Cowttack Mo htain ouht • @, 

Quadrangles, California and Nevada~ 

Anal ·c Dat 

I 

I 

U.S. GEOLOGICAL SURVEY BULLETIN 1783 I 

I 

Cowtrack Mountain and Glass Mountain 

Quadrangles, California and NevadaAnalytic Data 

By PAUL C. BATEMAN, KONRAD B. KRAUSKOPF, 

and MICHAEL F. SHERIDAN 

Modal and chemical data on the 

granitic rocks of the Cowtrack Mountain 

and Glass Mountain quadrangles 

U.S. GEOLOGICAL SURVEY BULLETIN 1783 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1988 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

library of Congress Cataloging-in-Publication Data 

Bateman, Paul Charles, 1910-

Cowtrack Mountain and Glass Mountain quadrangles, 

California and Nevada-analytic data. 

U.S. Geological Survey Bulletin 1783 

Bibliography 

Supt. of Docs. No.: I 19.3:1783 

1. Rocks, lgneous-California-Cowtrack Mountain 

region-Analysis. 2. Rocks, Igneous-California-Glass 

Mountain region (Mono County)-Analysis. 3. Rocks, 

Igneous-Nevada-Mineral County-Analysis. 4. 

Intrusions (Geology)-California-Cowtrack Mountain 

region. 5. Intrusions (Geology)-California-Giass 

Mountain region (Mono County). 6. Intrusions 

(Geology)-Nevada-Mineral County. I. Krauskopf, 

Konrad Bates, 1910- II. Sheridan, Michael F. Ill. 

Title. IV. Series. 

QE75.B9 No. 1783 557.3 s 87-600068 

[QE4611 [552' .3'0979448] 
CONTENTS 

Abstract 1 

Introduction 1 

Geologic sum mary 1 

Sampling and analytical methods 2 

Wheeler Crest Granodiorite 2 

Granite of Casa Diablo Mountain 2 

Fine-grained granite and aplite 3 

Diorite 3 

References 3 

FIGURES 

1. Index map showing location of Cowtrack Mountain and Glass Mountain 

quadrangles 2 

2-13. Simplified geologic maps showing: 

2. Sample locations, Cowtrack Mountain quadrangle 4 

3. Sample locations, Glass Mountain quadrangle 5 

4. Volume-percent quartz, Cowtrack Mountain quadrangle 6 

5. Volume-percent quartz, Glass Mountain quadrangle 7 

6. Volume-percent alkali feldspar, Cowtrack Mountain quadrangle 8 

7. Volume-percent alkali feldspar, Glass Mountain quadrangle 9 

8. Volume-percent plagioclase, Cowtrack Mountain quadrangle 10 

9. Volume-percent plagioclase, Glass Mountain quadrangle 11 

10. Volume-percent mafic minerals, Cowtrack Mountain quadrangle 12 

11. Volume-percent mafic minerals, Glass Mountain quadrangle 13 

12. Bulk specific gravity, Cowtrack Mountain quadrangle 14 

13. Bulk specific gravity, Glass Mountain quadrangle 15 

14. Plots of modes and norms of granitic rocks 16 

TABLES 

1. Chemical analyses and norms of representative granitic rock samples 17 

2. Modes and specific gravities of granitic rock samples 18 

m 

Cowtrack Mountain and 

Quadrangles, California 

Glass Mountain 

and NevadaAnalytic Data 

By Paul C. Bateman, Konrad B. Krauskopf, and Michael F. Sheridan 

Abstract 

Modal and major-element chemical data on the 

Mesozoic plutonic rocks of the Cowtrack Mountain and 

Glass Mountain quadrangles are presented in tables, 

maps, and diagrams. These rocks crop out in about 2.0 

percent of the two quadrangles, and the remaining 

area is largely covered by Cenozoic volcanic rocks. 

The dominant plutonic rocks are the Triassic Wheeler 

Crest Granodiorite and the Jurassic granite of Casa 

Diablo Mountain; small masses of diorite, fine-grained 

granite, and aplite are also present. 

INTRODUCTION 

The Cowtrack Mountain and Glass Mountain 

quadrangles lie between the Sierra Nevada on the west 

and the White Mountains on the east. The Cowtrack 

Mountain quadrangle and almost all of the Glass 

Mountain quadrangle are in Mono County, California, 

but the northeast corner of the Glass Mountain 

quadrangle extends into Mineral County, Nevada (fig. 

1). This report provides modal and chemical data on 

the granitic rocks of the two quadrangles. Data on the 

widespread Cenozoic volcanic rocks are not included 

here because many reports on the volcanic rocks have 

already been published and others are being prepared 

in connection with an intensive study of the 

geothermal potential of the Long Valley caldera 

immediately to the south. This report supplements the 

geologic map of the Glass Mountain quadrangle 

(Krauskopf and Bateman, 1977), but a geologic map of 

the Cowtrack Mountain quadrangle has not been 

published. 

GEOLOGIC SUMMARY 

Cenozoic volcanic and sedimentary rocks cover 

most of the region; granitic rocks crop out in less than 

20 percent of the quadrangles, chiefly in uplifted or 

tilted fault blocks. Extensive volcanism in the general 

area during the Cenozoic culminated in eruption of the 

Pleistocene Bishop Tuff, a rhyolitic ash-flow deposit, 

from the Long Valley caldera to the south and in 

eruption of the rhyolitic Mono and Inyo craters to the 

west. Glass Mountain, in the southwest corner of the 

Glass Mountain quadrangle, forms part of the northern 

rim of the Long Valley caldera and is the source of a 

widespread older ash-flow deposit. In addition to the 

rhyolitic deposits, Tertiary basalt and andesite flows 

and pyroclastic rocks underlie most of the north half 

of the Glass Mountain quadrangle and large parts of 

the Cowtrack Mountain quadrangle. 

The region is broken by an intricate system of 

normal faults, and granitic rocks are exposed in 

uplifted blocks and along the edges of tilted blocks. In 

the southern part of the Cowtrack Mountain 

quadrangle, granitic rocks crop out in the north rim of 

the Long Valley caldera; farther north in the 

quadrangle they crop out in uplifted fault blocks. In 

the southeastern part of the Glass Mountain 

quadrangle, where fault blocks are tilted eastward, 

granitic rocks form long north-trending ridges. 

Two principal granitic rock units are present 

within the quadrangles, the Triassic Wheeler Crest 

Granodiorite and the Jurassic granite of Casa Diablo 

Mountain. Small bodies of diorite, fine-grained 

granite, and aplite are present locally. The Wheeler 

Crest Granodiorite is a very large intrusion that 

extends northward along the eastern side of the Sierra 

Nevada from the type locality in Wheeler Crest and 

into the Glass Mountain and Cowtrack Mountain 

quadrangles. In earlier publications, including the 

geologic maps of the Glass Mountain and Casa Diablo 

Mountain quadrangles (Krauskopf and Bateman, 1977; 

Rinehart and Ross, 1957), this rock was called the 

granodiorite of the Benton Range. However, it is 

identical with the Wheeler Crest Granodiorite in the 

eastern escarpment of the Sierra Nevada (Bateman, 

1965) and is continuous with it except for alluvial and 

volcanic cover. The granite of Casa Diablo Mountain 

appears to form several rounded plutons that intrude 

the Wheeler Crest Granodiorite. Both rocks are highly 

altered in many places. The rock in many outcrops of 

the granite of Casa Diablo Mountain is strongly 

sericitized, and the Wheeler Crest Granodiorite is 

locally chloritized and epidotized. The time of this 

alteration is uncertain, but localization of alteration in 

1 
some places along gently dipping sheeting joints, which 

generally formed as a consequence of release of 

pressure during erosion, suggests that it may have 

occurred during Cenozoic volcanism. However, 

widespread alteration of hornblende crystals in the 

Wheeler Crest Granodiorite to decussate aggregates of 

biotite probably occurred during late stages of 

crystallization of the granodiorite. 

SAMPLING AND ANALYTICAL METHODS 

Discontinuous outcrops and alteration in these 

two quadrangles precluded collecting samples of the 

granitic rocks at regular intervals, and coverage is 

irregular. Additionally, some samples of the granite of 

Casa Diablo Mountain, which appeared unaltered in the 

field, were found to be strongly sericitized and not 

suitable for either chemical or modal analysis. 

Chemical analyses for major elements were 

made of 13 selected samples (table 1), and modes and 

specific gravities were determined for all of the 

acceptable samples (figs. 2-13 and table 2). Modes 

were determined by counting at least 1,000 regularly 

spaced points on s~wed and stained slabs having areas 

of at least 70 em (Norman, 1974). Modal analyses 

commonly include percentages of hornblende and 

biotite, as determined in thin section and apportioned 

to the percentage of total mafic minerals determined 

on stained slabs. Here, however, this would have been 

meaningless because the granite of Casa Diablo 

Mountain contains no hornblende and the hornblende in 

the Wheeler Crest Granodiorite of these quadrangles is 

largely altered to aggregates of tiny biotite flakes. 

WHEELER CREST GRANODIORITE 

The Wheeler Crest Granodiorite is exposed 

discontinuously in both quadrangles, but it probably is 

more or less continuous at shallow depths between 

CALIF 

outcrops. It is a medium-gray rock that generally 

contains alkali-feldspar megacrysts of varied size and 

abundance. Unlike exposures farther south in Wheeler 

Crest (Bateman, 1965), the rock rarely has a 

discernable foliation within the two quadrangles. 

Modes on a Q-A-P triangular diagram (fig. 14) plot 

most abundantly in adjoining parts of the granite and 

granodiorite fields as do the modes of most other 

megacrystic rocks of the region. An absence of 

smooth fresh rock surfaces made it impossible to 

determine the abundance of megacrysts in the field 

over representative areas, so megacrysts were counted 

on the stained slabs together with groundmass alkali 

feldspar. Modes that plot distant from the alkali 

feldspar-plagioclase join probably reflect the uneven 

distribution of alkali-feldspar megacrysts on the scale 

of hand samples. The groundmass is medium grained in 

most places but is fine grained locally. The color 

index ranges from 2 to 23 and peaks at about 10 (fig. 

14). Megacrysts show a wide range of size, shape, and 

abundance, unlike those at Wheeler Crest, the type 

locality, which are well formed and tabular (Bateman, 

1965). Variations occur even within a single hand 

sample, and in some exposures megacrysts are 

absent. Some megacrysts are tabular and well formed, 

but others are rounded; many anastomose into the 

adjoining rock and have extremely irregular 

boundaries. Sample CT-27 from the Cowtrack 

Mountain quadrangle has yielded a discordant U-Pb age 

of 214 m.y., and a sample from Wheeler Crest, 50 km 

south, has yielded a concordant age of 207 m.y. (Stern 

and others, 1981). U-Pb ages on two size fractions of 

each of three other samples range from 159 to 217 

m.y. (Chen and Moore, 1982). 

GRANITE OF CASA DIABLO MOUNTAIN 

The granite of Casa Diablo Mountain crops out in 

the southeast corner of the Glass Mountain quadrangle 

and in the northwest quarter and along the south 

37" 30'L_ __________ L-----------~----------~----------~ 

2 

QUADRANGLE LOCATIONS 

Figure 1. Index map showing location of Cowtrack Mountain and Glass Mountain quadrangles and adjacent 

quadrangles for which U.S. Geological Survey geologic mapping has been done. 
margin of the Cowtrack Mountain quadrangle. 

Apparently it forms several separate plutons that 

intrude the Wheeler Crest Granodiorite. The rock 

generally is coarse grained and equigranular and shows 

no foliation. The color index is 1 or 2 in most samples, 

but it is higher in a few samples. Biotite is the only 

mafic silicate. Stern and others (1981) determined a 

concordant U-Pb age of 161 m.y. on sample GM-13 

from the Glass Mountain quadrangle. 

FINE-GRAINED GRANITE AND APLITE 

Small bodies of fined-grained leucogranite are 

present in both the Cowtrack Mountain and Glass 

Mountain quadrangles, and dikes and small masses of 

aplite are scattered through the Glass Mountain 

quadrangle. The rocks are compositionally similar to 

the granite of Casa Diablo Mountain and probably are 

cogenetic with it. 

DIORITE 

The small masses of diorite are altered but 

appear to represent a range of compositions. They 

consist chiefly of hornblende and plagioclase, but 

clinopyroxene is present as cores in some hornblende. 

Opaque minerals are bordered by exsolved titanite. 

Quartz and biotite that appear to be primary are 

present in sample 1528 from a mass in the northern 

part of the Cowtrack Mountain quadrangle. 

REFERENCES 

Bateman, P.C., 1965, Geology and tungsten 

mineralization of the Bishop district, 

California: U.S. Geological Survey Professional 

Paper 4 70, 208 p. 

Chen, J.H., and Moore, J.G., 1982, Uranium-lead ages 

from the Sierra Nevada batholith, California: 

Journal of Geophysical Research, v. 87, no. B6, 

p. 4761-4784. 

Krauskopf, K.B., and Bateman, P.C., 1977, Geologic 

map of the Glass Mountain quadrangle, Mono 

County, California, and Mineral County, 

Nevada: U.S. Geological Survey Geologic 

Quadrangle Map GQ-1099, scale 1:62,500. 

Norman, M.B., II, 1974, Improved techniques for 

selective staining of feldspar and other minerals 

using amaranth: U.S. Geological Survey Journal 

of Research, v. 2, no. 1, p. 73-79. 

Rinehart, C. D., and Ross, D.C., 1957, Geologic map of 

the Casa Diablo Mountain quadrangle, 

California: U.S. Geological Survey Geologic 

Quadrangle Map GQ-99, scale 1:62,500. 

Stern, T.W., Bateman, P.C., Morgan, B.A., Newell, 

M.F., and Peck, D.L., 1981, Isotopic U-Pb ages of 

zircon from the granitoids of the central Sierra 

Nevada, California: U.S. Geological Survey 

Professional Paper 1185, 17 p. 

Streckeisen, A.L., 1973, Plutonic rocks: classification 

and nomenclature recommended by the lUGS 

Subcommission on the Systematics of Igneous 

Rocks: Geotimes, v. 18, no. 10, p. 26-30. 

3 
3r 

EXPLANATION 

[For figs. 2-13] 

Undgated } CENOZOIC 

sedimentary and 

volcanic rocks 

~ Aplite 

l!f.tiiiiiil 

Fine-grained granite 

fJ'D?] 

kiBlliJ 

Granite of Casa 

Diablo Mountain 

JURASSIC 

~~=:;;~:' } TRIASSIC 

(formerly granodiorite 

of the Benton Range) 

Diorite and gabbro 

} MESOZOIC 

Metamorphic rocks } PALEOZOIC OR 

PROTEROZOIC 

•. 14 

X 

Contact 

Fault- Shown only where 

contacts are affected 

Modally analyzed sample - Number 

refers to tables 1 and 2 

Chemically analyzed sample 

Sample dated isotopically 

by the U-PB method 

1568.....-Rw 

0 2 3 MILES 

~Jc 0 2 3 KILOMETERS 

118° 45' 

Rw~~ \ 

v ~ Rw 

? 

45'~--------------------~~---------------------------------------------------------------=----~ 

Figure 2. Cowtrack Mountain quadrangle, Calif., showing principal bedrock units and sample locations. CTprecedes all one-, two-, and three-digit sample numbers. 

4 
Jc~ 2 0 

47~Rw r---~~-----r~----~ 

3T ~Jc 0 2 3 KILOMETERS Rw'iJ 

45'~--------------------------------------~~~~~~~~~------

~Rw 

Jc~l 

Figure 3. Glass Mountain quadrangle, Calif. and Nev., showing principal bedrock units and sample locations. OMprecedes all sample numbers. Explanation as in figure 2. 

5 
119° 00' 

38° 

00' 

37 

0 

a--Jc 0 

118° 45' 

27..---Rw 

2 3 MILES 

2 3 KILOMETERS 

45' L-------------------~~~---------------------------------------------------------------=~--~ 

Figure 4. Volume-percent quartz, Cowtrack Mountain quadrangle. Explanation as in figure 2. 

6 
118° 45' 118° 30' 38or----------------------------------------------------------------------------------------------, 

00' 

Jc~ 2 0 

25~Rw r---.-~-----r~----~ 

3r ~Jc 0 2 3 KILOMETERS Rw'6) 

45'L---------------------------------------~~~~~~~~~------

Figure 5. Volume-percent quartz, Glass Mountain quadrangle. Explanation as in figure 2. 
119° 00' 

38° 

00' 

37 

0 

o--Jc 0 

22...-Rw 

2 3 MILES 

2 3 KILOMETERS 

45' L-------------------~~~--------------------------------------------------------------~----~ 

Figure 6. Volume-percent alkali feldspar, Cowtrack Mountain quadrangle. Explanation as in figure 2; tr, trace. 

8 
118° 45' 118° 30' 

38°.----------------------------------------------------------------------------------------------, 

00' 

J 

Jc~ 2 3 0 

30~Rw ~--~-L~---r~----~ 

2 3 KILOMETERS 3JD ~Jc 0 

45'L---------------------------------------~~~~~~~~~----~~~L---~~~~---------------J 

Figure 7. Volume-percent alkali feldspar, Glass Mountain quadrangle. Explanation as in figure 2. 

9 
118° 45' 

0 2 3 MILES 

er-Jc 0 2 3 KILOMETERS 

3T 

45' ~------------------~~~------------------------------------------------------------~~L_--~ 

Figure 8. Volume-percent plagioclase, Cowtrack Mountain quadrangle. Explanation as in figure 2. 

10 
118° 45' 118° 30' 38°~---------------------------------------------------------------------------------------. 

00' 

Rw --.33 

Jc~ 0 2 3 

38~Rw ~----~-r---.-L----~ 

37' ~Jc 0 2 3 KILOMETERS 

45'L---------------------------------------~~~~~~~~~----~~~~--~--~----------------~ 

Figure 9. Volume-percent plagioclase, Glass Mountain quadrangle. Explanation as in figure 2. 

11 
118° 45' 

0 2 3 MILES 

IYJc 0 2 3 KILOMETERS 

37 

45' ~--------------------~~--------------------------------------------------------------~----_J 

Figure 10. Volume-percent mafic minerals, Cowtrack Mountain quadrangle. Explanation as in figure 2; tr, trace. 

12 
118° 45' 118° 30' 

38or---------------------------------------------------------------------------------------------~ 

00' 

Jc~ 0 

8~Rw r---~-L~--~L-----~ 

2 

3r ~Jc 0 2 3 KILOMETERS 

45' ~--------------------------------------~~----~~~~~----~LW~L-~~~~~--------------~ 

Figure 11. Volume-percent mafic minerals, Glass Mountain quadrangle. Explanation as in figure 2; tr, trace. 

13 
119° 00' 

38° 

00' 

3T 

0 

o-Jc 0 

118° 45' 

2 3 MILES 

2 3 KILOMETERS 

45' ~--------------------~~--------------------------------------------------------------~~--~ 

Figure 12. Bulk specific gravity, Cowtrack Mountain quadrangle. Explanation as in figure 2. 

14 
118° 45' 118° 30' 

38°.-------------------------------------------------------------------------------------------, 

00' 

2.58 

2J6~~ 0 

~Rw r---.-~-.--~~----~ 

2 

37' ~Jc 0 2 3 KILOMETERS Rw'29 

45'~--------------------------------------~~~~~~~~~------

Figure 13. Bulk specific gravity, Glass Mountain quadrangle. Explanation as in figure 2. 

15 
35 

35 

]~1:L EE 

~3;1 

5 

65 

1 5 10 

Color mdex ( • ) 

-1oL 0(/) 

.... Q) 

za. 

E E 5 

:::leo 

z(/)1 

1 5 10 

Color index ( • ) 

,~L 5 

5 

10 35 65 

Cowtrack Mountain quadrangle EXPLANATION Glass Mountain quadrangle 

65 

Granite of Casa Diablo Mountain 

Wheeler Crest Granodiorite 

Fine-grained granite 

- 10 ~ 0 (/) 

Q;~ 

Ll 0. 5 El ___§ 

~~1 rR§FfffmRnrBI 

1 5 10 15 20 25 

Color index ( o ) 

5 

90 35 65 

(/) 

Q) 15 0. 

E 

3; 10 

0 

Cowtrack Mountain quadrangle Glass Mountain quadrangle 

Q 

EXPLANATION 

Q Quartz 

A Alkali feldspar 

P Plagioclase (An5

_

100) 

5 

A ~-----L-----------------L~~~~~J---------------------~~p 

Modal classification 

(Modified from Streckeisen, 1973) 

Diorite and 

gabbro 

Quartz 

Orthoclase Plot of norms 

10 15 20 25 

Color 1ndex ( o ) 

90 

'0 Plagioclase 

(An+Ab) 

Figure 14. Plots of modes and norms of granitic rocks, Cow track Mountain and Glass Mountain quadrangles. 

16 
...... 

~ 

TABLE 1. Chemical analysis and norms of representative granitic rock samples, Cowtrack Mountain and Glass Mountain quadrangles, 

Calif. and Nev. 

[--, no data. CT-27 analyzed by wet chemistry, Elaine L. Brandt, analyst; all others by the rapid rock analysis method, Leonard 

Shapiro, project leader.] 

Wheeler Crest Granodiorite 

Field No... CT-2 CT-24 CT-27 CT-103 GM-4 GM-6 GN-10 GM-30 GN-123 

Lab No ••••• N-116095W N-116096W N-1161270 M-116097W N-116086W M-116087W M-116089W M-116090W M-116093W 

Sio2 ••••••• 

Al 2o3 •••••• 

Fe 2 o3 •••••• 

FeO •••••••• 

NgO •••••••• 

CaO •••••••• 

Na 2o ••••••• KzO.;_ ••••••• 

H~O , •••••• H;o-...... . TiOz ••••••• 

Pzos .....•. NnO •••••••• 

C02 ••••••• , 

Sum ••••• 

Q •••••••••• 

c •.••••.•.• 

or •.•••.... 

a b ••••••••• 

an ••••••••• 

d i ........ . 

hy ••••••••• 

mt ••••••••• 

i 1 ••••••••• 

ap ••••••••• 

hm ••••••••• 

Total. •• 

64.6 

15.8 

2.0 

3.0 

1.8 

5.1 

2.6 

3.7 

.78 

.11 

.48 

.26 

.11 

.01 

100.4 

21.7 

22.0 

22.1 

20.6 

2.5 

6.5 

2.9 

• 9 

.6 

99.8 

66.5 

15.1 

1.7 

2.7 

1.6 

4.4 

2.6 

4.0 

.82 

.07 

.45 

.24 

.10 

.02 

100.3 

24.3 

23.8 

2 2.1 

17.8 

2.1 

6.0 

2.5 

.9 

.6 

100.1 

65.77 

16.75 

2.01 

l. 63 

0.83 

2.69 

3.85 

4.95 

.44 

.09 

.32 

.13 

.11 

.09 

99.7 

17.5 

.s 

29.5 

32.9 

12.6 

3.1 

2.9 

.6 

.3 

99.9 

6 5.1 

16.0 

1.8 

3.2 

1.7 

4.6 

2.6 

3.6 

.85 

.07 

.52 

.24 

.13 

.01 

100.4 

22.9 

.os 

21.4 

22.1 

21.4 

8.0 

2.6 

1.0 

.6 

100.1 

67.8 

15.1 

1.4 

2.4 

1.4 

4.0 

2.6 

4.2 

.72 

.11 

.38 

.18 

.11 

.02 

100.4 

25.6 

24.9 

22.1 

17.2 

1.3 

5.7 

2.0 

• 7 

.4 

99.9 

Chemical analyses (weight percent) 

63.3 

16. 1 

2.0 

3.5 

2.0 

s.s 

2.7 

3.4 

.79 

.11 

.56 

.31 

.12 

.02 

100.4 

19.7 

20.2 

23.0 

21.9 

2.9 

7.7 

2.9 

1.1 

• 7 

100.1 

71.8 

13.6 

1.1 

1. 7 

.96 

3.0 

2.4 

s.o 

.77 

.10 

.20 

.12 

.08 

.01 

100.8 

CIPW norms 

30.8 

29.6 

20.3 

11.6 

2.1 

3.4 

1.6 

.4 

.3 

100.1 

68.0 

14.7 

1.4 

2.6 

1.5 

4.5 

2.6 

3.5 

.78 

.08 

.41 

.21 

.13 

.03 

100.4 

27.5 

20.8 

2 2.1 

18.2 

2.4 

5.8 

2.0 

.8 

• 5 

100.1 

69.4 

14.8 

1.1 

2.1 

1.2 

3.4 

2.5 

4.4 

.84 

.09 

.34 

.16 

.1 0 

.03 

100.6 

28.4 

0.1 

26.1 

21.3 

15.9 

5.6 

1.6 

• 6 

.4 

100.0 

Granite of Casa Diablo Mountain 

GM-9 GM-34 GN-106 GM-134 

M-116088W M-116091W H-116092W M-116094W 

76.1 

13.0 

.84 

.26 

.19 

.56 

3.0 

5.1 

.54 

.06 

.14 

.02 

.06 

.02 

99.9 

38.0 

1.6 

30.4 

25.6 

2.7 

.s 

.6 

.3 

<.OS 

.4 

100.2 

74.5 

13.5 

.so 

.52 

.34 

.91 

3.0 

5.3 

.60 

.13 

.15 

.04 

.07 

.o 1 

99.9 

34.6 

1.3 

31.6 

25.6 

4.3 

1.0 

1.2 

.3 

.1 

100.0 

74.1 

13.7 

.79 

.76 

.45 

1.2 

3.1 

5.1 

.52 

.07 

.20 

.06 

.os 

.01 

100.1 

33.4 

1.0 

30.3 

26.4 

5.6 

1.6 

1.2 

.4 

.1 

100.0 

72.6 

14.1 

1.0 

1.0 

.43 

1.6 

3.1 

4.8 

.71 

.16 

.1 7 

.06 

.os 

.01 

99.8 

32.3 

1.1 

28.7 

26.5 

7.6 

1.9 

1.5 

.3 

.1 

100.0 
TABLE 2. Modes and specific gravities of granitic rock samples from the Cowtrack Mountain and 

Glass Mountain quadrangles, Calif. and Nev. 

Modes (volume percent) Modes (volume percent) 

Sample Speci fie Sample Specific 

number Plagio- Alkali Mafic gravity number Plagio- Alkali Mafic gravity 

Quartz clase feldspar minerals Quartz clase feldspar minerals 

Wheeler Crest Granodiorite, Wheeler Crest Granodiorite, 

Cowtrack Mountain quadrangle Glass Mountain quadrangle (continued) 

CT-2 •••• 25 35 27 13 2.73 GM-53 ••• 21 40 29 11 2.72 

CT-5 •••• 27 40 18 14 2.71 GM-54 ••• 23 46 17 13 2.74 

CT-8 •••• 17 48 14 22 2.81 GM-55 ••• 23 42 19 16 2.72 

CT-9 •••• 10 54 13 23 2.80 GM-56 ••• 29 39 21 11 2.70 

CT-11 ••• 12 59 23 6 2.70 GM-57 ••• 28 40 22 10 ?,69 

CT-12 ••• 30 41 17 12 2.71 GM-58 ••• 24 42 27 7 2.66 

CT-13 ••• 34 42 14 10 2.69 GM-59 ••• 29 36 26 10 2.68 

CT-14 ••• 28 44 15 14 2.71 GM-61 ••• 28 38 25 9 2.68 

CT-15 ••• 32 35 26 6 2.69 GM-62 ••• 28 38 24 9 2.67 

CT-16 ••• 23 43 23 12 2.72 GM-63 ••• 28 38 23 11 2.71 

CT-17 ••• 25 45 20 11 2.66 GM-64 ••• 21 39 28 11 2.71 

CT-18 ••• 26 43 19 11 2.69 GM-64A •• 29 42 17 12 2.70 

CT-19 ••• 29 45 16 10 2.72 GM-65 ••• 21 45 24 10 2.68 

CT-20 ••• 25 45 17 13 2.70 GM-67 ••• 27 41 19 13 2.69 

CT-21. •• 23 45 16 16 2.73 GM-69 ••• 28 50 13 9 2.69 

CT-22 ••• 23 42 21 14 2.70 GM-72 ••• 29 40 20 12 

CT-24 ••• 27 38 23 12 2.72 GM-73 ••• 28 36 27 9 2.68 

CT-25 ••• 24 46 20 9 2.71 GM-74 ••• 18 45 25 12 2.71 

CT-27 ••• 10 46 35 10 2.68 GM-75 ••• 22 44 23 11 2.66 

CT-103 •• 24 43 20 14 2. 72 GM-76 ••• 29 36 26 9 2.68 

CT-104 •• 26 42 19 13 2.71 GM-77 ••• 30 30 30 11 2.70 

CT-105 •• 29 43 19 9 2.70 GM-80 ••• 27 41 21 12 2.69 

CT-106 •• 23 46 17 14 2.71 GM-83 ••• 24 42 25 9 2.71 

CT-107 •• 27 36 24 14 2.68 GM-84 ••• 24 38 27 11 2.72 

1517 •••• 14 36 47 3 2.63 GM-104 •• 24 47 12 16 2.73 

1526 •••• 18 37 42 3 2.63 GM-112 •• 32 44 22 3 2.65 

1531. ••• 14 48 28 10 2.69 GM-114 •• 33 42 15 11 2.71 

1550 •••• 15 44 21 19 2. 72 GM-115 •• 32 33 25 11 2.66 

1568 •••• 27 39 22 12 2.70 GM-117 •• 31 43 19 8 2.67 

1573 •••• 26 30 38 6 2.64 GM-122 •• 30 38 23 9 2.69 

1581. ••• 13 50 15 23 2.77 GM-123 •• 30 37 23 11 2.68 

GM-124 •• 33 34 27 7 2.67 

Wheeler Crest Granodiorite, GM-125 •• 31 37 25 7 2.68 

Glass Mountain quadrangle GM-128 •• 27 40 25 9 2.68 

GM-129 •• 29 37 25 10 2.64 

GM-2 •••• 28 34 30 9 2.69 GM-130 •• 23 36 27 14 2.70 

GM-3 •••• 34 33 26 7 2.67 GM-131 •• 32 40 17 11 2.71 

GM-11 •••• 28 36 25 11 2.69 GM-132 •• 36 35 19 9 2.67 

GM-5 •••• 18 46 18 18 2.75 GM-135 •• 23 37 20 21 2.75 

GM-6 •••• 20 47 18 16 2.74 GM-136 •• 29 40 26 6 2.65 

GM-10 ••• 39 33 22 7 2.67 GM-137 •• 33 37 21 9 2.68 

GM-11 ••• 30 36 22 12 2.70 GM-138 •• 28 37 25 10 2.66 

GM-15 ••• 28 38 23 11 2.70 GM-139 •• 32 37 24 6 2.67 

GM-18 ••• 32 36 23 9 2.67 

GM-21 ••• 24 42 20 14 2.74 Granite of Casa Diablo Mountain, 

GM-26 ••• 28 40 23 9 2.67 Cowtrack Mountain quadrangle 

GM-28 .... 32 38 19 11 2.69 

GM-29 ••• 28 39 19 14 2.70 CT-1 •••• 30 37 32 2 2.63 

GM-30 ••• 26 40 19 15 2. 72 CT-6 •••• 29 33 29 2 2.64 

GM-32 ••• 30 36 21 13 2.69 CT-10 ••• 28 34 34 4 2.65 

GM-33 ••• 25 37 28 10 2.68 CT-101 •• 26 38 35 2 2.64 

GM-36 ••• 19 41 27 13 2.71 CT-102 •• 38 28 34 0 2.59 

GM-46 ••• 29 33 32 6 2.66 1524 •••• 29 38 31 2 2.62 

GM-47 ••• 25 38 30 8 2.69 1525 •••• 31 36 33 tr 2.61 

GM-51 ••• 17 42 29 12 2.74 1554 •••• 27 40 26 7 2.67 

GM-52 ••• 22 41 25 11 2.71 1562 •••• 32 25 39 4 2.62 

18 
TABLE 2. Modes and specific gravities of granitic rock samples from the Cowtrack Mountain and 

Glass Mountain quadrangles, Calif. and Nev.--Continued 

Modes (volume percent) Modes (volume percent) Sample Specific Sample Specific 

number Plagio- Alkali Mafic gravity number Plagio- Alkali Mafic gravity 

Quartz clase feldspar minerals Quartz clase feldspar minerals 

Granite of Casa Diablo Mountain, Granite of Casa Diablo Mountain, 

Cowtrack Mountain quadrangle (continued) Glass Mountain quadrangle (continued) 

1575 •••• 31 24 40 5 2.62 GM-106 •• 31 28 38 3 2.62 

1576 •••• 32 29 37 2 2.60 GM-1 09 •• 34 30 36 tr 2.61 

GM-110 •• 34 27 33 1 2.60 

Granite of Casa Diablo Mountain, GM-113 •• 36 18 46 tr 2.58 

Glass Mountain quadrangle GM-126 •• 32 28 40 1 2.58 

GM-134 •• 29 30 39 3 2.65 

GM-1 •••• 30 31 38 2 2.59 

GM-7 •••• 30 25 44 1 2.60 Fine-grained granite, 

GM-9 •••• 36 25 38 2 2.61 Cowtrack Mountain quadrangle 

GM-12 ••• 34 24 41 1 2.60 

GM-13 ••• 37 25 37 2 2.61 1577 •••• 26 32 39 3 2.63 

GM-14 ••• 37 23 39 1 2.58 

GM-16 ••• 31 35 34 tr 2.5'7 Fine-grained granite, 

GM-20 ••• 35 31 33 1 2.60 Glass Mountain quadrangle 

GM-23 ••• 33 30 35 2 2.60 

GM-24 ••• 35 25 39 2 2.60 GM-8 •••• 32 23 44 1 2.61 

GM-25 ••• 32 27 41 1 2.61 GM-107 •• 34 26 38 2 2.61 

GM-31 ••• 28 35 33 5 2.64 

GM-34 ••• 33 29 36 3 2.61 Diorite and gabbro, 

GM-35 ••• 33 31 34 2 2.63 Cowtrack Mountain quadrangle 

GM-71 ••• 33 25 41 1 2.59 

GM-82 ••• 28 28 41 4 2.64 CT-26 ••• 4 52 tr 44 3.02 

GM-105 •• 34 29 34 2 2.62 1528 •••• 8 61 6 26 2.80 

19 
GPO 585-045/78031