Mount Abbot Quadrangle, 

Central Sierra Nevada, 

CaliforniaAnalytic Data 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 774-C 

Mount Abbot Quadrangle, 

Central Sierra Nevada, 

CaliforniaAnalytic Data 

By JOHN P. LOCKWOOD 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 774-C 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1975 
UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Lockwood, John P. 

Mount Abbot quadrangle, central Sierra Nevada, California-Analytic data. (Shorter contributions to general geology) 

(Geological Survey Professional Paper 774-C) 

Bibliography: p. Cl8. 

Supt. of Docs. No. I 19.16:774-C 

1. Geology-California-Mount Abbot region. I. Title. II. Series: United States. Geological Survey. Shorter contributions to 

general geology. III. Series: United States. Geological Survey Professional Paper 774-C. 

QE90.M77L6 557.94'82 75-61913 

For !~ale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 

Stock Number 024-001-02736-4 
CONTENTS 

Page 

J\bstract_____________________________________________________________________________ C1 

Introduction_________________________________________________________________________ 1 

(}eneral geology --------------------------------------------------------------------- 1 

J\nalytic data __ _ _ _ _ __ _ _ _ _ __ _ _ __ ___ _ _ __ _ __ _ _ __ _ _ _ _ __ _ _ _ _ ____ __ __ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ 1 

Mineralogical and compositional variation in the quartz monzonite of Mono Recesses _ _ _ _ _ 3 

References___________________________________________________________________________ 18 

ILLUSTRATIONS 

Page 

FIGURES 1-8. <1eneralized bedrock geologic map of the Mount J\bbot quadrangle showing: 

TABLE 

1. Locations of chemically analyzed samples-------------------------------------------------------------- C2 

2. Locations of modally analyzed granitic rock samples---------------------------------------------------- 4 

3. Quartz in granitic rocks in volume percent ------------------------------------------------------------ 5 

4. J\lkali feldspar in granitic rocks in volume percent ---------------------------------------------------- 6 

5. Plagioclase in granitic rocks in volume percent -------------------------------------------------------- 7 

6. Mafic minerals in granitic rocks in volume percent ---------------------------------------------------- 10 

7. Specific gravity of granitic rocks ---------------------------------------------------------------------- 11 

8. Ternary plots of modes and norms -------------------------------------------------------------------- 12 

9. <1raph showing relation between point-count and area-count methods of estimating alkali feldspar megacryst 

abundance in the quartz monzonite of Mono Recesses______________________________________________________ 16 

10. J\bundance of alkali feldspar megacrysts in the quartz monzonite ofMono Recesses______________________________ 17 

11. <1raph showing relation of alkali feldspar megacryst abundances to topographic relief in two profiles across the quartz 

monzonite of Mono Recesses ---------------------------------------------------------------------------- 18 

12. Graph showing variation of alkali feldspar megacryst abundances with matrix alkali feldspar abundances in the quartz 

monzonite of Mono Recesses _____ ________ _____ _____ _ _ _____ _ ___ _ _ ______ ____ _ ___ _ _ __ __ ____ _____ _ ____ __ ____ 18 

TABLES 

Page 

1. Chemical analyses, norms, and modes of rocks---------------------------------------------------------------- C8 

2. Modes, specific gravities, and grid coordinates of granitic rocks ------------------------------------------------ 14 

III 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

MOUNT ABBOT QUADRANGLE, CENTRAL SIERRA NEVADA, 

CALIFORNIA-ANALYTIC DATA 

By jOHN P. LOCKWOOD 

ABSTRACT 

Modal compositions and specific gravities were determined for 329 

samples of granitic rocks of the Mount Abbot quadrangle, California, 

and 23 selected granitic, volcanic, and metamorphic rocks were chemically and spectrographically analyzed. Modal data and specific 

gravities plotted on simplified geologic maps supplement the published geologic map of the quadrangle. Most of these data, except for 

specific gravities, do not show syst ematic, contourable variation 

within plutons. 

The largest pluton within the quadrangle, occupying an area of 

about 100 mi2 (260 km2 ) , is the highly porphyritic quartz monzonite of 

Mono Recesses. Alkali feldspar megacrysts are concentrated near the 

borders of the pluton. Megacrysts also increase in abundance with 

increasing elevation, which may indicate that the roof 0f this pluton 

was originally not too far above present erosional levels. Specific 

gravities and chemical analyses of samples show that the pluton is 

weakly wned, with the densest and most basic rocks located along the 

highly porphyritic borders. A plot of megacryst abundance versus 

matrix alkali feldspar content shows an irregular but generally inverse relation between the two, indicating that total alkali feldspar 

abundance was not the controlling factor in the growth of giant (up to 

8 em) megacrysts. The concentration of megacrysts in the more basic, 

marginal areas of the pluton indicates either that the bulk 

composition of the granodiorite magma was appropriate for growth of 

giant alkali feldspar megacrysts in these areas or that processes 

especially conducive to their growth operated near pluton borders. 

INTRODUCTION 

The Mount Abbot quadrangle covers about 240 mi2 

(620 km2) of dominantly alpine terrain lying across the 

high crest of the Sierra Nevada between Fresno and 

Bishop, California. The John Muir Trail crosses the 

quadrangle from north to south, and the area is visited 

and traversed by thousands of visitors each summer. 

The quadrangle lies near the center of an area of the 

central Siarra Nevada that has been intensively studied 

geologically over the past three decades (Bateman and 

others, 1963; Bateman and Eaton, 1967). 

This paper was prepared for use with the Geologic 

Map of the Mount Abbot quadrangle (Lockwood and 

Lydon, 1975). It summarizes results oflaboratory investigations conducted on samples collected in conjunction 

with geologic mapping of the quadrangle and is part of a 

continuing study of the bedrock geology of the Sierra I 

Nevada batholith. 

GENERAL GEOLOGY 

The geologic history of the quadrangle is briefly 

summarized in a text that accompanies the Geologic 

Map of the Mount Abbot quadrangle (Lockwood and 

Lydon, 1975). A generalized small-scale version of this 

map is given in figure 1. The oldest rocks of the quadrangle are Paleozoic marine sedimentary rocks principally along the north boundary of the quadrangle. 

Mesozoic volcanic rocks lie along the north boundary 

and in the southeast quarter of the quadrangle, where 

they are highly deformed and metamorphosed. These 

older metamorphic rocks are intruded by Mesozoic 

granitic rocks that range in composition from diorite to 

alaskite. Granitic rocks constitute about 95 percent of 

the bedrock in the quadrangle. The granitic and 

metamorphic rocks are overlain by volcanic flows oflate 

Tertiary age and by unconsolidated glacial and alluvial 

deposits of Quaternary age. 

ANALYTIC DATA 

During the course of geologic mapping, about 400 

bedrock samples were collected, 329 of them granitic. 

The specific gravity and modal mineral composition of 

these 329 samples were determined. For modal 

analysis, the samples were sawed into slabs with flat 

surfaces of at least 40 cm2 ; these slabs were then 

stained so that the two feldspars could readily be distinguished from each other and from quartz. The mineral 

constituents (quartz, alkali feldspar, plagioclase, and 

mafic minerals) present at each of 1,000-2,000 regularly spaced points on each slab were then observed with 

a microscope and tabulated. The volume percentages of 

these minerals were then calculated for each sample 

locality; the values are shown on simplified bedrock 

geologic maps of the quadrangle (figs. 2-5) and are given 

in table 1.1 The locations of all points for which modes 

are available are given in figure 6. Individual modes 

and specific gravities are given in table 2, along with 

1Modes and specific gra vities of samples from smaller plutons are not plotted in fi gures 2-5 

and 7 in order to conserve space; they are given in table 2. 

Cl 
C2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

119° 00' 118° 45' 

37° 30' ,---~ ~~~~~~~--~~~~~~c-.T-,--+ 

K 

0 2 3 4 5 MILES 

0 2 3 4 5 6 7 8 Kl LOMETRES 

FIGURE I.-Generalized bedrock geologic map of the Mount Abbot quadrangle showing locations of chemically analyzed samples. 
MOUNT ABBOT QUADRANGLE, CALIFORNIA, ANALYTIC DATA 

EXPLANATION 

C3 

p;Oqm[ 

I Kmf Tl 

Kmg 

> Trachybasalt flows 

Fine- and medium-grained equigranular quartz 

monzonite 

Quartz monzonite of Mono Recesses - highly 

porphyritic 

Granodiorite of Lake Edison - includes quartz 

monzonite along some borders 

Mount Givens Granodiorite - includes some 

porphyritic quartz monzonite 

Lamarck Granodiorite - includes some porphyritic quartz monzonite 

Granodiorite of Shelf Lake 

Undifferentiated diorite - includes abundant 

quartz diorite and gabbro 

Undifferentiated quartz diorite - includes granodiorite and some quartz monzonite 

[~ Alaskite of Graveyard Peak 

1?\@f\fl Quartz monzonite of Turret Peak - similar to 

quartz monzonite of Mono Recesses, but 

generally less porphyritic 

Granodiorite of Round Valley Peak 

Granodionte of Mono Creek 

Quartz monzonite of Ruby Lake 

Granodiorite of Chickenfoot Lake - includes 

abundant quartz monzonite. Highly sheared 

j.:.~Ki~4:::~ Quartz monzonite of Bear Dome - includes 

~ • · • ' • • • ~ abundant granodiorite 

Fine-grained facies of the quartz monzonite 

of Bear Dome 

Metamorphic rocks - mainly lower Mesozoic 

metavolcanic schists, but includes some Pa· 

leozoic metasedimentary rocks near northern 

quadrangle boundary 

grid coordinates for all sample localities shown on figure 

6. Specific gravities and a contour map of the specific 

gravity data are given in figure 7. The modal data (figs. 

2-5) were considered too variable for meaningful contours to be drawn and therefore were not contoured. 

In addition to the modal analyses of granitic rocks, 23 

samples of granitic rocks from 9 different plutons and 3 

dikes, a samples ofpregranitic metavolcanic rocks, and 

2 samples of Tertiary volcanic rocks were analyzed 

chemically by the rapid method of Shapiro and Brannock (1962). The locations of the chemically analyzed 

samples are shown in figure 1. These data, together with 

semiquantitative spectrographic analyses, CIPW 

norms, and modes of the chemically analyzed granitic 

rocks are given in table 1. 

The modes of the granitic rocks, normalized to 100 

percent, are plotted on ternary diagrams (fig. 8), whose 

corners are quartz, plagioclase, and alkali feldspar. 

Norms of the chemically analyzed samples are plotted 

on a ternary diagram whose corners are normative 

quartz, plagioclase (albite plus anorthite), and orthoclase. All ternary plots were computer-generated. 

Additional analytic data (mostly spectrographic 

analyses) are given for stream sediments and some 

bedrock in the western half of the Mount Abbot 

quadrangle by Lockwood, Bateman, and Sullivan 

(1972). 

MINERALOGICAL AND COMPOSITIONAL 

VARIATION IN THE QUARTZ MONZONITE 

OF MONO RECESSES 

The quartz monzonite of Mono Recesses is a large 

pluton of coarsely porphyritic quartz monzonite and 

granodiorite that underlies most of the northeastern 

half of the Mount Abbot quadrangle (Lockwood and 

Lydon, 1975). This pluton resembles the well-known 

Cathedral Peak Granite, a granitic pluton located 60 

km to the northwest (Bateman and others, 1963, pl. 1), 

although it is typically not as coarse grained. The distribution of alkali feldspar megacrysts2 in the quartz 

monzonite of Mono Recesses was studied in detail. Because the megacrysts are typically large (averaging 

about 25 x 14 mm in cross-section dimensions) and are 

21'he large alkali feldsfar crystals are deliberately termed megacrysts in this report to avoid any connotation o the time of their genesis in their name. The megacrysts have, however, been involved in movement of their host magma, are unquestionably of late-stage 

magmatic origin, and could doubtless be termed phenocrysts. 
C4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

0 2 3 4 5 MILES 

0 2 3 4 5 6 7 8 Kl LOMETRES 

FIGURE 2.-Generalized bedrock geologic map of the Mount Abbot quadrangle showing locations of modally analyzed granitic rock samples. 
MOUNT ABBOT QUADRANGLE, CALIFORNIA, ANALYTIC DATA C5 

0 2 3 4 5 MILES 

0 2 3 4 5 6 7 8 Kl LOMETRES 

FIGURE 3.-Generalized bedrock geologic map of the Mount Abbot quadrangle showing quartz in granitic rocks in volume percent. 
C6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

0 2 3 4 5 MILES 

0 2 3 4 56 7 BKILOMETRES 

FIGURE 4.-Generalized bedrock geologic map of the Mount Abbot quadrangle showing alkali feldspar in granitic rocks in volume percenc. 
MOUNT ABBOT QUADRANGLE, CALIFORNIA, ANALYTIC DATA C7 

0 2 3 4 5 MILES 

0 2 3 4 5 6 7 8 Kl LOMETRES 

FIGURE 5.·-Generalized bedrock geologic map of the Mount Abbot quadrangle showing plagioclase in granitic rocks m volume percent. 
cs 

Mount Givens Granodiorite 

Si02 ------------ AhOa ___ _ 

F.,O., ---------- FeO ------------ MgO __________ _ CaO ________ _ 

&0 NruO ---------- __________ _ 

1-hO+ 

1-hO- --- TiO., ___________ _ 

r,o, _______ _ MnO __________ _ _ 

co. ----

Sum __ 

B ---- - -----

A- 103 

61.7 

16.9 

2.3 

3.4 

2.4 

5.3 

3.3 

2.5 

.91 

.19 

.73 

.19 

.09 

<.05 

100 

Ba ______________ 1000 Be _____________ _ Ce _ _ _ _____ _ 

Co ________ ______ 20 Cr __________ 20 Cu ___ ________ 30 

Ga______________ 30 La _____________ 30 Nb ______ ___ 7 

Nd ------------ Ni ____ __________ 10 Pb _____ _____ 30 & ______________ 20 

Sr ------- 700 v ---------- 150 

y -------------- 30 Yb______ __ _ 3 

Zr ------------- 150 

Q ----- c -------------- or -------------

ab ------ an _ ·-----------

ne wo --------------

_____ _ 

en __________ _ 

fs __ ------------ fo _________ _ 

Ia __ _ 

mt ----------- hm __________ _ 

il 

ap ------------- cc 

hi 

fr 

Quartz 

K-feldspar 

Plagioclase _____ _ 

Mafic 

minerals 

17.3 

14.8 

28.0 

24.0 

.5 

6.0 

3.3 

3.3 

1.4 

.45 

21.2 

8.4 

50.8 

19.6 

A- 212 

66.0 

16.0 

1.6 

2.6 

1.8 

3.7 

3.1 

3.4 

.74 

.18 

.57 

.15 

.10 

< .05 

100 

1000 

100 

10 

10 

10 

20 

50 

10 

5 

30 

15 

500 

100 

20 

3 100 

23.6 .85 20.1 

26,3 17.4 

4.5 

2.7 

2.3 

1.1 

.36 

26.4 

17.2 

40.0 

16.4 

A-150 

67.1 

15.8 

2.0 

1.4 

1.0 

3.3 

4.0 

3.2 

1.1 

.23 

.47 

.20 

.06 

< .05 

100 

1000 

7 

3 

15 

20 

30 

10 

30 

5 1000 70 

10 

1 

150 

23.6 .24 19.0 

34.0 

15.1 

2.5 

.26 

2.9 

.90 

.48 

29.7 

* 17.5 

47.7 

5.1 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

TABLE 1.----Chemical analyses, norms, and modes of rocks 

Quartz monzonite of Mono Recesses Granodiorite 

of Round Valley Peak 

A-241 

71.3 

15.0 

l.l 

.96 

.50 

2.1 

3.9 

4.1 

.46 

.08 

.27 

.13 

.02 

<.05 

100 

1500 

100 3 

2 

7 

20 

30 

7 

30 

2 780 

30 

10 .7 70 

27.9 .64 24.3 

33.1 

9.6 

1.2 

.45 

1.6 

.51 

.31 

28.3 

*23.5 

43.9 

4.3 

A- 436 A- 450 A- 518 A- 555 A- 237 

Chemical analyses (weight percent) 1 

72.1 

14.7 

1.1 

.76 

.31 

1.7 

3.8 

4.3 

.37 

.08 

.23 

.11 

.10 <.05 

100 

70.2 

15.2 .00 

2.2 

.70 

2.6 

4.0 

3.5 

.67 

.00 

.36 

.13 

.05 

< .05 

100 

70.0 

15.2 

1.4 

.96 

.50 

2.1 

3.8 

3.8 

1.2 

.05 

.32 

.12 

.06 

< .05 

100 

70.6 

15.1 

1.5 

1.0 

.65 

2.4 

3.9 

3.8 

.37 

.11 

.39 

.05 

.04 

<.05 

100 

68.4 

15.2 

1.6 

1.8 

1.4 

3.4 

3.3 

3.6 

.68 

.09 

.40 

.15 

.10 

< .05 

100 

Semiquantitative spectrographic analyses• 

1500 3 

1 

7 

30 

50 

700 

15 

.7 

100 

1500 

1.5 

3 

20 

30 

10 

15 

2 

700 

30 

7 

100 

1500 1.5 

2 

1 

3 

30 

30 

7 

30 

2 1000 30 

10 

150 

1000 

100 5 

2 

15 

20 

50 

10 

20 

3 1000 

50 

10 

1 

150 

CIPW norms (weight percent) 

29.7 

1.0 

25.5 

32.3 

7.7 

.78 

.29 

1.6 

.44 

.26 

30.1 

*22.9 

44.5 

2.5 

25.8 .42 

20.8 

34.0 

12.1 

1.8 

3.6 

.69 

.31 

28.5 

1.3 

22.6 

32.3 

9.7 

1.3 

.19 

2.0 

.61 

.29 

27.4 .33 22.5 

33.1 

11.6 

1.6 

.03 

2.2 

.7 

.12 

Modes (volume percent) 3 

24.2 

*21.3 

50.8 

3.7 

28.0 

*20.3 

47.7 

4.0 

30.1 

*18.8 

46.8 

4.3 

1500 

100 7 

10 

20 

20 

70 

7 

5 

30 

7 700 

700 

15 

1.5 

70 

25.8 .05 

21.3 

27.9 

15.9 

3.5 

1.5 

2.3 

.76 

.36 

1R6 

22.6 

50.4 

8.4 

Quartz 

mon7_,0nite of Turret Peak 

A-304 

64.5 

15.8 

1.9 

2.6 

1.8 

3.9 

3.5 

3.2 

1.0 

.30 

.55 

.19 

.08 

< .05 

100 

1000 

100 

15 

10 

10 

20 

50 

7 

7 

20 

10 

1000 

100 

15 

1.5 

50 

20.5 

19.1 29.9 

18.1 

.07 

4.5 

2.5 

2.8 

l.l 

.45 

23.8 

15.ts 

49.6 

10.8 

A-425 

66.1 

16.0 

2.1 

2.0 

1.4 

3.9 

3.8 

3.3 

.53 

.12 

.55 

.20 

.07 < .05 

100 

1500 

100 

10 

7 

7 

20 

50 

10 

3 

20 

7 1000 

70 

15 

1.5 150 

21.2 

19.5 

32.2 

16.9 

.50 

3.5 

1.2 

3.0 

1.0 

.47 

21.4 

15.7 

52.0 

10.9 

Granodiorite of Lake Edison 

A-448 A-454B 

66.7 

16.1 

1.6 

2.2 

1.5 

3.5 

3.5 

3.7 

.31 

.07 

.44 

.16 

.08 < .05 

100 

1500 

100 

10 

7 

10 

15 

50 

7 

3 

15 

7 1000 

70 

10 

1 100 

22.0 .36 21.9 29.7 16.4 

3.7 

2. 1 

2.3 

.84 

.38 

25.6 

22.2 

44.3 

7.9 

66.4 

15.7 

1.0 

2.8 

1.8 

3.7 

3.5 

3.3 

.80 

.05 

.49 

.15 

.08 < .05 

100 

1500 

10 

10 

10 

15 

50 

10 

7 

10 

7 700 

100 

20 

1.5 100 

21.6 .002 19.6 

29.7 

17.4 

4.5 

3.7 

1.5 

.93 

.36 

21.5 

19.4 

48.8 

10.3 

A-490 

68.8 

15.4 

1.7 

1.4 

l.l 

2.9 

3.4 

3.9 

.70 

.09 

.39 

.17 

.10 

<.05 

100 

1500 

7 

5 

3 

20 

2 

30 

5 700 

50 

10 

1 

70 

26.4 .72 23.1 

28.8 

13.3 

2.7 

.71 

2.5 

.74 

.40 

25.3 

25.3 

41.2 

8.2 

' Rapid-rock ana lyses (Shapiro and Brannock, 1962) by L. Artis, S. Botts, G. Chloe, P. Elmore, J. Glenn, J. Kelsey, and H. Smith under the supervision of L. Sha piro. 0. 7, 0.5, 0.3, 0.2, 0.15, and 0.1, etc., which represents approximate midpoints of group data on a geometric scale. The assigned group for semiquantitative results will include the quantita- ti ve value for about 30 percent of the analyses. 2

All :;tnalyses performed in t he laboratory and under the supervision of Harry Bastron. All values m ppm. Looked for but not found: Ag, As, Au, Bi, Cd, Ge, Hf, Hg, In, Li, Mo, Pd, Pt, Re, 

Sb, Ta, Te, Th, Ti, U, W, Zn. Results reported in percent to the nearest number in t he series 1, 

irregularly distributed at hand specimen scale, their 

relative abundance is difficult to measure, and so a 

special field counting method was devised to obtain 

approximate percentages of megacrysts quickly at 

selected outcrops in conjunction with geologic mapping. 

'Ana lyst: 0. K. Polovtzoff. *Includes alkali feldspa r present as phenocrysts in stained slab. For percentages of alkali feldspar present in ma trix a nd as phenocrysts, see table 2. 

In this method, appropriately exposed and weathered 

outcrops were found in which megacrysts could be 

plainly seen, the number of megacrysts per given area 

(a map folder 30 by 27 em in size) were counted, and then 

the average length of megacrysts in the counted area 
MOUNT ABBOT QUADRANGLE, CALIFORNIA, ANALYTIC DATA C9 

TABLE !.-Chemical analyses, norms, and modes of rocks-Continued 

Quartz monzonite of Bear Dome 

A-511 

Quartz monzonite of Jackass Pike 

A-512 A-536 

Alaskite of Graveyard Peak 

A-514 A-406 

Lamarck 

Granodiorite 

A-481 

Diorite dike Mafic metavolcanic schist 

A-410 A-88A A-562 A-535 A-476A 

Felsic metavolcanic 

schist 

A-537 

Trachybasalt 

A-111A A-419A 

Chemical analyses (weight percent) 

SiG.! 

AbO:J 

Fe:zO:J 

FeO 

MgO 

CaO 

N!I:IO 

1<.20 

1-hO+ 

1-hOTiG.! 

P20s_ 

MnO_ 

CG.! - - --- - -

Sum_ 

68.8 

15.3 

1.1 

1.9 

.95 

2.4 

4.0 

3.9 

.65 

.06 

.44 

.14 

.10 

<.05 

100 

74.9 

13.6 .77 

.48 

.22 

.75 

4.2 

4.5 

.14 

.05 

.19 

.04 

.05 

<.05 

100 

72.4 

14.1 .84 

.96 

.38 

1.2 

4.1 

4.3 

.57 

.05 

.28 

.08 

.06 

<.05 

99 

76.9 

13.0 .23 

.44 

.04 

.54 

3.3 

4.7 

.67 

.07 

.06 

.02 

.04 

<.05 

100. 

76.1 

13.5 .08 

.40 

.04 

.60 

3.5 

4.8 

.28 

.05 

.07 

.00 

.03 

<.05 

99 

62.6 

16.5 

1.5 

3.7 

2.4 

5.0 

3.4 

2.9 

.87 

.03 

.64 

.20 

.09 

<.05 

100 

76.6 

13.1 .40 

.20 

.02 

.70 

3.5 

4.7 

.58 

.03 

.05 

.00 

.02 

<.05 

100 

47.7 

18.9 

3.7 

6.8 

5.1 

8.5 

3.7 

1.6 

1.3 

.13 

1.4 

.38 

.16 

<.05 

99 

56.6 

17.9 

2.6 

4.7 

3.5 

6.2 

3.5 

2.0 

1.2 

.17 

.90 

.31 

.10 

<.05 

100 

70.2 

14.9 

1.1 

1.7 

1.0 

.R5 

4.0 

5.1 

.59 

.05 

.35 

.14 

.08 

<.05 

100 

54.0 

17.4 

3.9 

5.4 

3.9 

4.4 

3.3 

3.3 

1.3 

.10 

1.3 

.37 

.59 

.21 

99 

75.7 

12.9 .00 

.48 

.03 

.07 

1.0 

9.0 

.44 

.05 

.11 

.05 

.00 

<.05 

100 

50.3 

14.9 

2.6 

5.1 

10.4 

8.5 

2.7 

1.8 

1.5 

.58 

.94 

.48 

.14 

<.05 

100 

50.3 

13.6 

2.7 

7.0 

9.6 

8.8 

2.5 

2.2 

.85 

.35 

1.2 

.56 

.15 

<.05 

100 

Semiquantitative spectrographic analyses 

B 

Ba _____________ 1500 Be _____________ _ Ce _____________ _ 

Co__ 7 Cr ____ 1.5 

Cu__ 2 

Ga__ 20 La______________ 30 Nb ____________ 7 

Nd 

Ni _____________ _ 

Ph______________ 10 

Sc -------------- 7 Sr ____________ 500 

\' -------- 50 y ------- 20 Yb______________ 2 Zr ______________ 100 

1000 1.5 100 

3 

20 

50 

10 

15 

3 150 

10 

20 

1.5 150 

2000 1.5 100 

20 

15 

30 

7 

20 

3 300 

10 

15 

2 200 

200 1.5 

3 

15 

50 

30 

2 

30 

50 

5 

70 

10 

200 3 

15 

15 

15 

30 

30 

20 

3 

50 

1500 

15 

15 

30 

15 

30 

7 

15 

10 

15 

100 

150 

15 

2 100 

70 

2 

10 

20 

50 

70 

20 

500 

30 

10 

70 

20 

7 

30 

7 

30 1000 

200 

30 

3 100 

700 

20 

30 

30 

20 

30 

7 

15 

10 

15 1000 

100 

20 

2 

150 

1500 

100 

7 

5 

.7 20 

50 

7 

15 

7 300 

50 

15 

2 

200 

1000 1.5 

20 

50 1500 

20 

15 

70 

30 

500 

200 

30 

3 150 

1500 

10 

20 

50 

10 

20 

70 

.7 

100 

1500 

50 

700 

70 

15 

50 

7 

500 

19 

20 1500 

200 

20 

1.5 100 

1500 

50 

700 

70 

15 

50 

7 

300 7 

30 1500 

300 

20 

2 

150 

CIPW norms (weight percent) 

Q -------------- c -------------- or _____________ _ ab ____________ _ an _____________ _ ne ___________ _ wo ____________ _ 

en _____________ _ fs _____________ _ fo _____________ _ fa _____________ _ mL ____________ _ 

hm ------------ il -------------- ap -------------- cc --------------

hi -------------- fr _____________ _ 

23.6 .47 23.1 

34.0 

11.0 

2.4 

2.0 

1.6 

.84 

.33 

31.5 .55 26.6 

35.6 

3.5 

.55 

.025 

1.1 

.36 

.095 

29.1 .72 25.6 

34.9 

5.5 

.95 

.72 

1.2 

.54 

.19 

38.3 

1.6 

27.8 

27.9 

2.6 

.10 

.59 

.33 

.11 

.047 

36.0 

1.5 

28.5 

29.8 

3.0 

0.10 

0.61 

.12 

.13 

16.4 

17.2 

28.8 

21.2 

.96 

6.0 

4.7 

2.2 

1.2 

.48 

36.8 .98 27.8 

29.7 

3.5 

.05 

.57 

.010 

.095 

9.5 

28.1 

30.5 

1.8 

4.0 

2.4 

1.4 

7.3 

4.7 

5.4 

2.7 

.9 

9.0 23.7 

1.6 11.9 30.1 29.8 33.8 27.4 3.3 

.63 

8.8 2.5 5.2 1.8 

3.8 1.6 

1.7 .66 .74 .33 

6.0 

1.8 

19.6 

28.1 

18.2 

9.8 

5.7 

5.7 

2.5 

.88 

.48 

35.1 

1.5 

53.3 

8.5 

.021 

.075 

.70 

.21 

.12 

10.7 

23.0 

23.4 

6.6 

14.8 

3.4 

7.9 

2.0 

3.8 

1.8 

1.1 

13.1 

21.3 

19.5 

8.7 

13.9 

5.2 

7.1 

2.9 

3.9 

2.3 

1.3 

Modes (volume percent) 

Quartz_ ________ _ 

K-feldspar _____ _ 

Plagioclase _____ _ 

Mafic minerals _____ _ 

19.3 

23.4 

49.7 

7.6 

28.0 

37.2 

31.8 

3.0 

8.7 

34.3 

53.6 

3.4 

28.0 

36.3 

35.2 

.5 

32.9 

35.3 

30.3 

1.5 

20.2 

16.6 

50.0 

13.2 

was estimated. Then, using 1. 73 as an average lengthto-width ratio of megacrysts in the quartz monzonite of 

Mono Recesses (on the basis of measurement of 46 

megacrysts), the volume percentage of megacrysts over 

the area of the map folder is equal toX¥2/14.01 where X 

equals the number of megacrysts per area, andY equals 

the average length of the megacryst. This method could 

be used only on plutons in which the shape of mega29.0 

41.1 

29.6 

.3 

crysts is relatively constant; for plutons with megacrysts of variable morphology, both length and width 

averages must be estimated at each count area. 

To check the approximate accuracy of the area-count 

method, the volume percentages of alkali feldspar 

megacrysts were determined by point counts at 23 

localities where the area counts also were available. 

Point counts were made by placing a 1,000-point grid of 
ClO SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

0 

I 

0 

'I I 

2 

I 

3 

2 

I 

I 

4 

3 

I I 

5 

4 

I I 

6 7 

5 MILES 

I 

I 

8 Kl LOMETRES 

FIGURE G.-Generalized bedrock geologic map of the Mount Abbot quadrangle showing mafic minerals in granitic rocks in volume percent. 
MOUNT ABBOT QUADRANGLE, CALIFORNIA, ANALYTIC DATA 

0 

I 'I 

0 

I 

2 

2 

I I I 

3 4 

3 

I 

I 

5 

4 

I I 

6 7 

5 MILES 

I 

I 

8 Kl LOMETRES 

FIGURE 7 .-Generalized bedrock geologic map of the Mount Abbot quadrangle showing specific gravity of granitic rocks. 

Cll 
C12 

CLASSIFICATION 

10 

Plagioclase 

EXPLANATION 

o Kle; granodiorite of Lake 

Edison-medium-grained 

facies 

• Klef; granodiorite of Lake 

Edison -fine-grained 

facies 

X Klep; granodiorite of Lake 

Edison -porphyritic 

facies 

EXPLANATION 

o KJg; alaskite of Graveyard 

Peak 

• KJgp; alaskite of Graveyard 

Peak -porphyritic facies 

35 

EXPLANATION 

X KJd2 and Lydon, 1974, for 

10 

a KJd1} diorite [see Lockwood 

• KJd3 explanation of symbols] 

quartz diorite [see 

o KJqd,} Lockwood and Lydon, 

• KJqd2 1974, for explanation 

of symbols] 

10 

35 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

Quartz 

65 

35 

0 

65 

35 

PLOTS OF MODES 

K-feldspar 

65 

65 

EXPLANATION 

o KJs; granodiorite of Shelf Lake 

c KJrl; quartz monzonite of Rose 

Lake 

• KJcl; granodiorite of 

Chickenfoot Lake 

EXPLANATION 

10 

o Kmg; Mount Givens Granodiorite 

• Kmgp; Mount Givens 

Granodiorite-porphyritic 

facies 

c Kmc; granodiorite of Mono 

Creek 

10 

EXPLANATION 

• Kqm J- o KJqm 

quartz monzonite [see 

Lockwood and Lydon, 

1974, for explanation of 

symbols] 

EXPLANATION 

o Kl; Lamarck Granodiorite 

• Kip; Lamarck Granodioriteporphyritic facies 

10 

10 

35 65 

35 65 

35 65 

35 65 

FIGURE B.-Generalized bedrock geologic map of the Mount 
MOUNT ABBOT QUADRANGLE, CALIFORNIA, ANALYTIC DATA 

PLOTS OF MODES 

EXPLANATION 

o Krv; granodiorite of Round 

Valley Peak 

10 35 

EXPLANATION 

o KJbd; quartz monzonite of 

Bear Dome 

• KJbdf; quartz monzonite of 

Bear Dome-fine-grained 

facies 

65 

10 

EXPLANATION 

• Kmr; quartz monzonite of 

Mono Recesses 

X Ktp; quartz monzonite of 

Turret Peak 

35 

PLOT OF NORMS 

EXPLANATION 

o Mount Givens Granodiorite 

• quartz monzonite of Mono Recesses 

a granodiorite of Round Valley 

Peak 

• quartz monzonite of Turret 

Peak 

.<:>granodiorite of Lake Edison 

... quartz monzonite of Bear 

Dome 

o quartz monzonite of Bear Domefine-grained facies 

• alaskite of Graveyard Peak 

11 Lamarck Granodiorite 

+aplite 

x diorite 

*mafic metavolcanic schist 

:f:l: felsic metavolcanic schist 

* trachybasalt 

Ab+An 

Abbot quadrangle showing ternary plots of modes and norms. 

011 

X 

* 

•• 0 

••o 

a 

+. 

• 

• a.<:> 

e OA * • .:. e 

10 

65 

C13 

35 65 

Or 
C14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

TABLE 2.-Modes, specific gravities, and grid coordinates of granitic rocks 

Modes (percent) Modes (percent) 

Map Map Specific Sample symbol Coordi- Alkali feldspar Specific Sample symbol Coordi- Alkali feldspar No. for rock nates gravity no. for rock nates gravity 

unit' unitt 

Plagio- Matrix2 Mega- Quartz m~~~~ls Pi agio- Matrix2 Megaclase crysts3 clase crysts3 Quartz m~~~~Js 

A-1 Kle D,3 44.7 18.1 24.0 13.2 2.715 A-130 Ktp J,5 36.8 24.5 34.1 4.6 2.656 

A-3 KJg D, 3 36.5 32.2 28.6 2.7 2.695 A-132 Kl I, 5 47.5 16.5 17.4 18.6 2.740 

A-4 Klef D, 4 47.1 18.3 21.6 13.0 2.699 A-133 KJbd I, 4 34.8 30.9 30.9 3.4 2.645 

A-5 Kle E,5 48.6 13.5 20.6 17.3 2.710 A-134 Kl H,4 45.0 13.9 20.8 20.3 2.737 

A-6 Kle E,3 44.2 17.6 20.8 17.4 2.700 A-136 KJbdf H,3 24.9 45.4 28.3 1.4 2.608 

A-SA KJg D, 3 33.9 29.8 35.0 1.3 2.629 A-138 KJbd J,3 34.8 30.7 28.9 5.6 2.659 

A-10 Kmr C,4 41.9 19.8 10.7 25.1 2.5 2.649 A-141 Kmr c, 6 44.5 20.2 4.1 27.0 4.2 2.648 A-ll Kmr 8,3 41.2 19.7 10.7 24.7 3.7 2.640 A-142 Kmr C,6 46.6 23.0 4.0 23.5 2.9 2.649 

A-13 Kmc D, 4 42.0 11.6 23.7 12.7 2.680 A-143 Kmr C,6 36.6 29.1 4.0 29.0 1.3 2.620 A-15 Kmr D,4 41.6 15.6 12.0 24.0 6.8 2.667 A-144 Kmr 8, 7 44.1 19.7 6.2 26.9 3.1 2.661 A-17 KJg C, 2 36.7 32.7 27.7 2.9 2.611 A-145 Krv 8, 6 46.5 11.7 23.8 18.0 2.729 A-18 KJg 8, 2 33.2 34.5 28.4 3.9 2.628 A-147 Kmr 8, 7 42.5 12.5 11.2 27.9 5.9 2.657 A-19A KJd3 8, 2 59.6 .5 8.8 31.1 2.830 A-148 Kmr 8, 8 39.9 16.0 9.0 29.7 5.4 2.636 A-208 KJg 8, 1 35.3 32.4 27.3 5.0 2.634 A-149 Kmr 8, 8 46.4 18.8 1.0 22.5 11.3 2.687 A-24 KJs c, 2 56.1 9.4 14.2 20.3 2.750 A-150 Kmr 8, 8 48.9 7.2 8.2 30.5 5.2 2.641 A25-4 KJd3 C, 1 65.6 .5 3.2 30.7 2.868 A-151 Kmr A, 6 49.4 9.7 6.5 22.0 12.4 2.698 A25-5 KJd2 C, 1 65.5 .7 5.7 28.1 2.865 A-157 Krv? A,4 47.6 13.0 29.3 10.1 2.699 A-26 KJg 8, 1 32.9 33.6 32.3 1.2 2.610 A-164 Kmr D, 8 46.3 18.8 5.0 28.2 3.7 2.649 A-28 KJg 8, 1 23.3 43.8 30.7 2.2 2.600 A-165 Kmr C,8 39.6 17.2 7.8 31.4 4.0 2.657 A-29 KJg . A, 1 33.2 32.7 31.3 2.8 2.642 A-166 Kmr C, 9 53.6 10.0 10.8 15.6 10.0 2.674 A-32 Kmr A, 2 43.6 23.0 7.8 20.4 5.2 2.645 A-167 Kmr C,9 48.7 20.3 2.0 19.8 9.2 2.680 A-33 KJd3 C, 1 64.2 1.1 8.4 26.3 2.820 A-168 Kmr D, 9 43.5 18.2 10.7 22.1 5.5 2.651 A-35 KJs 8, 1 45.9 15.5 16.6 22.0 2.755 A-169 Kmr D, 7 44.3 20.0 4.4 26.4 4.9 2.653 A-37 Kl F,2 47.6 14.6 19.3 18.5 2.745 A-170 Kmr D, 7 36.8 22.4 4.0 33.3 3.5 2.640 A-38 Klef F, 2 39.3 29.9 23.9 6.9 2.644 A-172 Krv A,9 45.9 16.0 24.1 14.0 2.716 

A-39 Kle F, 2 39.3 18.1 19.7 22.9 2.690 A-173 Kmr A,9 33.3 32.7 29.8 4.2 2.625 A-40 Klef F,2 46.9 19.6 22.7 10.8 2.711 A-174 Kmr B, 9 47.2 9.4 1.0 25.6 16.8 2.750 

A-42 Kle E,3 49.1 14.1 18.6 18.2 2.710 A-175 Kmr 8, 9 41.5 17.0 1.0 32.9 7.6 2.665 A-43 Klef F,2 51.5 12.6 21.0 14.9 2.720 A-178A Krv B, 9 47.7 11.7 18.9 21.7 2.750 A-44 Kmgp F,1 53.3 12.5 18.2 16.0 2.726 A-179 Kmr 8,9 39.1 23.0 1.0 31.9 5.0 2.654 A-45 Klef E, 1 52.5 21.1 18.1 8.3 2.682 A-181 Kmgp G, 1 52.9 16.8 17.6 12.7 2.704 

A-46A KJg F, 1 16.6 37.6 45.2 .6 '2.600 A-184 Kmg G,2 46.5 13.6 15.2 24.7 2.769 

A-468 KJg E, 1 29.2 29.0 40.1 1.7 2.630 A-188 KJbd H,2 49.7 19.1 18.8 12.4 2,691 

A-48 Klef E, 2 40.0 30.0 23.5 6.5 2.668 A-190 KJbd I, 3 39.2 28.9 24.6 7.3 2.679 

A-49 Kle E,2 46.7 23.1 17.5 12.7 2.690 A-191 KJbd I, 3 41.3 32.9 20.5 5.3 2.655 

A-52 Klef D, 3 45.2 17.4 25.5 11.9 2.705 A-192 KJbd H, 3 40.0 27.7 25.3 7.0 2.654 

A-56 Kle E,2 40.0 21.0 21.3 17.7 2.701 A-196A Kl G, 2 55.0 9.8 18.6 16.6 2.737 

A-57 Kle E,2 52.8 14.8 20.6 11.8 2.682 A-197 Kmg G, 2 39.2 27.3 22.2 11.3 2.691 A-58 Kqm1 E,2 35.3 33.3 28.9 2.5 2.625 A-199 KJqd1 G, 2-3 74.8 2.1 12.6 10.5 2.778 A-59 ~J~1 D, 3 27.6 35.1 37.0 .3 2.610 A-200 KJbdf I, 2 41.9 29.8 23.8 4.5 2.637 A-60 C,3 67.6 .1 10.4 21.9 2.842 A-202 KJbd I, 2 43.9 16.2 27.3 12.6 2.674 A-61 KJs C,2 50.0 13.0 14.6 22.4 2.760 A-203 Kmg I, 1 39.7 18.8 25.7 15.8 2.702 A-62 KJs C,2 54.5 6.7 12.7 26.1 2.650 A-204 Kmg G, 1 47.4 15.1 20.9 16.6 2.735 A-63A Klef D, 2 52.5 15.8 17.4 14.3 2.720 A-207 Kmg H, 1 46.0 16.4 22.7 14.9 2.722 A-64 Kle D, 2 41.3 23.7 24.4 10.6 2.679 A-210 Kmgp J, 2 50.7 9.9 20.0 19.4 2.754 A-65 Kmr D, 4 47.1 13.9 10.9 22.3 5.8 2.668 A-211 Kmg K, 2 45.2 18.5 22.1 14.2 2.714 A-66 KJg C, 1 29.7 38.3 31.3 .7 2.594 A-212 Kmg J, 1 40.0 17.2 26.4 16.4 2.710 A-68 KJg C, 1 11.8 45.0 42.7 .5 2.608 A-213 Kmg K, 1 45.8 16.7 21.4 16.1 2.695 A-69 KJs C, 1-2 64.9 .0 15.5 19.6 2.770 A-214 Kmg K, 1 43.1 16.1 24.8 16.0 2.710 A-71A Kqm1 8,2 33.0 36.4 23.7 6.9 2.643 A-215 Kmg K, 1 43.0 16.6 26.1 14.3 2.709 A-73 Kle D, 1 45.6 19.4 22.8 12.2 2.682 A-217 Kqm1 A, 3 58.6 26.2 8.8 6.4 2.663 A-75 Kmr 8,2 44.5 15.6 8.8 25.7 5.4 2.651 A-218 Kmr A,4 47.4 17.2 3.8 27.5 4.1 2.644 A-77 Kqm1 A, 1 52.4 12.6 21.4 13.6 2.720 A-219 Kmg K, 2 39.7 18.4 27.1 14.8 2.704 A-80 Kmr F,5 46.0 10.8 10.3 29.8 3.1 2.641 A-220 Kmg K,3 43.8 17.6 22.8 15.8 2.714 A-81 Kle F,5 45.5 23.9 24.3 6.3 2.671 A-222 KJbdf I, 4 31.2 36.3 29.7 2.8 2.619 A-82 Klef F,3 50.0 16.6 18.6 14.8 2.704 A-224 KJbd K,4 54.6 21.3 17.5 6.6 2.688 A-83 Kl F, 3 47.3 18.9 20.0 13.8 2.750 A-225 KJbdf K,4 37.9 29.8 28.9 3.4 2.632 A-84 Kmr F, 5 48.4 11.9 10.5 25.3 3.9 2.670 A-226 KJbd J,4 36.5 32.3 26.3 4.9 2.625 

A-85 Kle D, 1 35.0 28.2 28.6 8.2 2.635 A-227 Kmr D, 6 36.3 22.8 6.4 31.5 3.0 2.629 A-86 Klef D, 2 34.7 29.9 32.4 3.0 2.632 A-229 Kmr C,5 48.5 18.8 6.2 22.2 4.3 2.660 A-87 KJs C,2 56.0 1.0 12.5 30.5 2.837 A-230 Kmr C,5 47.8 25.0 4.8 19.4 3.0 2.661 A-89 KJs C, 2 48.9 10.1 19.6 21.4 2.758 A-231 Kmr 8, 7 45.8 17.8 6.4 23.8 6.2 2.676 A-90 KJd3 8, 2 55.1 .7 18.9 25.3 2.824 A-232 Kmr B, 5 40.8 20.2 6.0 29.9 3.1 2.639 A-93 KJg B, 1 23.7 38.8 36.2 1.3 2.620 A-233 Kmr B, 6 47.0 16.8 6.7 25.3 4.2 2.635 A-94 KJs B, 1 60.8 .5 12.3 26.4 2.811 A-234 Krv A, 7 46.0 20.7 23.5 9.8 2.689 A-95 Kqm1 B, 1 36.2 41.8 20.3 1.7 2.622 A-235 Kmr A,B 46.0 29.4 19.0 5.6 2.629 A-98 KJg 8, 3 34.8 36.0 28.6 .6 2.620 A-236 Kmr 8, 8 41.4 15.0 4.2 28.4 11.0 2.665 A-99 Kqm1 B, 4 46.1 29.2 21.7 3.0 2.650 A-237 Krv A, 7 50.4 22.6 18.6 8.4 2.697 A-100 Kmc D, 4 47.7 14.4 27.9 10.0 2.692 A-238 Krv A,B 40.3 24.5 27.7 7.5 2.674 A-101 Kle E, 1 36.0 30.0 26.3 7.7 2.682 A-239 Krv A, 7 56.0 5.1 18.9 20.0 2.760 A-102 Kmg H, 1 48.6 11.4 23.5 16.5 2.729 A-240 Kmr A, 5 51.0 10.2 14.4 20.4 4.0 2.656 A-103 Kmg H, 1 50.8 8.4 21.2 19.6 2.760 A-241 Kmr C,7 43.8 18.4 5.2 28.3 4.3 2.640 A-104 Kmgp H, 1-2 43.0 20.1 29.5 7.4 2.681 A-242 Kmr D, 7 45.9 19.1 4.1 26.8 4.1 2.638 A-106 Kmg J, 1-2 41.7 16.4 23.9 18.0 2.701 A-243 Kmr E, 8 41.1 22.7 7.6 23.6 5.0 2.653 A-107 Kmg I, 1 46.9 14.2 23.6 15.3 2.721 A-244 Kmr E, 8 41.1 22.8 6.6 26.0 3.5 2.641 A-108 Kmg J, 1 46.6 12.9 25.3 15.2 2.723 A-245 Kmr E, 7 44.4 16.8 6.2 29.0 3.6 2.634 A-109 Kmg I, 1 43.8 16.7 24.4 15.1 2.728 A-246 Kmr E, 7 48.5 21.0 4.3 23.0 3.2 2.639 A-112 Kmr A, 2 44.7 20.1 4.3 26.3 4.6 2.658 A-247 Kmr E, 7 47.2 23.3 4.2 22.0 3.3 2.632 A-114 Kmr A, 3 46.6 18.5 6.3 25.1 3.5 2.643 A-248 Kmr F, 8 45.5 23.1 4.5 21.7 5.2 2.644 A-115 Kmr A,4 43.5 20.9 8.0 26.3 1.3 2.635 A-250 Kmr A, 9 39.5 27.9 28.3 4.3 2.638 A-116 Kmr A, 4 42.8 11.7 10.9 27.9 6.7 2.678 A-251 Kmr 8, 9 54.9 9.0 18.9 17.2 2.751 A-117 Krv? A, 4 35.7 17.7 31.2 15.4 2.671 A-252 Krv A,9 38.5 23.5 29.5 8.5 2.672 A-118 Kmr A,3 41.5 18.7 7.9 27.4 4.5 2.652 A-253 Krv D, 9 46.7 15.0 25.2 13.1 2.705 A-119 Kmr 8, 4 41.7 23.2 5.0 24.9 5.2 2.650 A-254 Kmr D,9 44.2 17.6 5.7 21.4 10.9 2.692 A-120 Kmr B, 5 43.6 18.4 7.4 25.7 4.9 2.640 A-255 KJbd I, 2 48.2 21.2 20.4 10.2 2.690 A-121 Kmr C,4 39.2 22.6 6.8 28.5 3.1 2.633 A-256 KJqd1 H,2 56.2 21.6 7.1 15.1 2.778 A-122 Kmr B, 3 49.9 15.5 6.6 19.2 8.8 2.637 A-257 KJbdf H,2 32.0 35.7 29.8 2.5 2.617 

A-123 Kmr B. 3 43.5 18.3 9.2 24.2 4.6 2.650 A-258 KJg G,3 30.5 35.0 33.7 .8 2.626 

A-124 Kmg K,3 49.2 14.1 21.5 15.2 2.724 A-259 Kmr C-D,4 43.7 11.4 10.9 28.0 6.0 2.668 

A-260 Kmr D, 5 36.4 19.4 7.2 33.6 3.4 2.636 A-125 Kmg K, 4 52.9 11.6 19.3 16.2 2.735 A-261 Kmr E, 5 38.6 19.5 8.7 29.2 4.0 2.657 A-126 Kmg K,2 36.2 24.6 26.7 12.5 2.698 A-262 Kmr E, 6 43.4 19.1 8.2 26.8 2.5 2.648 

A-128 KJbd K,5 45.9 15.8 22.7 15.6 2.698 A-263 Kmr E, 6 49.1 14.2 8.1 24.3 4.3 2.628 
MOUNT ABBOT QUADRANGLE, CALIFORNIA, ANALYTIC DATA C15 

TABLE 2.-Modes, specific gravities, and grid coordinates of granitic rocks-Continued 

Modes (P£rcent) Modes (percent) 

Map Map 

Sample symbol Coordi· Alkali feldspar Specific Sample symbol Coordi· Alkali feldspar Specific 

1',/o. for rock nates gravity no. for rock nates gravity unit' unit' 

Plagio- Matrix2 Mega- Quartz m~~~~ls Plagio- Matrix2 Mega· clase crysts3 clase crysts3 Quartz m~~~~ls 

A-264 Kmr H, 7 43.9 25.3 3.9 24.0 2.9 2.656 A-461 Kle H,6 44.9 17.5 30.2 7.4 2.674 A-265 Kle G, 5 47.9 15.5 23.6 13.0 2.705 A-462 Kmr H, 7 42.9 21.1 9.8 24.7 1.5 2.632 A-266 Kle H, 6 46.4 16.8 24.8 12.0 2.698 A-463 Kmr G, 7 44.0 23.0 2.7 27.2 3.1 2.634 A-267 Kl H, 5 50.8 14.4 22.9 11.9 2.736 A-464 Kmr F-G, 8 39.8 31.6 2.4 23.7 2.5 2.633 A-268 Kmr H, 7 43.9 19.5 7.7 25.0 3.9 2.655 A-465 Kmr G, 8 41.0 25.6 2.3 27.6 3.5 2.627 

A-269 Kmr H, 8 43.1 21.9 5.4 26.1 3.5 2.629 A-466 Kle H,6 49.2 18.8 20.3 11.7 2.713 A-270 Kmr H, 9 39.6 24.5 4.0 24.5 7.4 2.636 A-467 Kl H,4 47.1 16.2 22.2 14.5 2.723 A-271 Kmr I, 9 40.2 25.0 5.5 24.6 4.7 2.638 A-468 Kl G-H, 4 52.5 13.8 17.6 16.1 2.750 A-272 Kmr H, 9 45.7 22.6 6.4 22.1 3.2 2.621 A-470 KJbd H,2 44.4 25.0 24.4 6.2 2.664 A-273 Kmr I, 8 40.8 14.3 11.9 26.2 6.8 2.659 A-471 Kl J, 6 47.2 12.2 20.9 19.7 2.753 A-274 Kmr I, 8 50.1 16.2 7.0 23.1 3.6 2.631 A-473 Ktp K,6 45.2 17.5 23.5 13.8 2.731 A-275 Kmr G, 7 43.4 22.8 5.3 26.6 1.9 2.631 A-474 KJbd J, 5 51.3 22.8 21.9 4.0 2.690 A-276 Kmr I, 7 45.7 19.1 10.2 21.5 3.5 2.630 A-475 Kl J, 5 53.7 14.2 18.4 13.7 2.771 A-277 Kle I, 8 47.4 19.0 28.7 4.9 2.668 A-477 KJqd1 K,6 33.7 34.0 24.2 8.1 2.670 

A-278 Kmgp F, 1 45.5 17.7 19.8 17.0 2.719 A-479 Kl I, 5 47.1 18.3 16.5 18.1 2.749 

A-280 Kmr E, 6 41.6 22.5 4.3 28.1 3.5 2.634 A-480 Kl H,5 41.2 19.5 24.2 15.1 2.720 

A-281 Kmr E,6 45.0 21.5 5.6 25.9 2.0 2.616 A-481 Kl J,6 50.0 16.6 20.2 13.2 2.754 

A-282 Kle F,4 48.1 16.9 25.0 10.0 2.687 A-482 Kle J,9 47.8 19.7 23.1 9.4 2.691 

A-283 Kle G-H, 5 41.9 24.0 26.3 7.8 2.687 A-484 Kle K,9 49.3 16.5 23.4 10.8 2.692 

A-284 Kl H, 4 49.3 15.3 19.4 16.0 2.720 A-485 Kle K,9 38.9 23.1 31.0 7.0 2.662 

A-285 Kle G,4 42.2 20.7 26.4 10.7 2.693 A-486 Kqm1 K, 9 48.9 18.3 26.6 6.2 2.673 

A-286 Ktp K,6 41.1 22.7 33.5 2.7 2.691 A-487 Kle K,9 52.4 11.9 19.0 16.7 2.734 

A-287 Kl J, 7 50.0 14.7 20.8 14.5 2.729 A-488 Kip K, 8 44.5 14.5 4.2 24.7 12.1 2.702 

A-289 Kl J, 6-7 50.3 14.7 20.6 14.4 2.726 A-489 Kle K, 8 47.6 17.1 25.4 9.9 2.710 

A-290 Kle J,8 43.5 18.8 25.4 12.3 2.704 A-490 Kle J,8 41.2 25.3 25.3 8.2 2.671 

A-291 Kle J,8 43.7 21.0 29.4 5.9 2.666 A-491 KJqm K, 6 39.1 39.6 19.2 2.1 2.621 

A-293 Klef J,8 37.4 30.1 30.9 1.6 2.640 A-493 KJqd1 K, 6 69.8 2.1 5.9 22.2 2.830 A-295 Klep K,8 39.2 28.2 27.0 5.6 2.653 A-495 Ktp K,6 71.1 7.1 11.5 10.3 2.699 

A-304 Ktp K,6 49.6 15.8 23.8 10.8 2.703 A-496 Ktp K, 7 49.1 19.0 24.4 7.5 2.705 A-308 Klef J,7 43.1 27.8 27.3 1.8 2.639 A-499 Klp K,8 46.9 21.2 19.1 12.8 2.717 

A-310 ~Tel I, 6 45.9 19.0 20.6 14.5 2.701 A-500 Kl K,7 42.3 19.2 25.1 13.4 2.721 

A312A F,9 38.4 24.3 25.8 11.5 2.701 A-503 Klp J, 7 39.4 23.0 26.6 11.0 2.698 A-313 KJcl E, 8-9 44.9 22.4 19.9 12.8 2.717 A-507 Kle I, 8 48.4 19.0 23.5 9.1 2.694 A-316 KJcl E, 9 35.5 27.7 28.6 8.2 2.672 A-508 KJbdf K,4 40.6 40.2 16.7 2.5 2.644 A-403 KJg F,3 32.8 34.9 32.0 .3 2.605 A-509 KJqd1 K, 4 67.4 .8 10.2 21.6 2.830 A-405 Klef F,3 51.8 14.1 21.3 12.8 2.729 A-510 KJbdf K, 5 54.9 9.3 28.9 6.9 2.647 A-406 KJg F,3 30.3 35.3 32.9 1.5 2.620 A-511 KJbd H, 2 49.7 23.4 19.3 7.6 2.675 A-407 Kl G, 3 45.4 14.6 22.0 18.0 2.724 A-512 KJbdf I, 4 31.8 37.2 28.0 3.0 2.612 A-409 Kl G, 3 53.3 7.4 20.7 18.6 2.736 A-514 KJg C, 1 35.2 36.3 28.0 .5 2.614 A-412 Kqm1 B, 5 35.8 36.8 26.7 .7 2.604 A-515 KJg B, 1 42.1 33.2 23.1 1.6 2.607 A-413 Kmr C, 5 45.9 22.7 5.2 22.7 3.5 2.658 A-518 Kmr A, 2 46.5 18.0 4.3 27.3 3.9 2.653 A-414 Kmr c. 4-5 48.5 15.9 7.4 24.2 4.0 2.649 A-519 Kmr A, 3 43.8 18.6 7.6 26.3 3.7 2.656 A-420 Kmr E, 5 44.9 17.7 9.2 24.9 3.3 2.663 A-520 Kmr A, 3 43.9 22.6 5.9 25.0 2.6 2.631 A-421 Kmr G, 6 43.0 21.9 6.8 26.3 2.0 2.661 A-521 KJgp B, 1 26.0 40.4 31.1 2.5 2.622 A-422 Kmr G, 7 43.5 24.9 3.7 25.0 2.9 2.633 A-536 KJbdf J,2 53.6 34.3 8.7 3.4 2.631 A-425 Kle G, 5 52.0 15.7 21.4 10.9 2.708 A-538 Kmr A,4 42.2 20.7 5.7 29.7 1.7 2.642 

A-426 Kmr F, 6 44.2 21.1 7.1 22.7 4.9 2.662 A-539 Kqm1 B, 4 53.4 28.8 14.0 3.8 2.652 A-427 Kmr F,6 44.1 17.5 6.1 27.2 5.1 2.650 A-541 KJbdf J,3 33.9 38.5 26.0 1.6 2.625 A-428 Kmr F,6 43.2 20.6 5.2 27.3 3.7 2.657 A-542 KJcl E,9 39.6 32.3 15.3 12.8 2.693 

A-429 Klef H, 5 49.9 11.4 21.3 17.4 2.742 A-546 KJcl E,9 34.0 37.5 21.8 6.7 2.658 A-430 Kmr G,9 41.4 25.8 2.0 29.6 1.2 2.637 A-547 KJqd2 D, 9 71.5 5.4 3.9 19.2 2.835 

A432A KJcl F,9 40.9 22.0 19.8 17.3 2.728 A-550 KJqd2 E, 9 51.1 17.8 15.5 15.6 2.734 

A-433 Kmr G,9 41.7 20.3 4.4 30.2 3.4 2.641 A-552 Kmr F,9 37.1 24.8 11.2 22.1 4.8 2.634 

A-436 Kmr H,9 42.1 21.7 5.3 28.5 2.4 2.640 A-554 Kmr F,8 34.7 22.5 10.3 29.0 3.5 2.628 A-438 Kmr I, 9 44.4 19.5 6.1 25.9 4.1 2.657 A-555 Kmr D, 5 43.3 17.4 7.5 27.8 4.0 2.650 

A-439 Kmr I, 9 39.3 20.3 8.3 24.6 7.5 2.656 A-556 Kle E, 5 48.1 18.3 22.6 11.0 2.710 

A-441 Kmr G, 9 39.8 26.1 2.4 27.7 4.0 2.639 A-558 Klep G, 5 46.0 23.4 25.0 5.6 2.681 

A-442 KJcl F,9 37.4 30.2 20.9 11.5 2.731 A-559 KJs C,2 49.1 19.0 22.0 9.9 2.706 A-444 Kqm1 I, 7 37.9 32.1 27.1 2.9 2.628 A-561 ~i~1 C,3 34.1 44 .. 2 20.4 1.3 2.610 A-445 Kle I, 7 55.0 17.3 19.8 7.9 2.729 A-562 C,3 61.4 .8 12.7 25.1 2.809 A-446 Klp I, 6 29.8 35.0 30.1 5.1 2.634 A-563 KJg C,3 31.7 40.1 27.4 .8 2.611 A-447 Kl I, 6 49.2 13.8 19.8 17.2 2.754 A-564 KJg D, 3 25.1 43.0 31.5 .4 2.619 A-448 Kle H,6 44.3 22.2 25.6 7.9 2.701 A-565 Klef D, 3 43.8 22.1 23.9 10.2 2.695 A-449 Kle H, 7 42.3 28.2 28.9 .6 2.637 A-566 KJg F, 1 22.2 40.3 37.2 .3 2.614 A-450 Kmr G, 6 49.2 18.0 5.8 23.4 3.6 2.657 A-567 ~f J, 2 43.3 18.2 23.8 14.7 2.720 A-451 Kmr D, 6 40.9 25.6 4.3 26.2 3.0 2.627 A-568 D, 9 58.9 3.1 9.8 28.2 2.685 

A-452 Kmr F, 7 40.0 24.2 4.6 28.5 2.7 2.629 A-569 KJqd2 D,9 38.2 23.9 26.7 11.2 2.858 

A-453 Kmr F, 7 44.6 18.8 4.8 27.6 4.2 2.660 A-570 KJcl D,9 35.8 22.3 26.5 15.4 2.732 A454B Kle E, 3 48.8 19.4 21.5 10.3 2.684 A-571 KJrl D,9 36.2 31.3 29.2 3.3 2.644 A-455 Kle F,4 48.1 16.6 23.2 12.1 2.704 A-456 Kle F,4 49.9 17.6 19.3 13.2 2.730 A-457 Kle G, 4 42.2 22.3 29.3 8.7 2.682 1See fig. 1 for location of samples and definition of symbols. See also Lockwood and Lydon A-458 Kle G, 4 47.0 18.3 21.9 12.8 2.717 0975) for description. A-459 Klef H, 4 54.4 14.0 21.3 10.3 2.719 2For Kmr samples, this is the matrix alkali feldspar (megacryst alkali feldspar excluded). A-460 Kmr G. 6 45.1 17.2 8.2 26.3 3.2 2.660 a For samples of Kmr only. This value taken from fig. 10. 

red dots printed on a transparent base ( 46 by 38 em in then adjusted to agree with the pattern shown by pointsize) directly over a suitably exposed outcrop and count- count percentages-that is, low percentages were ining those points that fell on megacrysts. Comparison of creased, and high percentages were decreased. Thus, for 

percentages determined by both methods on the same example, a field-determined area count of 5 percent 

outcrop (fig. 9) showed that the area-count percentages alkali feldspar megacrysts was adjusted to 8 percent 

were consistently too low for sparsely porphyritic rocks before being plotted. These adjusted percentages were 

and consistently too high for highly porphyritic rocks. used to construct figures 10-12. 

All percentages from the area-count method were The resulting adjusted percentages (386 points-fig. 
C16 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

w 

(!) 

25 

~ 20 

z 

w 

u 

a: 

w 

ll. 

1- 15 

z 

:::> 

0 

u 

..:. 

z 10 

0 

ll. 

Curve B 

10 15 20 25 30 35 

AREA-COUNT PERCENTAGE 

FIGURE 9.-Graph showing relation between point-count and areacount methods of estimating alkali feldspar megacryst abundance 

in th_e quartz monzonite of Mono Recesses. Curve A is average 

relatiOn between the two methods. CurveB is expected distribution 

if point-count and area-count methods give equivalent results. 

10) were plotted on an overlay of the pluton, and although a distinct pattern of megacryst abundances was 

observed, there was too much local variationa to permit 

simple contouring of data. To reduce and smooth out the 

purely local variation, all data were integrated over 

1-mi2 areas on a grid with approximately one-half-mile 

spacing and then hand contoured. Alkali feldspar 

megacrysts are concentrated along the southwest margin of the pluton and along most of the northeast margin 

(fig. 10). The large prong of the pluton that extends to 

the northeast is composed largely of nonporphyritic 

alaskite and is considered to represent a late-stage mass 

of highly differentiated magma that migrated northeastward from the main body of the pluton. Thus, the 

area of abundant megacrysts in figure 10 that projects 

across the northeastern prong is considered to mark an 

earlier margin of the quartz monzonite of Mono Recesses. The increase in abundance of phenocrysts upwards 

(fig. 11) is similar to the increase near lateral contacts of 

the pluton, suggesting that the upper contact of the 

pluton was only a short distance above present erosion 

levels. 

Figure 10 was drafted to facilitate construction of the 

adjusted modal values of alkali feldspar for the quartz 

monzonite of Mono Recesses shown in figures 3 and 8 

and in table 2. This adjustment was made necessary b; 

3Much_ofthis is apparently variation ofmegacryst abundance with elevation. In areas of large rehef (for example, Mono Cr~ek, where ~he local topographic relief in places exceeds 2,500 feet) megacryst abundance mcreases w1th elevation {fig. 11). This variation related solely to the topography frustrates direct contouring of the data. 

the large size (as much as 8 em long) and irregular local 

distribution of alkali feldspar megacrysts in-the Mono 

Recesses pluton. Because of the large megacrysts, 

measured modal compositions of a single sample can 

v.ary from intermediate granodiorite to alkali feldsparrich quartz monzonite, depending solely on where the 

slab is cut and whether or not large alkali feldspar 

megacrysts are exposed on the sawn slab. To adjust 

modes, megacrysts were excluded from the point-count 

analysis during counting; only fine- to medium-grained 

alkali feldspar grains in the matrix were counted in the 

mode, and this is the value reported as upercent alkali 

feldspar" for samples of the quartz monzonite of Mono 

Recesses in table 2. For each point at which a modal 

analysis was available in the quartz monzonite of Mono 

Recesses, the regional percentage of alkali feldspar 

phenocrysts was determined from figure 10, and then a 

new value was obtained for total alkali feldspar, equal 

to the matrix percentage plus the regional megacryst 

feldspar percentage. This value is plotted in figure 3 and 

was used to construct the ternary plots in figure 8. 

The alkali feldspar megacrysts are most abundant 

near the margins of the Mono Recesses pluton (fig. 10). 

In order to determine whether the abundance of megacrysts reflects the total abundance of alkali feldspar, a 

plot of the abundance of matrix alkali feldspar versus 

the abundance of alkali feldspar megacrysts (fig. 12) 

was constructed. This plot shows a weak inverse correlation between volume percent of matrix and megacryst 

alkali feldspar in the pluton. Thus the abundance of 

megacrysts does not simply reflect total abundance of 

alkali feldspar components in the magma but rather 

demonstrates that near the pluton margin a physical 

environment or total magma composition was conducive to growth of the giant crystals. 

The modes of specimens of the quartz monzonite of 

Mono Recesses lie in both the granodiorite and the 

quartz monzonite fields (fig.8). The modal variation is 

reflected in the whole-rock chemistry of the rocks and 

informal plots of normative quartz, orthoclase,' and 

plagioclase versus lateral position in the pluton for the 

six analyzed samples of the quartz monzonite of Mono 

Recesses show that the most calcic rocks are found near 

the margins of the pluton and the most silicic rocks are 

found in the center. A corresponding pattern is shown in 

the variation of specific gravity of samples from the 

pluton (fig. 7); the densest rocks are found along the 

margins and the least dense in the center. Thus, the 

quartz monzonite of Mono Recesses follows the trend of 

normal zoning (most silicic rocks in the center) found in 

other granitic plutons. This conclusion is also borne out 

by the distribution of hornblende, which is restricted to 

marginal areas of the pluton. 
MOUNT ABBOT QUADRANGLE, CALIFORNIA, ANALYTIC DATA C17 

• 

• • 

• • 

• 

• • • • 

• • 

• 

37°15' 

0 2 3 4 5 MILES 

I I I I I I I I I I I I I 

0 1 2 3 4 5 6 7 8 Kl LOMETRBS 

FIGURE 10.-Abundance of alkali feldspar megacrysts in the quartz monzonite of Mono Recesses. 
C18 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

0 

13,000 

1- 12,000 

w 

w 

LL 

~ 11,000 

z' 

0 

j: 10,000 <( 

> 

w 

.J 

w 9,000 

8,000 

0 

HORIZONTAL DISTANCE, IN KILOMETRES 

2 3 4 5 6 

A \6.9 3.3 7.2 

C 6.7 B 

10.0 9.6~ 

\.4 i 7.3 4.6 D 

~3.9 

2 3 

HORIZONTAL DISTANCE, IN MILES 

4 

4000 

!/) 

w 

a: 

1-

3500 ~ 

~ 

z' 

0 

i= 3000 ~ 

w 

.J 

w 

FIGURE H.-Relation of alkali feldspar megacryst abundances (in 

percent) to topographic relief in two profiles across the quartz monzonite of Mono Recesses in the Mount Abbot quadrangle. 

REFERENCES 

Bateman, P. C., Clark, L. D., Huber, N. K., Moore, J. G., and Rinehart, 

C. D., 1963, The Sierra Nevada batholith-A synthesis of recent 

work across the central part: U.S. Geol. Survey Prof. Paper 

414- D, 46 p. 

Bateman, P. C., and Eaton, J. P., 1967, Sierra Nevada batholith: 

Science, v. 158, no. 3807, p. 1407-1417. 

Lockwood, J. P., Bateman, P. C., and Sullivan, J. S., 1972, Mineral 

resource evaluation of the U.S. Forest Service Sierra Demonstration Project Area, Sierra National Forest, California: U.S. Geol. 

Survey Prof. Paper 714, 59 p. 

Lockwood, J.P., and Lydon, P. A., 1975, Geologic map of the Mount 

Abbot quadrangle, central Sierra Nevada, California: U.S. Geol. 

Survey Geol. Quad. Map GQ-1155, scale 1:62,500. 

a: 30 

<( 

a.. 

!/) 

Q 

.J 

w 

u. 

.J 25 <( 

>C 

....J 

<( 

~ 

a: 

~ 20 

~ 

lL 

0 

w 

l? 

<( 

1- 15 z 

w 

u 

a: 

w 

a.. 

10 

0 

X 

X 

X 

X 

X XX X X X 

X 

~ X 

X X X>fx X X X xx X XX 'S< xxxx X X 

X 

X X 

X * X 

xxxx 

X 

X 

X X 

X 

X X X X 

X 

X >$( X 

X 

3 4 6 8 9 10 11 12 13 14 15 

REGIONAL PERCENTAGE OF ALKALI FELDSPAR MEGACRYSTS 

FIGURE 12.-Graph showing variation of alkali feldspar megacryst 

abundances with matrix alkali feldspar abundances in the quartz 

monzonite of Mono Recesses. Line is the least-squares best fit solution for the data. 

Shapiro, Leonard, and Brannock, W. W., 1962, Rapid analyses of 

silicate, carbonate, and phosphate rocks: U.S. Geol. Survey Bull. 

1144-A, 56 p. 

*U.S. GOVERNMENT PRINTING OFFICE: 1975-0-690-036/32