DESCRIPTION OF THE GOLD BELT. GEOGRAPHIC RELATIONS. shore was apparently somewhat west of the Oro and the Mariposa slates, are found only on post-Juratrias upheaval, and that their age, present crest, and the sea extending westward the western flank of the Sierra Nevada. During therefore, is early Cretaceous.

The principal gold belt of California includes received Paleozoic sediments which now consti­ the earlier part of the Juratrias period portions SUPERJACENT SERIES. a portion of the Sierra Nevada lying between the tute a large part of the central portion of the of the Great Basin were under water, as is shown parallels of 37° 30' and 40° north latitude. It is range. by the fossiliferous beds of that age in Eldorado CEETACEOUS PEEIOD. bounded on the west by the Sacramento and San At the close of the Carboniferous the Paleozoic Canyon south of Virginia City and in the Hurn- Since no beds of early Cretaceous age are Joaquin valleys, and on the east by a diagonal land area of western Nevada subsided, and dur­ boldt Mountains, but nowhere from the foothills known in the Sierra Nevada, it is presumed that line extending from about longitude 120° 40' in ing the larger part of the Juratrias period it was of the Sierra Nevada to the east base of the during the early Cretaceous all of the present the neighborhood of the fortieth parallel to lon­ at least partly covered by the sea. At the close Wasatch, if we except certain beds near Genesee range was above water. gitude 119° 40' in the neighborhood of parallel of the Juratrias the Sierra Nevada was upheaved Valley, are any deposits known which are of late During the late Cretaceous the range subsided 37° 30'. There are other gold-bearing regions in as a great mountain range, the disturbance being Jurassic age. to some extent, allowing the deposition of sedi­ the State, both to the north and south of this accompanied by the intrusion of large amounts The following formations have been recognized ments in the lower foothill region. These belt, but by far the largest quantity of gold is of granitic rock. on the Gold Belt maps: deposits are known as the Chico formation, and produced within these limits. The area thus The Auriferous slate series comprises all of the (1) The Mariposa formation, which occurs in consist of sandstone with some conglomerate. denned contains approximately 9000 square sedimentary rocks that entered into the composi­ narrow bands along the western base of the In the area covered by the Gold Belt maps this miles. At the northern limit the gold deposits tion of this old range of Juratrias time. Forma­ range. The strata are prevailingly clay-slates, formation is exposed only near Folsom on the are scattered over nearly the entire width of the tions representing the Algonkian and all of the which are locally sandy and contain pebbles of American River up to an elevation of 400 feet, range, while to the south the productive region Paleozoic and Juratrias may therefore form part rocks from the Calaveras formation. Tuffs from and in the Chico district at elevations of from narrows to small dimensions, continuing as a very of the Auriferous slate series. contemporaneous porphyrite eruptions also occur 500 to 600 feet. Since their deposition these narrow strip for some distance south of latitude Fossils of Carboniferous age have been found in them. The fossils of these beds, such as strata have been but slightly disturbed from their 37° 30'. The whole southern part of the range in a number of places, and the presence of Silu­ Aucella and Perisphinctes, have their nearest original approximately horizontal position, but the is comparatively barren. North of the fortieth rian beds at the northern end of the range, north of analogues in Russia, and indicate a very late larger part of them has been eroded or covered parallel the range is not without deposits, but the fortieth parallel, has been determined. A Jurassic age. by later sediments. the country is flooded with lavas which effectu­ conglomerate occurs in the foothills of Amador (2) The Monte de Oro formation, occurring to Auriferous gravels are found to some extent V ally bury the larger part of them. and Calaveras counties, interbedded with slates the northeast of Oroville. This consists of clay- in the Chico formation for instance, near Fol­ containing Carboniferous limestone; this con­ slate and conglomerate containing plant remains \ I GENERAL GEOLOGY. som showing that the gold-quartz veins had glomerate is therefore presumably of Carbonif­ of late Jurassic age. already been formed before its deposition. The rocks of the Sierra Nevada are of many erous age. The conglomerate is evidence of a (3) The Sailor Canyon- formation, which kinds and occur in very complex associations. shore, since it contains pebbles of quartzite, horn- appears well up toward the summit of the range, EOCENE PEEIOD. They have been formed in part by deposition blende-porphyrite, and other rocks, which have and consists of clay-slates, altered sandstones, and In consequence of slow changes of level with­ beneath the sea and in part by intrusion as been rounded by the action of waves. The tuffs. It is separated from the Mariposa forma­ out marked disturbance of the Chico formation, igneous masses, as well as by eruption from vol­ presence of lava pebbles in the conglomerate tion by a broad belt of the Calaveras formation. a later deposit formed, differing from it some­ canoes. All of them except the latest have been shows that volcanic eruptions began at a very The fossils indicate that the period of its deposi­ what in extent and character. The formation more or less metamorphosed. early date in the formation of the range, for the tion covered both the later part of Triassic and has been called the Tejon (Tay-hone7). It appears The northern part of the range, west of longi­ hornblende-porphyrite pebbles represent lavas the earlier part of Jurassic time. in the Gold Belt region at the Marysville Buttes, tude 120° 30', consists prevailingly of clay-slates similar to the hornblende-andesites of later age. (4) The Milton formation, which has thus far in the lower foothills of the Sonora district, and and of schists, the latter having been produced by The great mass of the Paleozoic sediments of afforded no fossils; it is lithologically similar to it is extensively developed in the southern and the metamorphism of both ancient sediments and the Gold Belt consists of quartzite, mica-schist, a portion of the Sailor Canyon series, and future western portion of the Great Valley of California. igneous rocks. The trend of the bands of altered sandstone, and clay-slate, with occasional lime­ research may show that it really was deposited During the Eocene the Sierra Nevada remained sediments and of the schistose structure is gener­ stone lenses. On the maps of the Gold Belt at the same time. a separate, low mountain range, erosion continu­ ally from northwest to southeast, parallel to the these sediments are grouped under two forma­ ing with moderate rapidity but no great masses trend of the range, but great masses of granite tions : THE POST-JUEATEIAS UPHEAVAL. of gravels accumulating. and other igneous rocks have been intruded among (1) The Robinson formation, comprising sedi­ Soon after the Mariposa formation had been these schists, forming irregular bodies which ments and trachytic tuffs. This contains fossils deposited the region underwent uplift and com­ NEOCENE PEEIOD. interrupt the regular structure and which are showing the age to be upper Carboniferous. The pression. The result of uplift was the develop­ The Miocene and Pliocene periods, forming generally bordered each by a zone of greater formation is known on the Gold Belt series of ment of a mountain range along the line of the the later part of the Tertiary, have in this atlas metamorphism. These slates and schists and maps only in the Downieville quadrangle, a short Sierra Nevada. The Coast Range also was prob­ been united under the name of the Neocene their associated igneous masses form the older of distance south of the fortieth parallel. ably raised at this time. The action of the forces period. During the Neocene a large part of the two great groups of rocks recognized in the Sierra (2) The Calaveras formation, comprising by was such as to turn the Mariposa strata into a Great Valley of California seems to have been Nevada. This group is generally called the Bed­ far the largest portion of the Paleozoic sediments nearly vertical position, and to fold them and under water, forming perhaps a gulf connected rock series. of the Gold Belt. Rounded crinoid stems, corals other Juratrias beds in with the older Paleozoic with the sea by one or more sounds across the Along the western base of the Sierra occur beds (Lithostrotion and Clisiophyllum), Foraminifera strata. The Juratrias clay-shales, in consequence Coast Ranges. Along the eastern side of this gulf of sandstone and clay, some of which contain thin (Fusulina), and bivalves have been found in the of pressure, now have a slaty structure, which was deposited during the earlier part of the Neo­ coal seams. These are much younger than the limestone lenses, and indicate that a considerable appears to coincide in most cases with the bed­ cene period a series of clays and sands to which the mass of the range and have not shared the met­ portion at least of this formation belongs to the ding. This epoch was one of intense eruptive name lone formation has been given. It follows amorphism of the older rocks. They dip gently middle or lower Carboniferous. In extensive activity. The Mariposa and other Juratrias and the Tejon, and appears to have been laid down westward beneath later deposits, which were areas of the Calaveras formation no fossils have, older beds were injected with granite and other upon it, without an interval of disturbance or spread in the waters of a shallow bay occupying however, been found, and older rocks may be intrusive rocks. There is evidence that igneous erosion. Marine deposits of the age of the lone the Valley of California and portions of which present in these. It is not likely that post-Car­ rocks were intruded in varying quantities at dif­ formation are known within the Gold Belt only have been buried beneath recent river alluvium. boniferous rocks are present in these non-fossil- ferent times; but that the intrusion of the great at the Marysville Buttes. Along the eastern Streams flowing down the western slope of the iferous areas. mass of the igneous rocks accompanied or imme­ shore of the gulf the Sierra Nevada, at least Sierra in the past distributed another formation diately followed the upheavals is reasonably cer­ POST-CAEBONIFEEOUS UPHEAVAL. south of the fortieth parallel, during the whole of great importance the Auriferous gravels. tain. Those beds that now form the surface of the Neocene formed a low range drained by The valleys of these streams served also as After the close of the Carboniferous and before were then deeply buried in the foundations of numerous rivers. The shore-line at its highest channels for the descent of lavas which poured the deposition of at least the later Juratrias beds the range. position was several hundred feet above the out from volcanoes near the summit. Occupying (Sailor Canyon, Mariposa, and Monte de Oro for­ The disturbance following the deposition of present level of the sea, but it may have fluctu­ the valleys, the lavas buried the gold-bearing mations), an upheaval took place by which the the Mariposa beds was the last of the move­ ated somewhat during the Neocene period. The gravels and forced the streams to seek new Carboniferous and older sediments under the ments which compressed and folded the Aurifer­ lone formation appears along this shore-line as a channels. These have been worn down below then retiring sea were raised above water level, ous slate series. The strata of succeeding epochs, brackish-water deposit of clays and sands, fre­ the levels of the old valleys, and the lava beds, forming part of a mountain range. The beds lying nearly horizontal or at low angles, prove quently containing beds of lignite. with the gravels which they protect, have been were folded and compressed and thus rendered that since they were accumulated the rock mass The Sierra Nevada during this period was a isolated on the summits of ridges. Thus the schistose. Smaller masses of granite and other of the Sierra Nevada has not undergone much range with comparatively low relief. The drain­ Auriferous gravels are preserved in association igneous rocks were intruded at this time. compression. But the fact that these beds now age system during the Neocene had its sources with lavas along lines which descend from north­ occur above sea-level is evidence that the range near the modern crest of the range, but the east toward southwest, across the trend of the JUEATEIAS PEEIOD. has undergone elevation in more recent time. channels by no means coincided with those of the range. The nearly horizontal strata along the The areas of land and sea which existed during present time. Erosion gradually declined in western base, together with the Auriferous the earlier part of this period are scarcely known. THE GOLD-QUAETZ VEINS. intensity and auriferous gravels accumulated in gravels and later lavas, constitute the second Fossiliferous strata showing the former presence The extent of the gold deposits has been indi­ the lower reaches of these Neocene rivers, the group of rocks recognized in the Sierra Nevada. of the Juratrias sea have been recognized in the cated in the introduction to this description. In gold being derived from the croppings of veins. Compared with the first group, the Bed-rock southeastern portion of the range, at Mineral character they may be classed as primary, or Such gravels could accumulate only where the series, these may be called the Superjacent series. King, where the sediments are embedded in deposits formed by chemical agencies, and sec- slope of the channel and the volume of water

BED-ROCK SERIES. intrusive granite; at Sailor Canyon, a tributary ondary, or those formed from the detritus pro­ were sufficient to remove the silt while allowing of American River; in Plumas County at the duced by the erosion of the primary deposits. the coarser or heavier masses to sink to the PALEOZOIC EEA. north end of the range about Genesee Valley The primary deposits are chiefly gold-quartz bottom with the gold. During the Paleozoic era, which includes the and elsewhere; and in the foothill region from veins, fissures in the rock formed by mountain- During the latter part of the Neocene period periods from the end of the Algonkian to the end Butte to Mariposa counties in the slates of the making forces and filled with gold-bearing volcanic activity, long dormant, began again, of the Carboniferous, the State of Nevada west Mariposa and Monte de Oro formations. quartz deposited by circulating waters. The and floods of lavas, 1 consisting of rhyolite, of longitude 117° 30' appears to have been a land The land mass that originated with the post- gold-quartz veins of the Sierra Nevada are found andesite, basalt, and plagioclastic glassy rocks area of unknown elevation. This land probably Carboniferous upheaval became by gradual eleva­ in irregular distribution chiefly in the Auriferous chemically allied to trachyte, were ejected from extended westward into the present State of tion very extensive toward the end of the Jura­ slates and associated greenstone-schists and por- volcanic vents, and these eruptions continued to California and included part of the area now trias period. This continental mass of late phyrites, but they also occur abundantly in the the end of the Neocene. These lavas occupy occupied by the Sierra Nevada. Its western Jurassic time probably reached eastward at least granitic rocks that form isolated areas in the slate x The term "lava" is here used to include not only such as far as the east base of the Wasatch Mountains. series. While some gold-quartz veins may ante­ material as issued from volcanic vents in a nearly anhydrous This conclusion is based on the fact that the date the Jurassic period, it is reasonably certain condition and at a very high temperature, but also tuff-flows *Jointly prepared by Geo. F. Becker, H. W. Turner, and and mud-flows, and, in short, all fluid or semifluid effusive Waldemar Lindgren, 1894. Revised January, 1897. latest Jurassic beds of California, the Monte de that most of them were formed shortly after the volcanic products. small and scattered areas in the southern part of maximum glaciation. In this interval most of the Sierra Nevada the diabases and porphyrites are ' between a granite and a quartz-diorite, and is in the Gold Belt, increasing in volume to the north deep canyons of the range were formed. Such, of pre-Eocene age, and contain in most cases fact closely related to the latter. The large areas until, north of the fortieth parallel, they cover for example, are the Yosemite Valley on the secondary urn rals, such as epidote, zoisite, ura- occupied by it and the constancy of the type almost the entire country. They were extruded Merced River, the great canyon of the Tuolumne, lite, and chlorite. The unaltered equivalents of justify the special name.' mainly along the crest of the range, which still is and the canyon of the Mokelumne. The erosion these rocks basalt, andesite, dacite, and rhyo­ Granite. A granular intrusive rock composed crowned by the remains of the Neocene volcanoes. of these gorges may have been facilitated by the lite are, in the Sierra Nevada, chiefly of Neo­ of quartz, alkali and soda-lime feldspars, mica, An addition to the gold deposits of the range, fissure system referred to above, for many of the cene or later age. and sometimes hornblende. in the form of gold-quartz veins and irregular rivers of the range appear to follow one or another Tuffs are volcanic ashes formed by explo­ Aplite (also called Q-ranulite). A granitoid thermal impregnations, attended this period of set of parallel fissures for a long distance. sions accompanying the eruptions. Mixed with rock usually occurring as dikes, and consisting volcanic activity. At what point the limit between the Neocene water, such material forms mud flows; and when principally of quartz and alkali feldspar. "When the lavas burst out they flowed down and the Pleistocene should be drawn is a some­ volcanic ashes fall into bodies of water they Syenite. A granular intrusive rock composed the river channels. The earlier flows were not what difficult question. On the maps of the become regularly stratified like sedimentary chiefly of alkali feldspars, usually with some sufficient to fill the streams, and became inter- Gold Belt the great andesitic flows are supposed rocks and may contain fossil shells. Breccias are soda-lime feldspars and. hornblende or pyroxene. bedded with gravels. They are now represented to mark the close of the Neocene, and this divi­ formed by the shattering of igneous rocks into Amphibolite, amphibolite-schist. A massive or by layers of rhyolite and rhyolite-tuffs, sometimes sion is in fact the only one that can be made with­ irregular angular fragments. Tuffaceous breccias schistose rock composed principally of green altered to "pipe-clay." The later andesitic and out creating artificial distinctions. But it is not contain angular volcanic fragments cemented by a hornblende, with smaller amounts of quartz, basaltic eruptions were of great volume, and for positively known that this line corresponds consolidated mud of volcanic ashes. feldspar, epidote, and chlorite, and usually the most part completely choked the channels exactly to that drawn in other parts of. the world derived by metamorphic processess from augite- GLOSSARY OP ROCK NAMES. into which they flowed. The rivers were thus between these periods. porphyrite, diabase, and other basic igneous obliged to seek new channels substantially The Sierra, from an elevation of about 5000 The sense in which the names applied to igne­ rocks. those in which they now flow. feet upward, was long buried under ice. The ous rocks have been employed by geologists has Augite-porphyrite. An intrusive or effusive Fossil leaves have been found in the pipe-clay, ice widened and extended the canyons of pre­ varied and is likely to continue to vary. The porphyritic rock with larger crystals of augite and in other fine sediments at numerous points. existing topography and removed enormous sense in which the names are employed in this and soda-lime feldspars in a finer groundmass Magnolias, laurels, figs, poplars, and oaks are amounts of loose material. It seems otherwise folio is as follows: composed of the same constituents. represented. The general character of the flora to have protected from erosion the area it covered Peridotite. A granular intrusive rock gener­ Hornblende-porphyrite. An intrusive or effu­ is thought to indicate a warm and humid climate, and to have accentuated the steepness of lower ally composed principally of olivine and pyroxene, sive porphyritic rock consisting of soda-lime and has been compared with the present flora of slopes. Small glaciers still exist in the Sierra. but sometimes of olivine alone. feldspars and brown hornblende in a fine ground- the South Atlantic Coast of the United States. During the earlier part of the Pleistocene Serpentine. A rock composed of the mineral mass. period the Great Valley was probably occupied serpentine, and often containing unaltered remains Quartz-porphyrite. An intrusive or effusive THE NEOCENE UPHEAVAL. for a time by a lake dammed by the post-Miocene of pyroxene or olivine. Serpentine is usually a porphyritic rock consisting of quartz and soda- In the latter part of the Neocene period a great uplift of the Coast Ranges. Later in the decomposition product of rocks of the peridotite lime feldspar, sometimes with a small amount of dislocation occurred along a zone of faulting at Pleistocene this lake evidently was drained and and pyroxenite series. hornblende or biotite. the eastern base of the Sierra Nevada, and the alluvial deposits were spread over the valley. Pyroxenite. A granular intrusive rock com­ Quartz-porphyry. An intrusive or effusive grade of the western slope of the range was There is no valid reason to believe that the posed principally of pyroxene. porphyritic rock, which differs from quartz-por­ increased. These faults are sharply marked central and southern part of the Sierra has under­ Q-abbro. A granular intrusive rock consisting phyrite in containing alkali feldspars in excess from Owens Lake up to Honey Lake. There gone any important dynamic disturbance during of soda-lime or lime feldspars and pyroxene, or of soda-lime feldspars. was also a series of faults formed apparently the Pleistocene period, but renewed faulting with more rarely hornblende. Rhyolite. An effusive rock of Tertiary or at the very close of the Neocene within the small throw has taken place along the eastern Diabase. An intrusive or effusive rock com­ later age. The essential constituents are alkali mass of the range in Plumas County. Near base of the range in very recent times. posed of soda-lime feldspar (often labradorite) feldspars and quartz, usually with a small amount the crest the Sierra Nevada is intersected by a and pyroxene (more rarely hornblende). The of biotite or hornblende in a groundmass, which system of fissures, often of striking regularity; it IGNEOUS ROCKS. feldspars are lath-shaped. The pyroxene is often is often glassy. is believed that these fissures originated during Rocks of igneous origin form a considerable partly or wholly converted into green, fibrous Andesite. An effusive porphyritic rock of the Neocene upheaval. part of the Sierra Nevada. The most abund­ hornblende or uralite. From this change, also Tertiary or later age. The essential constituents ant igneous rocks there found are of granitic frequent in gabbros, rocks result which are refer­ are soda-lime feldspars (chiefly oligoclase and PLEISTOCENE PEEIOD. character. Rocks of the granitic series are red to as uralite-diabase or uralite-gabbro. andesine) and ferromagnesian silicates (horn­ During Cretaceous, Eocene, and Neocene times believed to have consolidated under great press­ Diorite. A granular intrusive rock consisting blende, pyroxene, or biotite), in a groundmass the Sierra Nevada had been reduced by erosion ure and to have been largely intruded into over­ principally of soda-lime feldspar (chiefly andesine of feldspar microlites and magnetite, usually with to a range with gentle slopes, and the andesitic lying formations at the time of great upheavals; or oligoclase) and hornblende or pyroxene (some­ some glass. The silica is ordinarily above 56 per eruptions had covered it with a deep mantle of they are thus deep-seated rocks, exposed only times also biotite). cent. When quartz is also present the rock is lava flows. The late Neocene upheaval increased after great erosion has taken place. Quartz-diorite. A granular intrusive rock com­ called a dacite. the grade of the western slope greatly, and the The rocks called diabase and augite-porphyrite posed of soda-lime feldspar and quartz, usually Basalt. An effusive rock of Tertiary or later rivers immediately after this disturbance found on the Gold Belt maps are not usually intrusive, with some hornblende and brown mica. age, containing basic soda-lime feldspars, much new channels and, rejuvenated, began the work but largely represent surface lavas which have Granodiorite. A granular intrusive rock hav­ pyroxene, and usually olivine. The silica content of cutting deep and sharply incised canyons in been folded in with the sedimentary rocks and ing the habitus of granite and carrying feldspar, is usually less than 56 per cent. It is often dis­ the uplifted crustal block. correspond to modern basalt and augite-andesite. quartz, biotite, and hornblende. The soda-lime tinguished from andesite by its structure. A period of considerable duration elapsed In like manner hornblende-porphyrite corresponds feldspars are usually considerably and to a vari­ Trachyte. An effusive rock of Tertiary or between the emission of the lava flows which to hornblende-andesite, quartz-porphyrite to able extent in excess of the alkali feldspars. This later age, composed of alkali and soda-lime feld­ displaced many of the rivers and the time of dacite, and quartz-porphyry to rhyolite. In the granitoid rock occupies a position intermediate spars, with biotite, pyroxene, or hornblende. .

GENERALIZED SECTION OF THE FORMATIONS OF THE GOLD BELT.

FORMA­ PERIOD. FORMATION NAME. TION COLUMNAR THICKNESS CHARACTER OF ROCKS. SYMBOL. SECTION. IN FEET. Recent. Pal 1-100 Soil and gravel. River and shore gravels. Pgv 1-100 Sand, gravel, and conglomerate. River and shore gravels. 10-400 Gravel, sandstone, and conglomerate. 10-100 Shale or clay rock. OQ 10-100 Sandstone. H a . Coal stratum. lone. Ni

oS 50-800 Clay and sand, with coal seams.

a PM 10-300 Sandstone and conglomerate. P Tejon. Et OQ Tawny sandstone and conglom­ 50-400 erate. Chico. Kc GREAT UNCONFORMITY

Monte de Oro. Jo Black clay-slate, with interbedded Mariposa. Jm 1000 or greenstones and some conglom­ more erate. Milton. Jml Sailor Canyon. Js

UNCONFORMITY . Intrusive granitic rocks. grd

ms M Q § Argillite, limestone, quartzite, w 4000 or chert, and mica-schist, with inter- Robinson. Crb more bedded greenstones. Calaveras. Cc

Intrusive granitic rocks. gr grd DESCRIPTION OF THE BIG TREES QUADRANGLE.

GEOGRAPHICAL RELATIONS. gently to the southwest. Its surface, however, Twomile Creek, Hull Creek, and the North 4500 feet is usually heavy, and few of the inhabi­ would be somewhat uneven, and above it would Tuolumne, after flowing some distance to the tants attempt to pass the winter above that The Big Trees quadrangle comprises the terri­ project several summits, such as Blue Mountain, southwest, turn sharply to the southeast. It is altitude. The herds of cattle and "bands" of tory between the meridians of 120° and 120° 30' composed of unusually resistant rocks belonging probable that the southeasterly courses of these sheep which find pasturage on these higher slopes west longitude and the parallels of 38° Extentof the to the Bed-rock series, and which, on account of streams are due to structural features. during the summer months are gathered together and 38° 30' north latitude, being thus a ^rangie. the durability of their materials, formed hills too The region as a whole is well watered, most of in the autumn and driven down to the Great quarter of a square degree of the earth's surface. lofty to be buried beneath the lavas. The larger the streams flowing the year round. The North Valley or to the lower foothills. In the forest It is about 34^ miles long and 2.7J miles wide streams have long since cut through, this volcanic Fork of the Mokelumne and the Middle and zone timber, chiefly yellow pine, is being cut at and contains about 938 square miles. It embraces mantle into the underlying Bed-rock series, and North forks of the Stanislaus are fed in part by several points, while between Murphy and Big portions of Amador, Alpine, Calaveras, and have carved deep canyons. The canyons of the melting snow from the crest regions of the Sierra Trees the smaller yellow pines, in part a second Tuolumne counties, but more than seven-eighths smaller streams are similar in character but not so until late in summer, and retain at all ordinary growth, are being extensively felled to supply of the area belongs in the two last named. Other deep, and break up into head-water ramifications seasons good volumes of water. They are usually the demand for mine timbers created by the large quadrangles immediately adjacent to it are the long before reaching the summit region of the fordable on horseback in summer at points where mines at Angels, in the Jackson quadrangle. Pyramid Peak on the north, the Dardanelles on Sierra. their beds are not too rocky or cumbered with Some of the high ridges capped with andesitic the east, the Sonora on the south, and the Jackson As a consequence of the energetic cutting of large bowlders. breccia are exceedingly dry and support scarcely on the west. In contact with its corners are the the streams during Pleistocene and present times, Vegetation and Culture. The greater part of any shrubs or trees, and when these are present Markleeville on the northeast, the Yosemite on traveling in a northwest-southeast direction, par­ the quadrangle falls within the heavily forested they are often of types that normally occur at the southeast, and the Placerville on the north­ allel with the crest of the range, is slow and zone of the Sierra Nevada locally known as the lower altitudes, as wild lilac (Ceanothus), digger west. The greater part of the Big Trees district toilsome. It is no longer possible to ride easily "timber belt." This belt crosses the quadrangle pine, and manzanita. lies within what may be termed the middle region along upon a nearly level ridge, but canyon after from northwest to southeast, and lies between the Two transmontane highways, once important of the western slope of the Sierra Nevada that canyon must be crossed by the tedious process of general elevations of 3000 and 6000 feet, although but now little used, cross the quadrangle. One, is, the well-watered and forested zone lying descending one of its steep sides and climbing not sharply limited by these altitudes. It is a the Sonora and Mono toll road, enters the quad­ laboriously up the other, sometimes a matter of between the alpine topography of the "high stretch of magnificento forests which Trees , of the rangle at its southern border, near the Phoenix Sierra" and the foothill district in which the hours. have in great part escaped the saw- tlmberbelt- Reservoir, and passes out of it, into the Darda­ gold mines of the Mother Lode are situated. In Drainage. The greater part of the Big Trees mills. In size and number the conifers dominate nelles quadrangle, northeast of Parsons. The the extreme northeast corner of the quadrangle quadrangle is drained by the Stanislaus and all other trees. They include the yellow pine other, the Big Trees and Carson Valley road, the country already begins to assume the charac­ Mokelumne rivers. The streams, however, which (Pinus ponderosa), the sugar pine (Pinus lam- extends from Big Trees northeastward to Silver teristics which belong to the higher portions of cross the southern border of the quadrangle to bertiana), and the famous "big tree" (Sequoia Valley and thence beyond the bounds of the the range, while the extreme southwest portion, the east of Shaws Flat flow into the Tuolumne gigantea). All of these species attain great size and quadrangle. on the other hand, lies in the foothills. River in the Sonora quadrangle, while those cross­ beauty (see fig. 5, page of illustrations), particu­ GEOLOGY. ing the western border between the divide north larly in the middle portion of the quadrangle, to TOPOGRAPHY. of Calaveras Valley and the divide south of San which district the Sequoias in the Big Trees BED-ROCK SERIES. Relief. The elevations range from a general Domingo Greek are tributary to the Calaveras quadrangle are restricted. The latter trees occur The Bed-rock series consists of sedimentary altitude of about 1500 feet near Robinson Ferry River in the Jackson quadrangle. The drainage as in two groves, the smaller one in Cala­ rocks, which were turned into a nearly vertical to over 8600 feet in the extreme northeast corner a whole is of the conseq^L uent type / -t i. e.,7 Consequent veras County, at the post-office and position during or before the post-Juratrias defor­ of the quadrangle, corresponding to an average the important streams show a well- streams- hotel of Big Trees, and the larger one mation, together with the associated igneous rocks. grade of about 165 feet per mile for this portion marked tendency to flow straight down the slope in Tuolumne County, about 5 miles southeast The sedimentary rocks of this period represent of the Sierra slope. Robinson Ferry itself, being in consequence of the general southwesterly of the hotel. The fact that these noble trees beds of clay, sand, and gravel which have been in a canyon incised below the general level of the inclination given to the region by orogenic or flourish only in these two places within the quad­ hardened and metamorphosed. These beds were country, has an elevation of only 700 feet above mountain-making forces, especially at the time rangle may be partly due to their exceptionally originally horizontal, but have since been folded the sea. With the exception of a few mountain of the Neocene upheaval. This parallelism of sheltered locations. They grow in quiet hollows, and greatly compressed by forces acting chiefly meadows, usually near the heads of streams, the streams, dependent upon original angle of slope protected from the winter storms by the partly from the NNE. and SSW. They have also been area as a whole is practically destitute of alluvial rather than upon the controlling influence of belts inclosing ridges and the surrounding forests of subjected to extensive erosion, so that the upper Valley bottoms, and is drained by streams of tor­ of weak rock, is well shown in the southeast pines. All the larger conifers flourish best in parts of the folds have disappeared. Intercalated rential character, flowing in narrow canyons. corner of the quadrangle; also in the region sheltered spots, but are likewise found on many in these sediments are layers of metamorphic The dominant features of the topography are between the North and Middle forks of the of the ridges. The forests are often very beauti­ lavas and tuffs, showing that volcanic eruptions long, rather narrow, flat-topped ridges, which Stanislaus. That all the streams, even under the ful. The conifers, standing some distance apart, occurred while the sediments were being depos­ usually have a northeasterly-southwesterly trend. nearest approach to ideal conditions possible, are frequently interspersed with black oaks. ited. Irregularly intruding the sedimentary rocks These ridges are, as a rule, capped with vol­ should flow in strictly parallel lines is not con­ Undergrowth is usually lacking except near with their included volcanic layers are masses ceivable. Such conditions did not obtain in the springs or small streams, and the ground is often canic breccia made upL of fragmentso Character_. . of. and dikes of various granular igneous rocks, such of andesitic lava. As their tops are theridses- Big Trees quadrangle. Inequalities in the resist­ thickly covered with a low bright-green plant of as granite and gabbro. often bare and fairly even, they have come to be ance of rocks, and structural features, have had the rose family (CJiamcebatia foliolosa), some­ SEDIMENTARY BOOKS. natural routes of travel through the region, and an important influence upon the course of the. times called by the inhabitants "mountain are followed by the sheep and cattle herders, who streams. But it is to be observed that where a misery," and a prostrate shrub known as '' Indian Calaveras formation. Rocks which have been make use of the highest alpine districts for large stream, such as the Middle Stanislaus, carpet," thus giving these forests an open, park- referred to this formation in the Big Trees quad­ pasturage during the summer months. Keeping departs from what may be considered its normal like character which is very pleasing. rangle may be divided into two portions differing upon the crest of one of these ridges, the traveler consequent direction, as is the case between its In the southwest corner of the quadrangle the on the whole in lithological character and in the may ride for hours on a scarcely perceptible grade mouth and Bakers Crossing, the streams of vegetation assumes the less attractive character degree of probability with which they can be toward the northeast. The general aspect of the secondary importance, as a rule, still retain their associated with the foothill districts. Foothill_ .. . assigned definite age. Together they occupy the country, as seen from such an elevation, is that of consequent direction. Thus, in spite of the depth The dark but fresh green of the larger re«ion- western and southern portions of the quadrangle, a somewhat uneven, gently sloping plain, below of the Middle Fork of the Stanislaus in this por­ conifers is here replaced by the sad bluish-green and are separated from the granitic rocks on the the surface of which the present canyons have tion of its course, it receives no drainage from the hue of the digger pine (Pinus sabiniana), with east by a very irregular line, extending across the been excavated. It is evident that the topog­ south except the insignificant amount gathered which tree are usually associated scattered oaks quadrangle in a southeasterly direction from Pan­ raphy of to-day is compound in character. The from the canyon wall itself. The streams on its (Quercus douglasii) of like dusty shades of ther Creek in the northwest corner to near the streams now rushing through the canyons have southern side usually head close up to the brink green. All the trees of this district are smaller mouth of Hull Creek in the southeast corner. The been for some time at work cutting and shaping of the canyon and then flow away in the normal and less symmetrical in form than those of the great bulk of the formation is composed of slaty the surface of the region, but they have not been direction of slope to the southwest. higher slopes, while many of the hills are covered or schistose rocks which have plainly been derived able to efface entirely an older land surface which In the northern portion of the quadrangle the with grass, which dries to a dusty brown in sum­ from siliceous sediments of varying coarseness. In existed before their present period of activity general trend of the forks of the Mokelumne and mer, or with thickets of low and stiff shrubs. all cases where such an observation Schistosity_ .. . .. began. Before the beginning of the present their main tributaries is westerly, and this is like­ This portion of the area has not the well-watered was possible, the schistosity was seen and beddin«- cycle of erosion an earlier cycle had OIderoded wise true, as a rule, of the lower parts of the aspect of the forest zone. Flowing springs are to be approximately parallel with the original passed through the successive stages of surface- tributaries of the Stanislaus to the south of the rare, and the drainage from the upper Sierra bedding. Associated with these sediments are its history, resulting in a low surface which, after Middle Fork. The relatively greater hardness slopes has here been concentrated into the larger limestones, frequently in lenticular masses, and a being covered with volcanic material near the of the quartzite of Blue Mountain streams flowing below the general surface of the smaller amount of schistose rocks which have close of the Neocene period, was elevated. Thus ridge seems to be an efficient cause for structural0 district. been derived from igneous material, probably in most cases intruded into the sediments . again exposed to the action of the streams and the northwest deflection of the Middle streams.the course of In the northeast corner of the area the vegeta­ Igneous other erosive agencies, it was carved into the Fork of the Mokelumne and for the tion also changes. The tamarack pine (Pinus at some early stage of their history, schists* present intricate detail of canyons, ridges, and southwest deflection of the South Fork, the murrayana) and the silver fir here subsequent to their deposition, but also in part of Alpine region. peaks. The significance of the present topog­ general trend of both forks being nearly due become abundant, the fir clinging gen­ volcanic origin and laid down contemporaneously raphy can be best understood by retracing briefly west. Rivers can erode channels parallel to bed­ erally to the ridges and higher slopes, while the with the siliceous sediments in the form of tuffs the steps by which it was produced. If the ding planes and planes of schistosity with greater tamaracks, in company with willows and poplars, and flows. present canyons were once more filled up with ease than across these planes, unless the rocks are prefer the relatively low and damp flats. Some The possibility of dividing this formation into the solid rock which in the course of Pleistocene shattered transverse to the bedding. As examples of the rock at this altitude has been swept bare two portions which differ in age is suggested by time has been disintegrated and carried down as of streams influenced by these structures may be by glaciers, and the trees often struggle for sub- the fact that one division as a whole sediment to the Great Valley, and if the lava cited Rose Creek from the Star mine westward sistance in the cracks and crevices of the granite. is more siliceous than the other and 7nwthelvisions . a ,. Calaveras. cappings of the ridges were extended so as again and the South Fork of the Stanislaus just north Damp meadows covered with luxuriant grass are does not contain lenses ot limestone. to cover the filled-in canyons, there would be of Mount Elizabeth, where canyons are cut in the abundant, and near them there usually are groves The line of division between the siliceous and reproduced a surface nearly identical with that quartzite parallel to its strike. The westerly of "quaking aspens." the more argillaceous and calcareous series may upon which the existing streams began their work. course of Fivemile Creek is likewise determined As a whole the quadrangle is a sparsely settled be considered as passing through Sheep Ranch It would be a great desolate lava plain, sloping by the same conditions. It will be observed that region. The winter snowfall at elevations above and running just east of the limestone lenses at American Camp. Even if the two hypothetical granodiorite are not uncommon within the lime­ divided into two groups which together form biotite of a reddish-brown color, and pyrrhqtite with little or no pyrite. v. These gneisses may be called pyroxene-diorite- portions of the Calaveras formation are separated stone area. When of sufficient size these masses very large areas. These are (1) biotite-granite gneisses. All of these diorite-gneisses are prob­ ably recrystallized igneous rocks or tuffs. It is Pyroxene- by an unconformity, the subsequent folding and are indicated on the map. The limestone is also and gneiss, and (2) granodiorite and quartz- , . .,, ,, ,° ,, . . ,. ., diorite= diorite. These two groups of rocks are not dis­ not impossible that many of the gneissic diorite gneisses. compression of the whole has been so intense cut by numerous dikes of diorite-porphyry, altered nodules found included in the granitic rocks and so complex that the fact might readily remain and decomposed. The very irregular shape of criminated on the geological maps, but are represent an earlier crystallization of the granitic magma; but undiscovered. On the other hand, it is quite pos­ this limestone area is probably due to indicated by a single color. all of these gneisses present evidence of having undergone -i P i mi Probable recrystallization. Many of the nodules show no banding. In sible that the entire series represents continuous a combination ot several causes. Ine causeirregular of the The granite and gneiss series will first be the bed of the North Mokelumne, on Mount Knight, and at sedimentation with a gradual change of lithologic fact that the beds, even in the middle fS!»t?n?e described. The largest area of these rocks forms a other points are found greenish quartzite-like rocks. These zone 4 to 9 miles in width lying imme­ differ from ordinary quartzite in containing green pyroxene, character from one portion to another. Dikes of of the series, are sometimes separated epidote, amphibole, titanite, and specular iron ore. They also diorite-porphyry and other igneous rocks are by thin beds of non-calcareous sediments shows diately east of the rocks of the Gala- gnefsscom- contain plagioclase, but in no cage are all of these minerals abundant in all of the rocks of the Calaveras that the deposition of the limestones was an veras formation. 1 This zone extends contained in any one specimen. Such gneisses have probably resulted from the recrystallization of more or formation except the massive quarfczites. interrupted process. Furthermore, each single from East Panther Creek diagonally across the less impure quartzites. Such rocks may be Quartz= The rocks belonging to the siliceous division bed when deposited was a lens, thickest at the quadrangle to its southeast corner. The eastern found on the north side of the North Mokelumne gneisses." border of the zone, or its contact with the large about 1 kilometer above the mouth of Blue lie to the northeast of the line above indicated as middle and tapering out at the edges; or perhaps, Creek, And also above the mouth of Bear River. In the separating the two portions of the Sjliceous by the admixture of ordinary clastic material, granodiorite mass of the eastern portion of the North Mokelumne Canyon at two points, and at Calaveras formation. These rocks are terrane- passed gradually into the siliceous sediments quadrangle, is a very irregular one. The irregu­ one point on the ridge north of the Middle gneisses.Lime-silicate Mokelumne to the northeast of Blue Mountain, almost without exception quartzites or highly which have given rise to the schists and quartzites larity of the western boundary, its contact with there were found in the gneiss series narrow bands of light- siliceous schists. Occasionally, as south of Sheep of the Calaveras formation. . Thus, before any the rocks of the Calaveras formation, is less colored gneiss composed chiefly of lime silicates, wollastonite, and garnet, with some titanite and quartz. Such lime-silicate Ranch, east of Collierville, and west and south of folding of the series took place, the limestone marked. gneisses may be completely metamorphosed impure lime­ McCormick's ranch, the quartzites are associated deposits consisted of a series of lenses of different The coarse biotite-granite, which is the most stones. All of the above gneisses are found in the series with schistose or gneissic bands which have shapes, sizes, and thicknesses, lying one above the conspicuous member of the granite and gneiss exposed in the canyon of the North Mokelumne. South of Big Trees are some streaks of pyroxene-gneiss probably been derived from igneous material. other. In their middle portions these lenses complex, is a rock usually susceptible Biotite= usually containing potash feldspar, and a minor As a rule these bands are too narrow and too might be separated by thin layers of ordinary of ready recognition in the field. Pot- gfanite- amount of quartz. The original nature of these Pyroxenic i i mi, u T, n j alkall-feld- ash feldspar is an abundant constituent, and by rocks is uncertain. They would be called spar gneisses. intimately associated with the quartzites to be sediments or be continuous one with the other. pyroxene-granulites by German petrographers. separated on a map of this scale. The quartzites Toward their peripheries, however, they would its conspicuous development in relatively large At many points in the gneiss series are found narrow bands may be in comparatively thick beds, nearly white become thinner, and thus be separated by increas­ crystals tends to give the rock a porphyritic composed almost entirely of coarsely granular quartz. It is possible that such quartz-gneisses in color, or in thinner, schistose beds, in which ing thicknesses of other sediments, or they would texture. Other minerals readily seen with the represent vein quartz which has become thor­ case the color is usually darker and the grain grade gradually into the latter by admixture of naked eye are quartz and biotite, the former in oughly granulated through crushing and recrystallization. finer. The massive white quartzite makes up the ordinary sedimentary material. With the subse­ distinct grains of irregular shape, and the latter While some of the gneisses of the Big Trees greater part of Blue Mountain and extends south­ quent intrusion of masses of granitic rocks, and in small scales, usually so arranged as to give a quadrangle are regarded as recrystaUized sedi­ ward across San Antonio Creek as a belt of with the intense compression and complex folding suggestion of gneissic or banded texture even in ments, in no case can they be considered contact resistant material which has determined some of the whole region, the originally flat-lying strata hand specimens. Perfectly fresh specimens are metamorphics. They are, to be sure, associated picturesque falls where it crosses that stream. were thrown not only into longitudinal folds but secured with difficulty, as the rock weathers to a in a very intricate manner with the biotite-granite- Thence it continues as a high ridge until it is into transverse folds as well. Finally, with the considerable depth and becomes somewhat friable. gneiss which is intrusive in them, but they are interrupted by the granitic area which extends planing off by erosion of all the upper portions Under the microscope the porphyritic texture is generally no more thoroughly recrystaUized at one point westward from Avery's ranch. South of the of the folds and their truncation down to the not conspicuous. The component minerals are seen to be than at another. Their complete metamorphism Stanislaus the quartzite masses of Mount Eliza­ microline, orthoclase, oligoclase, abundant quartz, some bio­ level of the present surface, it is not difficult to tite, and usually a few small zircons. More rarely muscovite, and recrystallization is rather to be regarded as beth, Mount Lewis, and Mount Provo may be see how the present shape of the area may have titanite, and apatite are present in small amounts. Thoroughly a kind of regional metamorphism, they being correlated with the Blue Mountain quartzite. been brought about, although it may not be pos­ typical biotite-granite of the kind described occurs in the canyon of the North Mokelumne, in the Calaveras Grove at deeply buried at the time the metamorphism took Under the microscope such quartzite is seen to be sible to follow it step by step. The structure the Big Trees hotel, in the South Grove, in the canyon of place. It is probable, however, that the biotite- composed of interlocking grains of quartz, with and character of the limestone beds are excellently the Middle Stanislaus northeast of Mount Knight, and at granite, which was intruded into the gneiss series some scales of mica. No fossils have been found shown where they are cut by the canyon of the various other points. at an earlier period, formed zones of contact met­ in the siliceous series in the quadrangle, but it is Stanislaus, northeast of Abbott Ferry. The lime­ Exposed on steep canyon walls, as northeast of amorphism at the time of the intrusion. The probable that these rocks are of Paleozoic age. stone area within which the town of Murphy Mount Knight, this gneissoidal granite usually entire series, both the intrusive granite-gneiss and Southwest of the siliceous terranes above lies is similar to that just described, as indeed weathers in yellowish tones and in forms sug­ the other gneisses, was intruded at a later date described the Calaveras rocks are chiefly dark are most of the smaller patches shown on the gestive of bedding, whereas typical massive gran­ by the granodiorite and quartz-diorite magma; slates, fine-grained siliceous mica-schists, geological map. They are nearly all composed of odiorite weathers in gray tints and in rounded but the gneisses having already undergone a com­ thin-bedded quartzites, and limestone. several beds of limestone separated by layers of masses with absence of parallel structure except plete recrystallization, no evidence of further __ 1 .. i r« 1 i Ine most interesting rock ot this south­ other sediments, and illustrate well the lenticular where it has been much jointed. The biotite- alteration along the contact is to be noted. western division of the Calaveras formation is the form and lack of horizontal continuity shown by granite has been greatly compressed "While the larger portion of the gneisses is limestone, as by it the Carboniferous age of the deposits of this character. The area about and sheared at many points, so that granitee"= included in the broad band extending across the 1 -i -11 gneiss. sediments with which it is immediately associated Murphy is somewhat noted as containing an much of it may be correctly called quadrangle, as previously described, isolated is determined in a fairly satisfactory manner. The interesting cave of unknown depth. The cave biotite-granite-gneiss. Although typical facies of masses are found at many points. Such is the large and fantastically irregular area shown in lies about a mile northwest of the town, and is the gneissic biotite-granite and of the massive area outlined on the geological map 5 miles east the neighborhood of Columbia extends for several frequently visited by tourists on their way to granodiorite are readily distinguished, yet this of Murphy, in the canyon of the North Stanislaus. miles into the Sonora quadrangle and is the larg­ Big Trees. The limestone near the cave, when difference is bridged by various intermediate This area is entirely surrounded by the sediments est member of a disconnected but linear chain of struck by the hammer, emits the fetid odor com­ facies, so that it is often a matter of great diffi­ of the Calaveras formation, which also contains limestone lenses extending in a southeast direction mon to similar rocks. culty to say just where the dividing line should at some points narrow streaks of the same gneissic across the Sonora quadrangle into the Yosemite be drawn. The gneissoidal granite may locally rock. Another isolated mass lies one-quarter mile district, and in a northwesterly direction into the The other rocks comprising the southwest division of the Calaveras formation and which are probably of Carboniferous lose its gneissic structure, while the granodiorite northeast of Clover Meadow, in the granodiorite. Jackson quadrangle. At Hites Cove, in the age, present few points of general interest. In the south­ may become gneissic or schistose, particularly On the summit of Grarnet Hill, east of the mouth Yosemite quadrangle, fossils (Fusulina) indicat­ west corner, in the vicinity of Robinson Perry, near contacts. these consist in good part of normal dark clay ^ou^siates. of Moore Creek, is an interesting deposit, which, ing Carboniferous age have been found in one of slates, sometimes a little micaceous. West of Intimately associated with the biotite-granite though of no economic importance, is the lenses of this chain. Columbia, between the limestone and the granodiorite, the are some fine-grained gneisses, 2 sometimes alter­ somewhat remarkable for the size and The Columbia area of limestone is remarkable rocks are highly metamorphosed, and at a point 2 miles west of the town occurs a beautiful mica-schist which the nating with the former in bands, but often occur­ beauty of the minerals which compose not only as being the largest exposure of lime­ microscope shows to be made up of clear interlocking grains ring in irregular patches and occasionally in it. It is made up of white quartz, green epidote in stone vet mapped in the Gold Belt, but , of quartz with abundant biotite and muscovite. This schist large areas. These gneisses vary much in com­ > . . Large area of weathers to a red soil, recalling that usually produced by the prisms 3 inches or more in length, and brown­ also for its exceedingly irregular and Hmestone- decay of basic igneous rocks. Some little-altered clay slates position. The most abundant kinds are diorite- ish-red garnets. The latter usually show brilliant curious outline. It partly surrounds a considerable occur just southeast of Vallecito, and also near the edges of gneiss and quartz-diorite-gneiss. crystal faces. This lode lies in a narrow tongue mass of granodiorite, toward which the bedding the quadrangle, west of the same town. "West of Murphy are siliceous slates, mica-schist, and some streaks of amphibolite- The diorite-gneiss is dark green in color and is composed of of gneiss which projects from the large area south on the inner margin of the limestone area dips, as schist and talc-schist. West and south of Sheep Ranch the soda-lime feldspar (chiefly oligoclase-andesine), green amphi­ of Moore Creek. The main mass of Garnet Hill shown by thin interbedded bands of schist and prevailing rocks are dark siliceous slates, frequently passing bole, brown biotite, magnetite, and pyrite. There is granodiorite. into slaty mica-schists. are two kinds of such gneisses; some are fine quartzite. On the outer margin of the area the grained and even textured, and are quite dark The granodiorite and quartz-diorite series is dip of the bedding and schistosity is usually The prevailing strike of all of these rocks, in color; others are coarser grained, with small rounded por­ exposed over wide areas in the eastern and north­ northeasterly at a high angle or practically verti­ when not too close to areas of massive igneous phyritic feldspars. The contact between these two rocks is often sharp. The fine-grained diorite-gneiss is sometimes eastern portions of the quadrangle, and Granodiorite cal. The strike is variable, swinging around near rocks, is northwesterly and southeasterly, with a penetrated by white anastomosing dikes of fine-grained in smaller detached areas in the south- dfo^iteYo'm- the contact with the Parrott Ferry granodiorite northeasterly dip of from 60° to TO0. Variations granite. It is possible that the dark fine-grained diorite- western part. As the rock of these plex* gneiss represents intrusions in the other gneisses. The so as to be everywhere approximately parallel in both dip and strike are, however, frequent, diorite-gneiss often occurs in rounded nodules included in circumscribed areas is, as a rule, less typical and with its periphery. Toward the north the lime­ even when not close to visible intrusive masses. granodiorite, as at Highland Creek. Sometimes these nodules less constant in character than that of the large stone is largely concealed beneath the Neocene are so abundant that the mass resembles a conglomerate. eastern mass, the latter will be first described. IGNEOUS ROCKS. Certain gneisses associated with the amphibole - diorite- gravels and lavas, but is exposed over a consider­ gneisses, just described, differ from the latter in containing Over most of the region drained by the Stanislaus able area at Douglas Flat, again disappearing Granodiorite^ quartz-diorite, granite, and pyroxene, which is more or less altered to green amphibole, River northeast of Bakers Crossing the grano­ beneath Neocene deposits to the northwest. Most gneiss. About two-thirds of the Big Trees quad­ diorite shows a fairly uniform character. It is a of the limestone, although retaining a distinct 1 On the Pyramid Peak geological map the northern exten­ rangle is underlain by a great complex of granitic sion of this gneissic area is represented as being composed of rather even-textured rock of only moderate coarse­ bedded or schistose structure, has become a gran­ rocks varying in age and in composition. Taken contact metamorphic rocks of the Calaveras formation, no ness of grain. The component minerals recogniz­ ular crystalline rock to which the name marble is as a whole this complex contains no deposits of attempt having been made in the adjacent portions of the Pyramid Peak quadrangle to separate the gneisses from schists able with the naked eye are plagioclase, properly applicable. When polished it is gener­ economic importance. The exceptions to this derived from sediments. quartz, orthoclase, biotite, hornblende, granodiorite. ally nearly white, marked with faint gray veinings, consist entirely of those masses which are inclosed, 8 The word gneiss is here used as a textural term, and does and1 frequentlyJ? j-l accessory titaniteJ.-J. 'i. in' and is rather fine grained. Pure white beds, as not define mineral composition. The rocks designated as or nearly inclosed, by the sediments of the Cala­ gneisses, while thoroughly granular, usually have the mineral crystals up to one-eighth of an inch or more in well as others of variegated pink and green tints veras formation. Thus gold-quartz veins are grains arranged in layers, so that they are roughly schistose. size. and containing bands of biotite, occur a short abundant in granodiorite east of Columbia in the Such rocks are often formed by the recrystallization of other rocks under pressure. The original texture is usually entirely Under the microscope such a- rock shows abundant plagio­ distance upstream from Abbott Ferry. The beds south part of the quadrangle, and north of Wood­ lost in this process of recrystallization, but the chemical com­ clase, chiefly andesine, which often has idiomorphic outlines, of nearly pure limestone are sometimes separated cock in the northwest part. While at many position may be the same in the original rock and the recrys­ grains of quartz and hornblende, and orthoclase in large tallized gneiss. Some gneisses are igneous rocks which have areas, acting as a matrix to the other minerals. Titanite, by thin bands of schist of various kinds, while points the members of this complex are inter­ become schistose by movements while still in a viscous con­ apatite, epidote, and small zircons are generally present as larger masses of mica-schist, siliceous schist, and mingled in a very intricate manner, it may be dition. accessory constituents. Microline is sometimes present, as in a fades rich in titanite which occurs near the head of Dry the Calaveras formation, are composed chiefly of SUPERJACENT SERIES. after the region had been flooded with andesitic Meadow Creek. The granitic rock near Bloods is, strictly speaking, not a granodiorite, but an amphibole-biotite-granite alkali feldspar without dark constituents. The lavas, a stream originating in the Dardanelles or quartz-monzonite. Its relations to the normal granodiorite outlines of the two areas last noted are only The Superjacent series consists of late Creta­ quadrangle entered the Big Trees district near were not determined. approximate. ceous, Eocene, Neocene, and Pleistocene sedi­ Clover Meadow and pursued a general south­ Along the North Fork of the Stanislaus the Gabbro. Granular rocks made up of basic ments, lying unconformably on the Bed-rock westerly course, crossing the site of the present granodiorite protrudes into the granite and gneiss lime-soda feldspars usually with pyroxene or series, together with igneous rocks of the same canyon of the Stanislaus at Parrott Ferry. The complex as a long tongue, extending southwest- amphibole are called gabbro. Such rocks occur periods. During late Cretaceous, Eocene, and former existence of this river is shown by a chain ward to a point about 1 mile northeast of in the Big Trees quadrangle at a great many Neocene times the Sierra Nevada was a mountain of areas of certain basaltic-looking lavas, desig­ Gardner's hotel. On the northern side of this points. On the geological map only the larger range and the Great Valley of California was nated latite, which appear to have flowed down tongue the contact line between the granodiorite areas are shown. The most abundant gabbro under water. During the same time the rivers the river channel from a source near the summit and the granite and gneiss complex is largely is a dark-green coarse-grained rock. This is, as flowing down the western slopes of the range of the range to Knights Ferry, at the east border hidden under andesitic breccia. On the south a rule,t ' composedA ^almost entirelyJ of Amphibole-. . .. , deposited the auriferous gravels. Volcanoes sit­ of the San Joaquin Valley. and west, however, it is concealed only by soil amphibole and basic plagioclase with «abbro- uated mostly along the crest of the range poured Auriferous gravels. The gravels deposited by and trees. It has nevertheless proved extremely some magnetite. Occasionally grains of pyroxene out floods of lava, chiefly in Neocene times. rivers that existed in the Big Trees quadrangle difficult of satisfactory delineation, even where and olivine are found in the rock, and sometimes During the Pleistocene, also, portions of the Great in Neocene time can be divided into two series: cut by the canyon of the North Stanislaus. The pyrite. Such a rock may be called an amphibole- Valley were under water, but there were few an older series, deposited before the eruption of massive granodiorite becomes gneissic or schistose gabbro. A large area of this gabbro occurs in volcanic eruptions. the andesitic lavas, and a younger series, deposited as the contact is approached, and is intimately the drainage of Beaver Creek. The area at the after the andesitic eruptions began. NEOCENE. mingled with fine-grained biotite-gneisses like tip of the granitic tongue about 2-J- miles north­ The older gravels are generally light in color, those of the granite and gneiss complex. Much east of Sheep Ranch contains hypersthene. This During late Cretaceous and early Neocene time being composed chiefly of quartzose pebbles. of the biotitic gneiss is plainly included in the mass is plainly intrusive in the Calaveras forma­ there appear to have been no mountain making They rest directly upon the eroded schistose granodiorite. The contact between the tion and sends dikes into the latter. The largest movements of importance in this part of the Sierra edges of the Bed-rock series, and are NeoceIner granodiorite and the granite and gneiss complex of these dikes is shown on the map. Nevada. During this long epoch the Big Trees frequently capped by a bed of rhyolitic is shown with more than usual sharpness a little The gabbro of the area in the northwest corner quadrangle was subject to erosion. About the tuff. Near Vallecito and Douglas Flat the older more than a mile southwest of Fennessy's house, of the .quadrangle contains olivine, Olivlne_ close of the Neocene nearly its entire surface was Neocene channel, as shown by the extent of the in the bed of Griswold Creek. Here the massive pyroxene, and little or no amphibole, «abbro- flooded with lava. In Neocene time the region gravels and residual cappings of rhyolite tuff, granodiorite is succeeded on the west by fine­ and may be called an olivine-gabbro. was a greatly eroded surface. The must have been very broad. The stream which grained pyroxene-gneisses containing hypersthene, The mass designated gabbro on the ridge 3 persistent process of rock decay, com- eroded16 occupied it flowed westward into the Jackson which in turn give place to the coarse gneissic miles due north of Sheep Ranch is in reality bined with the action of frosts, rain, quadrangle. This old channel is sometimes called biotite-granite. heterogeneous in character. These rocks are and streams, had succeeded in subduing a once the Central Hill channel. Even these earlier Three areas of granodiorite occur in the south­ largely altered, and while a part of the Urallte= rugged region to one of such gentle slopes that gravels, although usually consisting western portion of the quadrangle, entirely sur­ area may be called uralite-gabbro, other sabbro- the streams were largely deprived of their cutting chiefly of quartzose pebbles, are not Cravelscentra! HUIof the rounded by rocks of the Calaveras formation. portions contain little feldspar, and are largely power. Certain rocks of the Bed-rock series, entirely devoid of volcanic material. The smallest of these is traversed by Knight and made up of green amphibole, probably of second­ such as quartzite, are more resistant than others, At a point about 3 miles east of Douglas Flat, Rose creeks, and is composed of a granodiorite ary origin. There is perhaps also some diorite in and withstand longer the unceasing attack of the in a bluff overlooking the Stanislaus, the gravels differing but little megascopically from that of this area. erosive agencies. Masses formed of such rocks are exposed beneath a bed of rhyolite tuff. A the main mass on the eastern border of the quad­ Pyroxenite. Granular rocks composed chiefly at every stage of degradation stand tunnel has been run into them at this point, and Monadnocks. rangle. The hand specimens, however, do not of pyroxene are called pyroxenite. There are higher than the surrounding country, it can be seen that pebbles of rhyolite occur, show any crystals of titanite, and the two areas in the drainage of Jesus Maria Creek forming what are known as monadnocks. An together with those of quartz, quartzite, chert, microscope shows that orthoclase is less which are so called. The larger of these extends excellent example is seen in Blue Mountain, which and siliceous porphyries, showing that rhyolite abundant than usual. The rock thus northward across Esperanza Creek. Like similar rises boldly above the general level of the sur­ eruptions had actually begun before the gravels tends toward an ordinary quartz-mica-diorite. On areas in the Jackson quadrangle, the pyroxene is rounding country, and was never covered by were covered by the bed of tuff. Similar light- the western side of this intrusive mass there is largely altered to amphibole, so that many speci­ Neocene lavas. Mount Elizabeth, Mount Lewis, colored gravels have been preserved between evidence of contact metamorphism induced in mens in the areas designated pyroxenite might and Mount Provo, all of which are composed of Rose and Knight creeks, south of Stage's ranch. the inclosing schistose rocks of the Calaveras more correctly be called massive amphibolite. quartzite, are other examples. Portions of this It is possible that the last-named areas, taken in formation, the latter being here converted into Diorite -porphyry. Fine - grained, dark - green old eroded surface are preserved underneath the connection with the patches of rhyolite tuff thoroughly crystalline fine-grained biotite-schists, dikes are abundant in some portions of the lavas, and the nearly level lines of contact between extending as far east as Bradford's mill, mark which at one place carry red garnets of consider­ Calaveras formation in the western the lavas and the underlying older complex, as the general nearly east-west course of a broad able size. part of the quadrangle. They are par- seen on the canyon sides, furnish the datum plane river valley of early Neocene time, as previously porphyry. The Parrott Ferry area and the one west of ticularly. , , numerous in thej.1 Tlimestone , from which the old eroded surface, now so thor­ suggested. Vallecito present the characters usually found in area east of Shaws Flat and north of Columbia, oughly dissected by modern streams, may be In the drainage areas of the Jesus Maria and the intrusive masses of granodioriteo Parrott Ferry in the schists and limestones east of Collierville, reconstructed. Little can be said of the character Esperanza creeks there has been found a very occurring in or near the foothill belt J^ffiS? and in the schists, slates, and quartzites between of the topography during the earlier stages (Cre­ definite channel, called the Fort Moun­ of the Sierra slope. The rock of such areas' the North Stanislaus and the northwest corner of taceous time) of this long period of erosion, but tain channel. The gravel of this old areas is nearly always more basic than that of the the quadrangle. They are also common in grano­ the fact that the Bed-rock series consists of highly stream bed has been mined by drifting broad exposures nearer the summit of the range. diorite in the northwest corner of the district, and metamorphosed rocks and contains also large beneath the rhyolitic lava cap at a point on Jesus Hornblende is more abundant and frequently were noted in the gneisses of the North Mokel- areas of granitic rocks, which must have solidified Maria Creek and at several points on Esperanza shows a porphyritic development. Biotite is less umne Canyon. These dikes are usually small, from fusion at some depth, is an indication that Creek. The elevation of the channel on Jesus conspicuous and often lacking, while plagioclases and no attempt was made to represent them all the region has been deeply denuded and probably Maria Creek is about 2300 feet, and, so far as can are generally the only feldspars present. It is on the geological map, a few of the larger and passed through all the stages of a youthful topog­ be determined from the topographic map, the usually possible in these areas to find all grada­ more persistent ones only being shown. Under raphy, characterized by lofty peaks and ridges, deep altitude of the channel increases to the north, so tions from quartz-mica-diorite to more basic facies the microscope such rocks generally show decom­ canyons, and tumultuous torrents, before approach­ that it is quite certain that the stream drained to composed chiefly of hornblende with a little inter­ posed porphyritic feldspars, prisms of greenish- ing the quiet old age typified by a low plain. the south. On the ridge between Esperanza and stitial epidote. This is especially the case near brown hornblende, and an altered groundmass The volcanic material which was thrown out Jesus Maria creeks this channel forks. The main their peripheries. Strictly speaking, these rocks with abundant epidote, chlorite, calcite, and toward the close of the Neocene came chiefly from channel, or western fork, appears to be continuous are seldom true granodiorites, although they were quartz. Occasionally they lack the porphy­ vents near the crest of the range. Probably while beneath the lava and to connect with the gravels probably intruded at the same time as the main ritic structure and may be called fine-grained the eruptions were still in progress there began east of Railroad Flat, in the Jackson quadrangle. mass and may represent modifications of the same diorite. an elevation which increased the slope toward the The east branch extends under the lava ridge north magma. The area west of Vallecito resembles AmpJiibolite. This rock, in most places a schist, southwest. The streams which were then begin­ of the head of Esperanza Creek, and has not been the Parrott Ferry area very closely, both being forms small areas in the southwestern portion of ning to establish their channels on the lava- traced farther north with certainty. The Lampson probably parts of a single intrusion. It is com­ the quadrangle. One of these terminates at the cloaked surface were thus given great cutting channel of the Jackson quadrangle forms a west posed chiefly of a dark medium-grained rock of Stanislaus at Robinson Ferry, and is important as power. The impetus given the streams at that branch of the Fort Mountain channel. South of dioritic aspect. The microscope shows consider­ containing at this locality the gold-quartz veins time is in part still retained. The larger ones Jesus Maria Creek there is an extensive series of able alteration, the large crystals of green horn­ of the Mother Lode. This same belt of amphib- have long since cut through the volcanic mantle gravels, capped in part with rhyolite, which appear blende being surrounded by a granular aggregate olite-schist extends northwestward into the Jack­ and have sunk deep canyons into the underlying to be a part of the Fort Mountain channel. So far of epidote, quartz, and a little secondary feldspar. son quadrangle and there contains the famous Bed-rock series, which they are still engaged in as can be judged from the topographic map, the At its northern end the mass passes into a schistose mines of Carson Hill and Angels Camp. The deepening. elevation of these gravel masses is very nearly hornblendic facies which the microscope shows to schist is light green in color and fine grained. Drainage. In a broad way, it may be said that the same, or slightly lower than at the Banner contain epidote and a little pyroxene in addition The microscope shows it to be composed of num­ there is evidence that three considerable rivers gravel mine on Jesus Maria Creek. It is there­ to the hornblende. The granitic area extending erous prisms of green amphibole and grains of existed in Neocene time in the Big Trees quad­ fore likely that the river flowed south to near west from the canyon of the North Stanislaus to epidote in a groundmass of quartz, calcite, usually rangle. Two of these rivers flowed in broad O'Neil Creek, and thence took a westerly course near Sheep Ranch is regarded as granodiorite. It some feldspar, and sometimes biotite. Another valleys. One originated in the Pyramid Peak into the Jackson quadrangle, probably passing contains, however, more biotite and orthoclase small area of amphibole-schist occurs about a mile quadrangle and flowed nearly south through the near Cave City and down the drainage of Gala- than does most of the granodiorite of the quad­ north of Vallecito, and there, is a narrow streak northwestern portion of the district to near Sheep veritas Creek. rangle. just west of Murphy which is not shown on the Ranch, whence it drained westerly into the Jack­ On the south slope of an andesite-capped ridge Syenite. Granular rocks composed chiefly of map. Still another band extends in an east- son quadrangle. The other river had a westerly 3-^ miles northeast of Woodcock's mill, in the alkali feldspar, with usually some amphibole, west direction in the northwest corner of the course from near Bradford's mill to Vallecito, northwest portion of the quadrangle, is a small pyroxene, or mica, are called syenite. There are quadrangle, to the northeast of Woodcock. This and thence flowed farther west into the Jackson deposit of river gravel capped with rhyolite tuff. but few areas of such rocks in the Big Trees area lies between the Calaveras formation and quadrangle. The former existence of these two The gravel, as exposed at an hydraulic washing, quadrangle. That shown on Mill Creek, in the granodiorite. valleys, while not certain, is highly Neocene is about 30 feet in thickness. The pebbles are northwest corner, is an amphibole-syenite ; the A small lens of amphibole-talc-schist occurs in probable. The evidence rests largely rivers- chiefly of quartz, quartzite, and rhyolite. The dike by the road east of Calaveras Valley is a the western portion of the quadrangle west of upon the disposition of the rhyolite-tuff areas. rhyolite capping appears to extend north under mica-syenite; and the two small areas in the Murphy. Like the similar lenses in the Jackson The two rivers indicated above represent the the andesite. This gravel channel possibly con­ drainage of Rose Creek, a little to the west of the quadrangle, this rock is an altered form of dikes older river system of the quadrangle, and existed nected at one time with the Fort Mountain contact of the granodiorite with the schists of of the peridotite-pyroxenite family. during the pre-volcanic period. At a later date, channel, but the evidence is not conclusive. Big Trees 3. The gravels of the andesitic period will now Whitney, various bones of extinct mammals, par­ Rhyolite is the oldest Neocene igneous rock in defined and regular stratification (see fig. 4 on the be described. After the earlier gravels were ticularly those of the mammoth, were found. the quadrangle. As previously stated, it is cap­ page of illustrations). Such fine-grained stratified buried under rhyolite tuff, which was Although probably in the main of Neocene age, ped at many points by andesite, and on material is well shown around Calaveras Valley probably the first product of Neocene aadesitic the auriferous deposits on the limestone in the the ridge south of East Panther Creek near the western edge of the quadrangle. While Deriod volcanic activity in the Big Trees vicinity of Columbia, with the exception of the it is capped by both andesite and basalt. The the finer material is more common in the lower quadrangle, there followed an interval of erosion, patch about half a mile northwest of the town, peculiar lava called latite overlies rhyolite at foothills and along the edge of the Great Valley during which fresh gravels, usually of no great are not typical well-rounded stream gravels, but Bradford's mill, at Avery, and at several points to the west of the present area, yet its deposition thickness, were spread in part over the rhyolite are composed of subangular, little-worn fragments, along the Stanislaus River east of Murphy. was not confined to these districts. Well-stratified tuff and in part over the Bed-rock series. When largely qnartzose, which appear to have been Basalt. Lavas made up of basic lime-soda andesitic sands occur just beyond the limits of the not found resting directly upon rhyolite tuff or washed into the crevices by small streams from feldspars, augite, and magnetite, and usually quadrangle east of Clover Meadow, where they immediately beneath it, it is not always possible the waste of the rocks in the immediate neighbor­ olivine, are called basalt. Such lavas are found are capped by coarser conglomerate and breccia. to say whether a given deposit of gravel antedates hood. Much of the cherty material may have in the quadrangle only in the drainage of the The entire problem of the source, mode of erup­ or is subsequent to the rhyolite eruptions; for been derived directly from the limestone area, for Mokelumne. There are several small areas on tion, and method of deposition of these extensive the older gravel has evidently contributed its the soil covering portions of the latter is full of the ridge south of East Panther Creek, and two andesitic accumulations is one of much interest. resistant white pebbles to later deposits, and, as similar siliceous fragments. The deposits may small masses on a spur a little east of Devils Nose. The volcanoes whose eruptions furnished material has been seen, the gravels beneath the rhyolite thus be in part of Pleistocene age. The soil and All of these areas were perhaps formerly con­ in such great volume undoubtedly lay Location may contain rhyolitic pebbles. Three-fourths of detrital material over most of the limestone area nected and formed one flow. This basalt overlies to the east of the Big Trees quadrangle, eri|Ption- a mile southeast of Murphy there is a small len­ west and south of Columbia has been so thor­ rhyolite at one point and underlies andesitic tuff near the crest of the range, but their exact position ticular area of gravel of a peculiar character rest­ oughly worked over by the early miners that it at another on the ridge south of East Panther has not yet been and may never be determined. ing in a hollow in the limestone, which was evi­ is often impossible to determine what may have Creek. The basalt is therefore probably younger It is impossible to describe all that took place dently deposited in close connection with the been the original character of the surficial deposits than the rhyolite and older than the andesite. during this portion of Neocene time with the same rhyolitic eruptions. The upper portion of the in a given spot. Andesite. Massive andesite was nowhere certitude attainable in descriptions of the volcanic deposit, exposed in an open cut, is chiefly a fine In the higher eastern portion of the quad­ encountered within the quadrangle, but in frag- activities of the present day. But some attempt white silt, apparently of rhyolitic origin. This rangle gravels derived in Neocene time from the mental accumulations of varying coarse- to picture the events of a time that has left its contains abundant well-rounded pebbles of white rocks of the Bed-rock series are not known. ness, iromn linen tuns, rw to, coarse Tbreccias, oftheandes-Distribution mark so strongly affixed to the existing topog­ . ite. pumice which readily float on water. The mate­ Rhyolite. Those lavas that are rich in silica this rock is extremely abundant and raphy may lend additional interest to the andes­ rial shows the cross-bedding characteristic of (70 per cent or more) and in alkalies (6 per cent caps nearly all the important ridges in the area. itic accumulations which must attract the atten­ stream deposition. An inclined shaft, said to be or more), with little lime, are called rhyolite. Such ridges and peaks as are free from andesitic tion of any observant traveler in the region. While about 200 feet in length, has been sunk in the Such rocks are usually light in color, many rhyo­ material owe their exemption to one of two causes. some of the coarse breccia may have deposit, at an angle of about 28° with the horizon, litic tuffs being quite white on weathered surfaces. Either they are composed of resistant material poured down the slope as mud flows, fr and reaches an underlying bed of coarse gravel Rhyolite in the form of tuff is fairly abundant and stood sufficiently above the old eroded surface the, water necessary toi give fluidityn -! ,. to andesite. containing large, imperfectly rounded fragments within the limits of the Big Trees quadrangle. upon which the andesites were laid down to pro­ the mass being possibly derived in part from sub­ of quartz. This underlying gravel was washed Numerous areas occur near Vallecito ject like islands above the desolate waste of lava, terranean sources and in part from the copious Rhyolite tuff. for gold, with what success is not known. Another and Douglas Flat, where they evidently or else they have since lost their former volcanic and violent rains that are know to be a frequent patch of light-colored gravel, containing consider­ form fragments of a once extensive bed which covering by erosion which has brought them consequence of volcanic eruptions, much of the able rhyolitic material and cross-bedded white has been dissected by erosion. The rhyolite below the general level of the old Neocene sur­ finer material must have been deposited in broad silts, occurs about 1^ miles southeast of Vallecito, underlies the andesite, as can be seen at many face. Probable examples of the former class are bodies of water, probably produced by the clog­ beneath the latite of the Table Mountain flow. points east of Douglas Flat, to the northwest of found in the quartzite masses of Blue Mountain ging of the drainage by the vast amount of loose The post-rhyolitic erosion was interrupted by Sheep Ranch, on Esperanza Creek and near Hale's and Mount Elizabeth, while in the latter division material so suddenly thrown into the streams. the andesitic eruptions, which took place near the mill on the South Stanislaus. The tuff, while may be placed the long narrow ridges lying within On the other hand, the coarse conglomerates found crest of the range. In the western portion of the sometimes soft and friable, is usually consolidated and near the apex of the angle formed by the on the present ridge tops at altitudes above 7000 quadrangle the first manifestation of a renewal of into a firm fine-grained white or pinkish rock, of junction of the North and Middle forks of the feet indicate rapid and powerful, though probably volcanic activity appeared in the formation of somewhat porous texture. Such indurated facies Stanislaus River. shifting, streams of water high up on the Neocene gravels composed largely of andesitic pebbles but often contain crystals and fragments of sanidine and The extensive distribution of these andesitic slope. The old stream beds in the Bed-rock series including also pebbles of other rocks. These quartz, and when exposed in vertical bluffs, as is deposits over the quadrangle, and the shape of having been filled up with volcanic detritus, the earlier, partly andesitic gravels are Relationof often the case, they occasionally show a columnar the areas, show very clearly that the topography water, probably more abundant then than now, sometimes auriferous, and have been "Jveffand structure, the columns being generally 4 or 5 of early Neocene time must have been quite dif­ was compelled to find its way down the debris- hydraulicked northwest of Douglas tuffs' inches in diameter and in sections a foot or so ferent from that of the present day. Such a broad, cumbered slope as best it could, having no fixed Flat. They pass upward without any sharp in length between the horizontal joints. This even distribution of clastic material could have channels to carry it off. Prevented from perma­ break into andesitic breccias and tuffs, which are columnar structure is well shown in the hill cap­ taken place only upon a surface of prevailingly nently establishing new courses by the frequently represented by waterworn andesitic ped by rhyolite tuff just east of Vallecito and at gentle relief, before the deep dissection which is constant accession of fresh material EkeTonathe pebbles embedded in varying amounts of finer other points in the vicinity. The tuff might in so characteristic a feature of the existing land­ thrown out from the volcanic vents andesitic material. Where the number of pebbles such cases be mistaken for a massive lava flow. scape. That the old surface was not altogether above, the streams became overburdened and

derived from the Bed-rock series is proportionally The microscope, however, shows that the rock is devoid of irregularities has already been indicated. obstructed, and were forced to expand into tem­ ygrj large, and especially where the material has been a true volcanic ash, made up of small shreds of Evidence of a former depression below its general porary lake-like sheets, in which the finer materials washed for gold, it has been mapped as Neocene volcanic glass in a matrix of still more finely level is seen near the head of Beaver Creek in the were deposited in comparative quiet. Such a gravel. It should be understood, however, that comminuted material. A few broken crystals of eastern part of the quadrangle, where that stream lake existed in the neighborhood of Calaveras andesitic gravels, fine tuffs, and coarse breccias sanidine and quartz, with some scales of biotite, crosses a mass of andesitic breccia through which Valley and Esperanza Creek. Fossil leaves are were all laid down during the period of andesitic are usually scattered through this glassy matrix. it has not yet cut into the Bed-rock series although found in the shales or pipe-clay deposited in this eruptions, and that all three classes of material, Extensive beds of similar tuff occur from Sheep the rocks of this series occur much higher up on body of water. As will be later shown, there was with various intermediate facies, may be found in Ranch northward to Calaveras Valley. Smaller the slopes in the immediate vicinity. at least one interval during the period of andesitic the areas mapped as Neocene andesite tuff. The areas are found at intervals as far north as the The clastic andesites vary considerably in the eruptions in which a long stream was enabled to andesitic areas on the ridges northeast of Ameri­ ridge south of East Panther Creek. It is possible size of the fragments of which they are composed, establish its channel down the slope, and even to can Camp, to the south of the Middle Stanislaus, that these isolated patches were all connected at the amount of rounding which the latter have cut through the andesitic material into the Bed­ are chiefly volcanic gravel. Still other gravels one time, and that they were deposited in a river undergone, and the distinctness with, which the rock series. associated with light-colored sands and clays are valley extending from what is now the ridge material is stratified. The most common form, The larger fragments and pebbles of which the breccias and found in portions of the pre-andesitic channel south of East Panther Creek to Calaveras Valley, due in part to its resistance to erosion, is a rough conglomerates are composed are usually dark to light gray in color, somewhat harsh and porous in texture, and of typical preserved beneath the areas of latite, particularly where the Fort Mountain channel gives positive breccia composed of fragments of various sizes andesitic aspect. Some facies show phenocrysts of hornblende near Shaws Flat. These gravels, as a rule, are not evidence of a former river valley. A considerable and showing no traces of stratification or assort­ an inch in length, but the porphyritic crystals are usually smaller than this, and in some varie- Mineral com- extensive and are concealed beneath area of rhyolite tuff resting on granite is crossed ment. Breccia of this character is of very fre­ , . , . , , , . ,, , ,., , position of ties plagioclase feldspar is the only constituent the andesite. their lava covering. They have been Table Moun?e at A very on the road to Big Trees. Other patches quent occurrence as the topmost mem- Andesite apparent to the naked eye. Augite is not, as a . . ° . ' tain channel. mined at various points by tunneling occur south of the Middle-Stanislaus near Stage's ber of a series of andesitic beds capping breccia- rule, a conspicuous megascopic mineral in these rocks. Under the microscope the andesites are found to be hornblende- through the rim rock of the ancient channel until ranch, on Deer Creek, near Hale's mill, and at a ridge, and particularly so in the higher portions andesites, hornblende-pyroxene-andesites, pyroxene-horn- the bottom gravels were reached. The channel in other points in the neighborhood. An area at of the quadrangle. Another common facies is a blende-andesites, and pyroxene-andesites, There is no sharp which they lie was buried beneath andesitic silts, Stage's ranch shows clearly the relation of the breccia in which the angular fragments of andes­ line to be drawn between these varieties. gravels, and breccia, while the latite itself lies in rhyolite to the early gravels and to the overlying ite are smaller and lie in an abundant matrix of Latite. Associated with the clastic andesites a later channel cut in the andesitic deposits. The andesite. As previously suggested, the rhyolite more finely comminuted material of the same of the quadrangle is a series of massive lavas older channel, in which the gravels occur, has deposits extending westward from Bradford's kind. Andesitic conglomerates, in which the comprising three members. Two of these are been called the Table Mountain channel. 1 mill to Stage's ranch were probably deposited in pebbles are well rounded by water transportation dark, rather basaltic-looking rocks, to which the The gravels formerly washed on an extensive scale a broad river valley which may have connected (see fig. 3 on the page of illustrations), occur at name basalt has hitherto been commonly applied. near Columbia are of a character somewhat differ­ with that at Vallecito. The thickness of the many points in the quadrangle, very commonly On the geological map these two basaltic varieties ent from that of the gravels met with in Colulnbia various areas of rhyolite tuff in the quadrangle in the basal portion of a thick andesitic deposit; are shown as a unit. The third is a light- to dark- other portions of the quadrangle. They «ravels- varies from a few feet to 500 feet on Esperanza but they are not confined to the bottom of the gray, fragmental-looking rock, of somewhat harsh rest upon limestone which, previous to or during Creek. While the rhyolite lavas probably came series. A coarse andesitic conglomerate, with feel, usually containing abundant sparkling scales of black mica. These rocks were erupted as fluid their deposition, was dissolved and eroded away in largelyo J from vents east and north of Some_ rhyolite. ... pebbles frequently over a foot in Andesitecon. a remarkably irregular manner. Where the gravels the Big Trees quadrangle, there is evi- «"««n origin, diameter, occurs on the tops of some «lomerate- molten lavas and ran down an important stream have been removed the exposed limestone presents dence that some of it had a local origin. Thus of the loftier ridges, as, for example, along the channel which had been excavated during a lull a very rugged surface. The gold and gravels just north of the South Fork of the Mokel- crest of the high ridge overlooking the canyon of in the andesitic eruptions. They are thus younger were caught in the deep crevices between the umne at the western edge of the quadrangle is a the Stanislaus about 4 miles northeast of Fen- in age than one portion of the andesitic tuff- fantastically shaped projecting points of limestone, butte of massive rhyolite which evidently came nessy's house. In this case the conglomerate is breccias, but older than another portion. The as in huge natural riffles. Much of the material out at that point. Near the river a tunnel has the upper surviving member of an andesitic stream channel which these lavas TableMoun. found in these cavities is said to have been fine been run into this mass, and inquiry showed that accumulation at present 800 feet thick. From usurped entered the quadrangle just tainchannel- clay, and was the matrix in which, according to it had been exploited for precious metals. An these coarse deposits of volcanic mate- Andesite east of Clover Meadow and ran in a southwest­ assay was therefore made, which showed that the rial all gradations may be found down sand- erly direction to a point a mile and a half south 1 See "W. H. Storms, Twelfth Ann. Kept. State Min. Cali­ fornia, p. 482. rock contains both gold and silver. to the fine andesitic sands and tuffs showing well- of Fennessy's meadow. Thence turning west- ward, it crossed the present line of the North facies the two are practically indistinguishable. of canyon cutting, the ice sheet again advanced later intervolcanic stream, which cut out the Fork of the Stanislaus at Squaw Hollow, and con­ It is usually finer grained, with less abundant westward, gouging out the loose rock, polishing Table Mountain channel down which the latite tinued down the west bank of this river to Parrott porphyritic crystals, and as a rule contains a little the bed rock, and to some extent eating into it, flowed, did not reexcavate this buried hollow, but Ferry. Turning southeastward at the latter point, more silica. Like the first flow, it is confined to thus transforming the V-shaped river-cut canyon cut a new course to the southward, not very dif­ it again crossed what is now the Stanislaus Can­ the general line of the Neocene stream channel, into a glacial U-shaped canyon. ferent, as shown by the distribution of the latite, yon and continued on into the Sonora quadrangle but has not been certainly identified lower down The chief evidence of the first period of glacia­ from that of the present Stanislaus. Since that to Shaws Flat and thence southwest to Knights the slope than about 2 miles below McKay's mill. tion lies in the existence of the most western time later erosion has again brought partially to Ferry. This channel is known to miners as the A chemical analysis shows it to contain 59.4 per moraines above referred to on the ridge tops and light the old channel at Vallecito. Southeast of Table Mountain channel. The stream was a long cent of silica, 4.6 per cent of lime, 3.7 per cent of canyon sides, and in the gentle slopes of the upper the town are two patches of gravel whose situa­ one, holding much the same relation to the Neo­ soda, and 5.0 per cent of potash. part of the canyon. The upper gentle slopes are tions with reference to the existing topography cene slope that the Stanislaus, with its North and The distinctive chemical characteristic of all supposed to be the sides of the early shallow river allowed them to be formerly hydraulicked and in Middle forks, holds to the present general drain­ three of these lavas is a rather high percentage valleys. The canyons adjacent to the most western great part washed away. A considerable deposit age system. of total alkalies, with the potash slightly in moraines do not show the characteristic U-shape of gravel occurs about 1-|- miles southeast of Val­ The first of the three lava flows ran down this excess of the soda. Chemically they stand of glaciated canyons, strongly suggesting, as pre­ lecito, beneath a patch of the latite. This mass channel, following the course indicated, into the between typical andesites and typical trachytes, viously stated, that these moraines were left there was being worked by tunneling on the west side Sonora quadrangle, where its remnants now form and correspond to the intermediate group of at an earlier period when the canyons were shal­ of the hill in 1896, while an excavation on the the striking topographic feature of Tuolumne plutonic rocks called monzonites. Such lavas, lower. In the process of deepening the canyons east side attests the earlier employment of the Table Mountain. The relatively low northern the volcanic equivalents of the deep-seated mon­ in the supposed interglacial epoch, the glacial hydraulic method. The gravels north of Douglas

end of this mountain just appears within the zonites, have been named latites. (See Bull. 89, markings and scorings and the terminal moraines Flat,' which are JLpartly J andesitic,' were Gravels near southern border of the Big Trees quadrangle, U. S. Geol. Survey.) left by the retreating ice of the first epoch in the formerly hydraulicked on an extensive Dou«lasFlat- near Shaws Flat. Since its eruption, erosion has lower parts of the shallow river valleys would of scale, but nothing is now being done in this local­ greatly reduced the former continuity of the Table PLEISTOCENE. course be obliterated, and only the moraines on ity. In the neighborhood of Vallecito and Douglas Mountain flow, and to-day it is represented only Erosion. The geological record within the Big the ridges and higher slopes would "be left to Flat the Neocene gravels, of varying thickness, by a series of strips and patches which rest upon Trees quadrangle during Pleistocene time has attest the former presence of the ice. Some of cover a wide area, but they have not been exten­ a great variety of rocks, showing that the inter- been preserved mainly in the strong sculpturing the ponds and meadows of the upper drainage sively exploited except at the points noted. A volcanic stream had been able to cut a fairly deep by erosion, deposition having played an exceed­ of the Stanislaus were formed by the clogging of small patch of gravel occurs about a mile south of channel before its work was so summarily inter­ ingly unimportant part. With the cessation of the streams by morainal dams. Murphy, which was being worked in a desultory rupted. Where these residual patches occur volcanic activity at the close of the Neocene, the In fig. 2, page of illustrations, is shown a view manner in 1896. It is probably a continuation of along the canyon of the Stanislaus, as at Parrott streams were again able to assert themselves and of some potholes in the canyon of the North the deposit formerly hydraulicked on the south Ferry, east of Vallecito and Douglas Flat, and to set about the establishment of the present Mokelumne River 5 miles northwest of Bloods. side of the andesitic area north of Douglas Flat. south of Big Trees, they form flat benches which drainage system. With the increased fall given The potholes lie 25 feet vertically above the pres­ The gravels east and north of Sheep Ranch were

break off abruptly on the side next to the river them by the Neocene upheaval, they were enabled ent water level of the river. TheyJ are Glacial , . , pot=. formerly worked at several points, particularly at in picturesque columnar cliffs or palisades, some­ to attack with vigor the volcanic mantle which about 250 in number and cover a sur- holes- the eastern edge of the town. The river which times 200 or 300 feet in height. The unconform- covered the region, and to sink their gorges deep face of approximately 2000 square feet. To the deposited this gravel was perhaps a branch of the able relation of this flow to the andesite is best into the Bed-rock series. The andesitic tuffs and north is a glaciated cliff of granite about 40 feet one occupying the Fort Mountain channel, in seen about half a mile northeast of McKay's mill, breccias which once concealed nearly all of the high, on the side of which is another pothole. It which case the stream drained to the northwest where its vesicular base is well exposed resting older rocks were thus dissected into their present may be presumed that these potholes were formed and joined the Fort Mountain channel north of upon an eroded slope of andesite tuff, while only irregular and detached areas. The continuity of by a glacial river falling from this granite cliff. O'Neil Creek. Deposits which are regarded as a short distance away it lies directly upon the stream erosion was, however, broken in the higher Just above the potholes, salt water oozes out of belonging to the Fort Mountain channel occur on granite and gneiss of the Bed-rock series. portion of the region by the epoch of glaciation. cracks in the granite and, flowing into the nearest the ridge north of O'Neil Creek and thence north The rock composing the Table Mountain flow is character­ Gra/vels. Pleistocene gravels occur at intervals potholes, crystallizes into salt, which is gathered at frequent intervals to the vicinity of Railroad ized by its abundant porphyritic crystals of labradorite feld­ all along the present streams. Some of the loose by Indians and others for culinary purposes. 1 Flat. As much of this river deposit is hidden by spar lying in a dark, fine-grained matrix. Under materials lie distinctly above the present water No prominence was given to the study of glacial the rhyolite that overlies it, only a few the microscope it shows phenocrysts of labra- Sn'tatlte1.11" i 1 1 Thee aurifer-aurer- dorite, augite, and usually a little olivine, in a levels and were evidently deposited when the phenomena in the Big Trees quadrangle, and it areas appear on the geological map. ous gravels -IT r of the Fort groundmass of lath-shaped labradorite crystals, grains of rivers ran at higher levels. In some cases, as is probable that more moraines exist than are The name or the channel appears to augite and olivine, and globulitic glass. There is always a little accessory magnetite and apatite present. The rock may near. Vallecito, where the Pleistocene gravels rest shown on the geological map. have been taken from a picturesque be termed an augite-latite. Three chemical analyses, of speci­ partly upon Neocene gravels, it is not always andesitic hill which is situated 2 miles north of mens taken from portions of the flow 15 to 20 miles apart, ECONOMIC GEOLOGY. Calaveras Valley. This hill is locally known as show it to contain from 56.1 to 59.8 per cent of silica, 50 to 6.5 possible to discriminate sharply the former from per cent of lime, 2 5 to 3.9 per cent of soda, and 3.4 to 5.0 per the latter. Neocene auriferous gravels. The gravels depos­ Fort Mountain. There is no evidence, however, cent of potash. Alluvium. The proportion of alluvial, or bot­ ited by the Neocene rivers were formerly worked of any prerhyolitic river deposit at Fort Moun­ The second flow was poured out on top of the tom, land within the quadrangle is small, and is on an extensive scale, with large profits, in the tain. The volcanic conglomerates that make up Table Mountain flow, but did not descend so far almost confined to grassy meadows, usually in the southwestern portion of the quadrangle, but there the hill show evidence in their varied bedding of down the slope. The most westerly head-water regions of streams. Beautiful meadows is now little being done in this district. Columbia, shifting currents. But the waters that arranged Biotite=latite mass that can be referred with confi­ are found in Bear Valley in the northeast corner once the center of a stirring mining these conglomerates in layers probably belonged dence to this second flow is in the basin of Love of the quadrangle, at Lord's ranch in the south­ population, has sunk into decay, and about mines to a temporary sheet of water that accompanied Columbia. Creek, south of Big Trees. Two patches of very east corner, and others of less extent at other a similar fate has overtaken the little the volcanic eruptions. The Fort Mountain similar glassy lava occur on Mill Creek, south of points. In many of these the grass is cut for hay, settlements of Shaws Flat and Springfield. Their channel has been mined east of Railroad Flat, on Avery, which may possibly be a part of this flow; while others are simply fenced and used by the appearance of semi-desolation is strangely height­ Esperanza Creek, 'and at the Banner Blue gravel but their correlation is somewhat doubtful, as one stockmen as feeding and gathering grounds for ened by the bare and bleached points of limestone mine on Jesus Maria Creek. At the Banner mine of them is overlain by lava indistinguishable from their cattle preparatory to the annual autumn which stand like closely set gravestones about the gravel is worked by means of a Banner that of the Table Mountain flow. The lava of retreat to the Great Valley. the dilapidated houses. On account of the depth shaft sunk through the rhyolite cap- « vei mine. the second eruption differs in its distribution from Glaciation. There is abundant evidence of the of the cavities in the limestone in which the ping. The channel is said to be 125 feet wide. those which immediately preceded and followed former existence of glacial ice in the high eastern gravels near Columbia lay, and the difficulty of A level line run north from the Banner mine it, inasmuch as it is not confined to the general portion of the quadrangle. This evidence consists securing deep drainage, most of the auriferous shows the present grade of the Fort Mountain line of the buried Neocene stream channel. It of bare granite slopes showing glacial polish and detritus had to be hoisted with derricks, and channel in this vicinity to be 70 feet to the mile. occurs in small patches in various parts of the scoring, of transported bowlders of granite left washed into the sluices from raised dumping plat­ The river gravels on the ridge north of O'Neil Stanislaus drainage, as well as in the drainage stranded on rocks of unlike character (see fig. 1, forms. As much as $100,000 per week is said to Creek have been mined at several points. In 1896 area of the South Mokelumne, and even in that page of illustrations), and of definite piles of loose have been shipped from Columbia between 1853 the gravel at the Brassila mine was being worked of the Tuolumne River at Bradford's mill, It is rocks moraines, composed of materials which and 1858, but the industry had already greatly by drifting under the lava cap. The Fort Moun­ generally much thinner than the Table Mountain have fallen on the ice and been carried down the declined in 18YO, and in 1896 mining was going tain channel is supposed not to have crossed flow, being usually less than 50 feet in thickness. slope and left on the ridge tops and canyon sides. on in a small way at one point only. O'Neil Creek, but to have drained west into the It is typically shown in the vicinity of McKay's River canyons that have been occupied by glaciers The deeper gravels beneath the Pleistocene Jackson quadrangle. mill. It sometimes exhibits a rude columnar are commonly U-shaped. As only the upper por­ gravels just east of Vallecito, although not on Pleistocene auriferous gravels. Wherever parting, the columns being short and stout. The tions of the main canyons, chiefly to the east of limestone, resembled those of Columbia Qravels about gravels occur bordering the existing stream beds rock cleaves most readily in planes transverse the quadrangle, exhibit this form, it would appear in the difficulty experienced in secur- Vallecito- in the southwestern and western part of the quad­ to the columns, and shows brilliant scales of bio- that the ice streams never extended far down the ing the requisite deep drainage whereby they rangle they have been washed to some extent for tite lying in a dark-gray ground. Pebbles and present drainage. There is some evidence, how­ could have been profitably washed by ordi­ gold. Several areas are indicated along the angular fragments of andesite and latite are found nary hydraulic methods. It was necessary to Stanislaus from Robinson Ferry up to Abbott ever,' that at an early > stageo of the First_. ^ period in many specimens, giving the rock a decidedly Glacial epoch the Pleistocene rivers of «laciation- mine the gravel by drifting, and raise it to the Ferry, and most of them have been exploited by tuff-like aspect. The matrix is evidently highly occupied shallow valleys, and it was perhaps dur­ surface through vertical shafts, some of which the hydraulic method. Although never occurring glassy, and contains blebs and flamboyant wisps ing this time that the glaciers extended farthest are said to have been over 100 feet in depth. far from the stream, yet they are as a rule dis­ of dark obsidian. west, where they left moraines which are still pre­ The reported depth of this part of the old channel tinctly above its present high-water mark, and The microscope shows the rock to contain crystals of labra­ served at some points. Thus in the neighborhood is interesting, as it lies below portions of the later record a stage when its bed stood higher than it dorite, biotite, and a little augite, lying in a streaked glassy of Bear Creek on the slopes of the North Mokel­ channel covered by the latite flow to the east, and now does. Most of the gravel forming the upper groundmass. The peculiar structure of the groundmass is due is nearly surrounded by the ancient rocks of the part of the deposit immediately east of Vallecito to the drawing out of the viscous lava by the movement of umne Canyon, at Squaw Hollow in the canyon of flow after crystallization had already begun, the resulting the North Fork of the Stanislaus, and on the Bed-rock series. Its gravels are apparently con­ appears to be Pleistocene, although it has been so streaks and bands being distorted and broken as the cooling ridge south of the Middle Stanislaus south of tinuous with those exposed below the andesites thoroughly turned over in many places that there magma became more pasty. This rock may be called a biotite- latite. Chemical analyses of two specimens, taken about ten Bakers Crossing there are small remnants of on the northwest of Vallecito, and the former is considerable doubt as to the original position miles apart, show from 61.0 to 62.3 per cent of silica, 3.2 to 4.9 moraines. After this early period of greatest outlet of the stream must have been in that direc­ and age of much of it. It does not appear to of lime, 3.7 to 4.2 of soda, and 4.4 to 5.2 of potash. ice extension, when the river valleys were shallow, tion. Before and during the andesitic eruptions have ever had any great depth over Auriferous The last flow, called, from its typical occurrence it may be supposed that the ice sheet retreated to this depression in the early Neocene stream bed much of the area, as the bed rock is must have become filled with gravel and buried exposedi in. several11 places wherei appar­ streams. on a group of peaks a few miles east of Clover the highero mountains to the east of the Second_ . period Big Trees quadrangle. During this of g'aclation- beneath the volcanic tuffs and breccias. The ently no great amount of gravel has been arti­ Meadow,7 the Dardanelles flow,' is an Dardanelles , augite-latite so closely resembling the latlte- interglacial epoch the rivers are thought to have ficially removed. The pebbles consist of andesite, rock of the Table Mountain flow that in certain greatly deepened their canyons. After this period 1 Ain. Jour. ScL, 3d series, Vol. XLIV, 1892, p. 453. rhyolite, quartz, and other rocks, all of which may Big Trees 5. have been derived from the immediate vicinity. amounts of sulphides in the Belleview vein. rides, in which case probably a large proportion mine, on the ridge slope north of the Licking Fork Pebbles from the dioritic area just west of the Galena, containing some antimony, and chalco- of the gold was lost in the tailings which were of the Mokelumne, has been worked at different town are abundant. Near Columbia, Pleistocene pyrite were noted in small amounts. The region not saved. The strike of the Collier-Homestake times. The ore is very base, being composed gravels are still being worked to some extent by north and east of American Camp is a ratner vein is nearly due E.-W., and the dip about 80° largely of sulphides. Pyrite, zinc blende, and hand sluicing at Browns Flat, and by hydraulick- promising one and contains numerous quartz N., although sometimes nearly vertical. The arsenopyrite are present in large amount. ing at Yankee Hill. Other deposits which were veins, most of them as yet undeveloped. The True Business and Sailor Boy veins, on the east The granodiorite area north of Woodcock's mill formerly worked at a profit occur southeast of Keltz mine, situated in the canyon of bank of the river, strike, like the Collier, nearly contains numerous quartz veins, many of which Keltz mine. Douglas Flat on Grapevine Creek, on the South the South Fork of the Stanislaus, is on E.-W., which is also the general strike of the have been exploited for gold. These claims are Fork of the Stanislaus, and near Murphy. a vein lying within the siliceous schists of the dark siliceous slates and accompanying limestone in the West Point district, which in the Jackson In addition to these earlier Pleistocene gravels, Calaveras formation, just to the west of a dioritic lenses on both sides of the river. The North quadrangle has afforded some producing mines. the present beds of nearly all the streams in the dike. The dip varies, but is usually from 35° to Chimney Rock vein has apparently a nearly NE.- The Lockwood mine is a type of the mines of the

western part of the quadrangle have proved more 45° SE. The vein rock of the Keltz, in contrast SW. strike, with a steep southeasterly dip. The West Point district. It is located Lockwood, , or less auriferous, and there are few or none of to that of the Robinson Ferry group, is free mill­ country rock is hard siliceous slate, and the vein about 1^ miles northeast of Wood- mine- them that have not had their gravels turned over ing, consisting chiefly of quartz, pyrite and free rock quartz, containing abundant pyrite. The cock's mill. The quartz vein has a northwest- and washed, in many cases more than once. gold. The Riverside mine, now idle, is on the strike of the schists and slates is here nearly southeast course. The ore is free gold, pyrite,

Qold-qua/rtz veins. Some activity was manifest north bank of the South Fork of the _.Riverside E.-W., and the dip 65° S. The Dorsey vein is pyrrhotite, and other sulphides, in a gangue of in 1896 near Robinson Ferry, where prospecting Stanislaus, about a mile west of the mlne- nearly vertical and strikes about N. 54° E., and, quartz. The sulphides are present in very large

was beingo carried on at the Melones, ' Robinson .. Keltz. "Where seen, the vein is a strong one, as exposed at the surface, is 6 or 8 inches wide. amount. A fine-grained dioritic dike cuts the Stanislaus, and Calaveras Consolidated Ferry mlnes- upward of 5 feet in thickness, and is composed The Oro y Plata vein, formerly the Blue Wing, vein of the Lockwood mine, and the ore is said mines situated on the south slope of Carson Hill, largely of ribbon quartz. The ore shows both outcrops just north of Murphy, in limestone close to have been richer near the dike. at the Adelaide at Robinson Ferry, and at the copper and iron sulphides. The Star mine is in to the contact with the Calaveras Gold and silver in rhyolite. There is a butte Norwegian mine on the south side of the river. schist on the north side of Rose Creek, schists. It was formerly extensively orBuiewng of rhyolite shown on the geological map just north Star mine. None of them, however, were established on a and is working upon two diverging worked,, , andT possesses interest j. j. on veln- of the South Mokelumne, at the west margin of paying basis, although the Carson Hill group had veins. Nearly all the quartz seen is of a dark account of the unusual association of sulphides in the sheet. This rhyolite appears to have been been producers several years ago. The Mother color. It is said to be very rich in spots. The the ore. Ordinary vein quartz forms a part of erupted at this point. It has been exploited by Lode, as exposed on the south slope of Carson mine has recently been reopened and a rich body the deposit, but is accompanied by brown jasper. means of a tunnel, the mouth of which is near Hill, comprises several veins which show a ten­ of ore found, containing free gold and sulphides Cinnabar, stibnite, and galena are present in the the river. A sample of the rhyolite from the dency to converge near the ferry. They are, of copper, iron, and lead. The dark color of the ore, and it is also said to contain copper. The dump was assayed by the Selby Smelting and however, exceedingly irregular, and in the Stanis­ quartz of the Star mine has been shown by Dr. Mayflower and Mayday claims are prospects in Lead Company of San Francisco, the result show­ laus mine the ore occurs in small cross stringers Stokes, of the United States Geological Survey, the Calaveras schists northwest of Murphy. Their ing that it contains .03 ounce gold and .25 ounce of quartz in black Calaveras slates, near a mass to be due to finely disseminated carbonaceous veins, like those near Collierville, conform to the silver per ton. of talcose schist. The ores of the mines in the material. On the north side of Knight Creek, nearly E.-W. strike of the inclosing schistose Iron. A deposit of limonite, which has been immediate vicinity of Robinson Ferry TeIIur!des of within the granodiorite area, a prospect was noted rocks. The Sheep Ranch mine has been more prospected to a small extent, occurs in the Cala­ are, as a rule, rich in tellurides of gold, gJJ; |"Jer> in which the vein material consists of dark quartz extensively developed than any other Shee Ranch veras formation adjacent to a small lens of lime­ silver, and lead. Petzite, hessite, and mckel> containing pyrite and scales of molybdenite. The mine in the quadrangle, but is at pres- mlne- stone about a mile northeast of Murphy. It is calaverite (tellurides of gold and silver), and vein of the Eagle prospect, on Eagle EagleproS!, ent idle. The vein lies in dark siliceous slates, not likely to prove of economic value. altaite (telluride of lead), have all been described Creek, is from 6 inches to 3 feet in pect- and strikes N. 55° W. The dip is northeasterly Marble. Several small quarries have been from the Stanislaus and Melones mines, as well thickness, and strikes nearly N.-S. magnetic, dip­ about 75°. The thickness of the vein varies from opened in the limestone on the Bannister ranch, as the rare mineral melonite, a telluride of nickel. ping about 44° E. The country rock of the mine a few inches up to several feet, and consists of about half a mile northeast of Abbott Ferry. The In addition to the tellurides, the veins contain is the Calaveras formation. A dike was noted numerous stringers of quartz with intermingled marble is apparently of fair quality and the supply free gold, pyrite, and a little galena, in a gangue along the vein. Free gold, pyrite, chalcopyrite, slate. The ore consisted of pyrite and free gold is practically unlimited. Veined, pure white, and of quartz with usually some dolomite and occa­ and zinc blende are present in the ore. in a gangue of dark quartz, and was free milling. variegated marbles are all present within a com­ sionally a little albite. A series of quartz veins occurs on both sides of It is said that in the lower levels the sulphurets paratively small area. The markings of the veined The other gold-quartz veins of the quadrangle the Stanislaus in the Calaveras formation near were not considered worth saving, all the gold variety are a little too faint for a thoroughly all lie to the northeast of the linear system of the Collierville. Although several tunnels have been being caught on the plates. effective stone of this class. The material is Mother Lode, of which so short a section is run on them, they are all in the prospecting stage A large number of quartz veins containing some dressed in the quarries to supply local demands, included within the general area near Robinson of development. The vein rock of the Homestake gold and silver have been exploited in the rocks the lack of transportation facilities restricting it Ferry. The Belleview mine, formerly known as claim, near Collierville, is a dark quartz Mines near of the Calaveras formation to the north and west to the home market. the Hyde mine, is in the same granitic Belleview containing pyrite, free gold, and a little Collierville- of Blue Mountain. In many of these claims the H, W. TURNER, area as the mines of the Soulsbyville mine* galena. A small mill was formerly run on the ore quartz is dark in color, as at the Star mine on F. L. RANSOME, district in the Sonora quadrangle. Unlike most from the Collier claim, which adjoins the Home- Rose Creek. None of these veins appear to have Geologists. of the mines of that district, there are not large stake, but the ore is said to have contained tellu­ developed into permanent mines. The Cook May, 1898.