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 SUPERJAGENT 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 CRETACEOUS PERIOD. 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. defined 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 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 som showing that the gold-quartz veins had GENERAL GEOLOGY. 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 PERIOD. 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 tuft's. 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-hone'). 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 rnetamorphism 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-JURATRIAS UPHEAVAL. of gravels accumulating. and other igneous rocks have been intruded among (1) The JRobinson formation, comprising sedi Soon after the Mariposa formation had been these schists, forming irregular bodies which ments and trachytic tuft's. This contains fossils deposited the region underwent uplift and com NEOCENE PERIOD. 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 south of the fortieth parallel, during the whole POST-CARBONIFEROUS UPHEAVAL. 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 JURATRIAS PERIOD. 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-QUARTZ 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 were sufficient to remove the silt while allowing BED-ROCK SERIES., intrusive granite; at Sailor Canyon, a tributary ondary, or those formed from the detritus pro of American River; in Plurnas County at the duced by the erosion of the primary deposits. the coarser or heavier masses to sink to the PALEOZOIC ERA. 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 nd 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 granitic rocks that form isolated areas in the slate occupied by the Sierra Nevada. Its western Jurassic time probably reached eastward at least 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 minerals, such as epidote, zoisite, ura- occupied by it and the constancy of the type almost the entire country.. They were extruded Merced E-iver, 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 G-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 PERIOD. 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 CHARACTER OF ROCKS. SYMBOL. SECTION. Recent. Pal 1-100 Soil and gravel. River and shore gravels. Pgv 1-100 Sand, gravel, and conglomerate. River and shore gravels. Ng 10-400 Gravel, sandstone, and conglomerate. 10-100 Shale or clay rock. GQ 10-100 Sandstone. . Coal stratum.
02 lone. Ni
50-800 Clay and sand, with coal seams. O
03 W PH Et 10-300 Sandstone and conglomerate. D Tejou. 02 Tawny sandstone and conglom 50-400 erate. Chico. Kc mmwi GREAT UNCONFORMITY
Monte de Oro. Jo Black clay-slate, with interbedded Mariposa. Jm greenstones and some conglom erate. Milton. Jml i^ Sailor Canyon. Js
UNCONFORMITY Intrusive granitic rocks. DO grd ita i 03
o o °? Q Argillite, limestone, quartzite, H 4000 or chert, and mica-schist, with inter- PQ Robinson. Crb more bedded greenstones. Calaveras. Cc
'-'i-t: A' T^&-'< Intrusive granitic rocks. gr grd r%7>^.-/"\;~ ' ' * 1 DESCRIPTION OF THE TRUCKEE QUADRANGLE.
TOPOGRAPHY. the Sierra Nevada, it may in a certain sense 6000 feet to 48 inches at 7400 feet. A large quartzites. All are greatly disturbed and most be regarded as the southern continuation of proportion of this is snow, which near the sum of them have been strongly compressed. Geographic position. The Truckee quadrangle Truckee Valley. The lake covers about 190 mits may accumulate to a depth of 20 feet on the The igneous rocks consist partly of a diabase- includes the territory between meridians 120° and square miles, of which about 112 square miles fall level. In Truckee Valley the winter temperature porphyrite, accompanied by tuffs, and certainly 120° 30' west longitude and parallels within the Truckee quadrangle. The outlet of the is more severe, the records showing a minimum of of Juratrias age; partly, and predominantly, of 39° and 39° 30' north latitude. The Counties. lake is through Truckee River, which -25° F. or -32° C. The precipitation during the granitic and dioritic rocks, all of which are prob area is 34J- miles long and nearly 27 for 13 miles flows nearly due north, t£'tirelt ed winter is much smaller, the snow rarely falling to ably somewhat later than the Juratrias sediments. J Basin. miles wide, and contains 925 square miles. It then turning to the northeast, traverses greater depths than 4 or 5 feet at Truckee. Near embraces portions of Sierra, Nevada, Placer, and Truckee Valley and breaks through the east Lake Tahoe the climate is intermediate between CARBONIFEROUS PERIOD. Eldorado counties, California, while the State of ern range in a deep canyon. At the northeast the two types referred to, as the influence of the Qala/veras formation. Within this quadrangle Nevada adjoins it on the east. corner of the quadrangle the river emerges from large body of water produces an equalizing effect. the rocks referred to the Calaveras formation (Cc) Relief. The quadrangle has, on the whole, a the eastern range into the broad flood plains The lake has never been known to freeze over. occur only in the drainage basin of Theoldest rugged and mountainous character, including, as about Verdi and Reno. Truckee River receives The only towns are Truckee, with a population Duncan Creek, a tributary to the ^Tcl*// it does, a part of the summit region several tributaries, of which the more important of 1400, and Boca, with 260 inhabitants. The Middle Fork of American River, but boni^rous- General of the Sierra Nevada. Many peaks topographic are Prosser Creek and Little Truckee, which join permanent population is chiefly con the area extends far into the adjoining Colfax rise above 9000 feet, and the central it in Truckee Valley. The fall of this river and centrated in the vicinity of Truckee 2dSWBt§ quadrangle. The beds consist of dark quartzites Truckee Valley is the only area showing a of its tributaries is much smaller than that of the and at other points along the railroad. and clay slates to which weathering soon imparts moderate and hilly configuration. The lowest rivers belonging to the Pacific drainage. From Only a few people remain during the winter at a gray color. They have a northwesterly to west point is found in the canyon of the North Fork the lake, which has an elevation of 6225 feet, to the different road stations and summer hotels erly strike and a steep northerly dip. As far as of American River, which descends to an eleva the city of Truckee the fall is only 28 feet per about Lake Tahoe. During the summer, however, can be determined, the schistosity approximately tion of 3700 feet, while the highest peak, located mile. From this point on, the grade varies the region is populated by tourists and by cattle follows the stratification planes; better exposures 4 miles north of Hot Springs on Lake Tahoe, between 33 and 50 feet per mile, the highest men and sheepmen, who pasture their herds and on the adjoining quadrangle show, however, that attains 9300 feet. Less majestic than the crest being found in the canyon north of Bronco. Little bands on the mountain meadows. this does not always hold good. The large mass region of the southern Sierras, this region is still Truckee River has grades ranging from 14 feet The principal industries are cattle raising and of Duncan Peak is composed of a dark-gray or of surpassing interest,- combining with the grand per mile up to 37 feet. timber cutting, the latter industry being centered light-gray, very fine-grained, nearly massive, sili est mountain scenes a great variety of geologic According to the few observations available, in the vicinity of Truckee. Another important ceous rock of a chert-like appearance, which may formations and structure. the depth of Lake Tahoe is very considerable, the industiy is the cutting of ice in numerous ponds have been derived from limestones by meta- The quadrangle may be divided into three parts, deepest sounding yet made, 1635 feet, being found constructed for that purpose in the vicinity of somatic replacement. Toward the eastern base of different topographic types': a short distance south of Hot Springs. The Prosser and Boca. of Duncan Peak these fine-grained quartzitic First, the western mountain mass, forming a deepest depression extends southward from this The main line of the Central Pacific Railroad rocks are interstratified with clay slates. Still part of the main block of the Sierra Nevada. Its point, and the slopes from the shores are in crosses the quadrangle, following the South Fork farther east the clay slates predominate. The lower part is, in this quadrangle, characterized by general very sudden. Like most mountain lakes, of Yuba River up to Donner Pass, and thence age of these rocks has been determined as prob broad ridges, separated by deeply trenched can Tahoe is distinguished by the extreme trans descending in winding curves to the level of ably Carboniferous, from a few imperfect fossils yons; its topography is thus similar to that of parency and exquisite color of its water. Truckee Valley. Continuous snow-sheds protect found near the mouth of Sailor Canyon, in the quadrangles adjoining on the west. The upper Many glacial lakes of great beauty dot the the road from Emigrant Gap, in the Coif ax quad northward continuation of the formation, where region is more irregular, and culminates in a series summit region of the Sierra Nevada. The largest rangle, to Cold Creek, a few miles west of Truckee. it adjoins the Sailor Canyon beds, which are of of lofty peaks, reaching elevations of from 7000 are found at the foot of the steep eastern slope From Truckee the railroad follows the canyon of Juratrias age. to 9000 feet, along the divide which extends which descends from the water partings. Most the river out to the flood plains at Reno. Three The sedimentary rocks bordering against the diagonally across the quadrangle. prominent among them are Independence Lake chief transmontane wagon roads traverse the granite and granodiorite show extremely irregular Second, the irregular depression of Truckee and Donner Lake, each about 3 miles long and quadrangle. One, the so-called Henness Pass contact lines, whose jagged forms indi Valley, deeply sunk between two parallel ranges three-fourths of a mile wide. These lakes are in road, crosses the mountains along the northern cate actual tearing asunder and shatter- of granitic , . . . intrusions. and separated into several parts by projecting general not deep. Level meadows of alluvial border; the second follows the railroad as far as ing by the intrusion ol granitic magma. lower ridges. Southward and northward the val soil mark the site of many former lakes, which Truckee; the third, extending along the southern While the sedimentary rocks in general can not ley is limited by high ridges connecting the east have been drained by silting or by corrasion of boundary, connects Georgetown, Eldorado County, be said to be extremely metamorphosed, the action ern and western range. their outlets; such are, for instance, Twin Valley with McKinney on Lake Tahoe. of the granitic magma has produced an intense Third, the eastern range, sometimes referred to and the meadows of Little Truckee River to the The abundant water supply on the western metamorphism along the contacts. The effect has as the Carson Range, of which only a small part is east of Webber Lake. slope is utilized and stored, especially at the head been to alter the beds to schistose, micaceous shown on this sheet. Narrow, with abrupt slopes Vegetation, climate, and culture. The forest waters of the South Fork of Yuba River. Meadow rocks, sometimes resembling gneiss and often con eastward and westward, this range follows the zone of the western slope of the Sierra Nevada, Lake, Fordyce Lake, and the Cascade Lakes have taining aiidalusite. This contact-metamorphic eastern shore of Lake Tahoe and culminates, at which lies between the elevations of 2500 and been artificially dammed, and constitute some of zone is of varying width, as apparently certain an elevation of 10,800 feet, in Mount Rose, in the 6000 feet, is represented to only a small extent in the most important reservoirs of the South Yuba rocks are less susceptible to metamorphism than adjoining Carson quadrangle. The whole width this quadrangle. In the southwest corner excel Water Company. The main ditches, however, others. On an average its width may be said to of the range appears, on this sheet, only near the lent timber is found for a distance of about 6 take their water from the river lower down, in be less than a mile, but it is not uncommon, northeastern corner. miles above French Meadows along the Middle the Colfax quadrangle. The North and Middle especially in smaller isolated areas in the granite, Drainage. The main water parting between Fork of American River, and the gently sloping forks of American River are not at present utilized to find highly metamorphosed rocks at a greater the Pacific and the Great Basin follows the sum ridges between the Rubicon and the Middle Fork for water supply, although a ditch has been con distance than this from the contact. mit of the main range diagonally across the sheet also carry an abundant growth of fine timber. structed from the Middle Fork at French Meadows Sailor Canyon formation. Of special interest from a point 2 miles east of Rubicon Springs on The species most frequently represented are the to carry water down on the Long Canyon divide among the sedimentary rocks of this quadrangle the south to a point 2 miles west of Webber Lake yellow pine (Pinus ponderosa) and sugar pine in the adjacent area. Gerle Creek, along the is the Sailor Canyon formation (Js). It is the on the north. To the west of this water parting (Pinus lambertiana). The summit region of the southern boundary of the quadrangle, is utilized only fossiliferous horizon thus far found, the the rivers flow into Sacramento River, the drain Sierra Nevada is here, as everywhere, by the Georgetown Water Company, and Pleasant imperfectly preserved remains of ammonites and age being divided between the Yuba and Ameri only scantily covered with timber, offorested0" Lake, connecting with Loon Lake, forms one of other shells found indicating that the beds are of can rivers. The Middle Fork of Yuba River among which different kinds of fir and the reservoirs. Truckee River carries a large Juratrias age. heads in the extreme northwest cor- tamarack of no great value prevail. Large areas volume of water (from 500 second-feet at low The Sailor Canyon beds lie partly in the Colfax, ner of the quadrangle, while the South Tributariesof th" sacera- in this belt are entirely barren, all the soil having water to 7000 second-feet at high water), which partly in the Truckee quadrangle, and are well Fork-n-r-i.,1 drams the country. adjoiningi. . . the , mento. been swept away by the action of the Pleistocene is extensively distributed in the vicinity of Verdi exposed along the North Fork of Thejtira. Central Pacific Railroad. The North Fork of ice sheet which once covered the region. The and Reno for irrigating purposes. In Truckee American River, as well as in Sailor {J^SSes, American River, heading in the vicinity of granitic rocks, as well as the slates and schists, Valley, however, the climate is considered too Canyon. The rocks consist of dark- Granite Chief Peak, forms, near the western are in general destitute of forest, while the andes- severe for successful agriculture. A number of gray or black calcareous slates, without pro boundary line, the remarkable canyon known as ite and breccia in the glaciated areas, on account reservoirs might be constructed at the headwaters nounced fissility, interbedded with subordinate the American Royal Gorge, which attains a depth of their crumbling nature, are more apt to support of the western tributaries of Truckee River. strata of quartzite and limestone. Near the dia- of 4000 feet.. The southwestern part is drained a growth of timber. GEOLOGY. base-porphyrite tuffaceous rocks occur, tending to by the Middle Fork of the American and by one A very valuable forest area covers the ridges show that the eruption of the igneous mass was of its tributaries, the Rubicon, the former flowing of Truckee Valley and the slopes of the lower BED-ROCK SERIES. approximately contemporaneous with the deposi in a broad valley with comparatively gentle Truckee Canyon, and connects along the upper Under this general heading are included all of tion of the beds. The reddish or brownish color slopes, while the Rubicon throughout its course Truckee Canyon and across the Mount Pluto the older rocks of the Sierra Nevada, consisting of the outcrops and the lines of stratification are in this area has cut a deep canyon. ridge with the forest zone fringing Lake Tahoe. of sedimentary rocks deposited during or before well shown in the rocky bluffs forming the west The grades of these rivers, nearly all of which In this area the yellow pine is most abundantly the Juratrias period, together with eruptive and ern part of Snow Mountain. The strike of the have a westerly or southwesterly course, are very represented. The sloping prairies of Prosser intrusive igneous rocks, which mostly date from series is about N. 30° W., and the dip is from 50° steep. That of South Yuba River ranges from Creek and Martis Valley are unforested. the Juratrias period, or possibly in part from the to 70°, constantly toward the east. The schis 50 to 200 feet per mile, and averages 100 feet per Owing to the moderating influence of the early Cretaceous. None of the igneous rocks tosity is far less strongly marked in this series mile. The North Fork of the American falls 200 Pacific Ocean the climate is not so severe as the belonging to the Bed-rock series in this quad than in the older sediments to the west of Sailor feet per mile between the western boundary and altitudes would lead one to suspect. Climatic rangle are younger than the early Cretaceous, and Canyon. If the beds really form one uninter Soda Springs. The Middle Fork of the American Moreover, it varies greatly in the dif- conditions- there are probably none which are older than the rupted series, their total thickness between the descends less rapidly, averaging only 100 feet per ferent topographic divisions. On the whole it is Juratrias. Paleozoic limestone of Big Granite Canyon (Col mile between the western border and a point due characterized by dry, warm summers, with occa The fossil evidence of age is very scant in the fax quadrangle) and the diabase of Snow Moun south of Soda Springs. Considerable stretches sional thunder showers and by a heavy snowfall sedimentary rocks, but it is believed that enough tain must be approximately 6000 feet. But the of it have a grade of only 37 feet per mile. That during the winter. Over the western slope of the has been adduced to justify their formation has not been studied in sufficient detail part of Rubicon River which lies within this quad Sierra Nevada the temperature at an elevation of division into an older, Carboniferous aeego"th" to assert that such a continuity exists. One of . older rocks. rangle has an average grade of 124 feet per mile. 7500 feet may reach 90° F. during the summer, group and a younger group ol Juratrias the principal fossil localities is near Sterrett's The water courses east of the summit line while during the winter the thermometer very age. To a considerable extent this division is mine, on the western side of Sailor Canyon, just referred to find their way to the saline sinks of rarely falls below 0° F. or -18° 0. On the other based on comparison with or extension of forma over the line, in the Colfax quadrangle. Many the Great Basin, a part of them first emptying hand, frosts frequently occur during the summer tions of approximately known age in adjoining poorly preserved ammonites and shells of Daonella into the great natural storage basin of Lake at elevations above 6500 feet. areas. were found here. At the mouth of New York Tahoe, well known as one of the most beautiful The annual precipitation is very high over the The sedimentary rocks consist of clay slates, Canyon, a short distance west of the boundary mountain lakes in the world. Occupying a broad western slope of the mountains, ranging from a quartzitic sandstone, and some limestone, met line, the beds contain Monotis shells. A third depression between the two summit ridges of maximum of about 57 inches at an elevation of amorphosed near the granite contact to schist and fossil locality is opposite the mouth of Big "-T
/
Canyon, the first large stream entering the North below Soda Springs, black clay slates alternate contact with the sedimentary rocks, banded tuffs larger grains of quartz. The upper basin of North Fork from the south. At this place specimens of with siliceous, fine-grained rocks and quartzites. appear. Creek, as well as the basin of the South Fork ammonites were found just below the tuffs of the On the Middle Fork of American River the bold, The small wedge-shaped area extending from of Yuba River, is eroded chiefly in normal gran western edge of Snow Mountain. The fossils are rocky outcrops have a dark-brown to black color, Meadow Lake to Fordyce Lake consists chiefly odiorite. This mass extends down to Donner thought to indicate beyond doubt a Juratrias age, and the stratification may be plainly seen from a of uralite-diabase. Diabasic rocks consisting of Lake, Euers Valley, and Twin Valley, until the although more perfect remains than any yet found distance. These rocks are black quartzitic slates, augite, plagioclase, and brown mica occur at the eastern andesitic contact is reached. will be required for an exact correlation with any alternating with finer-grained and fissile clay northern end of Fordyce Lake. The two smaller areas inclosed in slate and of the subdivisions of that period. It is prob slates. ' The area included in the Juratrias slates south diabase to the west of Lola Peak are composed of able, however, that the time of the deposition of South of Greyhorse Valley the sedimentary of Webber Lake is generally a diabase-porphy normal granodiorite. At the head of Independ the beds ranges between the upper Trias and the rocks consist of banded quartzites alternating rite, and appears as a dark-green, dense rock with ence Lake and from there up to the divide, the lower Jura. with dark slates in narrow ribbons. Similar are smaller crystals of uralite and epidote. Many granitic rock contains many inclusions of darker Toward the northwest, in the Colfax quad the rocks exposed in the canyon of the Rubicon secondary minerals, such as epidote and brown dioritic material. Immediately south of White rangle, the Sailor Canyon beds are cut off by and along the lower part of Five Lakes Creek. mica, are developed in this rock. Rock Lake the above-mentioned normal granite granodiorite and are strongly metamorphosed. The above-mentioned black quartzites and slates The largest area of diabase-porphyrite is that appears in smaller masses. In the vicinity of Toward the south a sudden bend of the Calaveras of the Middle Fork of American River crop out extending from Granite Creek across the North Donner Pass and at the head of Cold Creek the formation throws the Juratrias beds eastward, again in the northern part of Five Lakes Creek. Fork of American River, forming a belt from 1 to rock is a granodiorite of grayish color, somewhat and below the andesite ridge forming the divide Some of these rocks, though at a distance of 2 or 3 miles wide, bordered on the east and west by more basic than the normal rock. A specimen between the North and the Middle forks of even 3 miles from the granite contact, are strongly sedimentary rocks. It makes up the large, flat- from near Donner Pass contains 59-J- per cent of American River they are again cut off by later metamorphosed to hornfels and knotty schists. topped mass of Snow Mountain, and the river, silica, 6^ per cent of lime, 2J per cent of potash, intrusions of granodiorite. While there is no The rocks of the northeastern part of this sedi cutting through it, has produced one of the deep and 3-|- per cent of soda. This rock is more positive proof of an unconformity between the mentary area, excellently exposed in the vicinity est gorges in the Sierra Nevada. The area is closely related to the normal diorite than to the Juratrias and the Calaveras formations, still it is of Ward Peak, consist of beautifully banded red characterized by dark-gray, rough outcrops, strik granodiorite. very probable, from facts explained in the text of and gray quartzites, with some clay slates. In ingly different from the light-gray granodiorite In the basin of Palisade Creek and to the west the Colfax folio, that such an unconformity does places this series contains limestone, and a ledge and the dark-brown sedimentary rocks. The dia of Devil Peak the granodiorite is chiefly normal, exist. of highly crystalline marble crops out on the trail base-porphyrite is hard and massive, dark grayish- though a rock collected half a mile west of Devil from Scotts Springs to Five Lakes Creek, near green in color, and contains small porphyritic Peak somewhat approaches a granitite in appear JURATRIAS PERIOD (?) the bed of the latter. crystals of augite and feldspar. Grains of pyrite ance and composition. Near the slate area of Besides the well-established Juratrias beds The isolated sedimentary area at Soda Springs frequently occur in it. Under the microscope Soda Springs porphyritic modifications of granite adjoining the Calaveras formation, there are a is extremely metamorphosed by the surrounding the rock appears as a normal diabase-porphyrite. and granodiorite appear, and similar rocks form number of areas of generally altered granodiorite, and contains numerous masses and Secondary changes have frequently altered the dikes within the slates. At the head of Squaw sedimentary rocks (si and slm) almost areasIsolated in dikes of granodiorite. The area consists, as usual, rock considerably. Schistosity and accompany Creek and Bear Creek appears a reddish, crum or wholly embedded in the prevailing of banded quartzitic rocks and clay slates, the ing conversion to amphibolitic schists appear at bling granite, which is separated from the grano granitic rocks. These areas extend in a northerly latter becoming strongly micaceous near the con the northern end, along the contact with the diorite adjoining to the west by a comparatively direction from Rubicon River to Webber Lake, tact. Garnet and pyroxene rocks are common granodiorite. The strike of the vertical schis- sharp contact, and which is composed of large and probably at one time formed a continuous and indicate that the series contains much lime. tosity is parallel with the contact. Again, where grains of quartz, microcline, and a little plagioclase. series, with a general northerly strike. The great A few small streaks of slate are embedded in the the belt crosses the Middle Fork of American The quantity of hornblende and biotite present intrusion of the granitic rocks during late Meso- granodiorite southwest of Soda Springs. River an imperfect schistosity has developed, the is small. zoic time shattered this already folded series and The small area inclosed by volcanic rocks near strike of which is N. 53 W. The granodiorite of the Middle Fork of Ameri left it represented only by torn fragments. The Barker Peak consists of clay slates and quartzites, In the extreme northeastern corner of the can River and of the Rubicon basin is, as a rule, a general character of the series is siliceous; it con with an abnormal east-west strike and -a dip to Truckee quadrangle appears a small area of dark- rock of normal composition, but extending from sists chiefly of quartzitic sandstones, clay slates, the south ranging from 38° to 60°. It does not green, fine-grained diabase, massive but highly a point a short distance west of Rubicon Springs aiid fine-grained banded siliceous rocks. Lime appear much metamorphosed at the contacts. altered by the development of secondary minerals. beyond the divide separating the Rubicon from stone occurs northeast of Fordyce Lake and near The small area near McKinney consists chiefly of In places there is evidence of pressure, shown by Lake Tahoe there is an area in which the grano the head of Five Lakes Creek. The color of the quartzitic rocks in dark-brown, prominent out the drawn-out form of the minerals. In the diorite is decidedly darker in color and more basic rocks when fresh is gray to black, but they crops. Sierraville quadrangle, adjoining to the north, in character than usual. This area, similar to the weather almost invariably to dark-brown or red In the northwestern corner of the quadrangle this diabase occupies a considerable area. one near Donner Pass, is in places fairly sharply dish color, thus making the outcrops very con appears, imperfectly exposed by the erosion of G-ranodiorite, diorite, and granite. The granitic separated from the normal granodiorite, while at spicuous, contrasting against the gray granitic the superjacent volcanic masses, a series of schists rocks occupy a large space in the .Truckee quad other places it changes into that rock by imper rocks. The heat and the emanations of the and slates which are supposed to form the con rangle, but are confined chiefly to the western or ceptible transitions. About the headwaters of granitic rocks at the time of their intrusion have tinuation of the Juratrias rocks of Sailor Can main range of the Sierra Nevada. The areas Meeks Creek the rock is again of normal compo near the contacts more or less extensively meta yon or of the isolated bodies to the east of Sailor form the northward continuation of Qeneral sition. morphosed the sedimentary rocks to hornfels, Canyon. Toward the northwest the series is the great southern granitic mass of the The granodiorite of the range rising on the quartzites, and knotty schists. The width of this continuous as far as Sierra Buttes, at which place Sierra Nevada. This granular igneous rocks' eastern side of Lake Tahoe is largely covered by contact metamorphic zone is very variable, slate, Mesozoic fossils are said to have been found. It rock, the most recent member of the Bed-rock enormous masses of andesite. Near Hot Springs for instance, being much more easily changed than is not improbable that this series is the equivalent series, shows by its relations to the sedimentary and State Line Point normal granodiorite appears, the quartzitic sandstones. Especially in small of the rocks called the Milton formation, which rocks that it is of intrusive origin, or, in other but the outcrop along Truckee River in the areas the metamorphic zone is wide, evidence of occur in the Downieville quadrangle. Masses of words, that it was pressed into the torn sedimen northeast corner of the quadrangle shows a dif the changing action being found 2 or even 3 diabase and diabase-porphyrite are intercalated in tary rocks as a molten, more or less perfectly fluid ferent type. The rock here is a coarse-grained, miles from the granite contact. Dikes of granite- the slates, and tuffaceous rocks are of frequent mass by forces the magnitude of which we can dark-gray biotite-granite, distinguished by large, porphyry and diorite-porphyrite are very common occurrence. The exposures northeast of Fordyce hardly understand, and consolidated far below the reddish orthoclase crystals. Small foils of black near the granite contacts. Lake consist generally of siliceous micaceous former surface of the range. These masses are mica occur. The quartz in the rock is not promi These areas have been tentatively referred to schists, strongly metamorphosed, appearing as now exposed through the agency of erosion by nent. This porphyritic granite is not known the Juratrias, the reason being the often striking gneissoid rocks close to the contact. On the road the removal of the covering rock masses. The elsewhere in the Truckee or Pyramid Peak resemblance of the rock to the Sailor Canyon from Meadow Lake to Webber Lake, near the prevailing rock is granodiorite, intermediate in quadrangles, but is found in large masses in the beds and the fact that in contrast to the Carbon diabase, there appear greenish or reddish peculiar composition between diorite and granite, but in southeast corner of the Markleeville quadrangle iferous series (Calaveras formation) the compres rocks, strongly metamorphosed, and now. largely it are contained irregular masses of more basic and along the crest of the Sierra to the south of sion which the rocks have undergone is often made up of pyroxene. They are supposed to be rock diorite or more acid rock granite. that area. The granite in Truckee Canyon is relatively slight. On this account the dip and metamorphic forms of limestone, though the dis These areas have not been separated from the soft, decomposed, and crumbling, with yellowish strike of the stratification are easier,to determine, tance from the granite contact in this case can not prevailing granodiorite in mapping the rocks, but outcrops. It is also very much crushed and and the dips may in general be said to be less be less than 2 miles. their occurrence is indicated briefly in another fractured, as may be seen a mile north of the steep than those usually found in the sedimentary To the west of Mount Lola the sedimentary paragraph. The normal granodiorite is a light- bridge, where it contains dikes of andesite. The rocks lower down on the western slope of the rocks reach an elevation of 8300 feet. The east gray rock, weathering into rounded outcrops and rock of Granite Peak and its slopes also crumbles range. Still they are, as there, prevailingly to ern part consists of gray quartzites and black easily disintegrated by erosion. The form of the to a -coarse sand, but contains a great quantity of the east. It is difficult without more detailed clay slates, while on the west, near the diabase outcrops and their brilliant light color are espe hard, white residuary bowlders. work to obtain satisfactory results in regard to contact, greenish, banded rocks appear, which cially marked in the glaciated region. The gran Gabbro. Rocks of a gabbroitic character do the stratigraphic structure. The beds have prob probably are diabase tuffs. odiorite is a medium- to coarse-grained rock, the not occur abundantly, and are in fact found in ably been closely folded, and the folds in part Diabase-porphyrite. Diabase-porphyrite is an average diameter of the grains being 2 to 3 milli only two localities. They are dark-green, very overturned, as schematically shown on the struc igneous rock consisting largely of augite and a meters. The grayish quartz and white feldspar coarse rocks, composed of gray feldspar and dark- ture-section sheet. To complete the description basic soda-lime feldspar, combining por- grains are of about equal size. Black mica and green pyroxene, often altered to uralite. A small a brief review of the characteristics of the phyritic structure with comparatively ofcfgneoCse hornblende are usually present in about equal area of gabbro occurs about a mile west of r J . r J rocks older separate areas may be given. coarse gram. In this quadrangle con- quantities. The foils of the former reach 2 to 3 Anderson Peak, in the glacial amphitheater, where The two long-drawn masses at the southern siderable masses of this rock occur, millimeters in diameter, while the hornblende is it adjoins metamorphic schists. Another and boundary, in the vicinity of McKinstry Peak, are usually in close connection with the Juratrias roughly prismatic, the crystals sometimes reaching larger area, about 3 miles in diameter, and con in larger part extremely metamorphosed and beds. In most cases these masses should be 1 centimeter in length. Titanite is nearly always nected with the granodiorite by gradual tran converted to a dark-brown micaceous rock of regarded as effusive rocks old lava flows present, in isolated, small, brownish grains. Mag sitions, occurs in Rubicon Canyon west of finer or coarser grain. Somewhat less altered poured out from volcanoes existing during the netite is another universal accessory constituent. McKinstry Peak. On the east it adjoins the rocks light-colored quartzites and black clay Juratrias period. This view is strengthened by The appearance and composition of the rock are metamorphosed sediments. This rock also con slates are found about a mile west of Went- the fact that tuff or stratified fragmentary igneous very constant over large areas, with only small tains some biotite and appears to be an interme worth Springs. The structure in these small rocks occasionally connect the normal diabase- variations in the quantity of hornblende and diate type between diorite and gabbro. areas is.very confused and can rarely be satis porphyrite with the purely sedimentary series. biotite. SEQUENCE OF ROCKS AND STRUCTURAL FEATURES. factorily made out. Some of the diabase-porphyrite may, however, The small area west of Webber Lake is a North of these masses appears a large mass of represent intrusions, solidified at comparatively normal granodiorite. Along the contact from the The oldest rocks in the Truckee quadrangle sedimentary rock, with extremely irregular out slight depth. The contacts of diabase-porphyrite eastern end of Fordyce Lake up to Enumeration are in all probability Carboniferous, and consist of line, partly buried under andesite flows (Na). It with the granitic rocks show that the latter are White Rock Lake there is a small JtgES1*,, the cherts, quartzites, and slates of the is surrounded by granite, except on the western the younger. development of granitite. The rock descnptlon- Calaveras formation. This sedimentary T -.-,-, -, rock masses side, where a belt of diabase-porphyrite separates For those interested in the petrographic details is indicated by a slightly yellowish color of the series was apparently tolded and com- it from the Sailor Canyon formation. Except the following brief notes on the separate areas outcrops, and contains large, prominent grains of pressed before the Juratrias period. near the contacts the metamorphism is not are given: orthoclase and biotite, but no hornblende is The compression was so intense that a series of extreme, and the true stratification can in many The areas south and west of Webber Lake con present. Due south of Webber Lake there isoclinal folds has been formed, generally slightly places be ascertained without difficulty. sist of a dark-green rock filled with epidote and occurs, inclosed by diabase, a small area of granite- overturned toward the west. At the time of the Along the North Fork of American River other secondary minerals. On the east, near the porphyry, a white porphyritic rock containing compression a cleavage was superimposed upon this series, ordinarily, though not always, coincid near the eastern boundary line, 3 miles north of which the rhyolite lavas were much eroded, the along the railroad in Truckee Canyon, 1^ miles ing approximately with the bedding. Bronco. volcanoes along the Sierra Nevada poured out from the point where the line reaches the eastern Next in age follows the Juratrias of the Sailor The rhyolite of the Truckee quadrangle is a masses of a basic lava known as andesite. The boundary oj the quadrangle. Canyon formation. The isolated areas in granite white, gray, or pink, fine-grained rock, somewhat extensive andesite areas in the Truckee Another series of volcanoes extended along the were probably also deposited during this period. porous and easily dressed with the hammer. It quadrangle are composed partly of Generalcharacter eastern or Genoa Range, which between Truckee IP , iiiT- i and so«rce Although greatly disturbed, these strata show carries small sanidine and quartz crystals in a rock fragmentso em beaded in volcanic lavas. and Reno is almost flooded by volcanic masses. evidence of much less compression than do those fine-grained, often streaky and glassy groundmass. mud, forming tuff breccia, partly of Other independent points of eruption were evi of the Calaveras formation. The cleavage is less Very rarely a little brown mica appears. In some massive andesite. The former predominates along dently located near Mount Pluto and probably pronounced, and the dips of the strata are, as a places, as north of Soda Springs, and also toward the summit and on the western slope of the main also at other places north of Truckee. The ash rule, at smaller angles than in the slate areas the headwaters of Long Canyon, the rhyolite is range, while the massive andesites are found cones and the craters have been swept away by farther west. The detailed structure has not tuffaceous, like clay or fine white sandstone- in chiefly in the Truckee basin and on the eastern erosion. All that is now visible is the interior been made out, but it is believed that the dia appearance. Bodies of gravel, so commonly found range. A separation of the two kinds does not structure masses and necks of solid andesite grams on the structure-section sheet illustrate the in the rhyolite farther down the slope, do not appear practicable. irregularly traversing breccias and tuff breccias true conditions i. e., that the series forms folds occur here. The rhyolite has a decided tendency The andesite is a rough and porous rock of dark- of varied appearance. less closely compressed than those of the Calaveras to form bluffs and terraces, often with nearly per gray to dark-brown color. Porphyritic crystals of The evidence shows beyond doubt that the formation and somewhat overturned toward the pendicular escarpments, as, for instance, near plagioclase are invariably present, as are also stratified tuff breccias which once covered the west. From this general relation of the two for Summit station and on both sides of French crystals of augite and hypersthene ; hornblende is whole western slope nearly continuously were mations it is believed that an unconformity exists Meadows. A coarse columnar structure may less abundant, but appears in many rocks as small, largely poured out as successive mud flows, though between them, though of this there is no direct occasionally be observed. The thickness of the black, glistening needles. The groundmass in it may be conceded that volcanic ash showers may proof. flows, which, as stated above, are confined to the which these crystals are embedded has a structure have added to their volume, especially near the The deposition and folding of the Juratrias river valleys of the Neocene period, does not varying from glassy to very fine-grained crystal summit. The equal distribution of large andesite was followed by the great intrusion of the granitic exceed 1000 feet and is frequently much less. line. fragments in the tuff breccia all over the slopes is rocks, all probably of late Juratrias or early The area near Webber Lake was overwhelmed Biotite-andesites are of rare occurrence, while one of the arguments tending to show the pre Cretaceous age. By this intrusion the sedimen by a great sheet of rhyolite, now largely covered olivine sometimes enters into the composition of dominance of actual flows of mud. It is difficult tary rocks were fractured along extremely irreg by andesite and moraines. The thick- Detalls Ol some pyroxene-andesites ; the latter may occasion to estimate the enormous explosive action which ular lines; parts of them were torn away, and now ness of this sheet does not exceed a thlurhyoimc ally merge into fine-grained varieties allied to must have been necessary for the production of lie in the granitic mass as detached fragments. few hundred feet. Outcrops of rhyo basalts. The hornblende-andesites are mostly of all these fragmentary rocks. Nor is it easy to An intense contact metamorphism affected both lite are found all along the contact with the lower a somewhat lighter color than the pure pyroxene- understand whence the volume of water necessary the Calaveras and the Sailor Canyon formations. andesite flows to the southeast and west of andesites ; a light-gray is frequently noted. to form the mud flow could have been derived. The pressure of the intruding granodiorite did Webber Lake. Especially fine are the outcrops The tuff breccias consist of angular fragments The andesitic masses about Webber Lake con not produce extensive schistosity in the adjoining in the canyon a mile below the outlet of the lake, of andesite bound in a cement of finer andesitic sist of tuff breccia, though in a few places smaller older rocks parallel to the contact. Locally it where the columnar structure of the rock is detritus. Exceedingly little non-andesitic material masses and flows of massive pyroxene- Detailed may have had such an effect, as seen, for instance, prominent. Two miles east of Webber Lake the is present ; scattered granite bowlders may occur. andesite appear. The volcanic masses descHption. in the rough schistosity of the diabase-porphyrite rhyolite begins to dip eastward, and disappears Very rarely, as, for instance, on the ridge 2^ miles near Mount Lola show excellently and typically along the contact southwest of Devil Peak and below the later accumulations in Little Truckee east of Devil Peak, there are small quantities of the structure of the volcanoes along the crest of from the eastern end of Fordyce Lake eastward. Valley. This rhyolite probably connects under metamorphic, well-washed gravel intercalated in the Sierra. Tuff breccias, varying in appearance It can not be said that the succession of the dif the andesite with the flow which filled the deep the tuffs. and stratified or massive in structure, are irregu ferent granitic rocks has been definitely ascer valley extending from a mile north of Fordyce The irregular fragments of andesite contained larly mixed with necks of massive pyroxene or tained, but, judging from the disposition of the Lake in a northwesterly direction to Musgrove in the tuff breccia are of all sizes, from a diameter hornblende-andesite. true granites along the sedimentary rocks, it seems Valley and English Lake, the latter located in of several feet down to grains of minute dimen A short distance below the summit, on the probable that the granites preceded the grano the adjoining Colfax quadrangle. A small knob sions. Within a small mass of breccia a great southern side, is a neck of gray hornblende-andes diorite. The granitic rocks are not affected by of a rock allied to rhyolite, probably marking a many varieties of andesite may be found, differ ite showing exceptionally beautiful columnar schistosity. former volcanic vent, is found surrounded by ing slightly in color, structure, and composition. structure. On the southern side of Mount Lola The Bed-rock series is more or less affected by andesite on the summit of the ridge one-half mile The exposures of tuff breccias often reveal a three massive flows slope gently eastward from jointing, but in this quadrangle the jointing is southeast of White Rock Lake. beautiful stratified structure, resulting from the the divide, while toward the west only tuff breccia nowhere so regular and intense as in the southern The heaviest rhyolite flow in this part of the superimposing of numerous flows slightly different appears. The larger part of the ridges to the half of the Pyramid Peak quadrangle. The joints Sierra Nevada extends from near Castle Peak in structure and appearance. Some of the areas, northeast of Mount Lola consists of massive in the granodiorite are most prominent, and the down to Michigan Bluffs and Forest Hill, in the especially near the summits, show a more massive pyroxene-andesite. The long ridges between following directions have been noted: Two miles adjoining Colfax quadrangle. The old valley, structure, and, becoming harder and more compact, Independence and Donner lakes consist of breccia, south of Webber Lake, N. 70° E., dip 70° S; which is filled with the lava, began near Castle merge imperceptibly into necks and smaller bodies with a great number of massive necks. A colum railroad bend 1 mile west of Cascade station, Peak, extended thence to Summit Valley and of andesite. The latter commonly protrude nar, gray hornblende-andesite crops on the south N. 40° E., dip 70° E.; eastern side of Castle across to Soda Springs, thence to French Meadows, sharply from the surrounding breccias. The ern shore of Donner Lake. Castle Peak and the Peak, N. 42° W., dip 60° E. under the western ridge, and to the headwaters of andesitic ridges are dark gray or reddish gray, volcanic areas about the head of Rattlesnake Long Canyon. The exact point where the flow contrasting strongly with the light-gray granite Creek, north of Yuba River, consist chiefly of SUPERJAGENT SERIES. originated is probably south of Castle Peak, where on the dark-red slate; long gentle slopes covered tuffaceous breccia, but in some places a massive Under this heading are described the Neocene the rock is now traced to its highest occurrence. by scattered vegetation alternate with precipitous black andesite, sometimes carrying olivine and and Pleistocene sedimentary rocks and the lava It undoubtedly crosses the creek 1^ miles north walls strongly resembling fortifications. Excel closely related to basalt, appears below it. This flows, as well as the superficial accumulations due east of Soda Springs station, although covered by lent instances of this are found in Castle Peak, as basaltic andesite crops out at the head of Rattle to the glaciation of the range. debris, but can not there be much more than 100 seen from the Central Pacific Railroad, as well as snake Creek at an elevation of 7000 feet, and feet thick. It widens rapidly at Donner, or Sum in the vicinity of Mount Mildred and the high appears again with columnar structure north of NEOCENE PERIOD. mit station, and increases in thickness to 400 feet ridges near Twin Peaks. The andesitic rocks the Cascade Lakes on the projecting bluff known Awiferous gravels. The gravels, which were or more; it extends below Summit Valley, and is almost universally cap the ridges, and rest either as the Porcupine. What is probably the same deposited in the depressions or river channels of exposed along the creek in several places; it filled on the Bed-rock series or on the rhyolite. It is massive flow appears on the hill a mile east of the western slope of the Sierra Nevada Qold,bearlng the Neocene Soda Springs Valley to a depth of evident that t|je andesitic masses once covered Soda Springs station, where it rests on a thin before it was covered by andesitic lava j fi'^ 1000 feet. This valley was evidently guarded by nearly continuously the whole summit region, mass of breccia and is covered by a flow of black flows, are in this quadrangle only spar a narrow outlet, for south of the North Fork of possibly excepting the tops of Snow Mountain basalt, probably of Pleistocene age. It occurs also ingly present, and do not form masses which can American River the flow decreases rapidly in and Granite Peak and a small area adjoining the at the bottom of the Neocene depression crossing be separately indicated on the map. The heaviest thickness to 500 feet. A nearly level sheet, now southern boundary, in which McKinstry Peak Five Lakes Creek. On both sides of Mount gravels probably occur below the rhyolitic flows beautifully exposed and free from moraine, covered and Guide Peak form the culminating points. Lincoln the stratified tuffaceous breccias are in the vicinity of French Meadows. Their exist the Cascade basin. Near Cascade it is only 300 Subsequent erosion has removed at least two- excellently exposed, and are in full view from the ence has been shown by prospecting shafts, feet thick, but the thickness increases rapidly thirds of these masses along the main range, line of the Central Pacific Railroad. The long though they do not crop on the surface. Their southeastward. On both sides this wide, trough- while in the Truckee basin, where erosion has ridges between the North Fork and the Middle thickness is not definitely known, but may exceed like valley was bordered by ridges 2000 feet been less active, the underlying rocks are not yet Fork of the American, and between the Middle 50 feet. high on the west by the porphyrite mass of exposed. The thickness of the andesitic flow is Fork and Rubicon River, consist almost entirely Rhyolite. The period of volcanic activity Snow Mountain, on the east by the granite of considerable, in places reaching 2000 feet. The of normal breccia. Only near the eastern end at began toward the end of the Neocene with exten the main divide between Lincoln and Anderson depth of the lavas in the Truckee basin is prob the Needle and about Mount Mildred do massive sive eruptions of rhyolite, a siliceous peaks. ably not less than 1000 feet and may in places necks and flows appear. The Needle is a promi lava, which flowed down the valleys character The great rhyolite flow of Summit Valley con exceed 3000 feet. nent and extremely steep neck of olivine-augite- 1 -ITT and source of the Neocene range but did not Jj^jj^ tinues down in a south-southwesterly direction, The volcanoes which ejected these enormous andesite. cover the whole slope. As Tertiary and is exposed along the edges of the breccia volcanic masses during the later part of the Neo The great volcanic center of Mount Mildred gravels are generally absent in this quadrangle, ridges between the North and the Middle forks cene period were to large extent located along contains, besides much tuff breccia, some promi the rhyolite rests on the Bed-rock series, and is to of American River. The rhyolite bluff, which is the crest line of the western range, while few nent massive flows, magnificently exposed in the great extent covered up by the succeeding erup about 500 feet high, skirts the Middle Fork, and of them, if any, were found lower down on the glacial amphitheaters. A flow of gray pyroxene- tions of andesite. Erosion in post-Neocene time at Chalk Bluffs and French Meadows comes down western slope. The principal foci of eruption andesite forms the long ridge extending south of has cut through the covering masses of andesite to the river level. It is also finely exposed on were Mount Lola, Castle Peak, Mount Mount Mildred. Squaw Peak, with its many Volcanoes Duncan Creek and around the headwaters of Lincoln, Tinker Knob, Squaw Peak, which emit- surrounding well-exposed necks, evidently forms and exposed the edges of rhyolite sheets at the ' . T^ i -i ted andesite. base of andesitic ridges. Somewhat extensive Sailor Canyon. At French Meadows it crosses Mount Mildred, Twin Peaks, and the core of one of the Neocene volcanoes. It is areas of rhyolite occur on the western slope of the Middle Fork, and its steep bluffs surround the Mount Ellis. From each of these foci the lavas composed largely of a gray, massive augite-andes- the main range and indicate quite accurately the headwaters of Long Canyon. were extruded through a great number of vents. ite, but breccia appears on its northwestern side. principal Neocene valleys. A small rhyolite area is noted at the head of It is not often that these vents are satisfactorily The volcanic area between the main divide south The volcanic vents from which the lava streams Cold Canyon, indicating an overflow from the exposed. One excellent example is, however, of Mount Lincoln and Truckee River is made of rhyolite flowed can not always be located with Soda Springs rhyolite basin across the old divide. shown half a mile west of Scotts Springs, the two up very largely of massive andesite or of mixed accuracy, as the masses were much eroded before The only area farther south along the main range small rounded areas marking two separate vents. masses of breccia and massive andesite. A prom they were buried beneath the succeeding ande is the steep butte 3 miles north of Rubicon Most of the vents were probably of the character inent flow of columnar augite-andesite, ordinarily sitic eruptions. It is certain, however, that they Springs. It has all the character of a volcanic shown at the locality mentioned that is, small normal but sometimes appearing with almost are scattered along the main summit of the range, neck, but no flows have been noted in connection rounded or oblong orifices around which the basaltic habit, occupies the summit at the head of from which the flows extended westward. with it. Small outcrops of a thin flow of rhyo granitic rocks were greatly shattered. Long dikes Deep Creek and Pole Creek and continues east Below the great andesite areas of the Truckee lite are found on the northwestern side of Grey- are conspicuously absent. Small and irregular ward as a gently sloping flow. basin rhyolite may exist, but it is completely cov horse Valley and where the deep Neocene channel dikes of andesite occur in the granite in several The extensive volcanic complex near Ward ered by these later flows. A small knob of rhyo crosses Five Lakes Creek. places on the eastern slope of Squaw Peak. Simi Peak and Mount Ellis is made up chiefly of lite, probably marking a volcanic vent, occurs Andesite. After a considerable interval, during lar dikes, 1 to 2 feet wide, were noted in granite breccia, but along the summit a great number Truckee 3. of massive necks forming high projecting points contains, besides the clayey and sandy beds, they cover a deep Neocene Valley which extended eruption must have been near the highest point appear. Its western end is occupied by a very several layers of coarser tuff. In Little Truckee continuously from Lake Tahoe up to Sierra Valley. of the peak. The topography of the surrounding prominent massive flow of augite-andesite, form Valley, a mile above Dry Creek, the lake beds The high and narrow Carson Range rises east country has evidently not been greatly modified ing a level table. Barker Peak is a neck of fine crop out extensively; they all dip south or south of Lake Tahoe and continues northward, forming since the eruption, though the gulches have been grained hornblende-andesite. west 8 to 10 degrees, and are here almost exclu the eastern barrier of Truckee Valley. This range cut considerably deeper. The ridges encircling the northern end of Lake sively andesitic tuff, but so distinctly stratified also existed in Neocene times, though the part of The largest basalt flows are met with in Tahoe are composed partly of massive rock, partly that they must have been deposited in water; it which falls within this quadrangle has been Truckee Valley and along the north shore of Lake of breccia. Mount Pluto and the ridges which they are very different from the coarse tuffaceous greatly increased in width and height by masses Tahoe. The area adjoining Tahoe city originated radiate from it are made up of gray pyroxene- breccia of the higher ridges, and do not contain of lava poured out over its flanks. The old from a vent located high up on the andesitic ridge andesite. A sheet of coarse biotite-andesite crops large bowlders of andesite. granitic core may be seen near Crystal Peak and overlooking Truckee River. The surface of the out on the northwestern side of Mount Pluto at One and a half miles and 2 miles northeast of has been exposed in Truckee Canyon by ero flow is extremely rough and rocky, and the basalt an elevation of 6800 feet. The same volcanic Boca, at an elevation of 5800 feet, the lake sion of the volcanic flows. The contact lines of has a very vesicular character. As indicated by flow crops out opposite the mouth of Pole Creek, beds mostly white clays crop out again below granite and lava show that a low gap with a several flat tables and abrupt slopes there were and a similar biotite-andesite occurs at the foot the basalt, thus proving that the basaltic flow is present elevation of 6500 feet existed in this range probably several successive flows. Near the lake of the high basalt bluff a quarter of a mile west of later. One mile southeast of Boca, on the Juniper to the southeast of Crystal Peak. Again a part yellowish-gray basaltic tuffs are common. The Tahoe city. At the gap where the road from Mill road, where it climbs up on the basaltic pla of the granitic core is shown near Hot Springs on bluff at Tahoe city and eastward is made up Hot Springs to Truckee crosses the divide, ande- teau, andesitic tuffaceous beds are found, dipping Lake Tahoe, the contact line against the lavas partly of basalt tuff, dipping 25° south, partly of sitic breccia prevails, but massive andesite appears slightly southwest and overlain by basaltic tuff rising rapidly eastward. sand and gravel. It is evident that this flow farther east along the high peaks and ridges near and massive basalt. The elevation here is about Fault lines. No evidence of important faulting filled Truckee Canyon, previously cut in andesite, the Nevada State line. The slope toward Hot 5800 feet. Along the railroad one-third mile east is found on the western slope of the Sierra Nevada and dammed the lake to a height of at least 700 Springs is largely built up of breccia. Most of of Boca there are some tuffaceous lake beds again, in this quadrangle. The eastern scarp, on the feet above the present level. Two minor flows the andesitic area along the eastern edge of the resting on andesite and covered by a basaltic sheet. other hand, is the result of an important fault occur along the shore between Tahoe city and sheet is normal tuff breccia, and only the higher Lake beds also crop in Stampede Valley, which along a line following its base; but no important Hot Springs. The rock in these contains but peaks and ridges consist of more resistant massive probably formed a small detached basin. dislocation has occurred along it since the lavas little olivine, and in places is a typical hypersthene- rock. The ridge east of Jumper Creek consists Lake beds, which are probably of Neocene age were poured out, and it probably antedates the basalt. partly of massive andesites. West of Juniper and are very similar to those of the Truckee Neocene period. Smaller remnants of basaltic flows occur in Creek and adjoining the basalt area is a red, basin, occur near Verdi, where Truckee River A similar fault line follows the western base of Ward and Blackwood creeks. The great basalt coarse, hornblende-biotite-andesite. The ridge debouches from its canyon into the flood plain at the Carson Range, although covering lavas mask flow around the town of Truckee is composed of between the Truckee and the Little Truckee is the foot of the eastern range. Small outcrops of its presence to great extent in this black, dense olivine-basalt, and had probably composed of yellowish-gray breccia, necks of mas them are found, covered by fluviatile material, Quadrangle. It is possible that in oiThe s?eersra several vents of eruption on a line from north to . . Nevada. sive andesite frequently appearing along the in the extreme northeastern corner of the quad recent times slight movement may south. It is clear that here again the previously summit. rangle. The beds consist of whitish or yellowish have occurred along this fault, as indicated in the excavated Truckee Canyon was dammed to a con In several places the andesite has been sub clays and lie nearly horizontal. description of the Pleistocene period. siderable height during the eruption, probably, jected to thermal alteration, due to the action The topography in the Neocene period. The A third fault line follows the eastern base of however, not to exceed 300 feet. This fiow filled of hot mineral waters on the rock. It voluminous lava flows of the Neocene period filled the Carson Range and enters this quadrangle only a large part of Truckee Valley and extended is manifested in bleaching of the rock, Thermalact1o on the older valleys and buried many heights. Since in the extreme northeastern corner. Along this eastward. Basaltic tuff overlain by massive basalt accumulation of secondary silica, and that time deep canyons have been cut, exposing line there have been several recurring movements. is exposed along the railroad 1 mile east of impregnations of iron pyrite which carries a little the relations of the lavas to the older rocks. These The first movement antedates the Neocene; the Truckee. gold and silver. Thermal zones of this kind relations have not been disturbed by second dates from the Neocene volcanic epoch; Equally extensive flows are those north and occur along Truckee Kiver opposite the mouth faulting in Neocene or post-Neocene the Neocene the third and smallest dislocation has occurred south of Boca. The northern part of the flow of Squaw Creek, and 2 miles northwest of the time, and the surface on which the during recent times. But these movements have appears to have originated 2 miles northwest of divide, on the road between Hot Springs and lavas accumulated therefore remains unmodified not taken place equally along the line, and in this Bronco. Still another focus was located on Truckee. A similar altered area was noted in except where streams flowing in the later canyons quadrangle no strong evidence appears of exten Juniper Creek, and from this the whole eastern Truckee Canyon 3 miles south-southeast of Crys have removed some parts of it. The numerous sive post-volcanic faulting along the eastern base side of Martis Valley was flooded. The rock in tal Peak and just south of the railroad bridge. contacts of the lavas with the older rocks define of the Carson Range. this flow is of a glassy character, containing but An area of thermal alteration half a mile wide the old topography. By supposing the lavas little olivine, instead of which hypersthene often PLEISTOCENE PERIOD. and 2 miles long here extends across the can removed and the later canyons filled up, we may appears. These flows dammed Truckee River yon, affecting not only the andesite on both sides, restore the ancient hills and valleys. This applies The Pleistocene period, which is elsewhere in a third place to an elevation of probably 6200 but also the small granite area surrounded by chiefly to the western part of the quadrangle, for defined by that change of climate which caused feet above the sea. Masses of yellowish-gray andesite marked on the map. The altered zone in the Truckee basin the Neocene eruptives com the development of widespread ice Definition basaltic tuff in places, as for instance 1 mile south contains, besides some bleached and pyritic rocks, pletely conceal the old surface. sheets, is here assumed to have begun and extent- west of Boca, accompany the massive rocks. An massive hornblende and hornblende-biotite-ande- The Neocene surface was one of mountainous soon after the andesite eruptions ceased. It extensive eruption of normal olivine-basalt sites, which have a more or less pronounced green character. On the whole it sloped gradually might be called the post-andesite period. It com occurred at the same time near the summit of the ish color and decomposed aspect, recalling the westward from a summit line which practically prises two epochs, an earlier one, during which range to the east of Truckee Canyon, in the appearance of older porpyhritic rocks. This is coincided with the present water-parting, and most of the principal canyons that now score the adjoining Carson quadrangle. Branches of this undoubtedly the result of thermal alteration. more steeply to the east of this divide down to a surface were eroded and active volcanoes produced flow found their way down the ravines into Olivine-dolerite. Intimately connected with level of about 6000 feet. Thence eastward the numerous flows of basalt, and a later one, char Truckee Canyon as veritable cascades of molten the andesitic eruptions is a flow of a coarse rock old slope is covered by andesite. The old divide acterized by the growth and disappearance of rock. These can be excellently seen from a high which presents certain similarities in the field to has at present elevations of from 7000 to 8000 glaciers on the range. point opposite, such as Crystal Peak, the basalt an augite-andesite, but which upon closer exami feet. The Neocene surface to the west of the The earlier epoch. In consequence of the ande contrasting with its brownish color against the nation proves to be an extremely coarse form of divide appears to have been an irregular table site lava flows which had filled the former valleys, dark-gray andesite. basaltic rock. This has provisionally been desig land, with few sharp peaks rising above it. In the streams sought new channels with the begin The later or Glacial epoch. The later epoch of nated olivine-dolerite. Similar rocks have been this table-land the water courses had cut valleys ning of Pleistocene time. They rapidly eroded the Pleistocene period was characterized by exten found in the northern part of the Downieville which were broad and deep, thoug^ not so sharply canyons in the steep slopes and estab- Theepochof sive glaciation, during which fully one- Extent and quadrangle. The olivine-dolerite occupies an area defined as the canyons of the present time. It is lished the principal features of the erosion- half of the quadrangle was continually results o"' bordered on the north by a line drawn somewhat not an extremely steep slope, and it bears some present river systems. The gravel, sand, and mud covered by ice and snow. Finally the g ac'a I0°' north of the Little Truckee, on the south by Sage evidence of having been modified by erosion to a which they swept downward form deposits in the glaciers receded, giving to the region its present Hen Creek, and on the west by Independence considerable extent before the andesitic eruptions. Great Valley of California. While the canyons aspect. Even the smallest remnants of actual Creek. It forms steep bluffs along the creeks A strongly marked depression began in the were being thus carved additional eruptions glaciers have now disappeared. Small patches of and appears as a rough, brownish rock with very vicinity of Fordyce dam and extended in a north occurred from volcanoes along the Sierra. The snow remain during the summer at elevations small feldspar crystals and larger augite crystals westerly direction. This was the head- The Neocene lava differed mineralogically, however, from the above 8000 feet. of greenish color. A similar dolerite occurs on waters of the Neocene Middle Fork of valleys- andesite lavas, and is of the black fine-grained The glaciated region includes practically the the isolated hill a mile west of Boca. the Yuba. Another deep valley began a short kind called basalt. The following is an account whole area west of a line drawn along the shore Neocene lake beds. At the close of the epoch distance south of Castle Peak and continued by of its occurrence. of Lake Tahoe to Tahoe city, thence along the of volcanic activity which produced the andesites, Summit Valley and Onion Creek across to the Along the main range, and also in Truckee river to Truckee, thence to a point at longitude Truckee Valley was occupied by a present ridge between the North and Middle forks Valley, are many large areas of basalt, the flows 120° 18' along the northern boundary. Nearly lake, into which sand and clay were feds^lpos^ of the American, and thence down by French in places reaching a thickness of 600 feet. Their the whole of this area was once covered by vast ,. . . , .-,-. T , ited in lakes. washed from adjoining mils. In the Meadows toward the head of Long Canyon. This distribution indicates that they spread Basaltic neve fields, above which only the highest volcanic vicinity of Truckee these deposits are mostly cov extremely definite canyon .was the headwaters from many independent vents. The eruPtions- peaks protruded and beyond the edges of which ered by subsequent (Pleistocene) lake beds and of the Neocene North Fork of American Eiver. topography shows that considerable erosion has glacier tongues projected in every valley. The basaltic lavas, and only at Prosser House, near In a section from Snow Mountain to Granite Chief taken place since their eruption. The basalt is eastern part of the quadrangle evidently received the road, may some of the sands and clays be seen the bed rock may be seen to rise within short dis distinctly later than the andesite; on the other a less amount of precipitation. Though it con under the covering wash. In Little Truckee tances 2000 feet westward and 3000 feet eastward hand, abundant morainal material frequently cov tained many neve fields, few if any real glaciers Valley the lake beds are much better preserved. above the old channel. A short tributary to this ers the basalt, which was therefore erupted before seem to have existed in this area. Two miles north of Boca they outcrop in a low Neocene stream came from the vicinity of Sailor the close of the Glacial epoch. Basaltic rocks By the continuous and slow downward move bluff on the east side of the river and consist of Canyon, flowing in an easterly direction, between rest on andesite in many small and scattered areas ment of the ice to the melting-line, enormous yellowish sands and clays, the latter predominat the high hills of Duncan Peak and Snow Moun along the main range. Several such areas occur masses of loose debris were swept down ing, covered by a brilliantly white substance, tain. Another important tributary headed near in the vicinity of Mount Lola, forming black out from the summits and accumulated as which is probably a volcanic ash and which con Barker Pass and crossed Five Lakes Creek. Its crops of normal olivine-basalt, often with pro morainal heaps and ridges, chiefly along the edge tains diatoms. Some of the lower clayey strata abrupt character is apparent. From Five Lakes nounced columnar structure. Another basaltic of the ice sheet. While smaller debris heaps may are dark and contain small seams of very impure Creek this channel was evidently followed by area caps the andesite 1 mile north of Summit be found at higher elevations, the great moraines lignite. The strata dip southward at an angle of the volcanic flow down toward Greyhorse Valley Valley, and isolated outcrops of the same flow are lie at elevations ranging from 5000 to 7000 feet. 8 degrees. Unconformably above these strata lie to the head of Long Canyon. The flat summit of found on the andesite ridge 1^- miles south-south Above this extend vast stretches of bare rock sur Pleistocene gravels, which are probably fluviatile, McKinstry Peak formed a prominent feature in west of Castle Peak. A prominent basalt neck faces, dazzling white smooth outcrops of grano- spread by the present river. the Neocene landscape. protruding through andesitic breccia forms the diorite, and reddish-brown slate areas. The The region about Dry Creek and the Little The escarpment of the main range eastward is precipitous cliffs of Devil Peak. Small areas of glaciated ridges of andesite or andesitic breccia Truckee is occupied by these lake beds, covered well marked from Independence Lake southward, basalt were noted south of Soda Springs and in are in part bare, with sombre slopes which exhibit by thin Pleistocene gravel wash; the low plateau and the conclusion can not be avoided that it the valley of the Middle Fork of American the flow structure; much of them is, however, is dissected by sharply cut gulches. Wherever the existed before the Neocene eruptions. Nothing River. Remnants of a basaltic sheet, often with covered by scattered vegetation. The rock sur lake beds crop out they are usually distinguished definite is known of the configuration of the older columnar structure, dot the southern slope of face is frequently smoothed and scratched and by a brilliant white or yellowish color. The out rocks below the lavas of the Truckee basin. McKinstry Peak. The occurrences are grouped striated by rocks held firmly by the moving ice crop where the road to Verdi crosses Dry Creek Good reasons exist, however, for believing that in such a manner as to show that the center of sheet. The terminal moraines on the eastern slope valleys, leaving moraine-dammed lakes at their lateral moraine between McKinney and General a series of Pleistocene lakes. No considerable cease at elevations of 5900 to 6500 feet. On the lower ends. creeks is very typical, extending down as a long amount of moraine lies at the mouths of the western slope they extend farther down, though Below French Meadows the river makes a sloping ridge with straight back. At McKinney tributary creeks, whose ravines are sharply cut it is often difficult to determine with accuracy sudden bend to the southwest, and the character the moraine is modified by the 40-foot terrace; canyons in their lower courses but widen to how far down into the rocky canyons the ice of the valley suddenly changes from a broad that is, the 40-foot stand of the lake was contem amphitheaters with small meadows in their upper tongues protruded; probably, however, they did U-shape to a sharply incised canyon with steep poraneous with or later than the moraine. courses. From the flat where' the Greyhorse not descend below an elevation of 4000 or 3500 grade. It might be assumed that the glacier There can be no doubt that the great Rubi trail branches, a dim trail leads down to Hell feet. ceased here but for the fact that abundant angular con glacier overflowed toward the lake through Hole. The joints of the granodiorite run down The areas designated as moraines on the map morainal material occurs high up on the divide Rubicon Pass, which is very low (7150 feet). slanting westward, and have given rise to a series include only the heavier deposits of the terminal, between Duncan Canyon and the Middle Fork, At the lakes on Rubicon Pass there is but little of shelves, along which the trail winds. These lateral, and ground moraines; scattered thin drift and on the divide between Chipmunk Creek and morainal matter, and the same is true of the hills shelves are covered by morainal debris and are is not indicated. The moraines are composed of the Middle Fork. Immediately below French surrounding the pass. But the granite basin of hardly visible from a distance, the canyon side rough and angular, not waterworn bowlders of Meadows the ice must have reached up to an Miller Creek, and in fact the whole lower country appearing inaccessible. At Hell Hole there is a all sizes, admixed with finer detritus and sand. elevation of 6000 feet; above this the andesite between Miller Creek and Barker Creek, is covered series of gravel flats covered with large oaks and The topographic form of the valleys changes as appears free from glacial drift. How far the with granitic moraine, so that it is often difficult firs. The valley of the Rubicon viewed from this soon as the lower limit of glaciation is reached. glacier tongue extended down the river can not to tell whether there is rock in place or not. locality is a most imposing sight. Below they are narrow and V-shaped; above, be decided. Even high up on the andesite point There is certainly much rock in place on the East of Truckee River there are only indis broader and U-shaped, often also characterized between Chipmunk Creek and Long Canyon, at broad ridge % between Cothrin Cove and Miller tinct traces of glaciers, which hardly seem to have by stretches occupied by meadows, separated by an elevation of 5700 feet, there are bowlders of Creek. Assuming a connected ice sheet between been more than extensive snow fields. In a few rocky portions with steep grade. The long lateral rhyolite and granite. McKinney Creek and the Rubicon, a great deal of the gulches leading down from Mount Pluto, moraines with their sloping straight ridge lines The head of Donner Creek is swept bare except of debris would naturally have been swept into some evidence of glacial action . is found, as, for are often conspicuous; the best defined of these for a small amount of glacial debris in a few the sag between Miller and Barker creeks. instance, in the upper part of Shaffers Mill Creek, are on the eastern slope near the mouth of gulches. The volcanic riclges on both sides of General Creek had a much smaller glacier, the heading on the northwest side. Meeks Creek, for instance. Little lakes and Donner Lake are also comparatively free from terminal moraine of which may be found about 3 Juniper Creek, heading among the high ridges meadows of glacial origin dot the landscape. moraine. A heavy terminal moraine accompanied miles above the place where Bellevue Hotel near the State line, was probably occupied by a Near the crest of the main range the canyons end by smaller lateral moraines lies between Truckee formerly stood. The ridge north of General smaller glacier, and accumulations which resemble in glacial cirques or amphitheaters, separated by and Donner Lake and has dammed the latter, Creek is, as mentioned before, entirely morainal small moraines were found at an elevation of 6500 sharp ridges (aretes) leading up to rocky peaks. although the basin was in the first place undoubt up to the higher points; the south ridge has feet. In the andesite the glacial sapping is especially edly produced by the basaltic eruption. granite in place nearly all along its slope; the No distinct evidence of glaciers was found in marked, and the cirques in the volcanic complex Along Cold Creek there is but little morainal glaciated granite of the upper part is clearly out the range east of Little Truckee Valley, ade of Twin Peak are perfect types of their kind. debris on the valley slopes. A rough bottom lined and contrasts with the non-glacial part below quate snow reservoirs having been lacking. A Though there are many evidences of oscillations moraine covers the valley and connects immedi the terminal moraine. The top of the same ridge small glacier may have existed in the amphithe of the lower limit of the ice sheet, due to slight ately with the Donner Creek moraine. It is has, however, been covered by a lateral moraine ater east of Lady Bug and Granite peaks, in climatic changes, and shown by parallel morainal somewhat doubtful whether the Cold Canyon of the Meeks Creek glacier, and presents a long, the northeast corner of the quadrangle. Great ridges, no satisfactory proof has been brought out glacier connected with the Donner glacier. The sloping, straight profile line. The bottom of the numbers of large angular bowlders are found in in favor of two distinct divisions of the Glacial point of the ridge between Truckee River and valley below the terminal moraine is a gently morainal heaps at its mouth, at an elevation of epoch, separated by a time interval during which Cold Creek is covered by glacial detritus up to sloping terrace about one-fourth mile wide and 5100 feet ; but their glacial origin is not estab the climate was milder. an elevation of 6300 feet. composed of gravel and sand; this continues lished beyond doubt. The glacier of Webber Lake basin flowed down Immediately at Truckee, lake beds and stream down to the lake, widening and forming a great Pleistocene lake beds and sti'eam terraces. along the Little Truckee to a point at longitude terraces join the moraines. The canyon of the ill-defined terrace about 100 feet above the lake. During the Neocene period and the earlier Pleis One-half mile south of Bellevue the heavy and tocene epoch, the waters of Lake Tahoe stood 120° IS':' below this there are stream Detailed_ . ., . Truckee River between Truckee and Lake Tahoe terraces, but no moraines. Extensive descriPtion- has evidently never been glaciated, though several exceedingly well-marked lateral moraines of much higher than now. The andesitic and moraines cover the ridge north of the Little glaciers from tributary creeks from the west Meeks Creek begin. The ridges southwest of basaltic lavas dammed the basin to a level of 700 Truckee, while the highest parts of the ridges nearly or quite reached the main river. At Pole Meeks Bay are morainal up to an elevation to 1000 feet above the present water stage, but extending north from. Mount Lola were above the Creek and at Deep Creek the glaciers hardly of 7000 feet, although in places the granite may no beaches corresponding to the higher stages level of the ice sheet. Large bowlders of rhyo- reached the river, or at least did not leave any not be far from the surface. Standing at now remain. The waters did not stand long at lite and granite may be found far down the river. large terminal moraines. Below Deep Creek Murphys and looking north, three well-defined the high levels, and the shore records . n . T -i ,. -r-v- Lake deposits lateral moraines may be noticed, one rising behind were wiped out by glaciation. JJis- and stream They probably were transported by floating ice. there is a meadow, and from there down to -, . , . -. gravels of Very heavy moraines dam the lower end of Truckee remains of a terrace occur at intervals. the other. The Meeks Creek glacier projected tinct beaches are found in this quad- Independence Lake. The moraine ends about 2^ About a mile from Truckee the glacial debris below the present lake level, and its terminal rangle up to an elevation of about 100 miles below the outlet, and from there down to from Cold Creek begins. The upper part of moraine is covered by the water. feet only. At Tahoe city the principal beach, the Little Truckee there are remains of stream Squaw Creek contains comparatively little An ice sheet, originating in the high range 50 feet above the lake level, is underlain by terraces only. Heavy moraines lie in the lower morainal material, but it is evident that a glacier north of Pyramid Peak, filled Rubicon Valley and basaltic tuff and is covered with fine gravel ; this parts of Twin Valley and Euers Valley, down to of considerable size once occupied the valley. polished and swept clean enormous areas between terrace is distinct as far as Observatory Point. 6100 feet above sea. Its terminal moraine, largely granitic, reached Rubicon Springs and McKinstry Peak. Just how The higher terraces are not plainly indicated. The glacier-worn basin of North Creek contains Truckee River and must have dammed it to a con far down the Rubicon glacier extended is a matter The point between Truckee River and the lake is but a relatively small amount of glacial debris. siderable height. The same end moraine also of some doubt, as no terminal moraines have been covered with fine gravel, as is also the shore up In the valley of the South Fork of the Yuba there dammed Squaw Creek, and the Squaw Valley left in the canyon. It certainly extended below to 100 feet above the lake along to Ward Creek. is considerable glacial debris on the south side of meadows were evidently a lake not long ago. an elevation of 4500 feet and it may have reached At State Line Point, however, there is no beach, Summit Valley and from Soda Springs station Below the terminal moraine there is a long terrace the southern boundary of the quadrangle. Grey- and between Hot Springs, and Observatory Point down as far as Cascade. There the moraines 20 to 30 feet above the river, extending almost to horse Valley was filled by a separate glacier, fed only a very low one, 15 to 20 feet above the water. cease abruptly, and down to below Cisco, in the Pole Creek. Bear Creek sent down a glacier as from the glacial cirque at its head and connected Scattered gravel occurs in places at elevations Colfax quadrangle, the canyon is scoured out far as Truckee River, but with comparatively with the Rubicon glacier. The high ridge at reaching 6700 feet. The first beach deposits clean. A great morainal mass has been pushed small moraines. the head of Long Canyon extending up to Mount along the road north-northwest of Hot Springs over the low gap at the Icehouse Lakes, south of The glacier of Ward Creek extended nearly Mildred rose along the glacier. On McKinstry are found at an elevation of 6400 feet, but no dis Soda Springs station, and looks very heavy from down to the lake. The south ridge is polished Peak the ice flow did not extend above an eleva tinct terraces are present. The small pebbles the road, where the rhyolite still may be seen off and almost free from morainal accumulations, tion of 7000 feet. Cottonwood Canyon, adjoin along the beach between Hot Springs and Observ in large outcrops, for about 1^ mile westward. which seem to have been unloaded on the north ing GreyLorse Valley on the west, is full of atory Point are largely made up of black, hard, West of this the great rhyolite sheet lies almost ridge. This is largely composed of breccia, which moraine, and much of it was also pushed over by banded slates ; there are also larger cobbles of the entirely denuded of glacial debris. was easily torn up by the ice. The whole slope, the main glacier into the South Fork of Long same kind on the beach up to 8 inches in diame While the upper part of the North Fork above about 1^ miles wide, is covered with glacial debris Canyon, through the low gap at Big Meadow. ter. The exact locality whence these pebbles are Soda Springs is comparatively free from glacial and shows its origin by numerous meadows, Seen from that gap, the canyon of the Rubicon derived is not certainly determined, but they debris, large masses of morainal material have marshes, and hummocks. appears glaciated and polished for a long distance probably come from one of the slate areas along been swept into Onion Creek and the tributaries The Blackwood Creek glacier undoubtedly above and below. High up on the rocky slopes, the western or southern shore, where such banded on the opposite side. Very fine glacial striae were reached down as far as the basalt knob near its at an elevation of 6000 feet, below Table Moun slates are found. They have possibly been trans noted at Soda Springs on the rocks above the mouth, but it has not left any very prominent tain, and at 5500 feet a mile northwest of the ported by floating ice. Along Agate Bay occur hotel. Again, below Onion Creek the rock is moraines. On the south side glacial debris is 7510-foot spur of McKinstry Peak, are seen small sand dunes 10 to 15 feet high, forming in places bare all the way down through the Royal Gorge, scattered up to an elevation of 200 or 300 feet. morainal ridges, appearing from a distance as continuous embankments. Between Blackwood but it is probable that the glacier filled the latter Among the debris very many granite bowlders perfectly straight lines, usually of white granite Creek and McKinney there is a fringe of terraces only partially; the sides are extremely rough and are noted. No large granite areas exist in the bowlders strongly marked against gray volcanic of fine gravel and above this is the talus from the do not show glacial striae. Tributary glaciers valley hence it would seem likely that the rocks or red slate. Below the 7510-foot point steep volcanic hills. There are here, as well as came down through lateral valleys. In Sailor granite bowlders were carried across the range by there are several other moraines at different ele at various places around the lake, at least two Canyon, however, the glacier does not appear to the ice. Toward the head of the valley, above vations. well-marked terraces, one about 40 feet and the have reached the river. The granite exposed at an elevation of 6500 feet, there is heavy bottom A branch of the Rubicon ice sheet overflowed other about 80 feet above the lake. On some Palisade Creek is thoroughly glaciated from moraine composed of slate ^ and volcanic rocks. the low divide west of Rubicon Springs and filled slopes, however, as near the mouth of Ward Devil Peak down to the river. It is doubtful A lake probably once covered the lower part of the basin of Loon Lake and Gerle Creek. As far Creek, there are well-washed pebbles occurring as how far down the North Fork the glacier pro the valley; hence the character of the broad slop down as Gerle the surface is scoured nearly clean, high up as 200 and even 300 feet above the lake. jected. A small tongue possibly reached below ing bottom, which is quite level, with meadows but between Gerle and Jacobsens, as well as These may, however, be due to the action of the mouth of Sailor Canyon. There is no termi alternating with sandy or gravelly stretches. The northwest of Gerle, the morainal material is glacial rivers rather than to wave action on the nal moraine. smaller gulches between Blackwood and McKin- thick, in places entirely covering the ridge. Scat beach. The principal beach line north of McKin The Middle Fork of American River is also ney, heading up near Mount Ellis, were possibly tered granitic bowlders and other glacial drift ney is the one about 40 feet above the water swept bare above the sharp bend south of occupied by small glaciers. are found on the andesite tables on both sides of level, which consists of glacial debris assorted Soda Springs, but below that, down to French The moraine which fills McKinney Creek and the Rubicon at the southern boundary of the by the waves of the lake. Nearly all along Meadows, enormous masses of glacial detritus the creeks south of it is composed almost entirely quadrangle, though the canyon between them Truckee River, from the lake to Truckee, there accumulated on both sides of the broad valley. of granite in very large bowlders, and forms broad does not show marked evidence of glaciation. are stream terraces at an elevation of from 20 to From an elevation of 5900 feet there is, for 3 ridges extending out into the lake. One-half Five Lakes Creek along its whole course as far 30 feet above the river. miles down, a very distinct terrace, through which mile north of McKinney the granitic moraine south as the crossing of the andesitic area is a In Truckee Valley the Pleistocene deposits the river has cut down 20 to 30 feet. The cut begins, and the contrast between it and the U-shaped valley, mostly with flat, moraine-covered are of a more complicated character. After the is with steep sides and is partly in moraine, partly terrace of fine pebbles is quite marked. From bottom. While the sides are largely rough, rocky close of the andesite eruptions followed a long in bed rock. The deposits of this terrace appear McKinney for about 3 miles up along the creek hills, the bottom is covered by moraine from one- period of erosion, during which Truckee Canyon to represent a later part of the Glacial period, the moraine covers everything, and no granite eighth to one-fourth mile wide, and level, sandy was cut out very nearly to its present depth. when the ice streams had retired to the upper outcrops are seen below about 7000 feet. The flats appear, suggesting the former existence of Then came the basalt eruption, covering large Truckee 5. parts of the valley and damming up the lake the Neocene period lies a gap in the geological ECONOMIC GEOLOGY. No quarries have been developed in the quad afresh to an elevation of 6000 feet. This Pleisto record, difficult to fill. A great mountain range AURIFEROUS GRAVELS. rangle. cene lake probably remained during a part of the was probably built up where the Sierra COAL. Neocene. Auriferous gravels of Neocene age Glacial period, gradually diminishing in size as Nevada now stands and planed down are exposed only to a very limited extent in the Although no workable coal beds occur in the Truckee River cut down the outlet. Its beach by erosion to moderate relief. Then fol Truckee quadrangle. Shallow gravel containing area, attention may be called to the fact that beds gravels are found all around the Truckee basin, lowed, previous to the Neocene period, the first coarse gold has been found in the deep depression of coaly shale, with thin strata of lignite, are generally at a constant maximum height. On the differentiation of the Sierra Nevada by breaks under the rhyolite near the head of Sailor Canyon, found in the Eocene lake beds of Little Truckee western side, toward Sage Hen and Truckee, the and movements along the fault lines on both sides at the western boundary of the quadrangle. On River and in the vicinity of Verdi. height where the wash gravel begins is a little of Lake Tahoe and on the eastern side of the the opposite side of Sailor Canyon, at the place MINERAL SPRINGS. above 5900 feet. In Stampede Valley the height Carson Range. The probable positions of the called Sailor Meadows, similar deposits have been varies between 5900 and 6000 feet. The shore first two fault lines on each side of the Tahoe- Mineral springs are quite abundant in certain found. The gravels are developed by means of Truckee depression are shown on the map. parts of the area. Most of them are found along gravel runs over in river terraces, where tribu tunnels run into the bed rock. taries entered the lake. Along the Little Truckee Direct evidence of the fault is not found, but no the summit region of the Sierra Nevada. Extinct At Chalk Bluffs, on the Middle Fork of other explanation of the topographic features mineral springs, indicated by their deposits, are the stream terraces reach far up to the base of American River, about 4 miles above French appears reasonable. After the outlines of the found in a few places, notably to the south of the terminal moraine. The middle of Martis Val Meadows, an inclined shaft was sunk .. . . ' Gold=beanng Euers Valley, on the road to Truckee. The only ley is mostly covered by finer sediments, fine range had been thus blocked out, new river sys some years ago for a distance of 400 srave!s rare- tems were established, probably during the Eocene hot mineral spring is found on the north shore of gravel, and sand, while coarser gravels are found feet, with the intention of reaching the bottom of period, and their valleys were erodejl, broad and Lake Tahoe, near State Line Point. The spring nearer the shore line. On the basalt table south the gravel channel known to exist under the ridge deep near the summits. The auriferous gravels emerges in the lake about 20 feet from the shore. of Boca well-washed, silicified andesite pebbles north of the river. It is said that good prospects were deposited and the epoch of volcanic activity The flow is strong and the temperature of the are found abundantly at an elevation of a little were found, although the bottom of the channel began. During the epoch a great recurring fault water 138° F. There is hardly any taste of over 6000 feet. Along the low^er part of Juniper was not reached. ing movement took place along the old break at mineral salts, but a faint smell of sulphureted Creek a distinct terrace ascending along the creek Pleistocene. As this region lies outside of the the eastern base of the Carson Range, while it is hydrogen may be noted. corresponds in elevation with the beach deposit Gold Belt proper, Pleistocene auriferous gravels thought that no important faulting occurred on The cold mineral springs may be divided into just mentioned. of economic importance occur only in a few places, either side of Lake Tahoe. two groups: (1) those characterized by alkaline On the western slope of the Truckee River though by panning colors may be obtained from No important movement appears to have taken carbonates along with a considerable amount of Range the gravel is, however, found at a higher many creeks in the area. Sailor Canyon has place after the andesitic eruptions along the west free carbonic acid, and (2) the cold sulphur elevation, pointing to a small uplift. In the yielded a considerable amount of gold, especially ern fault line, though north of this quadrangle, springs characterized by the presence of sulphu ravine between andesite and basalt, 3 miles north near its junction with American River, in the along the same line, such later movements have reted hydrogen. A number of springs belonging east of Boca, a very distinct pebble beach remains Colfax quadrangle. Some gold has also been occurred. Neither can it be said that there is any to the first group are found on the headwaters at a little over 6200 feet. Two miles farther found in the upper part of Duncan Canyon and conclusive evidence in favor of post-andesitic of the North Fork of American River. At Soda north the same beach line is found at 6200 or in the Middle Fork of the American below French faulting on either side of the Carson Range, in Springs, a well-known resort 5 miles south of 6300 feet, while scattered wash pebbles are found Meadows. The two branches of Long Canyon, this quadrangle, except possibly in one place, Summit station on the Central Pacific Railroad, even higher up. At the north end of the range which in the adjacent Colfax quadrangle are in north of Boca, referred to above. there are several springs characterized by an gravel is found at 6200 feet, though the beach places rich in gold, appear in this area nearly The questions of the faulting along the base of abundance of carbonate of soda and chloride of line is not very definite. barren. The gravel bars along the Rubicon the Sierra, the manner in which it was accom sodium, together with smaller quantities of car The last distinct moraine is found in the west River, from north of McKinstry Peak down, con plished, and the dates of the faults are confessedly bonate of lime and magnesium. Two miles below ern part of the town of Truckee. East of this tain a small amount of fine gold. there are gravel and bowlder terraces on each side difficult, and will bear more elucidation. It is Soda Springs, on the road to the railroad, there of the river, reaching an elevation of 5900 feet. certain that on the western block, the grades of GOLD-QUARTZ VEINS. are extensive calcareous spring deposits. Some The terrace northeast of the town is about 100 the rivers flowing westward have been greatly No gold-quartz veins are being worked at of these springs are still flowing from little mounds feet high and in its lower layers is composed of increased, resulting in an apparent tilting, but present within this quadrangle. On the rocky built up by their sediments, while others are wash bowlders closely packed; in the upper part how this has been accomplished is not definitely mountain slopes to the south of the American extinct. Still farther down on the same river, there are heavier bowlders. settled. Royal Gorge, in the Sailor Canyon beds, and in near Palisade Creek, are the so-called Heath Soda The Truckee lake was evidently drained dur A general uplift of the region was probably the adjacent diabase-porphyrite, a few quartz Springs. Their flow is very abundant and they ing the later part of the Grlacial period, and the accompanied by a sinking or settling of certain veins have been prospected and contain iron and are similar to the soda springs just mentioned, river began eroding the lake deposits. At less well supported blocks, such as that underly copper pyrites carrying some gold. Within the except in containing somewhat less carbonic acid. Truckee the river has cut into the terrace, form ing the Truckee basin and Lake Tahoe and that isolated schist area of McKinstry Peak a few The temperature of these springs is from 50° to ing the flat on which the town stands, and in this to the east of the Carson Range. The long quartz veins are found. One of them, cropping 60° F. or 10° to 15° C. Similar alkaline and newer terrace it is at present cutting still deeper. depression extending from Sierra Valley on the some distance west of Wentworth Springs, is carbonated springs are found at Scotts Springs The flat bench, which is of late Glacial or post- north to Lake Tahoe on the south is one of the said to contain as much as $3 per ton in gold. A and half a mile west of McKinney. The Rubicon Glacial age, extends with an elevation of 20 to 50 most interesting features of this region. As gold-quartz vein of some promise has Valley is characterized by a number of mineral feet above the river, and farther down widens already indicated, it was outlined before the Neo been worked at French Meadows on springs. The principal ones, Rubicon Springs, considerably toward Martis Valley. It is bor cene period, by the sinking of a block between the northern side of the Middle Fork furnish carbonated water which is extensively dered southward by a distinct bluff toward the two parallel fault lines, and this probably formed of American River. The granodiorite adjoining used for medicinal purposes. A small mineral older Pleistocene deposits of Martis Valley. a very deep and continuous valley, either closed it has been subjected to much pressure and made spring occurs near the mouth of Powderhorn Nearly disappearing in the basalt canyon at and filled by a lake or draining toward the north. schistose. Creek. Prosser, it is found again above and below Boca, Volcanic accumulations filled this valley during At the outlet of Meadow Lake a few ill-defined The cold sulphur springs are fewer in number. as gravel flats 20 to 40 feet above the river. In the latter Neocene and divided it into three veins carrying auriferous sulphides only have At the base of the morainal bluff on the south Truckee Canyon there are many very late alluvial basins. Truckee Valley, first a lake, found soon been found. Frequent attempts have been made side of Middle Fork, 5 miles below this pass, is a flats 10 to 20 feet above the river, and occasionally after the close of the volcanic period an outlet to work them but the isolation of the locality, cold spring flowing moderately and containing slight indications of a higher bench at 50 feet. along the present Truckee River across the the severe climate, and the low grade of the ore much sulphureted hydrogen. Near the junction Granite bowlders of considerable size (6 to 7 feet eastern or Carson Range, the outlet probably fol have thus far prevented success. The veins of Rubicon River and Five Lakes Creek there is in diameter) are found on the low terrace and on lowing an original depression in the surface of the belong to the Meadow Lake mining district, the found, on the south side of the Rubicon, a spring its slopes several miles below Truckee. Even as andesite. largest part of which falls in the Colfax quad flowing about a gallon a minute. It has a strong far down as Boca granite bowlders 4 to 5 feet in Lake Tahoe, likewise dammed high above its rangle. saline taste, and also smells strongly of sulphu diameter are occasionally met with in the river present level by the andesitic lavas, found its out GOLD-SILVER DEPOSITS. reted hydrogen. The temperature is about 45° F. Two similar springs are found a few miles terraces, and at Boca, between a hotel and a saw let northward into Truckee Valley. Several areas in the andesite north of Lake further down the river. A quantitative analysis mill, in a railroad cut, there is a mass of angular After the close of the volcanic period and its Tahoe have been subjected to extensive thermal of this water shows the presence of large amounts granite and basalt bowlders, probably transported orographic disturbances followed a period of rest. alteration, due to hot mineral waters permeating of chloride of sodium and chloride of calcium, by floating ice. Apparently no glacier reached The western range during this time became deeply the rocks. The result is a white, soft, decomposed besides a little silica and iron. down so far. scored by canyons, and Truckee River deepened rock, containing more or less iron pyrite. This At Wentworths, on the road from Lake Tahoe Along the Little Truckee alluvial flats extend its canyon all along to its present level and iron pyrite contains silver and gold, the former to Georgetown, two mineral springs emerge near little above the river level; the flats are bordered drained the Truckee basin. Then followed the preponderating. Prospects have been opened on the house, while two or three other springs issue by gravel-terraces of fluviatile, late Pleistocene basaltic eruption which obstructed Truckee River these deposits at several places, though thus far one-third mile eastward. The volume of water origin/20 to 100 feet above the river; finally at in at least three places: at the outlet of Lake no ore bodies of economic importance have been is moderate, and the temperature is 45° F. In elevations ranging from 5900 to 6200 feet are Tahoe, again raising its level; above Truckee, encountered. The places are as follows : at the mineral substances dissolved the springs differ found the shore gravels of the early Pleistocene creating a temporary lake between that locality head of Juniper Creek, where a tunnel 600 feet considerably, though they are close together. A lake. Similar relations obtain on Prosser Creek. and the lake; and at Boca, forming an extensive long has been run on a deposit of this kind ; in sample of the most saline water contains abun At the mouth of the lower Truckee Canyon, in lake in the Truckee basin. The Glacial epoch, the vicinity of Elizabethtown, a now abandoned dant chlorides of sodium, magnesium, and lime, the extreme northeast corner of the quadrangle, probably begun before the basaltic eruptions, settlement on the northern slope of the range, with carbonic acid and sulphureted hydrogen as are extensive fluviatile gravel terraces, covered continued long after their close. The barriers of north of Lake Tahoe, on the road from Truckee well as a little silica and iron. Much carbonate with large scattered bowlders, probably carried the basaltic dams were cut through before the to Hot Springs, at an elevation of 6500 feet, of calcium is also present. Such a composition down by torrents from cloud-bursts. end of the Glacial epoch. The erosion that has where many shafts and smaller tunnels were run of a mineral water is an unusual one for this Lakes. Over one hundred large and small taken place since the close of that epoch is of in this vicinity during the mining excitement region. lakes dot the summit region of the main range. trifling extent; along Truckee River it is con of 1864; and in the vicinity of the abandoned Superficial springs. The western part of the They are nearly all of glacial origin, either siderably less than 50 feet. Though no post- settlement of Knoxville, on the east side of andesitic faults can be shown to exist, it does not quadrangle receives, as stated above, a heavy pre dammed by moraines or occupying scooped-out Truckee River, opposite the mouth of Squaw cipitation, and many snow banks remain on the rock basins, the former being in the majority. follow that this region has not suffered any dis Creek. At the latter place there is an area of at turbance since the Neocene period. The Neocene northern side of the highest mountains through Webber, Independence, and Donner lakes have least one square mile altered by thermal processes, lake beds of Truckee Valley have been gently out the summer. Water issues from numerous morainal dams, though the latter may in the first and the altered rocks appear in fantastic red and tilted southward. Further, the fact above referred springs of superficial origin. The largest springs place have been dammed by the basaltic flow. yellow outcrops. Many partly caved prospect to, that remains of shore gravels of the Pleisto are, however, nearly invariably situated at the Lake Tahoe has been dammed by andesitic flows, holes and tunnels were noted. as stated above. Loon Lake, Pleasant Lake, and cene lake of Truckee Valley lie about 200 feet base of the andesitic and rhyolitic hills. The others along the southern boundary appear to be higher northeast of Boca than they do on the BUILDING STONES. atmospheric waters easily penetrate the porous rock basins. Many of the lakes have been drained opposite side of the valley, is of very great interest Many of the rocks of the Truckee quadrangle volcanic rocks and, collecting on the bed-rock since the close of the Glacial period and their as proving that some deformation has taken place are adapted for building stones, though at present surface below them, reappear at points along bottoms now form swamps or meadows. along the eastern side of Truckee Valley, though there is no extensive demand for this material. the contact. Such springs, fed by the porous its character can not be definitely decided at pres The granodiorites are especially suitable in many rocks of the lava hills, are characterized by ample SUMMARY AND GEOLOGICAL HISTORY. ent. Whether the basin of Lake Tahoe has places, and also the rhyolites. The latter are and constant flow and very low temperature. Between the granitic eruptions of late Juratrias undergone any deformation in Pleistocene times practically freestones, and, being easily dressed, WALDEMAR LINDGREN, or early Cretaceous age and the phenomena of the observations are not sufficient to decide. would be very well suited for building purposes. Geologist. January, 1898.