcanic rocks, such as the latite of Table Mountain, which crystallized under different physical conditions. The latite of Table Mountain occupies a buried valley, known as the Cataract Channel, that was cut in the Mehrten formation. Therefore, the latite must be younger than the youngest part of the underlying Mehrten for- mation. The Mehrten formation is regarded as of Mio- cene and Pliocene age, so that the latite could be as old as Pliocene. Jenkins (1948, p. 27) believes that the latite is late Pliocene. The river channel down which the latite flowed is older than the present drainage pattern, for not only does the latite in some places cross the course of modern streams, but also, in the mapped area, it forms the divide between the modern drainage of the Tuolumne and Stanislaus Rivers. Accordingly, the latite could be as young as early Pleistocene but probably is older than late Pleistocene. Some Problems of Correlation One of the serious geologic problems encountered in the western part of the Sierra Nevada is the correlation of stratigraphic units. Consequently, certain phyllites, conglomerates, and large areas mapped as green schist have not been assigned to any formation on the maps. However, we have found indirect evidence suggesting that some of these rocks may tentatively be correlated with the Cosumnes and Logtown Ridge formations ; in other words, that these rocks are slightly more metamor- phosed equivalents of the known Jurassic units farther west. Thus, phyllite and related rocks such as phyllonite, stretched conglomerate, and thin-bedded tuff are tenta- tively correlated with the Cosumnes formation ; the green schist and related rocks are tentatively correlated with the Logtown Ridge formation. This tentative correlation is based chiefly on lithologic similarity and partly on apparent stratigraphic relations. Therefore, we empha- size that the correlation here proposed is tentative and that no age assignment is made. However, all marble bodies, and fault-bound bodies of rock containing lenses of marble, tectonic breccia, and some phyllite and schist have been assigned to the Calaveras formation. Correlation of Marble and Interbedded Rocks In the earlier geologic investigations of the Gold Belt the rocks of the chlorite 2 subzone generally were mapped as Calaveras formation and associated amphibolite schist, not only because of their greater metamorphism and de- formation, but also because in places certain associated 20 Special Report 41 marble lenses contain Carboniferous fossils. As Ransome (1900, p. 2) says, "The fossils . . . indicate that the limestones are of Carboniferous age. Accordingly, that portion of the Calaveras formation in which the lime- stone lenses occur must also be Carboniferous." Eric (1948) points out that where small marble lenses and associated tectonic breccia are bounded by faults, the rocks outside the fault-bound rocks may be of a different age from those within the faults. In the mapped area, bodies of marble and associated tectonic breccia have been assigned to the Calaveras for- mation. This assignment is based on the arbitrary as- sumption that all the blue-gray marble in the area is Paleozoic in age. The schist east of the marble near Sonora has been assigned to the Calaveras formation be- cause it seems to be interbedded with the marble. How- ever, the two types of rocks might be isoclinally inter- folded. Tentative Correlation of Phyllite, Stretched Conglomerate, and Related Rocks The sedimentary rocks of the chlorite 2 subzone con- sist chiefly of phyllite, phyllonite, stretched conglomer- ate, and chert. The phyllite appears to have been derived in part from shale and in part from thin-bedded tuff. As stated previously, we believe that there is evidence to suggest a tentative correlation of some of these rocks with the Cosumnes formation. This evidence is briefly reviewed. (1) Conglomerate is one of the readily mappable lithologic units in the chlorite 2 subzone and is well exposed in parts of the Angels Camp quadrangle ; in the Sonora quadrangle mappable units of conglomerate are restricted to the northwest part. Except for the fact that the pebbles are stretched, the conglomerate is similar to the conglomerate at the type locality of the Cosumnes formation on the Cosumnes River. (2) Stretched pebbles of blue-gray marble (fig. 6) lithologically similar to the marble in mappable bodies, are scattered through the conglomerate. The marble in mappable units has been assigned to the Calaveras formation ; and the presence of similar marble as stretched pebbles in the conglomerate suggests that the conglom- erate is younger than the Calaveras. Certainly the conglomerate is younger than the marble from which the pebbles were derived. Similar marble pebbles occur in the Cosumnes formation at the type locality. (3) Much of the rock mapped as phyllite has been derived from thin-bedded tuff, especially in the southeast part of the Angels Camp quadrangle and the northwest part of the Sonora quadrangle. Except for slightly greater metamorphism these rocks are similar to thin-bedded tuff at the type locality of the Cosumnes formation. Turner (1894), in fact, originally mapped these rocks as "Mariposa slates," because of a Jurassic ammonite reported by Whitney (1880, pp.37, 41), although later Turner and Ransome (1897; Ransome, 1900) remapped them as Calaveras formation. (4) In the northwest part of the Sonora quadrangle, about half a mile southwest of Jackass Hill, somewhat phyllitic thin-bedded tuff and conglomerate, closely resembling the rocks of the Cosumnes formation at the type locality, are associated with a highly augitic greenstone. The greenstone is identical in every respect with the Logtown Ridge formation at the type locality, as well as with the Logtown Ridge on Bear Mountain and Peoria Mountain in the mapped area. This association of thin-bedded tuff and conglomerate of unknown age with rocks similar to the Logtown Ridge formation suggests that the tuff and conglomerate belong to the Cosumnes formation. Tentative Correlation of the Green Schist and Related Rocks Large parts of the chlorite 2 subzone within the mapped area consist of green schist derived from brec- cia, agglomerate, tuff, and flows. Like the closely associ- ated phyllitic rocks, the green schist is of unknown age but evidence has been found which suggests that some of it may tentatively be correlated with the Logtown Ridge formation. This tentative correlation is supported by the following evidence : (1) About 2\ miles west of Angels Camp, Cherokee Creek crosses the Logtown Ridge formation and drops abruptly into a valley underlain by slate of the Mariposa formation. The Logtown Ridge at this place is a massive greenstone rich in augite and resembles in every way the Logtown Ridge at the type locality. Both contacts of the Logtown Ridge are major faults but the west contact is not exposed at this place. At the east contact and for at least 40 feet across the strike, the rocks of the Logtown Ridge formation have been intensely sheared and converted into actinolite schist. This suggests that typical massive augitic greenstone of the Logtown Ridge formation can grade across the strike, within a space of a few feet, into actinolite schist typical of the green schist. (2) In places where exposures are good the green schist may be seen to contain "islands" or pods of rocks having typical Logtown Ridge lithology. One of the best places to see these pods is in a road cut at a sharp curve in Highway 49 about half a mile west of Tuttletown. The pods are composed of massive coarse-grained augitic pyroclastic rocks ; yet for thousands of feet across the strike on both sides the rocks are typical green amphibolite schists. An- other place where similar abrupt gradations may be seen between amphibolite schist and massive augitic pyroclastic rocks is in the Columbia quadrangle on the south side of Carson Hill about 100 feet east of Highway 49 at the hairpin turn at altitude 1,100 feet. Possibly the islands are patches of the original pyroclastic rock that have escaped the shearing and deformation experienced by the rest of the rocks of the green schist. Grain size may have been one of the controlling factors, as most of these bodies have coarse- grained texture. (3) Relict crystals of augite in rocks of the green schist have optic angles of 35° to 40°, which is in the same range as optic angles of the augite crystals in the Logtown Ridge formation in the chlorite 1 subzone. It seems unlikely that augite from two separate magmas would have attained the same degree of equilib- rium, whereas augite crystals from the same magma would vary only within narrow limits. That the augite was in equilibrium with the liquid phase is suggested by the almost complete lack of zoning in crystals from the massive Logtown Ridge formation as well as in relicts from the rocks of the green schist. The similarity of the augite crystals in the Logtown Ridge formation to the augite relicts in the green schist suggests, but does not prove, a possible close genetic relationship between the two rocks. (4) A relatively small area southwest of Bear Mountain, in the Angels Camp quadrangle, is underlain by rocks of the chlorite 2 subzone. These rocks, despite their somewhat greater metamor- phism, have been assigned to the Amador group because of their lithologic similarity to the Amador group and because of their stratigraphic relations. Thin-bedded tuff has been assigned to the Cosumnes formation, whereas the rocks of the green schist derived from coarse-grained pyroclastic rocks have been assigned to the Logtown Ridge formation. The two formations, in this area, are exposed in several belts that are inferred to be gently plunging anticlines and synclines. INTRUSIVE ROCKS The intrusive rocks of the area are younger than the sedimentary and volcanic rocks, which are of pre-Creta- ceous age. With the exception of a few quartz-bearing intrusive rocks in the Angels Camp quadrangle they are mafic and ultramafic, and are represented chiefly by stocks of gabbro and serpentine as well as by many meta- morphosed mafic dikes that intrude the older rocks. In- trusive rocks underlie only a small fraction of the Angels Camp quadrangle, whereas they underlie about a fourth of the Sonora quadrangle. The intrusives have not meta- morphosed the adjoining rocks except in one area, in the southeast part of the Sonora quadrangle, where a nar- row body, possibly a roof pendant, has been converted in part to spotted chiastolite schist. Geology op the Angels Camp and Sonora Quadrangles 21 Serpentine Two irregular shaped stocks of peridotite, now con- verted to serpentine, have intruded rocks of the Amador group and Mariposa formation in the Sonora quadran- gle. The larger of the two bodies is in the southwest part of the quadrangle and extends to the west, north- west, and south, beyond the limits of the quadrangle. The other body of serpentine is entirely within the quad- rangle and extends northwestward from about a mile southwest of Stent to French Flat. In the Angels Camp quadrangle massive serpentine is found chiefly on Car- son and Chaparral Hills, and is associated with gabbro. Massive serpentine also is found scattered, probably as inclusions, through the gabbro that extends northwest- ward along Highway 49 toward Angels Camp, and thus, in that area, seems to be restricted to the Mother Lode fault system. A highly foliated and slickensided variety of serpentine occurs southwest of Bear Mountain, where it is associated with altered granodiorite and diorite ; some of it has been prospected for chromite. No perid- otite has been seen in the mapped area, but there is some a few hundred feet to the south in the Chinese Camp quadrangle. Areas underlain by serpentine commonly are marked by a characteristic growth of brush, a feature clearly dis- cernible on aerial photographs. The serpentine rock gen- erally is massive, dark green to almost black, and weathers to lighter green and buff. The weathering clearly discloses the minute magnetite veinlets that are distributed throughout the rock. Bastite pseudomorphs are common in the massive serpentine. Locally the serpentine is intensely veined with cross- fiber chrysotile. Individual veinlets are about 1 mm thick and 2 to 3 mm apart, all roughly parallel. Locally the chrysotile veinlets attain a thickness of about an inch, and near Rawhide Flat some asbestos has been mined. In general, these small chrysotile veinlets lie in planes nearly at right angles to sheared joint surfaces or minor faults, but at an acute angle to grooves and striations on the slickensided shear surfaces. The serpentine is intensely sheared along major faults. Irregular rounded pods of massive serpentine, ranging from an inch to 3 feet in diameter, are suspended in a matrix of crushed and granulated serpentine. The sur- faces of the rounded serpentine pods are highly slicken- sided and polished, contrasting strongly with the dull massive unsheared rock. Such intensely sheared serpen- tine is well exposed where the road from Rawhide Flat to Melones Reservoir crosses one of the main faults of the Mother Lode system, about half a mile southwest of Rawhide Flat. Several areas of similar intensely sheared serpentine are found in the serpentine body along the west edge of the Sonora quadrangle, just north of Table Mountain, but no faults have been mapped in these areas because of the poor exposures. There are many small chromite prospects in the areas of sheared serpentine in this body, and in a few places chromite has been mined. Gabbro and Diorite Two bodies of a somewhat less mafic rock that is pre- dominantly gabbro are closely associated in the Sonora quadrangle with the two main areas of serpentine. A third main body of gabbro, not associated with serpen- tine, crops out in the southeast part of the quadrangle. A few small areas of slight compositional variation within the gabbro have not been delineated on the geo- logic map of the Sonora quadrangle. In the Angels Camp quadrangle small bodies of a light-colored facies of the gabbro have been mapped as diorite. In the vicinity of French Flat (pi. 2) the outcrop pat- tern strongly suggests that the gabbro is intrusive into the serpentine and that it has enclosed many small "islands" of serpentine. Careful observation of the con- tact between the two rocks, however, seems to show con- flicting evidence. In some places small fingers of gabbroic material extend into and enclose the serpentine, as though the gabbro were the later of the two rocks. Else- where the reverse is true, and serpentine encloses coarse- grained gabbroic rock. The contacts between the two rocks are gradational. Such relationships would seem to indicate almost contemporaneous intrusion of a mafic magma or differentiation in place. Almost identical re- lationships between serpentine and gabbro in an area in the foothills of the Sierra Nevada northeast of Visalia have been described by Durrell (1940, p. 74). There, ac- cording to Durrell, the two rocks represent either a single intrusive differentiated in place or two intrusives very closely related in time. In the Angels Camp quadrangle gabbro, locally grad- ing in composition to diorite, occurs in small scattered lenses confined chiefly to the Mother Lode fault system. In the vicinity of Carson and Chaparral Hills, it is asso- ciated with massive serpentine. The gabbro generally is a medium- to coarse-grained rock and consists essentially of saussuritized plagioclase and dark minerals, chiefly hornblende. The rock is fairly light-colored, although in areas where hornblende is abundant the color may be dark green to nearly black. Locally, the gabbro is dark gray-green, fine-grained, and dense, especially along contacts with sedimentary and volcanic rocks. The gabbro bodies generally are massive and poorly jointed, although some of those in the Angels Camp quadrangle are crudely foliated. Such secondary folia- tion has developed along faults and sheared contacts, as may be seen where Highway 49 crosses the small body of gabbro just west of the village of Carson Hill. In the southeast part of the Sonora quadrangle, poorly devel- oped flow banding along the edges of the gabbro also gives the rock a crude foliation. Hornblendite Massive hornblendite has been mapped in four small areas in the Sonora quadrangle : two of these are asso- ciated with gabbro in the southeast part of the quad- rangle ; one is associated with gabbro and serpentine along the south boundary of the quadrangle near High- way 49 ; and one is associated with gabbro and serpen- tine along Highway 49, 2\ miles southwest of James- town. In the Angels Camp quadrangle hornblendite has not been separately mapped but occurs as very small bodies associated with gabbro and serpentine on Carson Hill, and with diorite just west of the head of Texas Charlie Gulch and just north of the'Vallecito Western mine. The rock is dark green to nearly black. Crystals of hornblende, up to half an inch long, form the chief 22 Special Report 41 constituent, but actinolite also is present. Interstitial to the hornblende is saussuritized plagioclase, chlorite, epi- dote, a little clear albite, and minor amounts of prehnite. Porphyritic Diabase Massive feldspar porphyry occurs as dikes and sills in the volcanic rocks near Dogtown, just north of the Angels Camp quadrangle, and in the Mariposa forma- tion in the southern part of the Angels Camp quad- rangle and northwestern part of the Sonora quadrangle. The feldspar porphyry is dark gray-green and contains light-colored phenocrysts of altered feldspar up to half an inch long. The rock is massive and has not been sheared, but locally is well jointed. The texture is gen- erally diabasic and the rock therefore has been mapped as porphyritic diabase. Diabase Altered dikes of dark greenish-black diabase intrude marble of the Calaveras formation and are well exposed in road cuts along State Highway 49 just north of Sonora. Because of the strong contrast in the color of the two rocks the dikes are sharply defined. Similar dikes occur in the schist of the Calaveras formation, but most of them are too small to be shown on the geologic map. Moreover, where fresh the dikes in schist are not readily discernible, as the color of the two rocks is nearly iden- tical. However, the dikes generally weather to a much deeper red-brown than the country rock. Hornblende Lamprophyre In the Angels Camp quadrangle a dike of hornblende lamprophyre has been mapped in the northeast part of the quadrangle, and a small mass of similar rock occurs in the body mapped as ankerite-talc schist 2 miles due east of Angels Camp, where it is associated also with actinolite schist and talc schist. The lamprophyre is a fine-grained dark-green rock consisting essentially of brownish-green hornblende phenocrysts in a matrix of albite, pale chlorite, epidote, and pale actinolite or tremolite. Altered Quartz-bearing Intrusive Rocks Altered quartz-bearing intrusive rocks occur in a few places in the Angels Camp quadrangle. Granodiorite has been mapped near the southwest corner of the quad- rangle, just south of the Vallecito Western mine, and in a small body 2\ miles north of the southwest corner ; and muscovite granite has been mapped just northwest of the Vallecito Western mine. Age The evidence on the age relations of the intrusive rocks within the mapped area is inconclusive. We know that some of the intrusives cut Jurassic rocks and we have no reason to suppose that any of them are different in age. Possibly the intrusion took place in Late Jurassic time or later, beginning with peridotite and ending with the more acidic facies. Later studies may show that some of the intrusives of the Mother Lode area are hybrids, especially those emplaced in greenstones. In the mapped area fresh intrusive rocks are not ex- posed. In the hope of shedding some light on the problem of the age relations of the altered intrusive rocks to the fresh rocks of the Sierra Nevada batholith, thin sections were made of fresh-looking intrusive rocks. Specimens were taken from the main part of the batholith several miles west of Yosemite National Park, and from the intrusive rock just east of the Sonora quadrangle, which apparently is a lobe of the main batholith. The intrusive rocks from west of Yosemite Park are fresh and un- altered. The intrusive rocks from the vicinity of Sonora, though appearing fresh, are seen in thin section to be considerably altered ; feldspar has been largely saussuri- tized and hornblende has been partly converted to chlo- rite. Thus, extensions of the main batholith are altered to about the same extent as the mafic rocks. This sug- gests only that the altered intrusive rocks of the mapped area are not necessarily older than the fresh intrusive rocks of the main mass of the batholith. If the intrusive rocks of the Mother Lode region are of approximately the same age as the batholithic rocks to the east, the conclusion is unavoidable that the low- grade metamorphism, characteristic of most of the rocks of the region, was not caused by the intrusion of magma. The development of chiastolite in the schist near the southeast corner of the Sonora quadrangle probably was caused by the intrusions ; but the saussuritization and uralitization of nearly all the rocks must have some other causes, such as late dislocation and shearing. Dynamo- metamorphism continued in the mapped area after the intrusive rocks were emplaced. STRUCTURE Structurally, the mapped area is characterized by northwesterly strikes of beds and foliation, parallel to the trend of the Sierra Nevada ; steep northeasterly dips ; overturned, nearly isoclinal, major folds ; and longitudinal reverse faults. Folds The minor folds are more evident than the regional folds within the map-area, for the former can each be seen within the limits of one outcrop whereas the latter are largely inferred from the areal patterns made by the rock units. So far the major folds have been more useful than the minor folds in deciphering the structure of the area. Within the Angels Camp quadrangle re- gional folds are interpreted for the area southwest of the main Mother Lobe belt but in the Sonora quad- rangle the inferred regional folds are northeast of the Mother Lode belt. This indicates that folding is prob- ably the common thing rather than the unusual and would occur more often on geologic maps of the region but the lack of good exposures and conclusive field evi- dence. Major Folds The traces of the axial planes of the more prominent major folds are shown on the geologic maps (pis. 1 and 2) and on the structure maps (figs. 7 and 8). The evi- dence for many of the mapped folds is good, but in some places folds have been inferred in order to make a more reasonable interpretation of the structure. In parts of the chlorite 2 subzone, for example near Jamestown, the interpretation of anticlines and synclines is based on the assumption that phyllite and related rocks underlie the rocks of the green schist. If this assumption is in- correct, and if the rocks of the green schist underlie the phyllite, then the anticlines, as mapped, actually are synclines, and the synclines are anticlines. In general Geology of the Angels Camp and Sonora Quadrangles 23 the major folds are nearly isoclinal and are overturned to' the southwest with both limbs dipping 65° -85° NE. Bear Mountain, in the southwest part of the Angels Camp quadrangle, is structurally a series of anticlines and synclines, generally plunging about 5°-10° SB. At the south end of Bear Mountain the angle of plunge of one of these folds steepens to an average of 20° ; locally, plunges as steep as 40° have been measured. Southwest of Bear Mountain is another group of major folds, some of which plunge gently northwest. The rocks of the region north, northeast, and east of Bear Mountain probably have been intensely folded, but in large parts of that area the structure is so compli- cated by faults and shear zones that the presence of major folds cannot be demonstrated with certainty, and the folds shown in cross section on plate 3 in that area are largely inferred. In the southeast part of the Sonora quadrangle, an area of intrusive rock occupies, in part, a major anti- cline. Schistosity and bedding in the surrounding meta- morphic rocks bend around and parallel closely the edge of the intrusive body, showing that the intrusion of the gabbro was responsible for the bending of the surround- ing rocks, or that post-intrusion deformation took place. However, the presence of cross-cutting relationships and of several roof pendants of schistose rocks indicates that not all the country rock was pushed aside. In the south- west part of the Angels Camp quadrangle small bodies of intrusive rocks similarly occupy the cores of anti- clines, but in this area, although the intrusive rocks seem to have been localized by the anticlines, no further bend- ing has occurred. Minor Folds In addition to the major gently plunging folds re- vealed in regional mapping, the mapped area also con- tains many minor steeply plunging folds that can be seen in outcrops or groups of outcrops. These small folds generally plunge 40°-60°, although some have ver- tical axes. Most of the minor folds are believed to be drag folds associated with some of the faults and re- gional shear zones, and did not prove to be an aid in deciphering the major folded structure. For example, two small folds on the limbs of a major syncline in sees. 2 and 11, T. 2 N., R. 12 E., just southeast of Elkhorn Station in the Angels Camp quadrangle (pi. 1), plunge 50° and 40° N., although the major syncline plunges gently, probably about 10°, southeast. The patterns of many of the drag folds suggest, as do the patterns of the offsets along faults, that the rocks to the east have moved upward and northward with respect to those to the west. Faults A major zone of faults having, in general, reverse movement, and called the Mother Lode fault system, extends across the mapped area (pis. 1 and 2) in a north- westerly direction. Reverse faults have been recognized in this region for many years. Ransome (1900, p. 8), although he did not map any of these faults, recognized the fact that the quartz veins of the Mother Lode oc- cupied faults. In the present investigation an attempt has been made to map all known faults. In so doing it has been necessary to generalize considerably, especially along the mineralized zones, because in many places the faults are so closely spaced that, even on a scale as large as 2,000 feet to the inch, they cannot all be shown. In some areas, for example, the northeast part of the Angels Camp quadrangle and near Jackass Hill in the Sonora quadrangle, exposures are so poor that mapping of faults is not practicable ; field data suggests, however, that in these areas faults not only are present but are abundant. Mother Lode Fault System The Mother Lode fault system is a major zone of anastomosing reverse faults and shear zones extending in a continuous belt northwestward from south of the town of Mariposa, Mariposa County (Cloos, 1932), at least as far as the vicinity of Georgetown, El Dorado County, a distance of about 120 miles (fig. 1 and pis. 3 and 4). Gold-bearing quartz veins occur at intervals along this system of faults and, according to Fairbanks (1890, pp. 23-24), the series of veins was given the name "Mother Lode" by miners and prospectors during 1850 or 1851. In the Chinese Camp quadrangle, about a mile south of the south border of the Sonora quadrangle, the Mother Lode fault system may be said to consist of only one major fault zone. At the south border of the Sonora quadrangle the fault system is a shear zone ranging in width from 300 to 600 feet. Farther northwest, near Sullivan Creek, the fault system begins to branch and diffuse, and in the vicinity of Jamestown attains a width of about 2 miles. In the Angels Camp quadrangle, near Angels Camp, the fault system is between 24 and 2f miles wide. The "Main Fault" of the Mother Lode System. Ran- some (1900, p. 9), in his discussion of the Mother Lode veins, states, "It is customary among the miners to dis- tinguish one single vein as 'the Mother Lode.' Not only does such a terminology lead to endless and unprofitable discussion, but, in the light of what is known of the complex character of the Mother Lode, the restriction of that name to any single vein of the system is mislead- ing. ' ' Where he discusses the veins of the Mother Lode, Knopf (1929, p. 5) agrees with Ransome concerning this idea, yet where Knopf writes of the faults of the Mother Lode, rather than the veins, he distinguishes a single main or master Mother Lode fault (1929, p. 46). Evi- dently Knopf's "main fault" is the fault along which rocks of very low metamorphic grade (chlorite 1 sub- zone) on the footwall side have been brought into juxta- position with rocks of slightly higher metamorphic grade (chlorite 2 subzone) on the hanging- wall side. Thus, in the Sonora quadrangle, this main fault would correspond to the chief mineralized fault and would lie along the central part of the Mother Lode fault zone ; in the Angels Camp quadrangle the main fault would be well to the west of the chief mineralized faults and would lie along the western part of the fault zone ; whereas still farther to the northwest, beyond the mapped area, the main fault would be east of the chief mineralized fault. Zone of Intense Faulting Two elongate strips along the Mother Lode fault sys- tem, one in the south part of the Sonora quadrangle and one in the northwest part of that quadrangle and the southeast part of the Angels Camp quadrangle, con- tain outcrops of marble and other rocks mapped as Cala- 24 Special Report 41 EXPLANATION Grovels ond tuffs intrusive rocks Serpc (Granite to gobbro) Strike ond dip of beds Strike of vertical beds Chiefly volconic ond sed- imentary rocks Stippling, shows approximate loca- tion of Mother Lode belt Fault (doshed where approximately located, dotted where conceoled, auemed where doubtful) Metomorphtc boundary .ine ot overage strike of :leovoge, schisfosity, or lolmtion (d

---* r $ •-• *>.■ Figure 15. Photomicrograph of stretched conglomerate (X25). Section is taken normal to the shear cleavage and intermediate axes, showing long and short axes of stretched pebbles. Rock is composed largely of quartz and muscovite, with minor chlorite, albite and iron oxides. This rock has been considerably sheared and recrystallized and probably could also be called a phyllonite. Carbonate is rare, but may occur as small dissemi- nated grains or as small veinlets that in places wedge apart the antigorite lamellae of the bastite crystals. The refractive index of most of the observed grains is very close to that of balsam, and the mineral probably is ankerite or an iron-bearing magnesite. The highly sheared serpentine in the vicinity of major faults is composed almost entirely of a felt of antigorite crystals with patches of talc developed along shear planes. Porphyritic Diabase. Massive feldspar porphyry oc- curs as dikes and sills in the rocks of the Mariposa for- mation and Amador group. The porphyry is dark green- ish gray and contains phenocrysts of light-greenish saussuritized plagioclase up to about 15 mm long. Under the microscope the rock is seen to have an in- tersertal porphyritic texture with phenocrysts of plagio- clase (some slightly saussuritized and with a composi- tion of about An.jo, but much completely saussuritized) and augite ; the latter is less abundant than the feldspar and unaltered. The groundmass is composed of a net- work of plagioclase laths, abundant small crystals of augite, and minor amounts of brownish-green horn- blende. Grains of magnetite, iddingsite, and leucoxene, and a few scattered pools of light-green chlorite, prob- ably pseudomorphous after olivine, are the accessory minerals. Some nearly opaque material, thought to rep- resent original glass, is scattered throughout the rock. Rocks of the Chlorite 2 Subzone The rocks of the chlorite 2 subzone have fair to good schistosity; mineral reconstitution is well advanced, and in many places no relicts remain. The principal rocks of this subzone are : Quartzose and argillaceous rocks Phyllite and phyllonite Stretched conglomerate Quartz-muscovite schist Quartz-actinolite-albite schist Quartz-albite-muscovite-chiastolite schist Felsic tuff Amphibole crystal tuff and tuffaceous sandstone Green schist series Albite-actinolite schist Hornblende-andesite Plagioclase-chlorite-zoisite schist Albite-chlorite-epidote schist Marble Mafic intrusive rocks Gabbro Diabase Quartzose and Argillaceous Rocks Rock types such as some of the green phyllites, and stretched conglomerate, are relatively easy to distinguish in the field as separate lithological rock units. On the other hand, certain other quartzose and argillaceous rocks are not so easily delineated. Thus, in the northeast corner of the Angels Camp quadrangle the map unit "Pes" contains the following undifferentiated rock types : phyl- lite, quartz-muscovite schist, and quartz-mica schist, locally graphitic. In the Sonora quadrangle Pes includes quartz-actinolite-albite schist in addition to phyllite and quartz-muscovite schist. Quartz-albite-muscovite-chiasto- lite schist, "spotted schist" is contained in a narrow zone of phyllite near the gabbro intrusive contact of the Sonora quadrangle. Geology of the Angels Camp and Sonora Quadrangles 37 Phyllite and Phyllonite. The phyllite and phyllonite of the chlorite 2 subzone are dark gray to nearly black, and are composed chiefly of quartz, chlorite, muscovite, sericite, actinolite, and dark streaks of iron oxides. Quartzose pebbles and grains have been crushed and re- crystallized, and in places streaked out into long augen. Figure 14 shows phyllonite from the mapped area. We think that the chlorite in these rocks has resulted from the alteration of detrital biotite. Stretched Conglomerate. Conglomerate containing stretched pebbles is exposed in parts of the chlorite 2 subzone. The pebbles consist of a great variety of rocks, including volcanic rocks, slate, phyllite, schist, chert, vein quartz, intrusive rocks (largely diorite), and, in some places, marble that closely resembles the marble assigned to the Calaveras formation. In some of the coarser units of the conglomerate the pebbles attain a length of as much as 18 inches, but lengths of 1 or 2 inches are more common. In places the larger pebbles clearly have been stretched more than the matrix, which consists chiefly of chlorite, sericite, and fine angular quartz grains. In a very general way the amount of stretching increases toward the northeast: that is, in the conglomerate of the chlorite 1 zone pebbles are practi- cally undeformed, whereas in the chlorite 2 zone some of the pebbles have axial ratio of as much as 1:2:8. Generally the long and intermediate axes of the pebbles lie in the planes of shear cleavage, the short axes normal to the cleavage (Fig. 15). Quartz-Muscovite Schist. Probably interbedded with the marble body in the northeast part of the Sonora quadrangle is light-gray quartz-muscovite schist with interbeds of nearly pure quartzite that contains only a small percentage of muscovite. A photomicrograph of the quartz-muscovite schist is shown in figure 16. This rock splits into thin layers along muscovite bands and ex- hibits the bright luster typical of rocks rich in sericite and muscovite. The banding is believed to be bedding in a quartzose and argillaceous rock in which clay layers now are represented chiefly by muscovite. The quartz-muscovite schist is composed primarily of quartz (about 60 to 70 percent) with a granoblastic tex- ture and a grain size averaging about 0.15 mm. Two varieties of muscovite comprise the bulk of the re- mainder of the rock. The most abundant variety is faint greenish brown, slightly pleochroic, and is found chiefly in the muscovite bands, although it also is disseminated throughout the quartzose layers. The other variety is a completely colorless muscovite that forms better-devel- oped crystals whose preferred orientation is stronger than that of the pleochroic variety. The colorless mus- covite is disseminated throughout the rock. The greenish pleochroic variety may have been derived from original detrital biotite flakes that were altered, possibly in part to chlorite, with the separation of iron as the oxide, and later recrystallized to muscovite. In some of the bands in which the pleochroic variety of muscovite is concen- trated, a few areas of greenish, low-birefrigence chlorite is partly replaced by the muscovite. Dusty patches of magnetite grains are associated with these areas, which suggests derivation, in part at least, from detrital bio- tite. In addition, isotropic grains of a pale garnet also are concentrated along the muscovite layers. ,V; **' k- <* >^m Figure 16. Photomicrograph of quartz-muscovite schist (X25). Quartz and muscovite are the principal minerals. Dark patches are areas of magnetite grains and chlorite, probably representing origi- nal detrital biotite. Quartz-Mica Schist. In parts of the area mapped as quartz-muscovite schist, especially in the northeast cor- ner of the Angels Camp quadrangle, brown metamor- phic biotite is present. However, the distribution of the quartz-muscovite-biotite schist is so erratic that no at- tempt has been made to demarcate a quartz-mica schist. The quartz-mica schist (fig. 17) is composed essentially of quartz, brown biotite (altering on its edges to green chlorite), sericite, or fine-grained muscovite, albite, epi- dote, and minute needles of actinolite. A few of the thin sections show abundant calcite, chlorite, actinolite, and sphene and less tourmaline, leucoxene, and apatite. Sporadic residual biotite, mostly altered to chlorite, occurs elsewhere in the Angels Camp quadrangle*, nota- & *?& Figure 17. Photomicrograph of quartz-mica schist (X25). The irregular dark grains are crystalloblastic brown biotite. 38 Special Report 41 bly in an area about 2 miles southeast of Angels Camp. The presence of this biotite, together with the presence of minute crystals of garnel suggests that parts of the mapped area have undergone retrograde metamorphism. Quartz-Actinolite-Albite Schist. Near the east edge of the Sonora quadrangle, the quartz-muscovite schist, described elsewhere in this paper, grades into quartz- actinolite-albite schist. This rock, like the other quartzose rocks in the mapped area, is a fine-grained granoblastic, and has a grain size ranging from about 0.15 to 0.2 mm. The rock has only a crude schistosity and seems to be even less schistose when seen in thin section. Some of the specimens show a faint foliation, which results from barely visible layers of slightly coarser-grained quartz. This foliation may represent bedding. The quartz-actinolite-albite schist is composed chiefly of quartz (40 percent), actinolite (30 percent), and albite (20 percent) ; the remainder is muscovite, zoisite, epidote, magnetite, sphene in somewhat opaque patches, and apatite. The rock is almost entirely crystalloblastic ; the quartz and albite occur as xenoblastic grains, among which needles of a colorless to faintly green actinolite has grown. Scattered relicts of a somewhat more deeply col- ored uralitic hornblende remain in the rock. Muscovite, zoisite, epidote, magnetite, and sphene are disseminated in about equal amounts ; apatite is rare, but in a few places it occurs as crystals up to 0.15 mm long. Quartz-Albitc-Mnscovite-Ch iastolite Sch ist. Quartz- albite-muscovite-chiastolite schist or "spotted schist" is found in a narrow zone of phyllite and phyllonite in con- tact with gabbro near the southeast corner of the Sonora quadrangle. This schist is the only rock in the mapped area that shows contact-metamorphic effects. The spotted schist is composed of quartz, albite, mus- covite, chiastolite, iron oxides, and garnet (fig. 18). Quartz and albite form a xenoblastic matrix in which green pleochroic muscovite and streaks of red-brown oxidized iron occur. Porphyroblasts of sericitized chiasto- lite up to 2 mm long are conspicuous throughout the rock. Garnet in colorless rounded grains is found in minor amounts. The spotted schist has a fair schistosity; the planes bend around the chiastolite porphyroblasts. Some of these porphyroblasts seem to show slight evidence of ro- tation and development of coarse muscovite along the edges where shearing stress was greatest. Some specimens of the rock contain no chiastolite now, but display streaked out patches of sericite and muscovite that de- veloped from chiastolite. This suggests for the gabbro in this area that intrusion occurred before, or contempo- raneously with, the early stages of metamorphism but that dynamometamorphism continued after the emplace- ment of the igneous material. Sericite Schist Derived From Felsic Tuff A lustrous white sericite schist, stained to ferruginous brown where weathered, is exposed along State Highway 49 between Sonora and Jamestown. This rock is made up of quartz in xenoblastic grains about 0.2 mm in diam- eter, sericite, muscovite, and opaque minerals, possibly magnetite or pyrite. In thin section the rock is seen to be slightly foliated, for the quartz tends to be segregated into definite bands, with the sericite and muscovite inter- layered between them. Probably the rock was originally a felsic tuff. Near Altaville are a few small bodies of schistose rhyo- lite tuff; tli is rock is similar to the sericite schist except that it contains crystals of quartz up to 2 mm across. Amphibole Crystal Tuff and Tuffaceous Sandstone A more mafic crystal tuff, tuffaceous sandstone, and an interlayered andesite ( ?) flow extends southeastward from the city of Sonora to the sericite schist derived from felsic tuff. These rocks are well bedded nearly everywhere. Locally they contain distorted fragments of volcanic rocks. Figure 18. Photomicrograph of cliiast These rocks are composed of actinolite, quartz, plagio- clase (albite ?), zoisite, epidote, chlorite, muscovite, green hornblende, magnetite or ilmenite, and sphene, and have a crystalloblastic texture. The grains range in diameter from about 0.02 mm to slightly over 3.0 mm for some of the large actinolite crystals. Actinolite, displaying faint pleochroic colors with X colorless, Y pale yellow-green, and Z pale blue-green, is the most abundant mineral in these rocks. Generally it forms porphyroblastic crystals averaging about 1 mm in length. Aggregates of chlorite occur in places near the ends of the actinolite crystals. The chlorite is nearly colorless to pale green, is faintly pleochroic, and has a positive sign. Quartz, plagioclase (probably albite but with a composition near oligoclase), epidote, and zoisite make up a granoblastic groundmass with grains aver- aging about 0.5 mm in diameter but with a great range in extremes of size. Rarely, a green amphibole, probably an original clastic hornblende, is seen. Other minerals are scattered plates of muscovite, magnetite or ilmenite, and a few grains of dusty sphene. Judging from their present composition, these rocks probably are derived from intermediate or mafic, possi- bly andesitic, tuffaceous material mixed, in part, with components of sedimentary origin and then recrystal- lized to form actinolitic rocks. The schistosity is only Geology of the Angels Camp and Sonora Quadrangles 39 moderately developed and the well-banded appearance of the rock is believed to be due to bedding. Locally quartz is very rare and actinolite is abundant, and at these places the rock probably is a mafic tuff containing no sedimentary material. Albite- Actinolite Schist In the vicinity of Sullivan Creek the rocks of the green schist are represented by a fine-grained crystalloblastic albite-actinolite schist with a grain size average about 0.05 mm (fig. 19). Schistosity is very well developed. The principal minerals are albite in xenoblastic grains, and pale-green fibrous actinolite. Epidote and muscovite are scattered throughout the rock in minor amounts. Much of the epidote occurs as fine-grained dusty patches with scattered grains of sphene (?). In the Angels Camp quadrangle, rocks of the green schist extend in a broad band northwestward across the area. Under the microscope the schist is seen to be com- posed dominantly of saussuritized plagioclase and actin- olite ; it includes varying amounts of epidote, clinozoisite, chlorite, and sericite, which in places cause extreme turbidity of the plagioclase. In general, the greener schist seems to owe its color largely to predominance of clinozoisite. The actinolite usually shows a crude planar orientation and rarely a linear orientation ; it also oc- curs as radiating fibers. The groundmass usually is com- posed of albite, epidote, clinozoisite, chlorite, sericite, calcite, and actinolite, and generally it has been sheared. The preferred orientation of the chlorite, sericite, and actinolite gives the rock its schistosity. In a few thin sections relict augite is present, but most of the augite lias been replaced by actinolite or chlorite or both, and in places the actinolite has been replaced by deep-green to colorless chlorite. Minerals that occur sporadically in the green schist of this area are quartz, orthoclase, brown hornblende, leucoxene, apatite, sphene, deep-brown bio- tite (highly altered to chlorite), mucovite, and mari- posite (green chromiferous mica). Hornblende Andesite Closely associated with the schist units of the green schist in the Angels Camp quadrangle is a rock mapped as hornblende andesite. This rock occurs in two areas : one just west of Highway 49 between Carson Hill and A libels Camp and one just south of the northwest corner of the quadrangle. This rock does not have a well- developed schistosity, but it is largely reconstituted mineralogically. It consists of massive flows and flow breccias and is quite different in appearance from the associated rocks of the green schist. The hornblende-andesite is porphyritic, with small but conspicuous phenocrysts of euhedral green horn- blende, up to about 5 mm long, in a light greenish-gray fine-grained reconstituted groundmass. In a few places quartz is an important constituent, and the rock is horn- blende dacite, but these small areas have not been mapped separately from the main bodies of andesite. In thin section the hornblende is seen to range in color from pale brownish green to deep green and probably is an original constituent of the igneous rock, although the prominence of green in the color suggests possible uralitization, with loss of iron. Some of the hornblende crystals show nearly colorless splintery ends (actinolite), and alteration to nearly colorless chlorite is common. Plagioclase is represented by cloudy areas of albite, epidote, clinozoisite, and sericite, but some of the altered feldspar forms areas with sericite centers and clinozois- ite rims. Apatite is an abundant accessory mineral and probably is primary, as is the quartz of the dacite. Plagioclase -Chlorite -Zoisite Schist The schist in the area between Jamestown and Sonora seems to be characterized largely by a less schistose rock in which part of the original structure and texture are retained. Originally the rock was a coarse pyroelastic, probably a mafic breccia and lapilli tuff. The schistosity is only faily well developed, and scattered lenses are massive and jointed. Mineralogic reconstitution, how- ever, is well advanced, and the rock is plagioclase- chlorite-zoisite schist. A typical specimen from this area contains albite as well as scattered large crystals of plagioclase with the composition of oligoclase ; a positive green chlorite ; zoisite ; epidote ; muscovite ; and secondary quartz. Al- bite, chlorite, zoisite (with minor amounts of epidote), and muscovite form a fine-grained crystalloblastic groundmass in which scattered larger relict crystals of partly saussuritized plagioclase occur. Secondary quartz occurs in the rocks as cavity fillings. Albite-Chlorite-Epidote Schist Near the village of Stent the schist is albite-chlorite- epidote schist. The rock has a well-developed schistosity and a crystalloblastic texture ; the grain size averages about 0.05 mm. Xenoblastic albite and pale-green nega- tive chlorite make up the bulk of the rock through which small subhedral crystals of epidote are distributed. Some of the epidote crystals are porphyroblastic and have a maximum diameter of about 0.5 mm. In addition to these minerals, the rock contains a few widely scattered grains of calcite and magnetite. Lenses of Greenstone Within the Green Schist The lenses of unsheared and nonschistose greenstone within the green schist unit are of considerable interest and importance, as they give a clear idea of the original texture, structure, and mineralogic composition of a part, at least, of the material that now comprises the green schist rock unit. The rocks shown in figures 20 and 21 are typical of the unsheared volcanics from any of these lenses. The rocks are coarse-grained lapilli tuffs. Subangular to an- gular rock fragments, up to several inches across, are embedded in a coarse-grained tuff matrix. Mineralogi- cally the composition is as follows : Subealcie augite (optic angle 35°-40°) Actinolite Epidote or clinozoisite (iron-rich) Chlorite Albite Calcite Muscovite (pale greenish) Stilpnomelane Augite occurs as crystals up to 3 or 4 mm long both in the tuff matrix and in the porphyritic rock frag- ments. In most places the augite is completely fresh and unaltered. Along sheared areas within the massive rock, however, it is in part replaced by colorless needles of actinolite, as shown by figure 18. The fine-grained parts 40 Special Report 41 of both the tuff matrix and the rock fragments are crystalloblastic mixtures of albite, actinolite, chlorite, and scattered grains of epidote. Grains of calcite also are disseminated throughout this fine-grained material, but this mineral is more common in amygdules in the rock fragments. A very pale-green pleochroic muscovite oc- curs in minor amounts in these rocks. Strongly pleo- chroic brown stilpnomelane, in radiating or sheaflike structures, occurs associated with chlorite, calcite, and albite, especially in and the near amygdules in the vol- canic rock fragments. A photomicrograph of one of these fragments (fig. 19) shows the occurrence of stilpnome- lane. Stilpnomelane was not found in any of the more schistose rocks. Judging from the composition, texture, and structure of the material occurring in these relatively unsheared, - ► ■>». JUi^ ■ i^^^ . •■ \ i i i* ^ • n im* ■• - * -mm y.ik &. .53, pp. 741-742; XII p. 298; XIII, p. 472; XIV, p. 136; XVIII, p. 99; XIX, PP. 19, 74, 145; XX p. 19; BM 424, pp. 28-30 X, p. 55; XI, p. 508; XII, p. 299; XIII, p. 473; XIV, p. 136; XX, p. 12; XLV, p. 57 XXIV, p. 22; B 108, p. 174; XLV p. 57 XIII, p. 473; XXIV, p. 22 XIII, p. 473, XXIV, p. 22 XIII, p. 473; XXIV, p. 22; B 108, p. 174 VIII, pp. 660-661; XII, p. 299; XIII, p. 473; XIV, pp. 136-137; XVII, pp. 482-483; XIX. p. 144; B 18, pp. 130-131 ; see also Dutch; B 108, pp. 156, 157; B 141, p. 50; BM 424, pp. 36-41; PP 157, p. 78 B 108, p. 157 XIII, p. 473; XIV, p. 137; B 18, p. 129; B 108. p. 158 X, p. 737; XIII, p. 473; XIV, p. 137; XXIV p. 22; B 108 p. 158-174; BM 424 p. 66 Badger (1) 18 IN 14E Badger (2) 13 IN. 14E Beckwith & Saunders 36 2N. 13E 30 2 31 25 31 30 IS. 2N. IS. 2N. 2N. 2N. 14E Bell* 14E 14E 14E Black Slate* 14E Bluett & McCoddle (Car- 14E rington) 36 2N. 14E. Claims: Big Bonanza, Little Bonanza 29 2 31 IS. 2N. 14E. Buena Vista.. 14E. Cardinelle* (Jackson Flat & 29 2N. 14E. Parallel) 10 15 IN 14E. Claims: Carlin Ranch Carrington 25 2N. 13E Claims: Chileno, Santis- 29 30 2N. 14E. sima, Rice & Lyons, Stocker, Wilson & Means, Gillis & Fra, Last Chance A; Pine Tree, Bluett, Carring- ton, Street Ext, Stench- field Chantreau 7 IN. 14E. XI p. 508; XIII p. 474; XXIV p. 23 XXIV p. 23 XIII p. 474; XXIV p. 23 XIII p. 474; XIV p. 138; XXIV p. 23; B 108 p. 158 BM 424, fig. 5 XIV p. 138; XXIV p. 23 X p. 737 VIII p. 652 ; IX p.37 ; X p. 736 XI p. 511; XII p. 299 XIII p. 475; XIV p. 141 XVIII p. 99; XLV p. 60 BM 424 pp. 61-62 B 108 p. 175 B 108 p. 174 XIII p. 475; XXIV pp. 24, 30; B 108, pp. 175-176 XIV p. 141; XXIV p. 24 X p. 737; XIV p. 142; XVIII p. 99; XIX p. 19, 144; XXIV, pp. 11,36,37; B 18, p. 129; B 108. pp. 159-175; PP 157 p. 78 XXIV p. 25; B 108 p. 175 Geology of the Angels Camp and Sonora Quadrangles Table 6. Gold vein mines and prospects, Sonora quadrangle, California — Continued. 53 Name of mine, prospect, or shaft Chileno* — See Carrington. . Climax* Cloudman — -See Erin-Go- Bragh Colby (Last Chance I) Claims: Fairview Combination — See O.K Coughlin Cowen Crystalline* Claims : Crystalline, Shore, Junietta, Harris & Oliver, Ophir, Winnie Defender* — See Albion Cons. Darrow Location Sec. 30 2N. 14E. Dickey Boy*- Donovan — See Vulture Dorsey Dutch* — See Pacific Coast Gold Mines Corp. Claims: Dutch, Sweeney East Lode (Last Lode) Erin-Go-Bragh & Cloudman* Eureka. Fairview (Little Bonanza)*. See Bonanza Fischer Florence Gagnere* Gandolfo & Rocca.. Gerrymander Cons Gillis Gold Leaf — See Mountain View (1) Gold Ridge Mining Co. — See Tarantula (2) Golden Gate* Claims: Golden Gate, Golden Sulphuret, Golden Sulphuret Ext. 3olden Nugget jiolden Rule* — See Jumper.. 3rand Turk Iray Eagle* — See Santa Ysabel rreenstone jiross — See Gross-Street Mining Co ross-Street Mining Co.* Claims: Gross, Shaw & Schollar, Street Harris iarris & Oliver (Winnie) — See Crystalline harvard* Claims: McCann, Moon- ey, Trio, Whiskey Hill, Sobrante, Pacific, Vul- ture leslep* — -See Pacific Coast Gold Mines Corp. 2 IS. 14E 27 IN. 14E 36 2N. 14E 32 2N. 14E 30 2N. 14E 36 2N. 14E 9 IN. 14E 2 IS. 14E 5 IN. 14E 7 IN. 14E 12 IN. 15E 16 IN. 14E 36 2N. 14E 22, 23 IN. 14E 32 2N. 14E 27 IN. 14E 36 2N. 14E 36 2N. 14E. 31 2N. 14E. 33 2N. 14E. 32 2N. 14E. 27 IN. 14E. 1 IN. 14E. 30 2N. 14E. 31 32 2N. 14E. 1, 2 IS. 14E. 1 IN. 14E. 36 2N. 14E. 2 IS. 14E. 27 35 IN. 14E. 29 2N. 14E. 27 IN. 14E. 28 IN. 14E. 29, 30 2N. 14E. 29, 30 2N. 14E. 16 IN. 14E. 9 IN. 14E. 16 IN. 14E. 22 IN. 14E. References XIII pp. 482-483; XIV p 142; XVIII pp. 99-100; XIX pp. 19, 144-145; B 18 p. 129; B 108 p. 159; B 141 p. 54; BM 424 p. 66; PP 157 p. 78 XIII p. 476; XXIV p. 25; B 108, p. 175 X p. 737; XI p. 505; XIII pp. 476-483; XXIV pp. 25, 31 XIII p. 476; XXIV p. 25; B 108 p. 175 X p. 737 XIII p. 477 X p. 742; XIII pp. 477-479; XIV p. 143; XVIII p. 99; XIX pp. 19, 74, 145; XX p. 19; XXIV pp. 9, 26; BM 424, pp. 28-30 XII p. 301; XIII p. 477; XIV p. 143; XXIV p. 26; B 108, p. 175 XIII p. 477; XXIV p. 26 X p. 51; XI p. 509; XII p. 302; XIII p. 477; XIV pp. 145-146; XVII p. 482; B 18 p. 130; B 108 p. 161; B 141 p. 50; PP 157 p. 78 XIII p. 478; XXIV p. 26 XIII p. 478; XX p. 20; XXIV p. 27; XLV p. 64; B 108 p. 175 XII p. 302; XIII p. 478; XIV p. 148; XXIV p. 27 XIII p. 478; XXIV p. 27 XII p. 302; XIII p. 478; XIV p. 148; XXIV p. 27 BM 424, fig. 5 XX p. 183; XXIV p. 27 XXIV p. 28 BM 424 pp. 65-66 X p. 738; XI p. 511; XII p. 302; XIII p. 479; XIV p. 149, XXIV p. 28; B 18, p. 134 XXIV p. 28; B 108 p. 175 B 108, p. 167 XXIV p. 29, 34; B 108 pp. 176, 177 XIII p. 480; XXIV p. 29 XIV p. 135; XXIV p. 7; XLV p. 53 XIII p. 480; XXIV p. 29; B 108 p. 176 XLV p. 66 XIII p. 494; XXIV p. 29, 41; B 108 p. 176 X p. 53; XIII pp. 485, 493; XIV pp. 149-151, 164; XXIV pp. 9, 18, 29, 39, 40; XLV p. 60; B 18 p. 130; B 108 pp. 165, 176, 179; BM 424 pp. 30-36 VIII p. 660; XII p. 299; XIII D. 473; XIV p. 136: XIX o. II p. 660; All p. 299; XIII p. 473; XIV p. 136; XIX p. I. 144- XX n 20- XXTV r. p. 473; XIV p. 136; XIX p. p. 144; XX p. 20; XXIV p. 29; B 108 p. 157, 166, 176; B 141 p. 50 Name of mine, prospect, or shaft Hess* Hitchcock* (Senator Mining Co.) — See Pacific Coast Gold Mines Corp. Imperial Independence (4) Isabella & Gem Jackson Flat & Parallel — See Cardinelle John Moore John Ore Jones Jumper* Claims: Jumper, New Era, Golden Rule, Bagan Ranch Kaiser King Solomon Knox & Boyle — See Santa Ysabel Last Chance I — See Colby _ Last Chance II — See Car- rington Last Chance III Last Lode — See East Lode.. Lead & Tarn O'Shanter Claims: Toledo Cons., Buena Vista Little Bonanza — 'See Bo- nanza Little Gem (Harris) Lone Star — See Tarantula (2) Lookout — See Pena Blanco Lucky Star — See Pena Blanco McCann — See Harvard Madrid Malone* Mangante Manzanita Mark Twain Mining Co Incorporates the claims of Nevada Wonder Min- ing Co. Maryatt* Maryatt North Ext.. Mascot (2) May & Hunter. Mazeppa* Miller & Holmes* Ysabel -See Santa Mooney* — -See Harvard Mother Lode _ Mountain View (1) (Gold Leaf) Mountain View (2) Nevada Wonder Mining Co. Claims: Chileno, Carring- ton Rice, Santissima, Stocker, J. A., J. A. Gillis, Wilson & Means, Pine Tree, Last Chance New Era — See Jumper New G. T. Mine — See New Grand Turk New Grand Turk (New G. T. Mine) Neubaumer Nugget* Nut Pine Location Sec. T. 24 IN. 14E. 22 IN. 14E. 23 2N. 13E. 29 2N. 14E. 5 IN. 14E. 29 2N. 14E. 30 2N. 14E. 30 2N. 14E. 25 2N. 13E. 26, 27 IN. 35 25 2N. 32 2N. 27 IN. 36 2N. 30 2N. 29, 32 10 36 2N. 35 IN. 3 IS. 30 2N. 14E. 14E. 14E. 14E. 14E. 14E. 13 IN. 14E 32 2N. 14E 31, 32 2N. 14E 36 2N. 14E 16 IN. 14E 2 IS. 14E. 6 IN. 14E. 6 IN. 14E. 16 IN. 14E. 29 2N. 14E. 34 IN. 14E. 10, 15 IN. 14E. 1, 2 IN. 14E. 30 2N. 14E. 32 2N. 14E. 2N. 14E. IN. 14E. 14E. 14E. 27 IN. 14E. 16 IN. 14E. 32 2N. 14E. 31, 32 2N. 14E. 14E. 14E. 26 IN. 14E 29 2N. 14E 29 2N. 14E 29 2N. 14E 35 IN. 14E 32 2N. 14E References XXXII p. 309 XIII p. 482 XII p. 303; XIII p. 482- XXIV p. 30; B 108 p. 176 X p. 737 X p. 737 XI pp. 173-174; XIII p. 109- XIV p. 88 X p. 50; XIII pp. 479 ,482- XIV p. 152; XXIV pp. 9 28, 30; XLV p. 69; B 108 pp. 167, 175, 176; B 141 p. 50; BM 424 pp. 41-43- AR'68p. 42; AR'71 p. 33 ! AR 72 p. 62 XIII p. 482; XXIV p. 31 XIII p. 483; XXIV p. 31 X p. 51; XII p. 303; XIII p. 483; B 108 p. 176 XVIII p. 99; XXIV p. 31 XIII p. 483; XXIV p. 31 X p. 56; XIII p. 484; XIV p 154; XXIV p. 31; B 108 p. 177 VIII p. 663; X p. 742; XI p. 506; XII p. 302; XIII p 484; XXIV pp. 27, 31; B 108 p. 177; XLV p. 69 XXIV p. 31 XIII p. 484; XXIV p. 32; B 108 p. 177 XIII p. 484; XXIV p. 32 B 108 p. 177 VIII p. 658 XIV p. 155; XXIV p. 32 PR 8 p. 40 XI p. 506; XXIV p. 32 B 108 p. 159; PP 157 p. 78 XIII p. 485; XXIV p. 32; B 108 p. 177 XXIV p. 32; B 108 p. 177 XIII p. 485; XIV p. 155- XXIV p. 32 XIII p. 485 XI pp. 509-510; XIII p. 485; XIV p. 156; B 108 p. 177- BM 424 p. 43 XII pp. 302-304; XIII p. 486; XXIV pp. 29, 33; B 108 p. 176; Sonora folio, Econ. sheet XIII p. 486; XXIV p. 33 XXIV p. 33; B 108 p. 177 B 108 p. 177 B 108 p. 159; PP 157, p. 78 XI p. 509; XIII p. 487 B 108 p. 177 XIII p. 478; XXIV p. 34 XLV pi. 8 XXIV p. 34; B 108 p. 177 'A Special Report 41 Table 6. Gold vein mines and prospects, Sonora quadrangle, California — Continued. Name of mine, prospect, or shaft Nyman Cons.* — See Santa Ysabel Cons. O.K.* Claims: O.K., Combina- tion, O.K. N. Ext. O'Donnell Olsen Omega (Red Cross)* Claims: Omega Table Mt. Gravel, Omega, General Hooker Ophir (1) Pacific Pacific Coast Gold Mines Corp. Took under option: App, Dutch, Sweeney, Hitch- cock and Heslep mines Patterson* Claims: Patterson, Len- non, Atlas Pena Blanco Claims: Pena Blanco, Doctor, Lookout, Lucky Star, Sarah Francis Pine Ridge Pine Tree — -See Carrington Point Rock Pride of Tuolumne Prospect* Punter. Rappahannock* Rawhide* Rawhide No. 2 Red Cross — See Omega Reitz Group — See Taran- tula (2) Relief & Surplus Rice & Lyons — See Car- rington Ritchie Ross San Giuseppe* Location Sec. 22 IN. 14E. 32 2N. HE 5 IN. 14E 15 IN. HE 32 2N. HE 9 IN. HE 9 IN. 14E 15 IN. 14E 22 IN. HE 29 2N. HE. IN. HE. 16 30 IN. 2N. 13, 24 2N. 31 2N. 3, 6 2N. IN. IN. IN. HE. HE. 13E. HE. HE. HE. 14E. HE. References 4, 5, IN. HE. 8, 9 9 IN. HE. 9 2 29, 30 32 30 32 31 35, 36 IN. IS. HE. HE. 2N. HE. 2N. HE. 2N. 2N. 2N. HE. HE. HE. XI p. 508: XII p. 305; XIII p. 487; XIV p. 158; XXIV p. 34; B 108 p. 177 XIV p. 157; XXIV p. 34; B 108 p. 177 XXIV p. 35 XIV p. 158; XIX pp. 19, 145; XX p. 21; XXIV p. 35; B 108 p. 178; B 141 p. 50 XXIV p. 35 XIII p. 487; XXIV p. 35; B 108 p. 178 XVII pp. 482-83; B 108 p. 157; PP 157 p. 78 VIII pp. 656-657; XII p. 305; XIII p. 488; XIV p. 158; XVII p. 485; XVIII pp. 100-101; XIX p. 74; PR 8 p. 41; XXIV pp. 9, 35; B 108 pp. 170-178 XIII p. 488; XIV p. 159; XXIV p. 35; B 108 p. 178 XIII p. 488; XXIV p. 35 XVIII p. 99 XIII p. 116 XIII p. 489; XXIV p. 36 XXIV p. 36; B 108 p. 178 XIV p. 36 XII p. 306; XIII p. 489; XIV p. 159, XXIV p. 36; B 108 pp. 171, 178 X p. 54; XI pp. 507-508; XII p. 306; XIII p. 489; XIV pp. 159-160; XVIII p. 101; PR 8 p. 41; B 18 pp. 129- 130; B 141 p. 50; BM 424 pp. 21-28 XII p. 306; XIII p. 489; XIV p. 160; BM 424 pp. 21-27 Name of mine, prospect, or shaft Location Sec. R. Santa Ysabel Cons.* Claims: Nyman, Knox & Boyle, Miller & Holmes, Gray Eagle, Bastian Ranch Rights Santissima — See Carrington Mine Sarah Francis — See Pena Blanco Senator Mining Co. — See Hitchcock Shaw & Schollar — See Street, also see Gross-Street Mining Co. Shell Ranch Shore* Sobrante — See Harvard Sonora Wonder Stenchfield — See Carrington. Street (Shaw & Schollar)— See Gross-Street Claims: Eleanor Sweeney'* — See Dutch XIV 160; XIII p. 489; XIV p. mu XXIV p. 37; B 108 p. 178 X p. 737 XIII p. 489; XXIV p. 37 XTII 490- XXIV d. 37 XIII 490; XXIV p. 37 "III p. 654; X p. 740; XII p. 306; XIII p. 490; XIV p. VI .iuo; aj.ii p. i»u 161; XXIV p. 37 S werer ■ Tam O'Shanter (Lead & Tarn O'Shanter) Tanzy Claims: Tanzy Tarantula* Claims: Tarantula, Tar- antula West Ext. Tarantula (2) (Reitz Group: Jones-Tarantula) Claims: Tarantula, Lone Star, Omega, Western Ext., Golden Horse Shoe, Boulder Deep, Tarantula Hawk, Gold Ridge. Tarantula Hawk — See Tar- antula (2) Toledo* Trio mine* 22, 27 IN. 14E. 30 2N. 6 IN. 22 IN. 29 2N. 17 10 16 36 IN. IN. IN. IN. 30 2N. HE. 14E. 14E. HE. HE. HE. HE. 14E. HE. 29 2N. 14E. 15 22 IN. 14E 32 2N. HE 31 32 2N. HE 36 2N. 14E 5 IN. HE 32 2N. HE References X p. 51; XIII p. 490; XIV p 161; XVIII p. 101; XXI\ pp. 34, 37; B 18 p. 131 BM 424 p. 41; B 108 p. 17S XIII p. 490; XXIV p. 37 B 108 p. 179 B 23 p. 201 ; B 50 p. 248 BM 424 pp. 67-68 XIX p. 145; XXIV p. 38 XIII pp. 482, 492; XXIV r. 39; B 108 p. 129 XIII p. 492; XIV p. 163 XXIV pp. 38, 39; B 10 p. 179 XIII p. 492; XXIV p. 39 B 108 p. 179; B 141 p. 5C 7 ~ 7Q IS. HE. Utopia Vandelier* Vulture (Donovan) _ Waters — See Atlas Whiskey Hill mine — See Harvard Wick ham* ■ Wilson & Means — See Car- rington Winnii — See Crystalline Worcester (1) 31 16 IS. 2N. IN. 31 2N. 25, 36 2N. 15, 16 IN. 30 2N. 16 IN. 32 2N. 30 2N. 32 IN. 2N. HE. HE. HE. HE. HE. HE. HE. HE. HE. HE. HE. HE. I pp. 157 p. 78 XIII p. 493; XXIV p. 39 X p. 56; XIII p. 484; XIV 154; B 108 pp. 177, 179 XIII p. 493; XIV p. It XXIV p. 39 XIII p. 493; XIV p. 16' XXIV p. 39; B 108, p. 17 XIV p. 164; XVII p. 48; XXIV pp. 30, 39; B 1C pp. 176, 179 X p. 53; XIII p. 493; XI pp. 149, 164; XXIV pi 9, 18, 29, 39, 40; B 108 p 165, 176, 179; B 18 p. ■ XIII p. 493; XXIV p. 40 XIII p. 493; XXIV pp. 35; B 108 p. 179 B 108 p. 165 XXIV p. 41; B 108 p. 179 XIII pp. 477-479 XIII p. 494 Tahle 7. Gold placer mines and prospects, Xonora quadrangle, California. App Bedrock Blue Gravel (Vir- ginia) Claims: Saratoga, Gold Hunter, Jefferson Best Twenty Boston. - Buckeye (Rosedale Gravel) (hums: Buckeye placer Habacker* Hoseg: Dick & Kent Humbug Gravel* — See New York Jamestown & Comet — See New York Claim: Comet placer McKinley. - - Montezume Tunnel New York* Claims: Humbug, Helen A, -Jamestown & Comet, Rawhide 27 17 27 27, 34 20 32 4 33 4 17 20 4 33 IN. HE. 2N. HE. IN. 2N. 2N. IN. IN. IN. 2N. IN. HE. HE. HE. HE. HE. HE. HE. HE. IN. HE. IN. HE. IN. HE. 2N. HE. BM 424, fig. 5 XXIV p. 44 XXIV p. 44 X p. 738; XXIV p. 44 X p. 737; XIV p. 166; XXIV pp. 44', 46 XXIV p. 45 X p. 738; XIV p. 167; XXIV p. 45 IX p. 222; XXIV p. 45 XXIV p. 45 XXIV p. 45 Xp. 738; XXIV p. 34; B 141 p. 50 Punchbowl* Claim: Punchbowl Placer Rawhide Claims: Rawhide, Raw hide Ranch Placer, Rawhide No. 2, Keggan, Nevells Placer, Martin Placer, Ballard Placer Rawhide No. 2— See Raw- hide Rawhide Ranch — See Raw- hide Red Hill Rimin Cam Rosedale Gravel — See Buck- eye Rough & Ready Table Mt. & Alpha. Ventura Grubstake- Virginia — See Bedrock Blue Gravel 20 IN. 4, 5 8, 9 IN. HE. HE. 9 IN. HE. 4, 9 IN. HE. 29 IN. 14E. IN. HE. 27, 34 2N. HE. 30, 31 IN 25, 26 IN 9 19, 20 29 27 2N. HE. 13E. IN. HE. IN. HE. HE. XIV p. 167; XXIV p. 4 XLV p. 74; BM 424 p. X p. 54; XI pp. 507-508; 3i p. 306; XIII p. 489; X pp. 159-160; XVIII p. 1( XXIV pp. 8, 36; PR 8 41; B 18 pp. 129-130; 108 pp. 171, 178 XII p. 306; XIII p. 41 XIV p. 160 XXIV p. 45 BM 424 pp. 80-81 XXIV p. 46 XXIV p. 46 XXIV p. 46 : . Geology of the Angels Camp and Sonora Quadrangles Table 8. Prospects for products other than gold, Sonora quadrangle, California. 55 Location Location Name of mine, prospect, or shaft References Name of mine, prospect, or shaft References Sec. T. R. Sec. T. R. Asbestos Rough & Ready (Annex, 25 IN. 13E. XXIV p. 6; B 76, pp. 214, lawhide Asbestos Claims 5 IN. 14E. XLV p. 49 Richards)* 225; B 134 pt. Ill p. 27; No. 1, 2, and 3 BM 424, p. 87 Beryl Rowe and Swerer. . _ 5 36 IN. IN. 14E. 13E. B 134 pt. Ill p. 13 Shafer Lease (Pereira Mine). B 134 pt. Ill p. 26 Eimestown 10 IN. 14E. XXVII p. 90 Sims* . . _ . 5 IS. 14E. XXIV p. 6; B 76, pp. 214, 225; B 134 pt. Ill pp. 20, Chromite 29; Min Ind 1916, p. 102; nnex — See Rough & 25 IN. 13E. B 134 pt. Ill, p. 27 BM 424 p. 87 Ready, Richards Sullivan and Kahl* 25 IN. 13E. B 134 pt. Ill pp. 29, 30 eckwith Ranch Mines. _ . 1 IS. 13E. B 134 pt. Ill, p. 20, 28 Sunday. . . __ _. 5 IN. 14E. B 134 pt. Ill p. 13 Claims: Booker lease, Rosa A, Mapes-O'Hara, Copper Fagen Greenstone — See Mann Cop- 28 IN. 14E. ooker lease — See Beck- per Mine with Ranch Mines ggling and Williams 4, 5, IS. 14E. B 134, pt. Ill p. 18, 28 Kahl Ranch 6, 7 IN. 14E. XXIV p. 7; B 23 p. 201; B 50, p. 248 8, 9 Mann Copper Mine. 27, 28 IN. 14E. XIV p. 135; XXIV p. 7; XLV agen lease — See Beckwith 1 IS. 13E. B 134, pt. Ill pp. 20, 28 Claims: Red Mt. Iron p. 53 Ranch Mines Mine, Greenstone Cop- rassely Claims 25 IN. 13E. B 134 pt. Ill p. 26 per Mine, Copper King Claims: Horseshoe, Morn- Copper Mine ing Glory, May Fac- Mackey (Ohio Diggins)* 21, 28 IN. 14E. XLV p. 53 tion, Last Chance Marianno Iron & Copper 4, 5, IS. 14E. XXIV p. 7 'orseshoe (Pedro Claim) — 25 IN. 13E. Mines 8, 9 IS. 14E. See Grasseley claims Ohio Diggins ( Mackey) . . 21, 28 IN. 14E. XIV p. 135; XXIV p. 7; XLV !ahl, (Quigg) . . 6 IN. 14E. XXIV p. 6; B 76. pp. 213, p. 53; B 23 p. 201; B 50 p. 225; B 134 pt. Ill pp. 12-13; 248 Min Ind 1918 p. 84; BM 424 p. 87 Shell Ranch 17 IN. 14E. B 23 p. 201; B 50 p. 248 ast Chance — See Grassely 25 IN. 13E. B 134 pt. Ill pp. 26, 29 Claims Limestone opez Lease — See May Fac- 25 IN. 13E. Pacific Lime & Plaster Com- 1 IN. 14E. XIV p. 168; XVII p. 487; tion pany* XXIV p. 47, 49; B 101 p. [ackey (Maki, Peter)* 21 IN. 14E. XXIV p. 6; B 76, pp. 213, 225; B 134 pt. Ill p. 14; Min Ind 1915 p. 84, 1916 Claims: Ed Rudorff, Louis Ratte, Badgley Stone Entry 270; AR '24 p. 230 p. 102; BM 424 p. 87 U. S. Lime Products Co 1 IN. 14E. B 102 p. 177; B 103 p. 183 [aki, Peter (Mackey) — See 21 IN. 14E. 12 IN. 14E. B 105 p. 183; B 109 p. 149 Mackey B 107 p. 180; B 110 p. 160 [apes-O'Hara — See Beck- 1 IS. 13E. B 134, pt. Ill pp. 20, 29 B 111 p. 281; B 112 p. 155 with Ranch Mines* B 114 p. 150; B 116 p. 151 [ay Faction (Lopez lease) — 25 IN. 13E. B 134 pt. Ill pp. 26, 29 XIV p. 79; MR '29, 281 See Grassely claims Magnesite [orning Glory — See Gras- 25 IN. 13E. Mackey (Maki, Peter) 6 IS. 14E. sely Claims Maki, Peter (Mackev) 6 IS. 14E. XXIV p. 50; XLV p. 81; B edro lease ( Horseshoe) — 25 IN. 13E. Claims: Sunshine, Snow 79 p. 139 See Grasseley claims Drift erconi Ranch*. _ 5 IS. 14E. B 134 pt. Ill pp. 19-20, 29 Monarch 6 IS. 14E. XXIV p. 50; XLV p. 81 ; B ereira (Shafer lease). 25 IN. 13E. XXIV p. 6; B 76 pp. 214, 79 p. 139 225; B 134 pt. Ill pp. 26, White Rock Magnesite 6 IS. 14E. XXIV p. 50; XLV p. 81; B 29; BM 424 p. 87 79 pp. 139, 140; MR '16, hoenix __ 24 IN. 13E. B 134 pt. Ill pp. 29, 30 p. 397; MR '22, p. 47 uigg (Kahl)* G IN. 14E. Soapstone & Talc ichards — See Rough & 25 IN. 13E. B 134 pt. Ill pp. 27, 29 Brown, B... .. 36 2N. 14E. XXIV p. 53 Ready* Finch, W. E 36 2N. 14E. XXIV p. 53 osa A. — -See Beckwith 1 IS. 13E. B 134 pt. Ill pp. 20, 29 Hunter, A. D 36 2N. 14E. XXIV p. 53 Ranch Mines Whitney, John L. IN. 14E. B 107 p. 194; B 109 p. 164 336 5-54 2M printed in California state printing office