Geology of the 

Virginia City 

Quadrangle, Nevada

GEOLOGICAL SURVEY BULLETIN 1042-C

CONTRIBUTIONS TO ECONOMIC GEOLOGY

GEOLOGY OF THE VIRGINIA CITY QUADRANGLE,

NEVADA

By GEORGE A. THOMPSON

ABSTRACT

Most of the Virginia City quadrangle, Nevada, is covered by a thick series 

of Tertiary and Quaternary volcanic deposits, but pre-Tertiary rocks are exposed 

in small patches. The pre-Tertiary rocks consist of metamorphosed sedimentary 

nud volcanic rocks probably of Triassic age. They have been folded along axes 

Avhose average trend is a little east of north, and are intruded by granitic rocks 

of Cretaceous age.

The oldest of the Tertiary rocks are rhyolite pyroclastic rocks, which are tentatively considered to be of Oligocene age. Overlying these is a thick and 

complex sequence of andesitic flows and pyroclastic rocks, which have been 

divided into an older unit, the Alta formation, and a younger unit, the Kate Peak 

formation. The Davidson granodiorite is intruded into the Alta formation. 

Hypabyssal intrusions of andesite porphyry cut both the Alta and Kate Peak 

formations. The Alta formation and older rocks, and to a lesser extent the 

Kate Peak formation, were extensively altered. Much later, surficial weathering of the altered rocks that contain pyrite produced large areas of bleached 

rocks.

Stream and lake deposits of the Pliocene Truckee formation overlie and partly 

interfinger with the Kate Peak formation. The lake deposits were laid down 

in structural basins formed by warping and block faulting. Contemporaneous 

rhyolitic eruptions contributed pumice to the Truckee formation and also formed 

a large rhyolite dome at Washington Hill. The sediments of the Truckee formation were warped and faulted, and a surface of low relief was eroded on the 

soft sediments. Later, flows of basalt and basaltic andesite were erupted from 

several vents and covered large areas.

Still younger volcanic rocks, Quaternary in age, include andesite and olivine 

basalt. These are scattered and relatively small in volume. Quarternary 

stream and lake deposits were laid down in the intermontane basins and are 

still accumulating in parts of the basins. Extensive Quaternary hot-spring 

deposits have accumulated at Steamboat Springs. The Quarternary deposits 

have been warped and faulted like the older rocks, though to a lesser extent.

The pre-Tertiary structures, insofar as they are known, trend about north, 

and the Cenozoic folds and fault blocks, although divergent in detail, also trend 

generally north. The similarity between the older and younger structures is 

limited to their trend, however; for the older structures are compressional folds, 

like those of the Appalachians and other folded mountains. On the other hand, 

the Cenozoic (basin and range) structures are more diverse; they include many 

normal faults (exemplified by the Comstock fault), warped and tilted blocks

45
46 CONTRIBUTIONS TO ECONOMIC GEOLOGY

(well shown along the western side of the Virginia Range), and anticlinal folds 

(best illustrated by the anticline west of Virginia City). These Cenozoic structures are best interpreted as forming contemporaneously, or nearly so, over a 

long period of time beginning at least as early as Miocene and continuing, perhaps sporadically, to the present.

The present topography is the result of a long history of constructional 

volcanism, warping, block faulting, and differential erosion.

The best known metallic mineral deposits of the quadrangle are the famous 

silver-gold deposits of the Comstock lode. Similar deposits of quicksilver, 

gold, silver, and tungsten have been mined or prospected in several places.

INTRODUCTION AND ACKNOWLEDGMENTS

The Virginia City quadrangle comprises an area of 230 square miles 

in west-central Nevada just southeast of Reno. It includes parts of 

Washoe, Storey, and Lyon Counties, and also the old mining town 

of Virginia City on the Comstock lode. State Highway 17 connects 

Virginia City with U. S. 395 at the western edge of the quadrangle 

and with U. S. 50 2 miles south of the quadrangle. Most of the 

area is mountainous highland of the Virginia Range and the adjoining 

Flowery Range. The highest peak, Mount Davidson, rises precipitously above Virginia City to an altitude of 7,856 feet. The lowest 

point, about 4,270 feet, is on the Carson River near the southeast 

corner of the quadrangle. West of the Virginia Range is a chain of 

basins, including Steamboat Valley and Truckee Meadows, all drained 

by Steamboat Creek, a tributary of the Truckee River. Carson River 

and Steamboat Creek are the only permanent streams.

Geologic mapping of the Virginia City quadrangle and the Mount 

Rose quadrangle, which is adjacent to the west, was done in the field 

seasons 1948-52. The previous work of Calkins and Thayer (1945) 

in the Comstock lode district was an invaluable starting point, and 

their map lias been incorporated With Only minor modifications. (See 

index map.) V. P. Gianella's report on the geology of the Silver City

area has also been especially helpful. D. E. White mapped the 

geology Of Steamboat Hills and the Quaternary deposits of Steamboat valley and Truckee Meadows. Efficient assistance was given

in the field seasons of 1950-52 by J. G. Moore, in that of 1051 by

E. A. Pomeroy, and for parts of field seasons by R. c. Horton, 

F. L, Campbell, E, a. Beeves and w. J. cw. The present report

is intenaeA as a summary of tKe geology.

ROCK UNITS

The rock units are pre-Tertiary metkmOrphiC and granitic rocks 

unconformably overlain by Tertiary and (Quaternary volcanic rocks 

and sediments of streams and lakes.
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 47 

PRE-TEBTIARY SYSTEM

Pre-Tertiary sedimentary and volcanic rocks have been folded, 

regionally metamorphosed, and intruded by granitic rocks.

METAMORPHOSED SEDIMENTARY ROCKS

The metamorphosed sedimentary rocks are best exposed in several 

small areas along the west and south borders of the quadrangle and 

in a small patch half a mile southwest of Castle Peak. These rocks 

consist of argillite (indurated fine-grained sediments without fissility 

or cleavage), slate, conglomerate, sandstone, and limestone. Near 

granitic contacts, a more intense metamorphism has produced hornfels, contact schist spotted with andalusite and cordierite crystals, 

marble, and tactite. The conglomerate contains abundant pebbles of 

andesite, and much of the finer grained rock shows tuffaceous textures 

in places and has the chemical composition of an intermediate volcanic 

rock. Some of the fine-grained rocks in Steamboat Hills and elsewhere are not distinctly bedded, but the rounding of pebbles in the 

conglomerate, the presence of sandstone and limestone lenses, and 

the local occurrence of well-bedded rocks all indicate that the original 

sediments were largely water laid. Limestone lenses are found in 

Steamboat Hills, northwest of Jumbo, and southwest of American 

Flat; at the last place the limestone once supplied material for a 

small limekiln.

As no diagnostic fossils have been found, the age of the old sedimentary rocks is uncertain. Black, cherty-looking silicified wood, 

which was identified as a conifer, possibly Araucarioxylon, by Roland 

W. Brown, occurs in the area southwest of Castle Peak. Small pelecypods, which were first found by V. P. Gianella, occur in the same area; 

they were examined by S. W. Muller and found to be unidentifiable 

(oral communication, 1950). L. H. Daugherty (1941) reported 

Araucarioxylon in the Upper Triassic system of Arizona and also near 

Winnemucca, Nev. S. W. Muller (oral communication, 1951) has 

collected similar fossil wood in the Upper Triassic system in a number 

of widely scattered localities in Nevada.

Gianella (1936, p. 37-38) assigned the pre-Tertiary rocks in the 

southern part of the Comstock lode district to the Triassic (?) system 

on the basis of lithologic similarity to fossiliferous Triassic rocks in 

Eldorado Canyon, about 10 miles to the southeast in the Pine Nut 

Range, but he pointed out the possibility that some of the rocks might 

be as old as Paleozoic. Calkins, (1944, p. 9), on the basis of similar 

evidence, concluded that the pre-Tertiary rocks in the Comstock lode 

district are not younger than Jurassic.
48 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 

METAVOLCANIC BOCKS

Metavolcanic rocks are exposed in the southwestern part of the 

quadrangle; the original rocks were largely basalt. Metavolcanic 

rocks also occur immediately north of the quadrangle in the Truckee 

River canyon; these rocks are predominantly andesites. All of these 

lavas and pyroclastic rocks have been strongly metamorphosed, generally to albite-epidote-amphibole rocks. Contact metamorphism near 

bodies of granitic rocks has locally formed andesine-hornblendebiotite rocks, some of which are schistose.

The original thickness of the old volcanic rocks probably differed 

greatly from place to place; the estimated maximum thickness is at 

least 1,000 feet (Gianella, 1936, p. 40). In the Comstock lode district, 

the bulk of the pre-Tertiary volcanic rock is metabasalt overlying 

the old sediments, but some altered andesite is interbedded with the 

sediments (Calkins, 1944, p. 9). The predominance of andesite north 

of the quadrangle, as has been mentioned, coupled with the abundance 

of andesitic debris in the old sedimentary rocks also indicate that the 

pre-Tertiary sedimentary and volcanic rocks partly interfinger; the 

sedimentary rocks were derived partly from the volcanic rocks. The 

relations are similar to those in the Yerington district, where Knopf 

(1918, p. 13) concluded that all the pregranitic rocks are of Triassic 

age. The metavolcanic rocks in the Virginia City quadrangle are 

considered as Triassic (?) in age.

oitANorncmiTE AND RELATED ROCKS

Granodiorite and allied varieties of granitic rocks are exposed in 

small areas along the west base of the Virginia Range, along the east 

slope of the FlOWerj Range, and in the southern part of the Comstock 

lode district. From the southwest corner of infi quadrangle they are

exposed almost continuously southwestward across Lakeview summit

into the Carson Range of the Sierra Nevada. Intrusive contacts with 

the pre-Tertiary Sedimentary rocks are well shown east of Sutro 

Springs near the east border of the quadrangle, in Steamboat HlllS, 

and northwest Of Jumbo near the west border. Intrusive contacts with

the metavolcanic rocks are exposed in American Kavine, which is in

the southern part of the ComStOCk lode district, and southwest of 

Jumbo.

Although the granitic rocks range in composition and texture, by

far the mOSt abundant type is granodiorite containing about tWlC6 aS 

much plagioclase as orthoclaSG. GradatlOnal Changes in total amount 

of hornblende and biotite and also in the relative proportions of these 

two minerals are the most obvious, but the quartz and feldspar also 

range considerably in amount. These changes are not always marked 

by sharp contacts, and so all of the granitic rocks are shown on the
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 49

map under one symbol. Smaller bodies and in some places the border 

apophyses of large bodies tend to contain more orthoclase and quartz, 

less of the dark minerals, and less plagioclase; also the plagioclase is 

more sodie. The small intrusions in the Comstock lode district are 

quartz monzonite porphyry (Calkins, 1944, p. 10). Dikes of aplite 

and pegmatite and veins of quartz are abundant near the contacts of 

granitic bodies, and also cut the metamorphic rocks in many places 

where no granitic rocks are exposed. Large crystals of hornblende, 

orthoclase, and plagioclase, like those in the granodiorite, are common in the metamorphosed country rock and in xenoliths within a 

few inches to a few feet of the contacts. The rocks containing these 

metacrysts are somewhat similar to the granodiorite in appearance but 

are darker and have a porphyritic appearance, and the matrix of the 

metacrysts is finer grained than the granodiorite.

Most of the granodiorite is relatively structureless with strong 

lineation or foliation only in small areas. In the southwest corner of 

the quadrangle, the largest area of highly foliated granitic rock, is 

so distinctive that it has been shown separately on the map. Here 

massive rock grades eastward through a narrow zone into foliated rock 

in which the planar structure strikes about north and dips 35°-40° E. 

The foliation may be parallel to a contact with metamorphic rocks 

less than a mile to the east, but the actual contact is concealed beneath 

Tertiary volcanic rocks. In the field the foliation appears to represent a thorough shearing; inclusions of metamorphic rock are drawn 

out into biotite schist. Thin sections of the granitic rock show alined 

biotite flakes and an occasional bent plagioclase crystal. The larger 

crystals of feldspar, which are mostly of plagioclase but include a 

little orthoclase, lie in a matrix of smaller crystals of orthoclase and 

quartz, formed by crushing and recrystallization.

The granitic rocks of the Virginia City quadrangle extend southwestward in nearly continuous outcrops to the granitic rocks of the 

nearby Sierra Nevada; all were evidently emplaced about the same 

time. The age of intrusion of the main Sierra Nevada batholith has 

been, considered by several authors to be Late Jurassic or Early 

Cretaceous (Hinds, 1934, p. 192; Knopf and Kirk, 1918, p. 62).. More 

recently, Larsen and his coworkers (1954), using the lead-alpha activity ratios of the accessory minerals, found the age to be Cretaceous.

TERTIARY SYSTEM

The Tertiary rocks are volcanic agglomerates, tuffs, and lavas 

together with a small amount of sedimentary rocks derived from the 

volcanic rocks. In composition the volcanic rocks range from basalt 

to rhyolite, but they consist predominantly of different kinds of 

andesite.

386634 56 2
50 CONTRIBUTIONS TO ECONOMIC GEOLOGY 

HARTFORD HIIX RHYOLITE TUFF

The oldest of the Tertiary formations was called the Hartford Hill 

rhyolite by Gianella (1936, p. 45). It is here named the Hartford Hill 

rhyolite tuff. At the type locality, Hartford Hill, near Silver City, 

it is about 1,000 feet thick. At its base on the south slopes of Hartford Hill it includes a few feet of conglomerate, which contains pebbles 

of the underlying metavolcanic and granitic rocks. It is overlain by 

Alta formation. The Hartford Hill is extensively exposed in the 

Comstock lode district and south and southwest of the Virginia City 

quadrangle. Over most of the remainder of the quadrangle it either 

was never deposited or was removed by erosion before the deposition 

of the andesites. The most northerly exposures are in two small 

patches northeast of Sutro Springs and in a small area near Castle 

Peak; the main glory hole of the Castle Peak quicksilver mine also 

contains some altered rhyolite tuff seemingly interbedded with 

andesite.

The formation is composed of light-pink to dull-purple vitriccrystal tuff, tuff-breccia, and welded tuff. The bulk of the rock is 

made up of fragments of glass and pumice, which in most places are 

completely devitrified. Crystals of quartz, orthoclase, plagioclase, 

and biotite are abundant in places but almost completely absent in 

other places. Fragments of granitic and metamorphic rocks are common, and in a few places they constitute as much as 10 percent of the 

rock.

The Hartford Hill rhyolitic rocks were formerly considered to be 

largely rhyolite flows (Gianella, 1936, p. 45-47; Calkins, 1944, p. 11), 

but the preponderance of broken crystals, fragments of pre-Tertiary 

rocks, flattened pumice lapilli, and relict tuff textures in the devitrified 

matrix indicate a pyroclastic origin for most, if not all, of the formation. This conclusion is borne out by the presence of remnants of undevitrified welded tuff on the west and south slopes of McClellan Peak.

Similar rocks near the Carson airport, south of the quadrangle, were

mapped by Keid (1911) as pitchstone dikes, but they are in fact extrusive pyroclastic rocks. A small mass of irregularly dipping tuff-breccia on the slopes west of American Flat probably fills one of the source 

vents of the rhyolite tuff.

There is evidence of some interbedding of the Hartford Hill rhyolite tuff with overlying Alta formation; this can be seen near Jumbo 

and at the Castle Peak mine. Calkins (1944, p. 11) found similar

evidence south of the quadrangle at the Daney mine. It is probable,

therefore, that if the Alta formation is Oligocene the Hartford Hill 

rhyolite tuff is partly Oligocene, but it may be partly or mainly Eocene 

in age.
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 51 

AL.TA FORMATION

The older of the two extensive andesite f ormations was described by 

Gianella (1936, p. 53) as the Alta andesite, after the Alta shaft on the 

Comstock lode. The formation consists mainly of tuff-breccia, flow 

breccia, and lava flows, but it contains the sedimentary Sutro member, 

which ranges in texture from shale to conglomerate. The andesites 

are extensively exposed in the southern two-thirds of the Virginia 

City quadrangle; the Sutro member is present only in the Comstock 

lode district. In the northern part of the quadrangle the Alta is 

missing, but similar andesites reappear northwest of Reno on the slopes 

of Peavine Peak.

Calkins (1944, p. 12) divided the Alta andesite of the Comstock 

lode district into four members with an aggregate thickness of about 

2,700 feet, but this subdivision and thickness have only local significance, for elsewhere the section is less complete, and the members are 

less easily recognized. The lower member is most distinctive; it is 

commonly a tuff-breccia altered to shades of red and green. This tuffbreccia is composed of andesite fragments containing sparse phenocrysts of hornblende and abundant phenocrysts of plagioclase about 

1 millimeter in diameter. The sedimentary Sutro member is generally above the lower member, but it forms discontinuous lenses at 

different stratigraphic horizons. Where it is coarsest it consists of 

andesite and rhyolitic debris; its most characteristic rock, however, is 

a fine-grained evenly bedded grayish-green shale.

Above the Sutro is a pyroxene andesite, which where fresh is almost 

as dark as basalt and has many transparent phenocrysts of plagioclase 

about 2 millimeters in diameter, inconspicuous phenocrysts of pyroxene, and scattered phenocrysts of hornblende. Where the rock is 

weathered it is greenish gray, and the feldspar phenocrysts are white, 

and the pyroxenes are represented by conspicuous dark pseudomorphs. 

This pyroxene andesite, together with the tuff-breccia of the lower 

member, constitutes the most widespread rock types in the Alta formation. The uppermost member described by Calkins is hornblendepyroxene andesite with larger phenocrysts than the other members; it 

may be an intrusive rock with associated intrusion breccias.

In Steamboat Valley and near Jumbo the Alta includes a soda 

trachyte. The soda trachyte is generally a light to medium purple, 

but it has been derived from a black semivitreous rock; this unaltered 

rock is exposed in a small area in Steamboat Hills west of the quadrangle. The trachyte consists of small tabular phenocrysts of sodic 

plagioclase, with or without hornblende, in a very fine grained groundmass of plagioclase, potash feldspar, and red iron oxide. In many 

places the phenocrysts and elongated crystals of the groundmass show 

a striking alinement, which has given the rock a platy parting.
52 CONTRIBUTIONS TO ECONOMIC GEOLOGY

The Alta formation is more altered on the average than the younger 

rocks; the groundmass is everywhere devitrified, and the hypersthene 

is almost all replaced by secondary minerals.

One of the extrusive centers of the Alta formation was almost certainly in the Comstock lode district, for its thickness and its diversity 

of composition decrease rapidly away in all directions from this area. 

Possibly the main vents were in the area now occupied by the Davidson 

granodiorite. The Alta formation probably interfingers with the 

overlying Kate Peak formation in some places near Bailey Canyon 

and Sixmile Canyon but the rock types are not sufficiently distinctive 

to be absolutely sure of this relation; the division between the two 

formations is necessarily arbitrary in many areas. Unconformable 

relations are demonstrated locally by fresh andesite of the Kate Peak 

lying on Alta formation that has been hydrothermally altered and 

weathered.

The best indication of the age of the Alta is given by fossil leaves 

found in the Sutro member in a road cut in Long Canyon. They 

suggest a.n Oligocene age (Axelrod, 1949, p. 1935).

AMERICAN RAVINE ANDESITE PORPHYRY

The American Eavine andesite porphyry, which was named by 

Gianella (1936, p. 44), has been mapped only in the Comstock lode 

district, where it occurs in American Eavine and in Gold Canyon. 

The greater part of it is a fine-grained andesite with slender hornblende phenocrysts set in a groundmass composed largely of subparallel laths of labradorite; the interior of the mass in American Ravine 

consists of a coarser porphyry (Calkins, 1944, p. 17). The American 

Eavine andesite porphyry is clearly intrusive into the Hartford Hill 

rhyolite tuff and probably into the Alta andesite (Calkins, 1944; p. 16).

Of the extrusive rocks with which the porphyry might be correlated, 

some phases of the Alta formation and of the Kate Peak formation 

are similar, but the most striking resemblance in composition and texture is With the Lousetown formation 5 in fact, the only marked* difference is in the greater alteration of the porphyry. The age of the 

porphyry is therefore uncertain; Calkins regards it as probably intermediate in age between the Alta formation and the Kate Peak formation, and that position is tentatively assigned to it here.

The summit of Mount Davidson is part of a stock of what Qianeiia

(1936, p. 64 68) named Davidson diorite, here called Davidson granodiorite. This stock is the only deep-seated intrusion of Tertiary age in

the Virginia City .quadrangle. Smaller intrusive bodies are exposed 

to the north and west of the stock; in these the rock is porphyritic.
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 53

But in the stock the granodiorite is hypidiomorphic and medium 

grained, and presumably it crystallized under many hundreds of feet 

of cover. The chief constituent is zoned plagioclase, the average 

composition of which is andesine. Quartz and orthoclase occur in 

smaller grains between the other minerals. Augite and hypersthene 

were originally present, but the hypersthene has been almost completely replaced and the augite has largely been altered to fibrous 

amphibole and other minerals. The rock also contains biotite, commonly altered to chlorite, and perhaps a little original hornblende,

Becker (1882) and later workers called it a diorite; Gianella (1936, 

p. 66), although retaining the name diorite, noted that the rock is 

close to granodiorite in composition. Chemical analyses were made of 

two specimens in connection with the present study, one from the 

main body in Bullion Ravine and the other from the smaller intrusion a mile west of Mount Davidson. These two analyses, which 

are almost identical, indicate a composition between average quartz 

diorite and average granodiorite (Daly, 1933, p. 447 and 457). The 

silica content is 63.5 percent, much more than Daly's average for 

diorite (57.6 percent) and more than his average for quartz diorite 

(62.4 percent) but less than his average for granodiorite (65.7 percent). All of the other constituents are closer to granodiorite than 

to quartz diorite. This bears out petrographic observations of considerable amounts of quartz and orthoclase, which are not conspicuous 

because of their fine grain. The change in name, to Davidson 

granodiorite, is thus required.

The intrusive relation of the Davidson granodiorite to the Alta 

formation is shown by intricate intrusive contacts, by inclusions of 

andesite in granodiorite, and by metamorphism of the andesite (Calkins, 1944, p. 18). Partly on the basis of a chemical analysis published in 1878 (King, 1878, p. 676) the Davidson granodiorite has 

been correlated with the Alta andesite (Hague and Iddings, 1885, 

p. 21-22, 40; Calkins, 1944, p. 18). The old analysis was of a specimen taken from the "Eldorado outcrop" ("Gould and Curry croppings" on Becker's (1882) map), and although this entire area is 

shown as "diorite" on Becker's map, it actually contains several 

different rocks, including Alta andesite, as mapped by Calkins and 

Thayer (1945). The old analysis is very similar to recent analyses 

of the Alta and quite different from those of Davidson granodiorite. 

The recent analyses of Davidson granodiorite show that it is almost 

identical in composition with some of the andesite porphyry of 

the Kate Peak formation. It may therefore be younger than it has 

generally been considered in the past and may be contemporaneous 

with part of the Kate Peak formation. It cannot be younger than
54 CONTRIBUTIONS TO ECONOMIC GEOLOGY

all of the Kate Peak formation because it is cut by a few dikes of 

andesite porphyry of the Kate Peak formation.

KATE PEAK FORMATION

The Kate Peak formation, named for Kate Peak in the Flowery 

Range, east of Silver City (Gianella, 1936, p. 69), occupies the most 

extensive area of any formation in the Virginia City quadrangle. 

Coarse agglomerate that contains blocks of andesite of contrasting 

color and texture is perhaps the most abundant rock in the Kate 

Peak formation, but lava flows and flow breccias also occur in a 

great adimdance and variety. Though most of the Kate Peak rocks 

are andesites, their composition and texture are remarkably varied. 

Many have a groundmass of silicic glass, which makes their chemical 

composition more comparable to dacite than to andesite. Large, 

nearly equidimensional plagioclase phenocrysts occur in nearly all the 

Kate Peak rocks; hornblende is the most common dark mineral, but 

biotite is abundant in some places and orthorhombic and monoclinic 

pyroxenes are not rare; some specimens contain all these minerals. 

On the whole the Kate Peak formation is more silicic than the Alta 

formation, but it is also more varied, and there is considerable overlap 

in the range of composition of the two formations.

A vitrophyre member of the Kate Peak occurs in the northeastern 

part of the quadrangle. This member is composed of devitrified perlitic glass, containing phenocrysts of plagioclase, biotite, and hornblende ; a chemical analysis indicates that it is a rhyolite, locally it is 

spherulitic. It is generally characterized by highly contorted flow 

banding.

The maximum thickness of the Kate Peak formation is more than 

2,000 feet. The vitrophyre member is at least 1,000 and probably 

nearly 2,000 feet thick in its thickest part.

Most of the intrusions shown on the map as Kate Peak formation 

are composed of biotite-hornblende andesite porphyry so nearly identical in appearance, composition, and texture with the most distinctive of the Kate Peak lavas that they are believed to be products of the 

same period of vulcanism. Coats (1936) has studied the structure 

and petrography of five of these intrusions. The andesite porphyry

intrusions in the Comstock lode district were formerly considered to be 

older than the Kate Peak formation (Gianella, 1936, p. 68). But 

the continuity of the swarm of dikes north of Virginia City from 

areas where they cut the Kate Peak formation into areas where they 

CUt Only the Alta formation, and the lack of any difference other than 

degree of alteration, constitutes good evidence that the dikes are 

related to the younger formation.
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 55

The distribution of the Kate Peak indicates that it was erupted from 

many vents in the Virginia Range, the Flowery Range, the Steamboat 

Hills, and the Huffaker Hills, and in many places outside the quadrangle. Pipelike intrusions such as Sugar Loaf, and some of the 

dikes, probably served as feeders. A few of the dikes north of Virginia City are composed partly of andesite breccia resembling the 

extrusive agglomerates of the formation.

The top of the Kate Peak formation intertongues with the overlying Truckee formation, which contains fossil leaves and diatoms indicating an age near the Miocene-Pliocene boundary (Calkins, 1944, 

p. 23). This suggests that the Kate Peak formation is Miocene or 

early Pliocene in age.

TRUCKEE FORMATION

King (1878, p. 412-423) used the name Truckee Group for sedimentary rocks in western Nevada that he considered to be Miocene in age. 

According to King (1878, p. 415), the most important and characteristic exposures of these rocks are about 40 miles east of Reno in what 

are now called the Hot Springs Mountains. A thick section of sedimentary rocks exposed in the Truckee Canyon above Reno was also 

called Truckee by King. The name Truckee formation is here used 

for similar sedimentary rocks beneath the Lousetown formation in the 

northern part of the Virginia City quadrangle. In this quadrangle 

the formation is composed of stream and lake deposits, which occur 

in many disconnected areas. The Truckee formation is light-colored, 

commonly glaring white, as in the Chalk Hills north of Virginia City, 

and texturally the rocks range from shale to conglomerate and tuffbreccia. Beds of diatomite are common, and diatomite was formerly 

quarried as an abrasive in the Chalk Hills; tuffs are widespread; the 

dominant constituent, however, is andesitic detritus. The thickness in 

the Chalk Hills is uncertain because of many small faults but may 

be 3,000 feet or more; elsewhere in the Virginia City quadrangle it 

is much less.

As already noted, the base of the Truckee formation intertongues 

with the upper part of the Kate Peak formation; it may be in part 

contemporaneous with the vitrophyre member of the Kate Peak formation. Basaltic andesite of the Lousetown overlies the Truckee 

formation with an angular unconformity as much as 20° west of Chalk 

Hills, and with a smaller angular discordance, or none, at other places.

The age of the Truckee formation at the type locality, where King 

thought it was Miocene, is now thought to be early Pliocene (Yen, 

1950; MacDonald, 1950). The extensive exposures of the Truckee 

formation in the Truckee Canyon above Reno are also Pliocene, as
56

shown by fossil leaves found near Verdi (D. I. Axelrod, oral communication, 1951). In the Virginia City quadrangle, the best indication of the age of the Truckee formation is given by fossil leaves 

and diatoms found at and near the abandoned diatomite quarry in 

the Chalk Hills. K. E. Lohman, who examined the diatoms, and 

R. W. Brown and R. W. Chaney, who studied the leaves, agree in 

placing the age near the Miocene-Pliocene boundary (Calkins, 1944, 

p. 23). Later, D. I. Axelrod (oral communication, 1951) studied larger 

collections of the leaves and concluded that they are early Pliocene.

WASHINGTON HILL RHYOLITE

The name Washington Hill rhyolite is here given to the extrusive 

dome of devitrified rhyolitic glass and perlite in and immediately 

southwest of Washington Hill. Another large rhyolite dome 4 miles 

farther north, on the north side of the Truckee Eiver and outside the 

quadrangle, is about contemporaneous with the one in Washington 

Hill, for pumiceous tuffs erupted from both domes are included in the 

Truckee formation. It is possible that the rhyolite vitrophyre member of the Kate Peak formation is also correlative with the Washington Hill rhyolite, but probably the vitrophyre is somewhat older.

The rock is light gray and highly flow-banded. Sparse phenocrysts of sodic plagioclase and biotite are set in a groundmass of 

rhyolitic glass that is entirely devitrified in the main mass at Washington Hill, possibly as a result of slow cooling in so large a body 

after its initial solidification. The devitrified groundmass contains 

radiating feathery aggregates of crystals that transgress the flowbanding, which indicates that they formed after the rock had ceased 

to move. The smaller mass to the southwest of Washington Hill is 

also largely devitrified but contains small areas of fresh perlite along 

the southeast side and near the center.

Although the Truckee formation in nearby areas contains blocks of

devitrified rliyolitic glass identical WtK that in Washington Hill, the 

dome cuts through the adjacent pumice-bearing Truckee. This suggests tkat the dome Is an end phase of eruptive activity that earlier

supplied pumice to the Truckee formation. In the early stages of 

eruptive activity a large crater was blown out through the Kate Peak

formation. The explosions Spread pumiceous tuff and fragments of 

Kate Peak rocks over a wide area, where they now form part of the 

Truckee formation. In the final stages of eruptive activity the viscous

lava of the dome pushed up into the crater, cutting through Kate Peak 

rocks and earlier beds of the Truckee and possibly flowing out over

them locally. Still later beds of the Truckee contain blocks of the 

devitrified rhyolitic glass from the dome. The Washington Hill rhyo-
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 57

lite is therefore regarded as contemporaneous with the upper part of 

the Truckee formation, considered to be of Pliocene age.

UPPER TERTIARY AND QUATERNARY SYSTEM 

KNICKERBOCKER ANDESITE

The Knickerbocker andesite was named by Gianella (1936, pp. 73- 

74) for the Knickerbocker shaft, just north of American Flat. Calkins (oral communication, 1948) later decided that the lava at the 

Knickerbocker shaft is Alta and that what Gianella described as 

Knickerbocker is best represented by the outcrops on Basalt Hill, 

south of American Flat. This report follows Calkin's mapping in 

regard to the distribution and relations of the Knickerbocker in the 

Comstock lode district. Knickerbocker andesite also occurs in. small 

areas about a mile southeast of Basalt Hill, where much of it is intrusive. It also occurs along the west side of American Flat, where its 

petrographic character distinguishes it from the nearby Alta andesite, 

and in the canyon about a mile south of Sugar Loaf, where part of it 

is intrusive.

The Knickerbocker andesite, as represented by the exposures on 

Basalt Hill, has a general resemblance to the pyroxene andesite member of the Alta formation, but on fresh surfaces it is darker. On 

weathered surfaces, moreover, the Knickerbocker andesite is covered 

by a characteristic buff-colored rind. The Knickerbocker contains 

phenocrysts of plagioclase, augite, and hypersthene, in a partly 

glassy groundmass. In addition, it commonly contains scattered 

grains of olivine or green alteration products of olivine. The hypersthene is fresh, whereas in the Alta the hypersthene is almost all 

replaced.

The Knickerbocker clearly overlies the Alta formation, and dikes 

of it cut the Kate Peak formation. It is tentatively considered to be 

older than the Lousetown formation, but this is uncertain.

LOUSETOWN FORMATION

The type locality of the Lousetown formation is east of Lousetown 

Creek and 6 miles north of Virginia City (Thayer, 1937, p. 1648). 

The Lousetown is composed almost entirely of lava flows, and these 

came from at least four vents within the quadrangle: one on Clark 

Mountain, a second represented by the intrusive plug in the type area 

east of Lousetown Creek (Thayer, 1937, p. 1649), a third about 2 miles 

north-northwest of Castle Peak, and a fourth in Steamboat Hills. 

The flows immediately south of the quadrangle evidently came from a 

dissected cinder cone on the south slopes of McClellan Peak.

386634 56 3
58 CONTRIBUTIONS TO ECONOMIC GEOLOGY

The flows are gray olivine basalt in places, although, olivine is not 

always discernible without microscopic examination; pyroxene andesite with a basaltic habit predominates in some areas. Near the type 

locality the formation can be divided into two series of flows, the lower 

of which contains less olivine and has slightly larger feldspar phenocrysts. The upper division, and most of that farther south, has a 

satiny luster, owing to the subparallel orientation of the lath-shaped 

feldspar crystals.

The basaltic andesite flows on the southwest side of Clark Mountain 

are correlated with the Lousetown on the basis of composition and 

stratigraphic position. The basaltic andesite of Steamboat Hills IS 

regarded as probably Lousetown on the basis of similar composition 

and degree of erosion. Tentatively, it is considered to represent some 

of the latest of the Lousetown flows and to be later than the Steamboat 

Hills rhyolite, which is described below. This correlation, however, 

is rather uncertain; it is possible that this rock is as young as the 

McClellan Peak olivine basalt.

The Lousetown formation is post-Truckee. In a few places the 

Truckee formation grades upward into bedded basaltic pyroclastics 

beneath flows of basaltic andesite. This relation is well shown below 

the capping of Lousetown on the northernmost hill in sec. 32, east 

of the Chalk Hills, and also above the Tuffstone quarry, half a mile 

north of the quadrangle on Long Valley Creek. The degree to which 

the Lousetown has been deformed and eroded suggests that it is of late 

Pliocene or early Pleistocene age.

STEAMBOAT HILLS RHYOLITE

The Steamboat Hills rhyolite is here named for an occurrence of 

pumiceous rhyolite in the Steamboat Hills, 2% miles west of the Virginia City quadrangle. The rhyolite also occurs in two widely separated areas within the quadrangle; one along the west base of the Virginia KangCj northeast of Steamboat Hills, and the other at Sutro 

Springs, on the east side of the Flowery Range. All thfiSG OCClHTeilOeS

are extrusive domes of fresh pumiceous rhyolite, containing verysparse phenocrysts of sanidine, quartz, plagioclase, and biotite. Some

Of the jhyOlite iS perllte, and a very little is obsidian. The extrusion 

of the dome in Steamboat Hills was preceded and followed by GXplOsive eruptions, but there seems to have been little such activity at the

other domes, wkicK do not have craters. The Steamboat Hills rhyolite

is.probably COntempOraneOUS With Or Slightly older than the basaltic 

andesite in Steamboat Hills, tentatively correlated with the LouS6-

town, but younger than most of the Lousetown in the Virginia City 

quadrangle. The evidence on which this interpretation is based is as 

follows: (1) Pumice fragments thought to be from the earliest ex-
59

plosive eruptions of Steamboat Hills rhyolite are locally abundant in 

the gravels beneath the basaltic andesite in Steamboat Hills; (2) 

pumice lapilli, perhaps from the last explosive eruptions, are scattered 

very sparsely on the surface of the same flows; and (3) most of the 

Lousetown in the Virginia City quadrangle appears to be more eroded 

than the domes of Steamboat Hills rhyolite and therefore to be older. 

On the basis of this evidence, the Steamboat Hills rhyolite is regarded 

to be of Pliocene or Pleistocene age.

MUSTANG ANDESITE

The Mustang andesite, which is here named for Mustang, 9 miles 

east of Reno on the Truckee River, and north of the quadrangle, 

is well exposed on the slopes of Clark Mountain. It is the youngest 

andesite and is present only in the northeastern part of the quadrangle. 

It is a fine-grained gray rock with abundant large hornblende phenocrysts, which are commonly partly replaced by magnetite. It resembles some of the hornblende andesites of the Kate Peak formation, 

except that it lacks large feldspar phenocrysts. Flows that are 

generally from 100 to 200 feet thick, but of relatively small extent, 

issued from a vent at the summit, about a quarter of a mile north 

of the quadrangle; the original form of some of the flows is still 

well preserved. The flows lie in part on the Kate Peak formation, 

in part on the Truckee formation, and in part on the Lousetown 

formation. They are not directly overlain by younger rocks, except 

alluvium, but debris eroded from them lies beneath the McClellan 

Peak olivine basalt. The Mustang andesite is considerably less eroded 

and less deformed than the Lousetown formation, and is therefore 

very probably of Pleistocene age.

M'CLELLAN PEAK OLIVINE BASALT

The name McClellan Peak olivine basalt is here given to what 

Gianella (1936, p. 76-77) called American Flat basalt; the change 

in name is required because American Flat has been applied to a 

formation in Colorado. Remnants of a flow of McClellan Peak 

olivine basalt are found on the east slope of McClellan Peak, nearby 

on American Flat, and in American Ravine, where a few feet of gravel 

occurs at its base. At these localities the flow is not over 50 feet 

thick; it lies unconformably on Alta formation, Hartford Hill rhyolite tuff, and pre-Tertiary rocks. It is not directly overlain by 

younger rocks. Essentially identical olivine basalt covers a much 

larger area in the northeastern part of the quadrangle, where a flow 

spread over the flats south of Clark Mountain, ran down Long Valley 

Creek, and continued eastward down the canyon of the Truckee 

River. The rock is gray on fresh fractures and contains abundant
60

large phenocrysts of clear yellowish-green olivine. The weathered 

rock is coated with a thin black rind, and in some places the former 

Indian inhabitants of the area have chipped through the rind to 

make pictographs.

"The flow in American Flat and American Ravine issued from the 

east slope of McClellan Peak, where the basalt is scoriaceous. The 

basalt in the northeastern part of the quadrangle originated at the 

base of the two cinder cones at the eastern edge of the quadrangle, 

in sees. 10 and 15. On the plain south of Clark Mountain the basalt 

flow must have surged to different heights as it forms irregular terraces along the northern edge of the plain, In sec, IT in the southern 

part of this area, a tumulus, fed by a lava tube from higher ground, 

rises to a height of about 75 feet above the surrounding lava flow. 

The flow must have been fairly fluid, for in some places near Long 

Valley Creek it is less than 10 feet thick. Where it debouched into 

the canyon of the Truckee River it probably dammed the river as 

is indicated by a small patch of lake beds high on the north side of the 

river above the main highway. The basalt is younger than the 

Mustang andesite, for pebbles of the andesite occur beneath the basalt 

flow in the canyon of the Truckee River.

HOT-SPRING DEPOSITS

Hot-spring deposits consisting mainly of siliceous sinter are abundant near Steamboat, and a small terrace and some fissure-filling 

of travertine occur near the north edge of the quadrangle, 2% miles 

north of Washington Hill. East of the quadrangle, about 4^/2 miles 

east of Tibbie Peak, is a much larger area of travertine. The spring 

deposits at Steamboat Springs consist of siliceous sinter, ranging in

texture from porous opal to dense chalcedony and quartz. Steamboat Springs is the only one of these localities where hot springs are 

Still active, and there the stratigraphic relations indicate a considerable range in the age of the deposits; the oldest deposits antedate 

the basaltic andesite in Steamboat Hills, and the youngest are still

being deposited.

PRE-LAKE LAHONTAN GRAVELS

The pre-Lake Laliontan gravels include a diverse group of alluvial

fan and pediment gravel deposits. The recognition of these older

gravels is based primarily on soil formation, using the criteria d'Cscribed by Hunt and Sokoloff (1950) and by Boger Momson (oral 

communication, 1950). The stratigraphic relations, texture, degree

of structural deformation, and degree of erosion are also helpful criteria. In the mountain ranges these gravels cap remnants of dissected surfaces; in the basins they are found in irregular patches where
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 61

they have not been stripped away by erosion or concealed beneath 

younger deposits. In Sixmile Canyon and many other places, remnants of the pre-Lake Lahontan gravels are present but are too small 

to show on the map.

The deposits are composed of material ranging in size from sand to 

boulders several feet across. They generally contain an abundance 

of large boulders, which are scarce in the younger gravel deposits. 

The gravels are chiefly derived from granitic, metamorphic, and andesitic rocks, the proportions differing greatly from place to place. 

The soil formed on the gravels is characteristically much deeper than 

on younger gravels in the same area, being comparable to the soil on 

glacial moraines older than those of the Tahoe stage (Blackwelder, 

1931) in the Sierra Nevada a few miles away. The leached zone, 

where fully preserved, is brown and clayey and is 2 to 4 feet thick. 

Buried granitic boulders in this zone are thoroughly rotted, andesitic 

boulders less so, although boulders of the same age lying on the surface 

remain relatively fresh and sound. The underlying zone of lime or 

silica enrichment is from 4 to at least 10 feet thick.

In many places the gravels are known to be later than the Louse- 

'town lavas because they contain Loujsetown debris. The gravels 

capping tiie ridge a mile north of Lousetown, however, contain little 

or no debris of this kind and may be older than these lavas. They 

are composed largely of metamorphic rocks that were probably derived 

from the vicinity of Castle Peak, and the same is true of the gravels 

capping the hill just south of the junction of Lousetown and Long 

Valley Creeks; but gravel capping the hill a mile and a half southeast 

of the junction contains pebbles of basaltic andesite of the Lousetown. 

Some of the pre-Lake Lahontan gravel is overlain by McClellan Peak 

olivine basalt, and some is deposited on terraces eroded in the basalt. 

The age therefore ranges through a large part of Pleistocene epoch 

prior to the Lahontan Lake stage.

LAKE LAHONTAN, POST-LAKE LAHONTAN, AND STREAM DEPOSITS

The Lake Lahontan and post-Lake Lahontan deposits comprise 

sediments of Lake Lahontan proper in the southeastern part of the 

quadrangle (Russell, 1885), the deposits in the swampy .flood plain 

north of Huffaker Hills, which are slightly higher than Lake Lahontan, and the deposits of still higher ephermal lakes in closed basins 

such as the one 2 miles southeast of Lousetown. The stream deposits 

of Lake Lahontan and post-Lake Lahontan age include the alluvium 

deposited by the.streams that flowed to these lakes and alluvium deposited by the present streams. On the geologic map the color symbol 

used for this alluvium is also used for some landslide material, talus, 

and for mine dumps in the Comstock lode district.
62 CONTRIBUTIONS TO ECONOMIC GEOLOGY

The lake deposits consist of sand and silt. Those in the southeast 

corner of the quadrangle contain a large proportion of quartz, feldspar, and biotite derived from granitic rocks in the Carson River 

drainage basin; and those in most other places consist preponderantly 

of volcanic debris. 

The lake deposits along the Carson Eiver are continuous with the 

main areas of Lake Lahontan deposits to the east. Soils on these lake 

deposits in the Virginia City quadrangle have a leached zone as much 

as a foot thick, which suggests that the deposits belong at least partly 

to the early high stage of Lake Lahontan (Roger Morrison, oral communication, 1951). The lake deposits in the Truckee Meadows are 

higher than the Lake Lahontan deposits in the canyon of the Truckee 

to the northeast, and not quite continuous with them. When the 

Truckee River is in flood, a temporary lake still spreads over the 

meadows almost as far south as the Huffakef Hills, because of the very 

low gradient. During the high stages of Lake Lahontan, similar 

flooding was undoubtedly more frequent and was perhaps continuous.

The stream deposits consist of sand, gravel, and cobbles of rather 

local derivation. In a few places they are strongly cemented with 

silica and iron oxides derived from' nearby areas of bleached rocks; 

this may be seen in the lower reaches of Lon'g Valley Creek. Both 

lake and stream deposits have been redistributed in places by the 

wind. In much of the southeastern part of the quadrangle the lake 

deposits are thinly veneered with wind-shifted sand." Eblian sands 

are also fairly abundant on the east side of Steamboat Valley aiid in 

the mountain valleys south of it. Some patches of wind-blown sand 

are weakly cemented and covered with shallow soil; other sand 

deposits are Still moving, as demonstrated most convincingly by the 

wind-blown mill tailings in the lower part of Gold Canyon. ..'

The deepest soils on the Lake Lahontan, and post-Lake Lahontan 

deposits are comparable to those on the Tahoe and Tioga moraines 

Ul the nearbj Sierra Nevada; they are nowhere as deep as those on 

the older moraines.

BLEACHED BOCKS

Near-Surface alteration by acids has caused local bleaching in most 

of the rocks of the quadrangle. Most of the bleaching, except at 

Steamboat Springs, seems to have resulted from weathering of altered 

rocks containing pyrite. The end products are Chiefly secondary

quartz, opal, and clay in different proportions, together with residual

minerals from the original rocks, whose 'identity IS revealed Ul SOm.6 

places by relict teXtUreS, Irregularly distributed limonite in cracks 

and diffusion bands commonly gives the rock a highly colorful appearance. The largest areas of bleached rocks are near Virginia City, along 

the Geiger Grade, near Washington Hill,- and in Sixmile Canyon.
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 63

The unweathered rocks below bleached areas are best observed in 

mine workings or drill holes. In the Comstock lode district, bleached 

rock at the surface grades downward into greenish-gray altered andesite containing albite, cliiiozoisite, chlorite, epidote, calcite, and sometimes zeolites, all of which are peppered with pyrite. The bleaching, 

however, is dependent only on pyrite, and altered rocks that do not 

contain pyrite crop out more extensively than the bleached rocks 

(Coats, 1940). The bleached rocks near Washington Hill contain 

abundant opal in some places, in contrast to those in the Comstock 

lode district, where the silica is present as fine-grained quartz. Moreover, the unweathered rock in the Washington Hill area appears to 

have been affected by argillic and pyritic alteration without the 

chlorlite and epidote that are so characteristic of most of the altered 

but unbleached andesite in the Comstock lode district. At Steamboat 

Springs, the bleaching has been done by acid resulting from direct 

oxidation of rising hydrogen sulfide gas.

At that locality the bleaching affects Quaternary as well as Tertiary 

and pre-Tertiary rocks. Elsewhere in the quadrangle, rocks of the 

Kate Peak formation are the youngest that have been altered, with 

the exception of very local bleaching of the Truckee formation in the 

vicinity of Washington Hill. The widespread introduction of pyrite, 

whose oxidation caused bleaching, evidently preceded the deposition 

of the Truckee formation. The albite-chlorite-epidote alteration in 

the Comstock lode district affects not only the Alta formation and 

older rocks but also some of the biotite-bearing dikes of the Kate Peak 

formation.

STRUCTURE

The pre-Tertiary sedimentary and volcanic rocks strike, on the 

average, a little east of north and dip steeply east or west. The folding 

expressed by these steep dips did not affect the Tertiary rocks and 

is evidently part of the Mesozoic deformation of the Sierra Nevada 

region. The pre-Tertiary granitic rocks were seemingly emplaced 

during the end stages of this deformation or later, for they are sheared 

only locally.

The Cenozoic deposits were laid down on a surface of low to moderate relief cut on the metamorphic and granitic rocks. Repeated tilting and warping, accompanied by block faulting, took place along axes 

that trend from northeast to northwest and average north. In much 

of the area the strata have been tilted westward and also step faulted 

relatively downward to the east; a rather sharp anticline west of 

Virginia City is exceptional (see section G-C'}. The older Cenozoic 

deposits are progressively more deformed than the younger.

The general rough parallelism of Cenozoic structures with preTertiary structures suggest that the structural trend was established
64 CONTRIBUTIONS TO ECONOMIC GEOLOGY

primarily by the pre-Tertiary compressional folding and that subsequent deformation, though distinctly different in character, tended 

to follow the same trend. A general parallelism of Cenozoic faults 

with large-scale pre-Tertiary structures has also been noted in the 

Hawthorne and Tonopah quadrangles, Nevada (Ferguson and Muller, 

1949, p. 14).

DEFORMATION OF THE CENOZOIC BOCKS

The Cenozoic structural relief resulted from combined normal faulting, tilting, and warping (Thompson, 1952). The mountain mass 

constituting the Virginia and Flowery Eanges is bounded on its east 

side mainly by normal faults (section C-0'). But on its west side 

(sections A-A' and B-B'} it is bounded largely by westward-dipping 

strata that form one limb of a broad syncline the axis of which is in 

the Truckee Meadows, and the other limb of which is along the east 

front of the Carson Kange in the adjacent Mount Eose quadrangle. 

The rocks on the west side of the Virginia Range are also cut by normal 

faults formed contemporaneously with the syncline. But on most 

of these the east (or mountain) side is downthrown, and the basin side 

is upthrown. (See sections B-B' and G-Cf . ) The vertical components, 

of movements on the normal faults are thus generally opposed to those 

on the fold, and the structural relief is therefore much less than would 

be produced by folding alone.

Folding and tilting imply crustal shortening in a horizontal direction, as opposed to normal faulting, which implies crustal extension. 

Combined folding and normal faulting thus require less horizontal 

movement than would be required by either alone. The net horizontal 

movement may in fact be zero in any large area deformed by contemporaneous folding and normal faulting. The simplest explanation 

of the Cenozoic deformation in the Virginia City quadrangle appears 

to be differential vertical uplift (or depression); this results in both 

folding and normal faulting because either on© alone would have 

to be accompanied by large horizontal movements.

The sequence of structural events in the later part Of the Cenozoic 

is better known than in the earlier part. The oldest Cenozoic rocks, 

the Hartford Hill rhyolite tuff and the Alta formation, dip only a 

little more steeply than the Kate Peak and Truckee formations. During and after the deposition of the Kate Peak and the Truckee, these 

rocks were faulted, tilted, and warped. Following this, a period of 

Structural quiescence is indicated during the latter part of the PllOCCne 

by the fact that upland erosion surfaces of low relief were most extBIlSlVe at that time and have since been partly dissected, and by the

lack of basin sediments of that age, which suggests that Structural 

blocking of drainage had diminished or ceased. Eenewed deformation
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 65

in the Pleistocene was similar to the earlier deformation. The 

Lousetown flows in the central part of the quadrangle were tilted westward and cut by normal faults that block the drainage. The pre-Lake 

Lahontan gravels were also offset by many normal faults. The Lake 

Lahontan and post-Lake Lahontan deposits, in contrast, are little 

deformed, but whether this is due to structural quiescense or to the 

short time involved is an open question.

RELIABILITY OF STRIKES AND DIPS

In a volcanic terrane reliable measurement of deformation is often 

complicated by the lack of extensive stratigraphic markers and by 

initial dips that may have been very steep. Particularly in intermediate and silicic volcanic rocks, such as the predominant types in the 

Virginia City quadrangle, the flows and pyroclastics are not laid down 

nearly flat like marine sediments but may have initial dips as high as 

30°. In this area, moreover, the eruptions from an individual vent 

may have spread over an area with a radius of only 5 or 10 miles, in 

some cases much less. The resulting volcanic pile, erupted from 

numerous vents and structurally deformed, is complex.

An accurate measure of structural deformation is given, however, 

by strikes and dips taken in the finely laminated sediments of the 

Truckee formation and the Sutro member of the Alta formation. 

Next in degree of reliability are strikes and dips of flows or fragmental volcanics, but in these rocks the amount of initial dip is 

usually very uncertain, so that the measured dip does not indicate the 

amount of structural deformation. Where possible, however, dips 

were taken in lenses of water-laid volcanic rocks, which occur sporadically in the Alta and Kate Peak formations. Contacts between formations involve a similar uncertainty about the initial slopes of erosion surfaces. Least reliable as indicators of tectonic deformation 

are the strikes and dips of platy parting in flows and altered 

agglomerate.

The Hartford Hill rhyolite tuff and the Alta formation are generally 

conformable, and both formations are generally tilted westward about 

35°. That this is actual structural tilt and not merely initial dip is 

shown by the close correspondence between dips in the Sutro member 

of the Alta and in the volcanic rocks. The uniformity of the westward tilt is broken by an anticline near the crest of the Virginia Range 

west of Virginia City (section 6-6"). This anticline, which may be 

related in origin to the intrusion of the Davidson granodiorite, is expressed by dips in the Sutro member as high as 60° westAvard and 30°
66 CONTRIBUTIONS TO ECONOMIC GEOLOGY

eastward. Other folds are suggested by eastward and westward dips 

in the rhyolite in the southwestern part of the quadrangle.

The structural relief resulting from the westward tilt is in considerable part nullified by many normal faults, on nearly all of which 

the strata are displaced downward to the east. The Comstock fault, 

which passes under Virginia City, and the intersecting Silver City 

fault, in Gold Canyon, dip eastward about 45°. Many other faults 

explored in mine workings east of Virginia City have similar eastward dips of 30°-50°. These dips, which are unusually low for normal faults, are explained by tilting of the fault planes along with the 

enclosing strata. This is indicated by a rather constant angle of about 

70° between the fault planes and stratification planes.

The total vertical throw on the Comstock fault was estimated by 

Gianella (1936, p. 85), on the basis of displacement of the Sutro 

member near Crown Point Ravine, to be 3,450 feet, but if the eastward 

dips in the f ootwall strata are considered, the revised estimate is about 

2,500 feet. The escarpment west of the Comstock fault has a maximum height of roughly 1,500 feet, 1,000 feet less than the throw of 

the fault. Since faulting began, erosion of the footwall block has 

exceeded that of the hanging-wall block by at least 1,000 feet.

KATE PEAK FORMATION AND TRTJCKEE FORMATION

The Kate Peak formation and the Truckee formation, like the older 

Tertiary rocks, are generally tilted westward (section A-A'). Their 

average dip is about 30° on the west side of the Virginia Range but 

is a little less in the Flowery Range. They are thus tilted almost 

as much as the Hartford Hill rhyolite tuff and Alta formation. Nowhere are these formations deformed as much as the Alta is in the 

anticline west of Virginia City, but such deformation is local and 

unusual even for the Alta formation.

In some places the initial dips of the volcanic rocks were probably high, and where they were westward they would account for

pai't Of the apparent tilting. But the general correspondence of dips 

measured in lacustrine sediments of the Truckee in the Chalk Hills

with those measured in the Kate Peak volcanic rocks nearby supports the view tha,t most o:£ the measured dips represent actual StrilCtural deformation. The dips in the vitrophyre member, however,

have no significance as a measure of structural deformation, for the

flow banding is highly contorted, and the initial dips are as high as

90°. Another example of what are probably steep initial dips can 

be seen 3 miles northeast of Huffaker Hills, where well-bedded pyroclastics of pyroxene andesite slope away from a local source.

In Flowery Ridge dips in the Kate Peak formation are low and 

erratic and this led Calkins (1944, p. 32) to the conclusion that these
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 67

rocks may not be appreciably tilted. West to northwest dips averaging about 30° are the rule on the east side of Flowery Kidge and in 

the Flowery Range to the northeast. A possible explanation of this 

discrepancy is that the rocks in the upper part of the Kate Peak 

formation have been less deformed than those in the lower part. 

North of the Chalk Hills and east of Tibbie Peak, the dips measured 

on the flows and agglomerates in the lower part of the Kate Peak 

formation correspond closely with the dips in the underlying Hartford Hill rhyolite tuff. The conclusion seems warranted that the 

major part of the general westward tilting in the Virginia City 

quadrangle took place during and after the period of Kate Peak 

volcanism and Truckee sedimentation.

The eastward dip of the Truckee formation north of Castle Peak 

suggests the presence of a broad northward-trending anticline between 

that area and the west slope of the Virginia Range, where the andesites 

dip westward. A parallel syncline with its axis east of Washington 

Hill is indicated in the same way. The westward tilt of the Truckee 

formation in the Chalk Hills is remarkably uniform on the whole, but 

locally it is disturbed by strong folding. The best example of the 

local deformation is at the main diatomite quarry, in sec. 36, where 

the beds are nearly vertical. Some of the smaller wrinkles at other 

places in the Chalk Hills are similar to those formed in the soft sediments of modern lakes by the pressure of moving ice.

The faulting in the Kate Peak formation and the Truckee formation is similar to that in the older Tertiary rocks. The faults are 

normal; they generally trend between northeast and northwest, and 

most of them dip eastward. The northern extension of the Cornstock fault cuts the Kate Peak formation as well as the Alta formation. The faulting on the east side of the Flowery Range is probably 

much more extensive than is shown on the map; some of the most 

important faults are believed to be concealed by alluvium near the 

base of the range.

The Lousetown formation is much less deformed than the older 

rocks. The flows generally lie on an erosion surface cut across the 

Truckee formation and all older rocks; this is particularly well shown 

on the west side of the Chalk Hills, where flows of the Lousetown lie 

on the beveled edges of tilted beds of the Truckee (section A-A'). 

After the Lousetown flows were poured out of the vent in the central 

part of this area, they were themselves faulted and tilted westward 

roughly 5°. Although no strong folding of the Lousetown has been 

detected, some gentle warping is suggested by differences in the general westward slope of the surface west of the Chalk Hills.
68 CONTRIBUTIONS TO ECONOMIC GEOLOGY

The Lousetown, like the older formations, is cut by normal faults, 

most of which trend between northeast and northwest and dip eastward. Two miles west of the Chalk Hills there is a depression with 

a closure of 100 feet, which contains an ephemeral lake. The basin 

is bounded on the west by a fault that has thrown down the Lousetown 

flows on the east by more than 300 feet. This displacement, however, 

probably measures only the latest movement on a fault older than the 

Lousetown; for the Truckee formation 2 miles east of the fault is 

many hundreds of feet thick and dips westward, whereas it is entirely 

absent a mile west of the fault. A long series of movements in the 

same direction appears to have occurred; it began with the formation 

of the Pliocene lake basin in which Truckee sediments were deposited, 

continued with the westward tilting of the Truckee sediments, and 

ended with the displacement and westward tilting of the Lousetown 

flows. The fault is in line with the Comstock fault, which it resembles 

in strike and direction of displacement, and its aggregate throw may 

be as great as that on the Comstock fault. Together the two faults 

mark a major fault zone over 10 miles long. The later movements of 

the Comstock fault may well have been contemporaneous with the 

movements on this fault.

There are at least five other closed basins in the Virginia City quadrangle ; the failure of erosion and deposition to keep pace with their 

formation indicates that the faults along them are as young as those 

cutting the Lousetown flows.

QUATERNARY DEPOSITS

Warping and tilting of post-Lousetown deposits is generally on too 

small a scale to be readily detectable, but is evident in a few places. 

The gravels near the foot of Geiger Grade, at an altitude of 4,880 

feet, dip westward as much at 20°; and even allowing for probable 

initial dip they must have been tilted westward at least 5° or 10°. 

Faulting is well shown in many places. The pre-Lake Lahontan 

gravels in the Truckee Meadows are cut by many faults, some of which 

have displacements of several tens of feet. The uplifted gravels near 

the lower end of Sixmile Canyon are also faulted. The gray el-covered 

surfaces in the Chalk Hills appear to have been tilted northeastward, 

and if they ever formed a Single continuous surface, they have been 

stepped down toward the southwest along faults that have not been 

located. *yv«,r

GEOMORPHOLOGY

Early geomorphic history. Throughout the early part of the Tertiary, the drainage was well integrated, and the region Was undergoing erosion even when volcanism was very active. Volcanism was 

not a major factor in blocking the drainage. This is indicated by the 

deep erosion of pre-Tertiary rocks and the lack of notable lower
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 69

Tertiary sedimentary deposits, with the sole exception of the Sutro 

member of the Alta formation, .which is local and small in volume. 

The Hartford Hill rhyolite tuff and Alta formation formed volcanic 

piles thousands of feet thick locally, and this probably resulted in 

considerable topographic relief with the mountains roughly along the 

same axes as the present ranges. Perhaps by late Miocene and certainly by Pliocene time the drainage was broken by block faulting and 

warping, and the lake deposits of the Truckee formation were accumulating in local basins. Erosion in the highlands and deposition in 

basins, along with structural deformation and volcanism, have continued intermittently to the present.

Erosion surfaces. Upland surfaces of relatively low relief, in striking contrast to the rugged mountain slopes, are cut across the Tertiary 

strata in many places. These surfaces probably began at least as 

early as the time of the Truckee lakes, which constituted local base 

levels of erosion. One such surface is represented by the summit area 

of the Virginia Eange from McClellan Peak northward to Orleans 

Hill. Deep erosion of this area, prior to the formation of this surface, is indicated by the removal of rock which once covered the Davidson pluton; Gianella (1936, p. 99) suggested that at least 2,500 feet of 

rock has been removed. To the north and northeast this summit 

surface slopes downward to a lower extensive surface on which lie 

the Lousetown flows west of the Chalk Hills. Here the lower surface 

truncates the upturned edges of the Truckee strata, which are so soft 

that they must have been eroded rapidly; this surface is clearly postTruckee and pre-Lousetown. The northward extension of the Lousetown flows into the valley of Lousetown Creek shows that this preLousetown surface was already undergoing dissection along the main 

drainage lines before the Lousetown flows covered it. Extensive upland surfaces of low relief in the surrounding region, as well as in 

the Virginia City quadrangle, are cut on the Kate Peak formation 

and are covered by the Lousetown flows. These upland surfaces of 

relatively low relief were most extensive in the middle or late Pliocene; 

they had been much dissected by the time the Lousetown flows were 

erupted.

Many pediments have been cut at successively lower altitudes, and 

their dissected remnants slope away from the margins of the ranges. 

The broadest of these surfaces are on soft rocks such as lake beds or 

bleached, volcanic rocks. Some were cut after the extrusion of the 

Lousetown flows and are covered with gravel containing Lousetown 

debris. The lowest erosional benches are close to the Truckee and 

Carson Kivers.

The swamps along Steamboat Creek in the northwest corner of the 

quadrangle and the very low gradient of the Truckee Eiver across the
70 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Truckee Meadows farther north can only be explained by Pleistocene 

uplift of the Virginia Range relative to the Meadows. Reestablishment of a normal gradient by downcutting was perhaps delayed by 

Lake Lahontan, an arm of which occupied the Truckee Canyon 

through the Virginia Range. After Lake Lahontan receded the river 

cut through the soft lake desposits but has not significantly entrenched 

the bedrock in the canyon, which still controls the gradient in Truckee 

Meadows.

The Carson River meanders sluggishly through dissected Lake Lahontan sediments in the southeast corner of the quadrangle, because 

it is graded to volcanic bedrock in a canyon farther downstream, 4 

miles east of the quadrangle.

Summary of formation of present topography. The present topography, then, is the result of constructional volcanism, structural deformation, and erosion. Some of the steep mountain slopes are fault 

escarpments modified by erosion (east side of the Flowery Range), 

others are dip slopes modified by erosion, (portions of the west side of 

the Virginia Range), and still others are a direct product of differential erosion of hard and soft rocks. The latter are well shown 

where the mountains rise steeply from the upper edges of many of 

the pediments. North of the lower reaches of Sixmile Canyon, for 

example, a broad pediment, now dissected, is cut on the altered Alta 

formation, and above this the steep slopes cut on the more resistant 

Kate Peak formation rise precipitously.

MINERAL DEPOSITS

Deposits of silver, gold, and quicksilver have been exploited in the 

Virginia City quadrangle, the silver-gold deposits of the celebrated 

Comstock lode district having been by far the most important. Nonmetallic deposits that have been worked include sand and gravel, 

pumice, clay and silica, and diatomite. Thermal waters at Steamboat Springs have been utilized for heating purposes and for mineral 

baths.

METALLIC DEPOSITS

Metallic deposits of at least three ages have been mined or prospected. 

The oldest, which are pre-Tertiary in age, are in granitic and metamorphic rocks, generally close to the contacts of granitic bodies. 

Small amounts of gold, silver, and tungsten have been mined from

these Old deposits in scattered localities, but no important production 

has resulted. The Tertiary deposits include the famOUS SJlVei'-gOld 

deposits Of the ComStOCk lode district, a number of widely scattered 

prospects that contain a little gold and silver, the quicksilver deposit 

at the Castle Peak mine, and quicksilver prospects near Washington
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE. NEVADA 71

Hill. The youngest metallic deposits, which are of Quaternary, age, 

include small amounts of gold, antimony, and quicksilver associated 

with Steamboat Springs; several attempts to work these deposits have 

failed because of their low grade and because of the difficulties of 

coping with the hot water. , .;

PRE-TERTIARY

The pre-Tertiary deposits, which have been extensively prospected 

but have yielded no ore in commercial quantities, are mostly quartz 

veins in granitic and metamorphic rocks but they include material 

disseminated in contact-metamorphic rocks. The principal areas 

that have been prospected are (1) southwest of Jumbo, (2) 3 miles 

northwest of Jumbo, (3) in Steamboat Valley, (4) south of Sutro 

Springs, and (5) 2 miles east of Sutro Springs. These prospects 

commonly show pyrite, copper stain, and occasionally a little galena 

which is said to be argentiferous. Similar deposits 3 miles south of 

Steamboat Valley and a mile west of the quadrangle have produced a 

small amount of gold and silver. Scheelite has been found in contact 

rocks 2 miles northwest of Jumbo, where the granitic rocks abut 

against limestone; scheelite also occurs in contact zones in granitic 

rock west of Jumbo, and in quartz veins in granitic rocks in Steamboat 

Valley.

TERTIARY

The silver-gold deposits of the Comstock Lode district have been 

described by Becker (1882), Bastin (1923), Gianella (1936), and 

others. The total production is estimated to have been about $400 

million, and slightly more than half of this value was in silver (Smith, 

1943, p. 295). The ratio of silver to gold has been estimated as 40:1 

by weight (Nolan, 1933, p. 633). The Comstock lode was discovered 

in the 1850's and reached a peak of productivity in the 1870's. Since 

then, production has declined, and all mining had ceased by 1950. The 

deposits are associated with the Comstock fault, which dips eastward 

about 45° beneath Virginia City, and with the Silver City fault, a 

branch that extends down Gold Canyon and also dips eastward about 

45°. Great bonanzas of crushed quartz, in part exceedingly rich in 

silver sulfides and native gold, were found at intervals along the 

Comstock fault and in steeper fractures in the hanging wall. Nearly 

all of the production has come from depths no greater than 2,000 feet 

below the outcrop of the fault at Virginia City, in spite of extensive 

exploration to the depth of about 3,000 feet. Some of the production 

in the southern part of the Comstock lode district has come from many 

cross faults and branches of the Silver City fault. The Occidental 

vein, which lies parallel to the Comstock fault a mile and a half farther 

east, has yielded a relatively small amount of gold and silver. Two
72 CONTRIBUTIONS TO ECONOMIC GEOLOGY

veins roughly parallel with the Comstock fault have been mined by 

open pits on the north side of Sixmile canyon 3 miles east of Virginia 

City. Several veins in the Jumbo district have been extensively prospected but have not proved profitable.

The Comstock ore deposits were formerly thought to be older than 

the Kate Peak formation, which was regarded as overlying them unconformably (Gianella, 1936, p. 103). The present study, however, 

indicates that they are as young as the Kate Peak but probably older 

than the Truckee formation and are therefore probably Miocene in 

age. Quartz veins of the Comstock lode cut dikes and other intrusions 

of biotite andesite porphyry that is regarded by the present writer 

as part of the Kate Peak formation. The Kate Peak volcanics have 

been intensively altered over large areas, but the Truckee formation 

and younger rocks have been altered hardly at all, except locally at 

Steamboat Springs, where the process of alteration is still going on. 

It seems possible that the mineralization may have started as early as 

Oligocene and extended through the Miocene. Hot water, hydrogen 

sulfide, and carbon dioxide that were present in the Comstock mines 

(Becker, 1882, p. 386) might be regarded as an indication that processes associated with deposition of the Comstock ore did not stop in 

middle Tertiary time. The most productive deposits may have been 

formed in the older Tertiary rocks for reasons of depth, temperature, 

and pressure; or possibly because of the greater length of time these 

older rocks were subjected to the process of mineralization.

Cinnabar was discovered in 1927 near Castle Peak, 6 miles north 

of Virginia City, and over 2,500 76-pound flasks of quicksilver was 

produced from the deposit (Bailey and Phoenix, 1944, p. 184). 

The ore was localized along a fault trending northward and dipping 

55° to the east) and in jointed ground in the footwall. The ore was

mainly in the Aita formation, although alteration extends into the

overlying Kate Peak formation; the Lcmsetown formation is unalt6f6d. Scattered occurrences of cinnabar have been prospected in the 

vicinity of Washington Hill, but no workable 010 l^S been discovered 

there. In that area the volcanic rocks have been altered to opal, 

quartz, clay, and alunite. In the Washington Hill area there is much

bright-red iron oxide that looks so much like cinnabar that it has 

undoubtedly deceived some prospectors.

No Tertiary placer gold deposits are known, although stream 

deposits of the Truckee formation contain much detritus derived 

from bleached and altered

QUATERNARY

Deposits of placer gold, derived from the Comstock lode, have been 

worked in Gold Canyon. The most extensive of these gravel deposits
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 73

dies south of the Virginia City quadrangle. There have been attempts, 

on a much smaller scale, to work Quaternary gravels near the lower 

end of Sixmile Canyon.

Small amounts of stibnite, gold, and cinnabar are found in Quaternary siliceous sinter and other rocks at Steamboat Springs. Stibnite 

has been observed to precipitate in the pools of some of the hot springs, 

and native mercury has been detected in the vapor of a hot well (Brannock, Fix, Gianella, and White, 1948, p. 220-225); the mud in some 

of the hot pools also contains appreciable quantities of silver and 

gold. None of the minerals have been found in sufficient quantity to 

constitute ore, in spite of considerable prospecting.

NONMETALLIC DEPOSITS

Several nonmetallic materials useful in construction are available 

in the Virginia City quadrangle, and have been exploited to satisfy 

local needs in Reno and the surrounding region. Alluvial sand and 

gravel are abundant and have been dug in many places for road 

material and concrete aggregate. Coarse sand at the foot of slopes 

of disintegrated granitic rocks is commonly used for road material. 

The pre-Lake Lahontan gravels have been quarried in places, but 

it is advisable to avoid them where aggregate of high quality is required, for the pebbles have been weathered and softened to depths of 

many feet. Windblown .sand, very uniformly sized, is abundant in 

the hollows between granodiorite hills in the eastern part of Steamboat 

Valley and in a number of small valleys on the west side of the 

Virginia Eange farther south.

Pumice is plentiful in the Truckee formation and in the Steamboat 

Hills rhyolite; perlite occurs locally in the Steamboat Hills rhyolite, in the vitrophyre member of the Kate Peak formation, and in 

the Washington Hill rhyolite. Some pumice and perlite have been 

quarried in the Steamboat Hills rhyolite near Sutro Springs, but 

the most extensive quarrying of these materials has been done on Long 

Valley Creek half a mile north of the quadrangle, where pumiceous 

tuff of the Truckee formation is crushed and made into lightweight 

concrete building blocks. Similar but more coherent pumiceous tuff 

has been quarried on the north side of the Truckee River in the same 

area and has been used without crushing as lightweight building stone.

Intermixed silica and clay are available in enormous quantities in 

the areas of bleached rocks. Some of this material has been dug along 

the Geiger Grade for use in brick manufacturing in Reno.

Diatomite is widespread in the Truckee formation, though commonly it is thin bedded and impure. Massive pure diatomite was 

formerly quarried in the Chalk Hills and shipped out for use as a
74 CONTRIBUTIONS TO ECONOMIC GEOLOGY

silver polish, but it has been supplanted by diatomite that is more 

easily accessible in other areas.

THERMAL WATERS

The thermal waters of Steamboat Springs near the west border of 

the quadrangle have been used locally in mineral baths and for heating 

purposes. An effort was once made to pipe hot water into Reno for 

heating purposes; a later plan was to use hot water and steam taken 

from deep bore holes to generate electric power. Thus far, none of 

these extensive plans has been successful, partly because the highly 

mineralized waters tend to corrode pipes or to fill them with mineral 

precipitates; if these difficulties can be overcome the area has excellent 

possibilities for the establishment of greenhouses, and perhaps for 

other uses.

Because thermal waters in the Steamboat area contain much sodium 

chloride and boron, they are not suitable for irrigation. For this 

reason Steamboat Creek is not used for irrigation below the springs. 

Much ground water north and northeast of the springs also has been 

contaminated by subsurface discharge from the system, but warm 

water of good quality locally overlies contaminated water. Much if 

not most of the ground water on the east side of Truckee Meadows is 

warm and is high in mineral content. The major exception is east 

and northeast of Steamboat, where wells in the alluvial fans generally 

yield cold to slightly warm water of good quality.

LITERATURE CITED

Axelrod, D. I., 1949, Eocene and Oligocene formations in the western Great

Basin [abs.] : Geol. Soc. America Bull., v. 60, p. 1935-1936. 

Bailey, E. H., and Phoenix, D. A., 1944, Quicksilver deposits in Nevada: Nev.

Univ. Bull., v. 38, no. 5. 

Bastin, E. S., 1923, Bonanza ores of the Conistock lode, Virginia City, Nevada:

U. S. Geol. Survey Bull. 735-C. 

Becker, G. F., 1882, Geology of the Comstock lode and Washoe district: U. S.

Geol. Survey Mon. 3. 

Blackwelder, Eliot, 1931, Pleistocene glaciation of the Sierra Nevada and Basin

Ranges: Geol. Soc. America Bull., v. 42, p. 865-922.

Brannock, W. W., Fix, P. F., Gianella, V. P., and White, D. E., 1948, Preliminary 

geochemical results at Steamboat Springs, Nevada: Am. Geophys. Union 

Trans., v. 29, p. 211-226.

Calkins, F. C., 1944, Outline of the geology of the Comstock lode district, Nevada: 

U. S. Geol. Survey Prelim. Kept., 35 p.

Calkins, F. C., and Thayer, T. P., 1945, Preliminary geologic map of the Cornstock lode district, Nevada: U. S. Geol. Survey Prelim. Map.

Coats, R, K, 1936, Intrusive domes of the Washoe district, Nevada: Calif. Univ. 

Pubs., Dept. Geol. Sci. Bull., v. 24, no. 4, p. 71-84.

 1940, Propylitization and related types of alteration on the Comstock 

lode: Econ. Geology, v. 35, p. 1-16.
GEOLOGY OF THE VIRGINIA CITY QUADRANGLE, NEVADA 75

Daly, R. A., 1933, Igneous rocks and the depths of the earth: New York, McGrawHill Book Co. 

Daugherty, L. H., 1941, The Upper Triassic flora of Arizona: Carnegie Inst.

Washington Pub. 526. 

Ferguson, H. G., and Muller, S. W., 1949, Structural geology of the Hawthorne

and Tonopah quadrangles, Nevada: U. S. Geol. Survey Prof. Paper 216. 

Oianella, V. P., 1936, Geology of the Silver City district and the southern portion

of the Gomstock lode, Nevada: Nev. Univ. Bull., v. 30, no. 9. 

Hague, Arnold, and Iddings, J. P., 1885, On the development of crystallization

in the igneous rocks of Washoe, Nevada, with notes on the geology of the

district: U. S. Geol. Survey Bull. 17. 

Hinds, N. E. A., 1934, Jurassic age of the last granotoid intrusives in the Klamath

Mountains and Sierra Nevada, California: Am. .Tour. Sci., v. 227, p. 189-192. 

Hunt, C. B., and Sokoloff, V. P., 1950, Pre-Wisconsiu soil in the Rocky Mountain

region, a progress report: U. S. Geol. Survey Prof. Paper 221-G. 

King, Clarence, 1878, Systematic geology: U. S. Geol. Expl. 40th Par. Rept, v. 1. 

Knopf, Adolph, 1918, Geology and ore deposits of the Yerington clsitrict, Nevada:

U. S. Geol. Survey Prof. Paper 114. 

Knopf, Adolph, and Kirk, Edwin, 1918, Geologic reconnaissance of the Inyo

Range and eastern slope of the Sierra Nevada: U. S. Geol. Survey Prof.

Paper 110. 

Jjarsen, E. S., Jr., 1954, Age of the Southern California, Sierra Nevada, and

Idaho batholiths [abs.]: Program of 1954 annual meeting of the Geol. Soc.

America, p. 73. 

MacDonald, J. R., 1950, A note on the age of the Truckee formation: Am. Jour.

Sci., v. 248, p. 581-583. 

Jtfolan, T. B., 1933, Epithermal precious metal deposits, in ore deposits of the

Western States (Lindgren volume), Am. Inst. Min. Metall. Eng., p. 623-640. 

Reid, J. A., 1911, The geomorphogeny of the Sierra Nevada northeast of Lake

Tahoe: Calif. Univ. Pubs., Dept. Geol. Sci. Bull., v. 6, no. 5, p. 89-161. 

Russell, I. C., 1885, Geological history of Lake Lahontan, a Quaternary lake of

Northwestern Nevada: U. S. Geol. Survey Mon. 11. 

Smith, G. H., 1943, The history of the'Comstock lode, 1850-1920: Nev. Univ.

Bull., v. 37, no. 3. 

Thayer, T.\P., 1937, Petrology of later Tertiary and Quaternary rocks of the

north-central Cascade Mountains in Oregon, with notes on similar rocks in

western Nevada : Geol. Soc. America Bull., v. 48, p. 1611-1651. 

Thompson, G. A., 1952, Basin and Range structure'south of Reno, Nevada [abs.]:

Geol. Soc. America Bull., v. 63, p. 1303-1304. 

Yen, Teng-Chien, 1950, A molluscan fauna from the type section of the Truckee

formation : Am. Jour. Sci., v. 248, p. 180-193.

INDEX

Page 

Alta formation, age.------.....-...----------- 52

composition-_-. ....... ... 51-52

occurrence_._--...-.-.-. ._ ..... 51

structure.._.-.___-..-.-.______ 65-66 

American Flat basalt. See McClellan Peak

ollvlne basalt.

American Ravine andesite porphyry, age.-... 52 

composition--...---.---..-.-------------- 52

Bleached rocks, causecomposition..-_. 

largest areas.......

Cenozoic rocks, deformation.-..--------__, 64-68

Comstock ore deposits --.--------.._--... 71-72

Davidson diorite. See Davidson granodiorite. 

Davidson granodiorite, age..- ..- 53 

composition-_-------------- -.-.. 52-53

Deformation of Cenozoic rocks..____.._ 64-68 

Dips, reliability. - 65

Oeomorphology, early history................ 68-69

erosion surfaces...--- . -- 69-70 

present topography .. ... 70

Granitic rocks. See Granodiorite.

Granodiorite, composition.---------- ----- 48-49

occurrence_.....--.-------.--.-----.---- 48

related'Tocks.____1__________ 48-49 

structure...._ .- 49

Hartford Hill rhyolite. See Hartford Hill 

rhyolite tufl.

Hartford Hill rhyolite tuff, age.... _ -------- 50

composition-.-------------.-.-----.---.-- 50

occurrence_.......-..-.....--..--..--... 50

origin........ . . . -.. 50

structure..-._._-__-----___-__ 65-66

type locality._ . . . 50

Hot-spring deposits.. 60

Kate Peak formation, age .........__..... 54,55

composition.-------.._----------------- 54

origin. -._____. ._.-__ 55

structure---....-.--------.------------.- 66-67

thickness.. .-..--- -- - - 54 

Knickerbocker andesite, composition..... 57

Lake Lahontan deposits, composition........ 61-62

Location of area. ....._. --__.__ 46

Lousetown formation, age.. -.... 58

composition... ------ . ... . 58

structure.-..---..._.... .. -. 67-68

type locality__ _..____........ 57

McClellan Peak olivine basalt, occurrence.... 59 

origin.._...._....____________ 60

Metallic minerals, pre-Tertiary age____... 71 

Quaternary age_-..- ----------- 72-73

Tertiary age...-...-. 71-72

Mustang andesite--- _...__. . __ 59

Nonmetalllc minerals_........ ......._ 73-74

Post-Lake Lahontan deposits ------------- 61-62

Pre-Lake Lahontan gravels, age. ---.-. 61

composition-..--_____.___..__ 60-61

structure.. ------_-___-_____ 68

Pre-Tertiary rocks.....____.___._.... 47-49

Previous investigations of the area_......... 46

Quaternary rocks__--------- ..__ 57-62

Sedimentary rocks, metamorphosed, age. . 47

metamorphosed, composition.. 47

Steamboat Hills rhyolite, age_________ 59

composition..__..... . _ 58

occurrence__-- ...-. ____ 58

Stream deposits, composition . ... 62

Strikes, reliability. 65

Tertiary rocks...----------------------------- 49-57

Thermal waters, use_ 74

Truckee formation, age.... ____ 55-56

composition... ------------------------- 55

structure.__-----____.______ 66-67

Truckee group. See Truckee formation.

Volcanic rocks', metamorphosed, agemetamorphosed, composition..-.

Washington Hill rhyolite, agecomposition... --------

occurrence__ ._.. 

origin..-_................

48

48

57

77

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