UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY BULLETIN 1042 PLATE 8

pect R20E 40" RIE 35" ee

a eel

TION,
TION,

Lake Lahontan and post-Lake Lahontan
deposits, Qi, and stream deposits, Qa!
Gravel, sand, and silt; smaller areas shown only where significant; includes some scattered
wind deposits. The lake deposits near the southeastern corner of the quadrangle are sands
and silts of Lake Lahontan proper. Elsewhere the lake deposits were laid down in higher
lakes nearly contemporaneous with Lake Lahontan and in post-Lake Lahontan ies)
playa deposits of closed basins are included.
gravel ‘and sand partly contemporaneous with shontan po
bene? landslide, and mine dumps are included with the stream ‘in th
listrict

‘are composed of
‘and later.

Pleistocene and Recent

uf Hot-spring deposits
Siliceous sinter, Qs, and travertine, Qt, deposited thermal ings.
e,Qt, deposited by thermal springs. Age ranges from

@ Pre-Lake Lahontan gravels

: wels of alluvial fans and pediments. | Includes some high terrace gravels that are
Es iasohed vena hare preserine fa tones coe clayey, ond 4 bo hfe Bes gres
zone, 1) ed, is @ i gra
‘boulders in thie’ zone are thorou ‘andesitte boulders lees so. The winder-
ne cindaing eileen Hebe of oaletuncartanatsor alien and i alot 4 to 20
+ boulders of granodiorite are gene |. Areas underlain 0

I gIRPiAaWeHEd louldars fromm 8 mokes 10 uct sxichatuner se

QUATERNARY

Pleistocene
i
z

Qmp Qmpe

McClellan Peak olivine basalt
Flows, Qmp, and cinder cones, Qmpc, to black basalt with prominent yellowish-green
Qmp, and cin er pred ees wit iment yel

Qma

Mustang andesite
Thick hornblende andesite. A a ke contains inent
ick flows of gray « ine grained rod vining prominent large

7s
Steamboat Hills rhyolite Pp ee oma
Domes of extrusive pumiceous rhyolite containing sparse phenocrysts of sanidine, quarts, Contaet, showing dip
plagioclase, and biotite Dashed where approximately located, short dashed where indefinite or gradational

~~
Pleistocene(?)

1.16 NE
25

TBN.
25!

Lousetown formation
wy flows, Qtl, of basaltic andesite and basalt; intrusions, Qtli, similar

‘color and well-formed platy parting, with

rresulet nt of the plagioclase

‘a fine-grained pyrozene andesite with a basaltic habit and a

pee he re ery to
om on _

af underlying stream gravel included in some places.” In Steamboat Hills ly con-
temporaneous with or younger than Steamboat Hills rhyolite; elsewhere older

U
Cie rete Fault, showing dip

Dashed where approximately located, dotted where concealed. U, upthrown side
D, downthrown side;

nN,
Pliocene or Pleistocene

TERTIARY OR QUATERNARY

ee eee

Knickerbocker andesite Doubtful or probable fault
(Distinguished only in the Comstock lode district)
Dark pyroxene andesite with a thin buff-colored rind on weathered surfaces. Partly olivine a
bearing. Intrusive in part
Strike and dip of beds
Sedimentary rocks, bedded pyroclastic rocks, and lava flows

e
Washington Hill rhyolite Horizontal beds
henoerysts of pla~
‘with upper part es
Strike and dip of planar structure
Platy parting inlava flows and shallow intrusions; foliation in granitic and metamorphic
‘roc

Pliocene

‘Truckee formation +
Sadimentary rocks deposited in streams and lakes, with intercalated tuf. Includes diat- Efsine'ot gettical yiauar nirwetare,
‘mite, shale, i

ocrinrpneatin eapeenlpon gal peankg mamlonerente a aime gy
iti vi litie source a it uy urt Oo}
Tiere Peak formation pane

Strike and dip of joints in granitic rocks

oh aa

Quartz veins Anticline, showing trace of axial plane
Only large areas of quartz are shown Dashed where approximately located

: Syneline, showing trace of axial plane
Dashed where approximately located
Kate Peak formation, Tk, with vitrophyre member, a ce
Tkv, and intrusive andesite porphyry, Tki
ind agglomerates yposed chic hornblende andesite, biotite-
oie Saanaase Sica humserated patociis rroee
Strophyre member is made up af lowe
some Pappas jats of plagioclase, ,
‘te most. commonly
ind plagioclase phenocrys

Miocene or Pliocene

20
TAIN.

present in places
Formation. "Most of these eriteria, however, may be missing locally

ind. plagioclase phenocrysts are generally lay

TERTIARY

Davidson granodiorite
iht-gray medi ined intrusive rock composed ioclase, green clusters of altered
Sratnacian’ stnorate (oprocans, hornitenda, Bot, orth orthodlase, and quarts, ‘The
‘orthoclase and quartz are fine grained and inconspicuous. In the smaller intrusive bodies
the rock is strongly porphiyritic, with an aphanitic to fine-grained groundmass ; orthoclase
and quartz are almost entirely in the groundmass

Miocene(?)

‘American Ravine andesite
(Distinguished only in the Comstock lode district)
‘Most abundant type is fine-grained medium- to light-gray hornblende andesite with a sil
Granite beta Upmann tn dled cere gfe
‘some coarser andesite porphyry on the southivest side of American ravine

intrusions of hornblende and a

|. The Sutro member, which ia present only in
the Comstock lode district, is a se rrock derived in large part from rhyolitic and
andesitie volcante rocks; it ranges in texture from shale to conglomerate, with grayish-
green shale especially characteristic

indesite; gen-

i: x x r Sf6
Jarenen tata at See PAELY , Lavas

Ca
Qi

Oligocene(?)

INDEX MAP SHOWING LOCATION OF

Hartford Hill rhyolite tuff
Light-pink to dull-purple tuf, tuf-brecci, and welded tufl. Composed largely of devitrified VIRGINIA CITY QUADRANGLE
9 abundant in

rmice and glass, with a variable proportion of erystats of quarts,
Ticfislase! dnd Viskin: “Frepmants Of prandilo end metsmarbive ross ore
places
119°45 119°30"
ou VIRGINIA CITY QUADRANGLE |

err TI6N

Granodiorite, gd, and foliated granodiorite, gdt
Most abundant is a lig medin ined plutonic rock that consists of 20
ae ns Leo ee raat hae
eed ode oped fgets . The foliated itic
rock near the southwestern corner of the ‘is characterized by alined biotite and
@ porphyritic appearance, seemingly caused by movement during consolidation

o a
119°30'

Metavoleanic rocks

CRETACEOUS

39°15" R20 E 40! R. 22 E.
119°45" R20E

Base from U. S. Geological Survey map aca. Aa ten Re Dae ile: Mainly ‘h-green rocks irregularly stained with iron oxides. Composed of sodi
of Virginia City quadrangle, Nevada and J. G. Moore, 1948-52; Comstock lode Narnphibele, with variable amounts of quartz, biotite, chlorite, and ue
district from detailed map by F. C. Calkins egionally and thermally metamorphosed basalt and andesite

and T. P. Thayer, 1935-39

‘Metamorphosed sedimentary rocks
Argillite, slate, hornfels, and contact ‘with some conglomerate and some limestone and
psec ts rate is com ‘mainly of andesite pebbles; the finer grained
‘rocks were originally tuffaceous 80 ‘in large part

TRIASSIC (2)

Bleached rocks
(Shown by black dot pattern superimposed on several formations) ere)
White, yellow, and reddish-brown rocks subjected to near-surface acid attack resulting from
PIT ae eer Ee nm on carter Beenie ee ee INDEX MAP SHOWING LOCATION OF
Rees eres ee ee terete ee ecurinte te og weenie COMSTOCK LODE DISTRICT
RUT IeL ar apiaerea oun oren Gand ruetie oe ions; -bearing rocks
‘re similarly altered but have residual quartz. Caleite and gypeum abundant locally

‘Steamboat Valley

‘TRUE NORTH

APPROXIMATE MEAN
DECLINATION 1950

Mt. David E i A H cr
ne, a an fe E : 2 foe
ve 3 eeu : ited
a meek Sey es j bw
5000’ ‘ Jes ty “eae
4000'-4 = f * F4000
3000’. ee

GEOLOGIC MAP AND SECTIONS OF THE VIRGINIA CITY QUADRANGLE, NEVADA

Seale 1:62,500

0 5 Miles
=

Contour interval 40 feet
Datum is mean sea level