Structural geology of the upper Rock Creek area, Inyo County, , and its relation to the regional structure of the

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Authors Trent, D. D.

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Dee Dexter Trent

A Dissertation Submitted to the Faculty of the

DEPARTMENT OF GEOSCIENCES In Partial Fulfillment of the Requirements For the Degree of


In the Graduate College




I hereby recommend that this dissertation prepared under my direction by ______Dee Dexter Trent______entitled Structural Geology of the Upper Rock Creek Area . Tnvo County, California, and Its Relation to the Regional Structure of the Sierra Nevada ______be accepted as fulfilling the dissertation requirement of the degree of ______Doctor of Philosophy______

P). /in /'-/7. 3 Dissertation Director fJ Date

After inspection of the final copy of the dissertation, the following members of the Final Examination Committee concur in its approval and recommend its acceptance:*

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2 g ££2 3

This approval and acceptance is contingent on the candidate's adequate performance and defense of this dissertation at the final oral examination. The inclusion of this sheet bound into the library copy of the dissertation is evidence of satisfactory performance at the final examination. STATEMENT BY AUTHOR

This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrow­ ers under rules of the Library.

Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or re­ production of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the in­ terests of scholarship. In all other instances, however, permission must be obtained from the author.


During the progress and completion of this project I have re­ ceived assistance from various persons and organizations. I wish to express my deep appreciation to the National Science Foundation,

Division of Graduate Education in Science, for funds to support my research and to the members of my faculty committee for their sugges­ tions, criticism, and assistance. I am particularly indebted to Drs.

E. B. Mayo and W. B. Bull for their encouragement and suggestions during their field checks. Special appreciation is extended to Dr.

Mayo, who inspired me to undertake this project.

Dr. Richard D. Call of the Department of Mining and Geolog­ ical Engineering made available his computer program for plotting

Schmidt-net equal-area projections. Dr. Call has also been very generous with his time in discussing statistical analyses of structural geologic data.

Dr. W. Ray Henson and Mr. Leslie Follett of the University of

Arizona Computer Center kindly assisted in writing program Rosekol,

and Mr. Robin T. Holcomb generously helped in writing program Twenfiv.

For suggestions and criticism, I am indebted to numerous grad­

uate students at The University of Arizona, among whom are Drs. Eberhardt A. Schmidt and Robert E. West and M essrs. James A. Touts,

Daniel J. Lynch, and Robin T. Holcomb.

Hi iv

The White Mountain District of the U.S. Forest Service, espe­ cially Mr. and M rs. Walter Blackney at the Rock Creek Guard Station, also contributed aid and cooperation.

For many hours, especially on weekends which might otherwise have belonged to them, I take pleasure in thanking Patricia, Susan, and





ABSTRACT...... x

INTRODUCTION...... 1 f Location ...... 1 O b j e c t i v e s ...... 1 Previous In v e s tig a tio n s ...... 4


S a m p lin g ...... o> co rx Rock C reek Area . . Reconnaissance Areas Semistatistical Methods

THE R O C K S...... 10

M e ta g a b b ro ...... 10 Round Valley Peak ...... 13 Lamarck Granodiorite ...... 15 T ransition R o c k s...... 17 Cathedral Peak ...... 26


Preferred Orientations of and Inclusions ..... 31 Theoretical and Experimental Considerations...... 31 Field Observations ...... 38 S c h lie re n ...... 39 J o i n t s ...... 44 M arginal D i k e s ...... 45


Joints and the Interpenetrating F o liatio n ...... 47 Schlieren Dikes, Felsic Dikes, and Marginal Thrusts .... 49

v vi




Emplacement of the Cathedral Peak G ranite ...... 57 Reality of Interpenetrating F o lia tio n s ...... 57


Structural Mosaic of Rock Creek Salient...... 59 Observations in ...... 61 Interpenetrating Foliations on the Middle Fork of the San Joaquin R iver...... 63 Interpenetrating Foliations on the South Fork of Bishop C r e e k ...... '...... 65 R econnaissance in Lone Pine C a n y o n ...... 65 Relation of Interpenetrating Foliations to Regional Joints . . 66


Suggested Tectonic Plan of the Sierra N e v a d a ...... 69 Suggested Origin of interpenetrating Foliations...... 69

C O N C L U S IO N S ...... 72


Rose D iagram s...... 74 Elim inating "N oise" from Rose D i a g r a m s ...... 76 Random vs. Preferred O rientations ...... 77 Minimum Number of M easurements...... 78 Replication by Different W orkers...... 87 Replication at Different Sites That Are in C lose P ro x im ity ...... 88 . The Kolmogorov-Smirnov S t a t i s t i c ...... 90 R a tio n a le ...... 91 M e th o d ...... 92



Figure Page

1. View Southeastward across the Northern Half of Upper Rock C reek V a l l e y ...... 2

2. View Eastward across the Southern Half of Upper Rock Creek V alley ...... 3

3. Generalized Geology and Rose Diagrams, Central Sierra Nevada, C alifornia ...... ■ in pocket

4. Primary Foliation Map, Upper Rock Creek, Fresno and Inyo Counties, California. . . . in pocket 5. High Angle Joint Map, Upper Rock Creek, Fresno and Inyo Counties, California .... in pocket

6. Low Angle Joint Map, Upper Rock Creek, Fresno and Inyo Counties, California. . . . in pocket

7. Dike Map, Upper Rock Creek, Fresno and Inyo C o u n ties, C a lifo rn ia ...... in pocket

8. Cross Sections, Upper Rock Creek, Fresno and Inyo Counties, California ...... in pocket

9. Quaternary Diagram of the Mineralogical Composition of the Round Valley Peak G r a n o d i o r i t e ...... 16

10. Compositional and Textural Changes, in the Plutonic Rocks along the Eastern Brook Lakes—Mono Pass Traverse ...... r 19

11. Compositional and Textural Changes in the Plutonic Rocks along the Serene Lake—Summit Lake Traverse ...... 20

12. Quaternary Diagram of the Mineralogical Composition of the Transition Rocks ...... 25

13. Quaternary Diagram of the Mineralogical Composition of the Cathedral Peak Granite .... 30

v ii v iii


Figure Page

14. Long-axis Rose Diagram, Computed from Jeffrey's (1922) T h e o ry ...... 34

15. A Mafic Inclusion with a Xenolith Core of Hornfels in the Round Valley Peak Granodiorite...... 37

16. Primary Foliation Map, Rock Creek Salient, Sierra Nevada, California ...... in pocket

17. A Schlieren D ik e ...... 40

18. Arcuate Schlieren Dike in Lower , Yosemite National P ark ...... 42

19. Lower Hemisphere, Equal-area Projections of Poles to (1) Primary Foliation and (2) J o in ts ...... 48

: 20. Lower Hemisphere, Equal-area Projection of Poles to Felsic and Schlieren D ikes ...... 50

21. Lower Hemisphere, Equal-area Projections of Poles to (1) Schlieren Dikes and (2) Felsic Dikes .... 51

22. Drag Folds in a Schlieren D ik e...... 53 23. C rosscutting Schlieren D i k e s ...... 54

24. Schlieren Bundle Terminated by Steep Foliation Revealed by the Parallel Orientations of Dark Inclusions ...... " 67 LIST OF TABLES

Table Page

1. Counts of K- on the Lake Trail-Summit Lake Traverse...... 21

2. Counts of K-feldspar Phenocrysts on the Half Moon Pass Traverse...... 22


Structures in granite, including primary foliation, joints, schlieren, schlieren dikes, and marginal dikes, in several plutons in the upper Rock Creek Valley, Sierra Nevada, reveal the history of em­ placement and offer evidence of the forceful emplacement of three p lu to n s.

Compositional variations across the contact zone between two of the plutons suggest that emplacement of the youngest pluton caused potash feldspathization in the granitic wall rocks. Subtle structures, such as rolls and drag folds in or associated with marginal dikes, sug­ gest that heat and chemical activity softened the granitic wall rocks, lowered their rheidity, and promoted plastic adjustments.

Field measurements of the primary foliation in the plutons re­ veal the presence of interpenetrating east-west and north-south folia­

tions . Rose diagrams constructed from the orientations of mafic minerals

or K-feldspar phenocrysts also disclose northwest and northeast foliation

trends. Two sets of steep joints closely parallel the east-west and

north-south foliations. Reconnaissance in several other areas in the Sierra Nevada

reveals similar patterns of interpenetrating foliations and joint systems

that generally follow one or both of two principal systems of preferred

directions: (1) approximately northwest and northeast or (2) approximate­

ly north-south and east-west. Several rose diagrams indicate the pres­

ence of all four directions of foliation. Mapping of the internal structures xi of many plutons in the Sierra Nevada indicates that the structures are not wholly autonomous, as generally supposed, but may result from regional stresses that have prevailed throughout a long period of intru­ sion and cooling.

Larger tectonic units, such as entire plutons or metamorphosed septae, in the Sierra Nevada were recognized by earlier workers as fol­ lowing these same four directions. Apparently a coarse regional frame­ work is filled in by the finer foliation and joint network.

Possible origins of the interpenetrating foliations include pres­ ervation of relict structures and preferred orientation of minerals by regional compression. Whatever the actual mechanism, the interpene­ trating foliations, in common with the larger framework elements, are regional in extent and must therefore result from some regional cause. INTRODUCTION

L ocation

The focal point of this study is an area of the Sierra Nevada batholith on upper Rock Creek, Inyo County, California, centered at lat 36026' N. and long 118045' W. The area is about four miles long and ranges in width from about 2 to 3.5 miles (Figs. 1 and 2). Access is by paved road which begins at Tom's Place on U.S. Highway 395.

Travel within most of the upper Rock Creek basin is by foot or by horse­ back because most of it lies within the Wilderness where the use of motor vehicles is prohibited.

Studies of other granitic terrains were made by reconnaissance in Yosemite National Park and along the eastern side of the Sierra Nevada between Mammoth Lakes and Lone Pine. The locations of these places are shown on Figure 3 (in pocket). Measurements of crystal orientations were also made in the granitic rocks of the Santa Catalina Mountains, near Tucson, Arizona.

O bjectives

This research has three objectives: (1) to reveal in detail the internal structures of granitic plutons in the small but favorable area on upper Rock Creek in order, to distinguish those elements related to em­ placement of the plutons from an interpenetrating set of cross foliations;

(2) to establish beyond reasonable doubt the reality of this and other cross foliations and to demonstrate their regional, as well as local.

1 Figure 1. View Southeastward across the Northern Half of Upper Rock Creek Valley Serene Ridge extends across the center of the photograph. The eastern boundary of the study area is marked by the protalus rampart along the base of the ridge in the distance. to Figure 2. View Eastward across the Southern Half of the Upper Rock Creek Valley The contact of the Round Valley Peak Granodiorite with the older metagabbro extends diagonal­ ly across the center of the photograph. The sharp contact of the metagabbro and granitic rocks on the canyon wall is beyond the limits of the study. 4 distribution; and (3) to attempt an interpretation of the foliation and joint network in terms of the fit of this local pattern into the regional and con­ tinental mosaic.

As an aid in attaining the above objectives, the fabric of the granitic rocks was analyzed semistatistically, using lower hemisphere, equal-area azimuthal projections and rose diagrams. As a result of this treatment and of the field mapping it seems that the internal structures of many plutons in the Sierra Nevada are not wholly autonomous, as gen­

erally supposed, but may result in part from regional stresses that have prevailed throughout a long period of intrusion and cooling. Very impor­

tant in this regard is the interpenetrating foliation which, to my know­

ledge, has not been previously considered on a regional scale.

Previous Investigations

The earliest published maps showing plutonic rocks of the

Sierra Nevada are in the well-known geologic folios of Lindgren (1894),

Lindgren and Turner (1895), Turner (1894, 1897, 1898), Turner and Ran­

som e (1894, 1896, 1897, 1898, 1900), and Ransome (1900). Knopf pub­

lished in 1918 the results of his mapping in the eastern Sierra Nevada

where he studied separate plutons. Calkins (1930) divided the part of

the batholith in the Yosemite region into separate intrusions.

The first investigation of the internal structures of the plutons

of the Sierra Nevada was published in 1928 by Hans Cloos. Ernst Cloos

(1931, 1932, 1933, 1935, 1936), using the intrusions mapped by Calkins

(1930) as a base, carried out detailed granite tectonic investigations in

Yosemite National Park and in the Mother Lode region. 5

In 1934, Mayo published one of his investigations of general geology in the Sierra Nevada, which was followed (1935, 1937, 1941,

1947) by several studies that were concerned mainly with the structures of the granitic rocks.

Contributions on the petrology and ages of the metamorphic and

Plutonic rocks of the central and eastern Sierra Nevada have been made by Bateman (1965), Bateman and others (1963), Evernden and Kistler

(1970), Hamilton (1956a, 1956b), and Rinehart and Ross (1964). Sher­ lock and Hamilton (1958) studied the structure and petrology of plutons in the northern half of the Mount Abbott quadrangle, and investigations by Bateman and Kistler (1966) and Kistler (1966) emphasized the struc­ tural details of metamorphic rocks in the central and eastern Sierra

Nevada and their relation to the sequence of emplacement of the granitic intrusions. METHODS OF INVESTIGATION

The area on upper Rock Creek was mapped at a scale of one

inch to 1000 feet, using as base the U.S. Geological Survey Mount

Abbott and Mount Tom 15-minute quadrangles. The mapping technique

is basically that of granite tectonics which was developed by Hans Cloos

(1921, 1922a, 1922b, 1928) and presented in the English language by

Balk (1937).

Measurements of the attitudes of the foliation, schlieren,

schlieren dikes, and joints were made with a Brunton compass. At each

locality visited a mean value was determined for each set of foliation

and joint directions by averaging the measurements of each structural

element taken on three to five separate surfaces. The attitudes of each

type of structural element were recorded on separate base maps, and the

data were used to construct lower-hemisphere azimuthal equal-area pro­

jections of the poles to (1) steep primary foliation, (2) schlieren dikes

and thick and pegmatite dikes, and (3) the joint system. Figures

4,5, 6, and 7 (in pocket) are maps of the upper Rock Creek area which

represent, separately, each of the structural elements.

Four computer programs to analyze the field data were used on

the CDC 6400 computer at The University of Arizona. The lower hemi­

sphere equal-area azimuthal projections were constructed using a com­

puter program written by Richard D. Call of the Department of Mining

and Geological Engineering. Three other programs were written especial­

ly for this study: (1) Program Tenten for making histograms from

6 7 measurements of orientations, (2) Program Twenfiv for smoothing rose diagram data and tabulating histograms, and (2) Program Rosekol for comparing rose diagrams from the field with theoretically random rose diagrams by the Kolmogorov-Smirnov nonparametric test.

Sampling Procedure

Rock Creek Area

Sampling of the fabric elements on a mesoscopic scale* was done on a substantive basis in order to provide an independent check of the mapping results. Early in the study, rose diagrams revealed preferred trends of mafic minerals that suggested the presence of interpenetrating cross foliations in the granitic rocks. Data for these initial rose dia­ grams were collected at arbitrarily selected sites. In the selection of subsequent sites an attempt was made to follow a more formal method based on grid spacing. The sites were established along north-trending lines that were spaced about 2,000 feet apart with an approximate spac­ ing between sites of about 2,000 feet. Vegetation, soil, till, talus, lakes, meadows, and lack of nearly horizontal rock surfaces precluded rigid adherence to the grid spacing.

1. The use of the terms "microscopic," "mesoscopic," and "macroscopic" in this paper follows the definitions of Turner and Weiss (1963, p. 15-16): microscopic—covers bodies, such as thin sections, that can be conveniently examined with a microscope; .mesoscopic-- covers bodies that can be effectively studied by direct observation, with or without a low-power hand lens, which range in size from hand specimens to large but continuous exposures; macroscopic—covers dis­ continuous parts of a single body, bodies too large to be examined directly in their entirety. Observations at this scale require extrapola­ tion and synthesis of mesoscopic observations. 8 Rock specimens were collected by both purposeful and system­ atic sampling procedures. The purposeful samples were collected to establish the rock types underlying the area; the systematic samples, collected along two traverses that trend normal to the contact of the

Cathedral Peak Granite and the Round Valley Peak Granodiorite, were taken to determine the compositional and textural changes across the contact. The routes for the traverses were dictated by accessibility.

Modal analyses of the rock samples were made by studying stained thin sections and stained rock slabs.

Mapping in the western part of the Rock Creek area was re­ stricted by the presence of extensive talus, precipitous slopes, and lack of clean rock surfaces. Consequently, there is a decrease in the density of data in that part of the maps (Figs. 4, 5, 6, and 7; in pocket).

Reconnaissance Areas

Other plutons in the Sierra Nevada were visited briefly; their study was limited to collecting spot samples of structural data, espe­ cially with regard to the orientations of mafic minerals or phenocrysts.

Locations of sample sites were determined by the ease of access and the existence of nearly horizontal exposures of rock. Sites of the recon­ naissance studies are located on a regional map of the Sierra Nevada

(Fig. 3, in pocket). 9 Semistatistical Methods^

A number of rose diagrams were constructed from the measured orientations of mafic minerals in and phenocrysts in por- phyritic as an independent check on the field measure­ ments of foliation. In the early phases of this work some fundamental questions were raised on the significance of rose diagrams and several experiments were designed to test various aspects of their use. Details of these experiments are included in Appendix A. The general result of the rose diagrams is that they strongly support the directional trends gained from field measurements of mesoscopic foliations.

2. The term " semistatistical" is used in this paper to indicate that statistical techniques were employed in analyzing the data which, however, do not lend themselves to strict statistical interpretation be­ cause it was impossible to sample the data in a formal random manner. For example, tests of significance of the equal-area fabric diagrams of the poles to foliation and joints could be made with the Poisson binomial exponential function (Friedman, 1964, p. 468-469) if random sampling had been possible. Furthermore, the rose diagrams graphically represent two-dimensional polymodal distribution trends, but these are not formal­ ly statistical. Even had it been possible to sample randomly the data for the rose diagrams there are no statistical tests of significance ap­ plicable to nonvector directional data (Watson, 1966, p. 786-797). THE ROCKS

Upper Rock Creek is underlain by three granitic plutons and a metagabbro of diverse texture and composition. Contact relationships show that the metagabbro in the southern part of the area (Figs .4,5,

6, and 7; in pocket) is the oldest rock. Intruding the metagabbro and underlying most of the area is the Round Valley Peak Granodiorite, which has K/Ar ages of 81 to 87 m.y. (Kistler, Bateman, and Brannock, 1965).

Along the southern margin of the area is a body of the Lamarck Grano­ whose contact relations and radiometric age, 76-84 m.y. (Kistler and others, 1965), show that it occupies a younger position than the

Round Valley Peak Granodiorite in the plutonic sequence. The Cathedral

Peak Granite, youngest pluton in upper Rock Creek, underlies the west­ ern part of the area. Kistler and others (1965) report K/Ar ages for this pluton in the range of 77.4 to 79.6 m.y.

The rock types underlying the upper Rock Creek area were deter­ mined from modal counts of 44 thin sections and 10 stained slabs. De­ tails of the techniques and tables of the analyses are given in

Appendix B.

M etagabbro

Along the southern border of the mapped area is a body of mafic rocks here named metagabbro, which is composed of materials of diverse texture and composition. Included within the unit are and gab- bros, very dark gray hornblende-rich masses in which the hornblende

10 11 crystals may attain lengths of several centimeters, and scattered rem­

nants of metavolcanic and metasedimentary rocks. The heterogeneous

nature of the mafic rocks and the metamorphic inclusions have led me to

classify them as metamorphic rather than plutonic.

The is subhedral and generally lath shaped, ranging

in length from 0.5 to 4 mm. The composition varies with position in the

body from An4Q-52 *n the more central parts to Angg in the margins. Few

grains are zoned. twinning is ubiquitous, and is com­

mon in the plagioclase rims that contact K-feldspar. The arrangement of

the plagioclase laths resembles an ophitic texture, but instead of the

plagioclase being embedded in a mesostasis of it is usually

associated with a poikilitic anhedral, pleochoric green hornblende.

Pyroxene (augite?) is present in samples from the more central parts of

the mafic rocks.

The poikilitic hornblende is sieved with abundant droplets of

quartz, and some of the hornblende has distinctive color-zoned rims

that are slightly darker green. Probably the poikilitic hornblende is a

pseudomorph after pyroxene that was in an original or .

A similar interpretation of a metamorphic dolerite in Scotland is reported

, by Sutton and Watson (1951, p. 25-35), where they have traced the pro­

gressive alteration from pyroxene to hornblende to biotite over a wide

a re a .

Biotite, in ragged yellowish-brown anhedra, is always asso­

ciated with the hornblende, usually in clusters, and commonly encloses

hornblende, magnetite, sphene, and apatite. Chlorite (pennine?) locally 12 alters the biotite. The common association of biotite and hornblende suggests that the biotite is secondary after hornblende.

Only small amounts of quartz and K-feldspar are present. They are interstitial and enclose numerous tiny grains of biotite, hornblende, magnetite, sphene, and apatite.

Numerous thick aplite and pegmatite dikes derived from the younger plutons of the area penetrate the metagabbro. Xenoliths of the mafic rocks are identifiable in the contact zone between the metagabbro and the younger Round Valley Peak Granodiorite. The two rock masses form an intrusion breccia for several hundred feet along their contact.

Although, as mentioned above, the contact relationships indi­ cate clearly that the metagabbro has been intruded by the younger grano­ diorite s , there are several gabbro dikes rooted in the metagabbro which intrude the granodiorites. Two of these dikes are illustrated in section

A-A' in Figure 8 (in pocket), and others are present in the area of peak

11898 about 2,000 feet northwest of Long Lake (Figs. 4, 5, 6, and 7).

This seemingly anomalous behavior can be explained by the remobiliza­ tion of the metagabbro in the contact zone during the emplacement of the

Cathedral Peak Granite.

A thin-section examination of one of the masses of metaquartz­ ite from within the metagabbro reveals that the rock contains a signifi­ cant amount of tremolite and a small amount of cordierite in addition to quartz and feldspar. Tremolite is commonly presept in low-grade meta- morphic rocks which have been derived from ferromagnesian minerals in igneous rocks or from calcareous sandstones (Moorhouse, 1959, p. 76-

77). The texture of the metaquartzite and the mineral constituents seem 13 to favor derivation from a sediment. The cordierite probably has recrys­ tallized from argillaceous material in the original rock (Moorhouse, 1959, p. 106). The contact relationships of the metagabbro and the adjacent igneous rocks indicate that the metagabbro served as a resistant wall for the younger intrusions.

Round Valley Peak Granodiorite

Underlying most of the area (Figs. 4, 5, 6, and 7) is a pluton of hornblende biotite granodiorite that has been named the Round Valley

Peak Granodiorite by Bateman (1961, p. 75) for the type locality about

3.5 miles to the northeast. Megascopically, the granodiorite is medium grained equigranular with an average grain size of about 2 mm. Biotite

and hornblende are evenly distributed and together make up about 13

percent of the rock. Both plagioclase and K-feldspar are white, the

quartz is smoky gray; combined, the mineral constituents give the rock

a light-gray color. The color index of 15 modal analyses is 13. Dark-

gray, ellipsoidal, dioritic and amphibolitic inclusions are distributed

abundantly throughout the pluton and locally the inclusions form swarms.

Foliation in most places is mesoscopically discernible; joints are mod­

erately to widely spaced and conspicuous.

In thin section, the Round Valley Peak Granodiorite is hypidio-

morphic-granular. The plagioclase and hornblende are subhedral, the

biotite subhedral to anhedral. In contrast, the K-feldspar and quartz

are irregular anhedra. Plagioclase is sodic andesine with normal oscil­

latory zoning. The cores of the zoned grains average about Angg but

reach as high as Angg. Rims are calcic , ranging from An^g 14 to Ango. Twinning according to the carlsbad, albite, and pericline laws

is common. The plagioclase is notably fresh; saussuritic alteration is minor, and where present is restricted to the more calcic cores or to the

zonal boundaries within the crystals. Wormy myrmekite is notable at the boundaries of plagioclase and K-feldspar.

K-feldspar is interstitial or anhedral, generally untwinned but occasionally exhibits quadrille structure. The K-feldspar has a large 2V,

is commonly poikilitic, and has attacked and enveloped other minerals,

as shown by the embayment of quartz and plagioclase. Occasionally the

K-feldspar shows faint perthitic laminae.

Biotite is present in pleochroic ragged olive-brown flakes; 2V

is small. At some localities the biotite and other dark minerals are

separated, but commonly the biotite is in clusters associated with other

dark constituents. Often a magnetite grain surrounded by a rim of sphene

will be enclosed within a biotite flake.

Hornblende is the pleochroic green variety, commonly altered

with shreds of pennine. Hornblende and biotite are often intergrown,

suggesting that the biotite has formed by alteration and replacement of


The most common accessory minerals, metallic opaques (ap­

parently a titaniferous magnetite), apatite, and sphene are scattered

throughout the pluton. Characteristically, the sphene is in wedge-

shaped anhedra, closely associated with metallic opaques. Although

the opaques appear to be magnetite by reflected light, the close asso­

ciation of sphene and the opaque minerals suggests that is

present in the opaques from which the sphene has been formed. Small 15 amounts of and allanite are present. The Round Valley Peak Gran- odiorite bears a striking resemblance to the Quartz of the Tuolumne intrusive complex (Calkins, 1930) by its composition, texture, and geometric relationship to the Cathedral Peak Granite.

Plots of the modes (Fig. 9) produce small fields of limited scat­ ter which indicate the fairly uniform composition of those samples exam ined.

The distinguishing features of the Round Valley Peak Grano- diorite are:

1. The color index averages 13, with a total range of 7 to 21.

2. Mafic inclusions are common, often in swarms, and foliation

is generally obvious.

3. The rocks are typically medium grained, equigranular, with

mafic minerals scattered evenly throughout.

4. Biotite and hornblende are medium to coarse grained and are

present in subequal amounts.

The Round Valley Peak Granodiorite is important to my problem because it has interpenetrating foliation within it. Furthermore, along its western margin it records the chemical and mineralogical as well as mechanical changes associated with the emplacement of the Cathedral

Peak Granite.

Lamarck Granodiorite

On the southern edge of the mapped area (Figs. 4, 5, 6, and 7) is a small part of another pluton that Bateman (1965, p. 77) named the 16

Quartz Q u a r t z Round Valley Peak granodiorite

Grano- Granite

/ diorite Mafics

Plagioclase ISmodes Potassium Combined Diorite and feldspar and feldspar hornblende perthite gabbro

Figure 9 . Quaternary Diagram of the Mineralogical Composition of the Round Valley Peak Granodiorite 17

Lamarck Granodiorite. This pluton makes a sharp dynamic contact with the metagabbro. The rock was only briefly examined on a mesoscopic scale, but in general it resembles the Round Valley Peak Granodiorite, although the Lamarck Granodiorite has a darker color value and fewer mafic inclusions. Beyond the limits of the mapped area to the south, the Lamarck Granodiorite is intruded by dikes from the Cathedral Peak

Granite, indicating that it is older than the Cathedral Peak pluton.

Bateman (1965, p. 80) reported that contact relationships of the Lamarck

Granodiorite with other plutons outside the area considered here show that it occupies approximately the same position in the intrusive se­ quence of the Sierra Nevada plutonic rocks as the Round Valley Peak

Granodiorite. Radiometric dates of a pluton of Lamarck Granodiorite near Big Pine range from 76 to 84 m.y. (Kistler and others, 1965), in­ dicating that it is somewhat younger than the Round Valley Peak Grano­ diorite .

Transition Rocks

Underlying the area between upper Rock Creek and the ridge that culminates in Mount Starr are granitic rocks which I name the transition rocks. A second, much smaller, dikelike mass along the west side of the small valley of the Eastern Brook Lakes is also assigned to the transition rocks (Figs. 4, 5, 6, and 7).

The mineralogical composition and textural characteristics of the transition rocks are intermediate between those of the Round Valley

Peak Granodiorite and the Cathedral Peak Granite. The main m ass, over

4,000 feet wide, forms a broad gradational zone between the Round

J 18 Valley Peak Granodiorite and the Cathedral Peak Granite. In order to define the western limit of the zone, I used a semiquantitative method

suggested by W. B. Bull (personal communication, 1970) to locate the contact of the Cathedral Peak Granite as defined in Calkins’ (1930, p.

127) original description:

The distinguishing feature of the Cathedral Peak granite is that it contains unusually large phenocrysts of feldspar. Whereas in most porphyries the phenocrysts are only a frac­ tion of an inch in length, in the Cathedral Peak granite they measure not uncommonly two to four inches in length and from one to two inches in breadth.

The semiquantitative technique is based on the number of pheno

crysts per unit area. Counts of phenocrysts were made at sites along

two traverses that extended across the transition rocks and into the

Cathedral Peak Granite. At these sites the phenocrysts were counted

that lay within an area of 108 square inches, an area obtained by tracing

the outline of a clipboard on the rock. Only those phenocrysts that were

clearly discernible were included, and each was marked with a red spot

as it was counted to avoid duplication. Results obtained from the two

traverses are shown in Figures 10 and 11 and Tables 1 and 2. On the

Ruby Lake Trail—Summit Lake traverse there is an abrupt jump from 21 to

60 phenocrysts per measured area at the place which is selected as the

contact. On the Half Moon Pass traverse the change in den­

sity is not abrupt, a change from 18 to 38 phenocrysts per counting area

extending over a distance of nearly 200 feet. Tables 1 and 2 also show

that the phenocrysts increase in size as well as number in the contact zone. 19




0-2.------&&------. plagioclQse maximum percent An

percent plagioclase

sample number •

Figure 10. Compositional and Textural Changes in the Plutonic Rocks along the Eastern Brook Lakes-Mono Pass Traverse 20




0 20










sample number

• Compositional and Textural Changes in the Plutonic rene Lake—Summit Lake Traverse 21

Table 1. Counts of K-feldspar Phenocrysts on the Ruby Lake Trail- Summit Lake Traverse

Minimum Size Site C ount3 of Phenocrysts Comments

1 13 6 mm On Ruby Lake trail; no mafic inclu­ sions .

4 21 6 mm

6 16 10 mm

8 25 10 mm

9 23 10 mm At summit of Mt. Starr; most pheno­ crysts are 20 to 25 mm.

12 15 10 mm Rock has both hornblende and bidtite,

13 19 6 mm

14 21 10 mm Most phenocrysts are greater than 10 mm and less than 25 mm.

15 60 10 mm Many phenocrysts are greater than 25 mm, a few are 50 mm; "typical" Cathedral Peak Granite.

16b 44 10 mm Many phenocrysts are greater than 25 mm, a few are 50 mm, and one phenocrysts is 75 mm; "typical" Cathedral Peak Granite.

a . Averaged from counts made by D. D. Trent and W . B. Bull on two different surfaces spaced 50 feet apart. 22

Table 2. Counts of K-feldspar Phenocrysts on the Half Moon Pass Traverse

Minimum Size Site Count of Phenocrysts Comments

1 9 10 mm

2 17 10 mm A few phenocrysts are 25 mm.

3a 35 10 mm Site on a coarser rock just east of summit of Half Moon Pass.

3b 17 10 mm ■

4 18 10 mm Rock resembles Round Valley Peak Granodiorite more than on east side of p a s s .

5 9 6 mm Most phenocrysts are about 12 mm long.

6 18 10 mm

7 28 10 mm Most phenocrysts are 25 mm or more, a very few are smaller; almost "typical" Cathedral Peak Granite.

8 38 15 mm Clearly porphyritic; the contact is gradational over about 200 ft; most phenocrysts are 25 mm or more in len g th . 23 The contact of the main mass of the transition rocks and the

Round Valley Peak Granodiorite is gradational over the interval between

Rock Creek and the packer's trail west of Rock Creek. Contacts of the small, dikelike mass of transition rock and the Round Valley Peak Grano­ diorite are sharp where exposed and commonly are marked by schlieren or aplite zones.

The transition rocks are medium to coarse grained, equigranular to porphyritic. Groundmass plagioclase and K-feldspar are both white; the phenocrysts of K-feldspar are light pink and quartz is smoky gray.

The color index ranges from 16 where the transition rocks blend into

Round Valley Peak Granodiorite to about 8 near the contact with the Ca­ thedral Peak Granite.

Mafic inclusions are much less common in the transition rocks than in the Round Valley Peak Granodiorite. Schlieren are uncommon; foliation is obscure, probably due to the paucity of inclusions and the lower mafic content which is a consequence of the decrease in the amount of hornblende. The lower color index is also an effect of the decrease in the size of biotite grains toward the Cathedral Peak Granite.

Biotite in the Round Valley Peak Granodiorite is commonly in pseudo- hexagonal books that may be 4 to 6 mm thick, but in the transition rocks the biotite changes to small isolated thin sheets or clusters of small grains. Textural changes are also indicated by the K-feldspar pheno­ crysts which increase in both size and amount toward the contact with the Cathedral Peak Granite. Figures 10 and 11 illustrate the variations in the mineralogical composition and the texture from the Round Valley 24

Peak Granodiorite, across the transition rocks, and into the Cathedral

Peak Granite.

Under the microscope, the transition rocks show much the same mineralogical compositions and similar textures as observed in the Round

Valley Peak Granodiorite, except for the differences mentioned above and some textural characteristics of K-feldspar which offer striking evidence of potash addition in the transition rocks. K-feldspar occurs both as an- hedra and phenocrysts in the transition rocks, commonly as perthite. The anhedra are larger than their counterparts in the Round Valley Peak Grano­ diorite, and they enclose numerous grains of plagioclase, biotite, and hornblende which show embayed edges that record partial replacement by the enclosing K-feldspar.

Strain, probably associated with the emplacement of the Cathe­ dral Peak Granite, is recorded in biotite and plagioclase grains in the samples collected near the summit of Mount Starr. Biotite grains show deformation by bending and by kink bands, and the albite twinning in plagioclase shows offsetting along small fractures. Perhaps a combina­ tion of mechanical disruption associated with the emplacement of the

Cathedral Peak Granite and synkinematic potash addition accounts for the irregular interstitial K-feldspar and the enclosed fragments of "early" m in erals.

The plot of the modes (Fig. 12) produces an irregular field on the P-Q-K diagram which is aligned in the direction of the plagioclase corner. The scatter in the F-Q-M diagram reflects variation in quartz and total feldspar. The spread of the P-Q-K diagram clearly shows the 25

Transition rocks


13 m od es

Figure 12. Quaternary Diagram of the Mineralogical Composi­ tion of the Transition Rocks 26 transitional composition by overlapping from the granodiorite into the field.

In summary, the basic characteristics of the transition rocks are:

1. The color index averages 11, generally lower that that of the

round Valley Peak Granodiorite, and decreases toward the Ca­

thedral Peak Granite.

2. Inclusions are rare; foliation is vague.

3. Rocks are generally coarse grained, with occasional pheno-

crysts or large anhedral masses of light-pink feldspar.

4. Mafic minerals are fine grained, biotite dominant over horn­

blende .

The transition rocks are significant in that they mark the con­ tact zone of the Round Valley Peak Granodiorite with the Cathedral Peak

Granite and they record mechanical and chemical changes attendant to the emplacement of the younger pluton. The decrease of mafic inclusions

and the increase in size and number of K-feldspar phenocrysts across the contact indicates that felspathization and recrystallization of the

Round Valley Granodiorite accompanied the emplacement of the Cathedral

Peak Granite.

Cathedral Peak Granite

The western part of the study area is underlain by a distinctive

porphyritic granitic rock that is identical to rocks in the Tuolumne Mead­ ows area of Yosemite National Park that Calkins (1930) named the Ca­

thedral Peak Granite. More recent investigations of Sierran 27 reveal that several plutons of this rock type comprise a sequence of elongate masses for 160 miles along the crest of the range from Sonora

Pass to Mount Whitney (Bateman and others, 1963; Bradley and Lyons,

1953; Brodersen, 1962; Mayo, 1941). The Cathedral Peak Granite in the

Rock Creek area and elsewhere in the Sierra Nevada is a porphyritic quartz monzonite according to the classification of Travis (1955) and

Bateman and others (1963), but to conform to long-established usage, the rock will be called a granite throughout this paper. Radiometric dates indicate that the plutons of the Cathedral Peak Granite were em­ placed in the final intrusive epoch of the batholith in the Late Creta­ ceous period between 79 and 99 m .y.b.p. (Evernden and Kistler, 1970).

The Cathedral Peak Granite contains large pale-red phenocrysts of perthitic K-feldspar that constitutes 20 to 30 percent of the rock by volume. Dark dioritic inclusions and mafic schlieren, so common in the

Round Valley Peak Granodiorite, are rare within the Cathedral Peak

Granite; schlieren with large, aligned K-feldspar phenocrysts do exist along part of the contact between the transition rocks and the Cathedral

Peak Granite along the trail to Ruby Lake. The average grain size is 2 to 3 mm, excluding phenocrysts. Most of the are white, ex­ cept for the K-feldspar phenocrysts which are pale red; quartz is smoky gray.

The color of the Cathedral Peak Granite is very light gray with an average color index of 8 for the samples I examined. Bateman (1965) reported an average color index of 3 for the Cathedral Peak Granite. Be­ cause my samples were collected near the contact with the transition rocks, contamination of the Cathedral Peak Granite by the Round Valley 28 Peak Granodiorite of higher mafic content probably accounts for the dif­ ference in color indices. An elusive foliation is usually present in the

Cathedral Peak Granite, and jointing is similar in both density and ori­ entation to that in the Round Valley Peak Granodiorite and in the transi­ tion rocks.

Microscopically, the Cathedral Peak Granite is seriate por- phyritic. K-feldspar, present as interstitial anhedra and as perthitic euhedral phenocrysts, has a large 2V and commonly shows quadrille structure and carlsbad twinning. The carlsbad twinning is obvious on both microscopic and mesoscopic scales. Contained within the K- fe Id spar are numerous inclusions of plagioclase, opaque metallics, and biotite. Strongly embayed borders of the enclosed plagioclase grains indicate resorption and replacement by the enclosing K-feldspar.

The plagioclase is subhedral to anhedral, normally zoned, and commonly exhibits albite twinning. Some plagioclase grains are also twinned according to the pericline and the carlsbad laws. Quartz is in­ terstitial and often undulatory.

Biotite exists as fine-grained, pleochroic yellowish-to-olive- brown, ragged subhedra with a small 2V. Hornblende is essentially lacking with only a small percentage observed in one thin section.

Sphene appears to be derived from the alteration of titaniferous magne­ tite . Alteration of biotite has produced narrow bands of a chlorite min­ eral, and sericitic alteration is present in the more calcic cores of the plagioclase grains. 29 The tight, nearly circular fields shown on the quaternary plot

(Fig. 13) of the Cathedral Peak Granite modes may be due more to limited sampling than to uniform composition.

To summarize, the distinctive features of the Cathedral Peak

Granite are:

1. The color index is 8 or less, generally less than that of the

other granitic rocks of the area.

2. Inclusions are almost absent, and foliation is obscure.

3. The rock is seriate to porphyritic, with flesh-colored pheno-

crysts constituting 20 to 30 percent by volume.

4. Hornblende is rare, and biotite has a thin, medium-grained

h a b it.

The Cathedral Peak Granite is the youngest pluton in the Rock

Creek area. It served as the source of material for the marginal dikes of pegmatite and aplite that intruded the older wall rocks, and chemical alteration associated with its emplacement extended for about 2,000 feet into the granodioritic wall rocks. Cathedral Peak granite


3 modes plus Bateman's (1965) a v e ra g e mode(°).

Figure 13. Quaternary Diagram of the Mineralogical Composi tion of the Cathedral Peak Granite STRUCTURAL ELEMENTS

Preferred Orientations of Minerals and Inclusions

Previous structural investigations of plutonic rocks in the

Sierra Nevada have revealed a pronounced planar fabric, or foliation.

This structure is readily observed in the granodiorites and can usually be seen, albeit with difficulty, in more leucocratic rocks. The foliation is defined by the parallel or subparallel orientation of biotite flakes, hornblende crystals, feldspar phenocrysts, mafic inclusions, and local­ ly by mafic or feldspathic schlieren. Hornblende prisms lie in the plane of the foliation, either in random directions within the plane or aligned subparallel to one another, imparting a lineation to the rock. Tabular feldspar crystals in porphyritic rocks may show subparallel preferred alignment of their largest faces, especially near contacts. In the upper

Rock Creek area the foliation is clearly neither cataclastic nor proto- clastic; granulation of crystal boundaries is not present in thin sections in any specimen.

Theoretical and Experimental Considerations

Several processes have been suggested to explain the origin of the preferred orientation of inequidimensional elements in plutonic rocks;

1. A parallel orientation of platy or elongate objects developed

during laminar flow of a viscous ;

2. The interpenetrating foliations resulted from late-stage crystal­

lization on conjugate or fracture surfaces which developed

when the rock behaved as a plastic solid;

31 32

3. A relic fabric was inherited from a preexisting rock that had

been changed to a granitic rock by metasomatic processes;

4. Possible combinations of the above processes.

In the flowage stage the preferred orientation, or primary folia­ tion, is thought to develop by the external rotation of tabular grains and platy minerals into a parallel penetrative fabric as the magma moves in a series of parallel sheets that slide over one another in much the same manner as the playing cards in a sheared deck. Billings (1972, p. 373) describes the process:

Platy material in a magma characterized by lamellar flow tends to become oriented with the largest face parallel to the liquid layers. Consequently, platy inclusions, such as slabs of shale, sandstone, or schist, become oriented parallel to one another. Schlieren and platy minerals, such as biotite, align themselves in the same way. Feldspar crystals, if well- formed, will tend to lie with their larger faces parallel to the la y e rs .

A platy object within a magma that is flowing by laminar shear should be rotated at a rate that is a function of the orientation of the object relative to the flowage planes. A theoretical investigation of the movement of prolate and oblate ellipsoids in a viscous fluid was made by Jeffery (1922) and experimentally investigated by Taylor (1923).

Jeffery demonstrated that ellipsoids will rotate in orbits about their centers with a varying rate of rotation, the rate being least when the long axis lies parallel to the direction of flow. Because the ratio of the minimum to maximum angular velocity is the square of the axial ratio of the ellipsoid, the long axis of the ellipsoid spends more time in the near-parallel position than in a direction perpendicular to the flow. In the general case where the initial orientation of prolate spheroids is 33 random, the probability of any one orientation of any given long axis can be deduced and from this a rose diagram can be constructed. Glen,

Donner, and West (1957, p. 197) computed the case where the axial ratio of the prolate spheroids is 2:1, similar to the case for stubby crystals, which results in the rose diagram shown in Figure 14. In their rose diagram the radii vectors are measured from the circumference of the small center circle rather than from the center of the polar coordinate graph as I have done, and the lengths of the vectors are proportional to the number of spheroids which would have their long axes in the plane

in which the diagram lies. The direction parallel to flow extends from top to bottom of the diagram; the transverse direction is perpendicular to the flow direction. The computations and rose diagram illustrate that twice as many spheroids lie in the parallel position as in the transverse

position for spheroids with an axial ratio of 2:1. My observations of

strong foliation along the margins of plutons agrees with the theoretical

and experimental models. However, the interpenetrating cross foliations

revealed in my studies of fabric in plutons in the Sierra Nevada cannot

be explained as results of laminar flow.

Interpenetrating foliations of inequidimensional minerals have

been observed in other plutons. Krauskopf (1943) reported interpenetrat­

ing planar structures in the Wallowa batholith, Oregon. Inclusions lying

at 15 to 50 degrees from a platy flow structure are reported in the En­

chanted Rock pluton of Texas (Hutchinson, 1956). In the Loch Boon

pluton of Scotland, Oertel (1955a, p. 20-22, map III) observed two or

more directions of interpenetrating foliation crossing at angles ranging

from about 15 to 90 degrees. Presumably they formed when the pluton 34

Figure 14. Long-axis Rose Diagram, Computed from Jeffery's (1922) Theory

The diagram represents the orientation of prolate spheroids with an axial ratio of 2:1 in a viscous liquid assuming that the spheroids have been placed initially in the liquid at random. The top and bottom of the diagram represent the orientation parallel to the direction of flow (Glen and others, 1957). 35 was plastic. If such a pluton expands there will be a radial compres­ sion and diagonal shears will be generated parallel to which crystals and other solid inclusions will become oriented. In experiments, Oertel

(1955b, P. 84-107) discovered that the angle of the intersection of the shear planes was a function of the plasticity of the medium. The con­ jugate shear planes crossed each other at low angles in solids of low plasticity and high elasticity but at high angles at higher values of plas­ ticity and lower elasticity. He explained that crystallization along the shear surfaces was the cause of the several directions of foliation. This model may explain the origin of interpenetrating foliations in one pluton, but it does not seem applicable as an explanation of the interpenetrating foliations observed regionally in the many plutons of the Sierra Nevada.

The possibility was considered that one or more of the folia­ tions in the granitic rocks in the Sierra Nevada was inherited from pre- plutonic rocks. The criteria for recognizing inherited fabric are listed by Compton (1962, p. 283-284), but in general these criteria were not found in the areas considered in this investigation. A few observations suggest that at least some of the foliation in one area has been "in­ herited" by from bedding in sedimentary rocks and will be considered later in section "Structural Mosaic of Rock Creek Salient."

Mafic inclusions are one of the planar or ellipsoidal fabric elements that define foliation even where the foliation is oriented in more than one direction. These inclusions are apparently ubiquitous in the granodiorite plutons of the Sierra Nevada, and they are present, al­ though not as commonly, in the more silicic rocks. Their origin has been a subject of controversy for many years. Knopf and Thelen (1905, p. 36 239-240) considered them to be basic segregations, Pabst (1928), called them autoliths, and Hurlbut (1933, p. 614) proposed that they were re­ crystallized fragments of gabbro. Bateman (1965, p. 112-114) presented a lucid review of their texture, structure, mineralogy, and petrology and considered the relative merits of the alternative hypotheses of their origin: the inclusions are (1) clusters of early-formed minerals, (2) refractory material left from the selective fusion of the original rocks that formed the magma, and (3) xenoliths of the wall rocks or fragments of the early crystallized border zone of the pluton. He wrote (1965, p.


The first and second alternatives are difficult to evaluate. How early crystallized minerals would collect into clots of roughly the same size is not obvious. The second alternative is attractive because it explains what happens to material that is left over after selective fusion of part of the earth's crust . . . Unfortunately it is an alternative that cannot be te s te d /Jn the Sierra Nevada/ . . . Deeper level migmatic terranes where are presumed to have formed are suitable for testing this hypothesis.

The third alternative . . . has been tested and it can be shown that at least some mafic inclusions are of this origin. Any rock of appropriate chemical composition can be con­ verted into like that in the mafic inclusions by recrystallization. The formation of mineral assemblages such as are in mafic inclusions is assured because the meta- morphic grade is in the hornblende hornfels facies (Fyfe, Turner, and Verhoogan, 1958).

Mafic plutonic or volcanic rocks could be converted easily into mafic inclusions. But other rock types, e.g ., calc-silicate hornfels, would require some interchange of cations between the granite and the fragments of metamorphic rocks. Many examples of hornfels in various stages of conversion were observed in the Round Valley Peak Granodio- rite (Fig. 15). Some hornfels xenoliths were separated from the enclosing

38 granite by a thin amphibolite selvage, but generally the xenoliths existed as a core within the fine-grained mafic inclusions.

Commonly, mafic inclusions show strongly developed preferred orientation which may be in two or more crisscrossing directions. Like inequidimensional minerals they can be oriented by external rotation, but the change from rounded shapes in the interior of a pluton to increasingly flatter shapes toward the margins suggests that at least some of their orientation is related to flattening from plastic flow. Bateman (1965, p. 114) reasoned that "during flattening the inclusions probably were not much stiffer than the enclosing granite magma. The inclusions doubtless were softened by incipient or actual melting of the lowest melting con­ stituents, and the magma was stiffened by crystallization and increased viscosity of the melt as a result of lowering temperatures."

Bateman does not discuss inclusions in the more central portion of granodiorite plutons. Although far less common in the center than in the margins, they are indeed present in the center where their composi­ tion and texture again suggest that they are of refractory origin.

Field Observations

Attitudes were obtained by field measurements of planar fabric, or primary foliation, in the Rock Creek area as shown in Figure 4 (in pocket). The foliation elements represented are (1) K-feldspar pheno- crysts in the plutons of porphyritic quartz monzonite, (2) tabular biotite crystals and elongate hornblende crystals, and (3) mafic inclusions.

A distinct foliation is evident at most exposures of granodiorite, but foliation is less obvious in outcrops of the transition rocks and in 39 the Cathedral Peak Granite. Close examination of the foliation elements on a mesoscopic scale commonly discloses two or more interpenetrating directions of preferred orientation. The patterns of interpenetrating directions are expressed on the maps (Figs. 4 and 16, in pocket) and in the rose diagrams on Figures 3 and 4, each representing a hundred or more strike measurements of a particular foliation element, as well as in the lower-hemisphere equal-area projections of the poles to foliation, which will be presented with the discussion of foliation.


Throughout the granitic rocks of the Sierra Nevada are schlieren, stratiform or streaky bands of mesoscopic or macroscopic scale that con­ tain higher concentrations of mafic or feldspathic minerals than does the enclosing rock. These schlieren have several forms:

1. Isolated schlieren which range in length from a few inches to

several feet but are commonly less than 3 inches thick and

which are commonly wavy and discontinuous over short dis­

ta n c e s .

2. Isolated schlieren associated with or attached to mafic inclu­ sions, especially near the margins of plutons.

3. Schlieren dikes (Fig. 17), which have sharply defined walls and

may contain several parallel sheets of alternating concentra­

tions of felsic and mafic minerals. These may be continuous

for distances up to 1,000 feet and generally maintain a consis­

tent attitude. The thicknesses of schlieren dikes range from

less than one foot to perhaps 20 feet. Schliren dikes may 40

Figure 17. A Schlieren Dike Note the folds and rolls along the base of the dike. 41 contain only a few wispy streaks in an otherwise uniform ma­

terial, but more commonly they consist of several parallel

contrasting sheets between the dike w alls. Some of the struc­

tures seen in schlieren dikes resemble those found in turbidites,

e .g ., cross-bedded relations locally suggesting cross-bedding,

channeling, and mineral sorting that is similar to graded bed­


4. Arcuate schlieren dikes (Fig. 18), in which arching color bands

of mafic and felsic minerals are transverse to the longer dimen­

sion of the dike.

Several hypotheses exist to explain the origin of mineral layer­ ing in schlieren. Grout (1926) proposed deposition of the layers by con­ vection currents; Gilbert (1906, p. 323-324) and Sherlock and Hamilton

(1958, p. 1258-1259) postulated that the graded layers in schlieren are formed by magmatic sedimentation; shearing of inhomogeneities in magma was suggested by Hutchinson (1956); layering by flow sorting of minerals from the movement of magma has been proposed by Hans Cloos (1922a),

Mayo (1941), Tweto (1951), and Simkin (1967). The origin of some schlieren has been explained by Waters (1938), Mayo (1941), and Hamil­ ton (1956b) as a consequence of the shearing or drawing out of mafic inclusions.

My observations suggest that schlieren may form by one of two processes: flow sorting or shearing of mafic inclusions. Support for the hypothesis of flowage sorting comes from observations of two phenomena in schlieren dikes in the Sierra Nevada: 42

Figure 18. Arcuate Schlieren Dike in Lower Tuolumne Meadows, Yosemite National Park 43

1. The crystals in schlieren are not deformed or broken, which

suggests that they were immersed in a fluid when they formed.

2. The layers of mafic minerals are fine grained and consist of a

mixture of biotite, hornblende, sphene, apatite, and small

amounts of quartz and feldspar. The coarse-grained layers are

dominantly quartz and K-feldspar, but biotite and hornblende,

when present, are also coarse grained. Such a combination of

early- and late-formed fine-grained minerals in the mafic layers

is difficult to imagine as a gravity accumulation from a melt;

the dominant crystal size seems to be the important conse­

quence of the sorting process.

The actual mechanics of flow sorting has only recently been applied to schlieren by Wilshire (1969) even though experimental evi­ dence, beginning in 1836, has demonstrated that crystals can be aligned, segregated, and concentrated by shearing flow (Simkin, 1967). Evidence of flow sorting by size is observed in moving debris flows. In the U.S.

Geological Survey 16-mm film, The 1941 Wriqhtwood Mudflow (n.d.), cobbles and boulders can be seen rafted on the tops of debris flows and pushed at the front of the flows in spite of the higher density and greater inertia of cobbles and boulders as compared to the slurry. Such behavior can be explained as a consequence of dispersive pressure (Bagnold,

1954, p. 62) causing flowing sediment grains of mixed size to be sorted by size and forcing the larger grains to drift toward zones of lower shear stress. Experiments by Bhattacharji and Smith (1964) indicate that crys­ tals suspended in a moving fluid migrate away from the wall at a rate 44 that is a function of grain size. Dispersive pressure caused by varia­ tions in shear stress appears to account for the sorting by size and the layering of schlieren. Flow sorting is probably involved in the process.

The internal structure of arcuate schlieren dikes is similar to the arching flow structures observed in endogenous volcanic domes (H.

Cloos and E. Cloos, 1927) and in the clay deformation experiments of

Riedel (1929) and probably originated by a similar process.

W ilshire's (1969, p. 258-259) conclusion, although written about layering in a pluton in Colorado, applies equally well to schlieren in the Sierra Nevada:

None of the hypotheses discussed above is free of defects, but flow soring with the principal controls being repeated variations in shear-stress, and grain-size variations of crystals in suspension, appears to offer the best explana­ tion. . . . Axial migration of coarse felsic crystals during early stages of intrusion may have contributed to the gross compositional zoning of the intrusion. Repeated intrusive movements of the crystal-rich magma over a period of time may then have produced the prominent grain-size layering in - marginal zones of high shear-stress. This, in conjunction with recent recognition of the operation of similar processes in sedimentary rocks . . . might usefully lead to a more critical examination of igneous structures that superficially resemble products of gravity sedimentation in sedimentary ro c k s.


Two major sets of steep joints prevail in all of the plutonic rocks examined by me in the Sierra Nevada. The two sets of joints are orthogonal. Commonly, one set will be coated by a thin veneer of epi- dote. Small feather fractures are often associated with the mineralized joint set, and bleaching of the rock for a few inches on either side of mineralized joints is common. The joints were given only cursory 45 attention in the reconnaissance areas in the Sierra Nevada. Neverthe­ less , two steep, nearly orthogonal sets seem to prevail, but the average strikes of the sets vary from locality to locality. The impression exists that one and locally both of two systems may be present, consisting of _ either (1) north-south and east-west sets or (2) northwest and northeast sets. At some places all four sets are present. Field work accomplished to date (E. Cloos, 1936; Mayo, 1941) appears to support this impres­ sio n .

A third group of moderately dipping joints is present in most areas visited. Their relationship to the external contacts of the plutons suggests that they are marginal joints. Most of the joints of a fourth group, with dips of less than 20 degrees, are considered a result of ex­ foliation. These are not dealt with in the joint analysis because they lack significance regarding the mechanics of plutonic emplacement.

Marginal Dikes

Commonly, in the border zones of plutons are swarms of felsic dikes which dip at moderate angles from the wall rocks into the pluton.

They are formed in the zone of greatest stress where marginal joints have opened along the border of a rising pluton in much the same manner as marginal crevasses originate in a glacier. Their origin and tectonic sig­ nificance was first explained in 1925 by H. Cloos (p. 54-60). Several workers (E. Cloos, 1936, p. 389-391; Mayo, 1941, p. 1030-1031;

Sherlock and Hamilton, 1958, p. 1260-1261; Bateman and others, 1963, p. D24-D25) have noted marginal dikes at various localities in the Sierra

Nevada, but I have examined only those in upper Rock Creek. Here the 46 marginal dikes vary in texture from aplitic to pegmatitic with some dikes having both textures. They form a subparallel swarm, as reported else­ where in the Sierra Nevada (E. Cloos, 1936, p. 389-391; Mayo, 1941, p. 1031), and dip westward into the Cathedral Peak pluton. ARRANGEMENTS OF THE STRUCTURAL ELEMENTS IN THE UPPER ROCK CREEK AREA

Joints and the Interpenetrating Foliation

Three sets of joints are obvious in the upper Rock Creek area.

Two sets are steeply dipping to vertical, and the third set has moderate westward dips essentially parallel to the inclinations of the schlieren dikes. Figures 6 and 7 (in pocket) represent the attitudes of the joints, and the poles to joints are plotted on lower-hemisphere, equal-area pro­ jections (Fig. 19).

The two sets of steep joints have average strikes of about N.

15° E. and N. 80° W .; for convenience these will be referred to as the north-south set and the east-west set. The north-south set establishes a basic weakness of the rocks along which have been eroded numerous north-south-trending swales and passes in the bedrock knobs of Rock

Creek valley and which is responsible for the trend of the valley itself.

The east-west joints form countless steep cliffs on the leeward sides

of bedrock outcrops; in localities of higher joint density, east-west­

trending defiles are eroded along these joints.

A veneer of sugary coats most of the north-south joints

which are commonly associated with small feather fractures; the rock is

bleached for a few centimeters on either side of these joints. Slicken-

sides on some of the joints, varying in plunge from 3 to 25 degrees on

either side of horizontal, indicate relative motion of the blocks. The

geometry of the associated feather fractures indicates left-lateral

47 Total plot of joints

1012 points

Figure 19. Lower Hemisphere, to (1) Primary Foliation and (2) Joints Equal-area Projections of Poles 49 movement of the blocks. The east-west joints are barren and usually devoid of slickensides or striations.

The third joint set is responsible for flat surfaces on the west sides of bedrock knobs which slope at angles from about 20 to 40 de­ grees. Generally these joints are barren, but the felsic and schlieren dikes have been emplaced along fractures that belong to this set, as shown by comparing the equal-area projections of joints and dikes (Fig.

19) with Figures 20 and 21.

The two sets of steep joints closely parallel the two major sets of primary foliation (Fig. 19), and a comparison of the total plots of these structural elements clearly discloses their correspondence and suggests a cause-and-effect relationship. The foliation directions ap­ pear to introduce a structural weakness into the rocks along which joints can open.

Schlieren Dikes, Felsic Dikes, and Marginal Thrusts

The schlieren dikes are concentrated in the area of the grano- diorite wall rocks, and they are laced throughout Serene Ridge. Perhaps their presence gave reinforcement to the ridge, making it more resistant to glacial erosion and thereby accounting for the anomalous position and relief of Serene Ridge along the axis of an otherwise typically U-shaped glacial canyon. Felsic dikes, 1 to 6 feet thick, rooted in the Cathedral

Peak Granite, occur in great swarms, making up a large volume of the cliffs in the vicinity of Box Lake and to the south beyond the limits of the study area. The swarms of felsic dikes probably reflect a brittle response of the metagabbro to the stress of the rising pluton of Cathedral 50

Total plot of felsic and schfieren dikes

153 points

Figure 20. Lower Hemisphere, Equal-area Projection of Poles to Felsic and Schlieren Dikes 51

Total plot of schlieren dikes ™ 6 5 points b

Total plot of felsic dikes

8 5 points mm

Figure 21. Lower Hemisphere, Equal-area Projections of Poles to (1) Schlieren Dikes and (2) Felsic Dikes 52

Peak Granite. In contrast, the structures in the granodioritic wall rocks, from Mack Lake northward along Serene Ridge, indicate that the grano- diorite accommodated the emplacement of the Cathedral Peak Granite largely by plastic deformation as attested by folded schlieren and by drag folds within schlieren dikes (Fig. 22). Some rupturing of the dikes produced offsets (Fig. 23) where strain exceeded elastic lim its, but these breaks are healed by materials that flowed in from the host rock.

Folds within some schlieren dikes, folded and ruptured dikes, dike- filled feather fractures along dikes, and offset inclusions on opposite sides of dikes indicate thrusting movement toward the east and south within the granodiorite. Arrows representing the directions of movement implied by these structures are shown on Figure 7 (in pocket). The wide zone of transition rocks, discussed in the section on petrography, sug­ gests that chemical alteration and/or perhaps partial melting accom­ panying the emplacement of the Cathedral Peak Granite was responsible for softening the granodiorite wall rocks and promoting plastic deforma­ tion, which provided some of the space required by the Cathedral Peak

G ra n ite .

A dilatational origin of the felsic dikes is shown by matching the irregularities of the dike walls and fragmented inclusions on opposite sides. Strangely, however, in a few locations what appears to be a faint continuation of the steep foliation of the host rocks can be traced across felsic dikes by the alignment of a few mafic minerals. This suggests, although not strongly, that some of the dikes formed outward from the initial fracture or channel of entry by metasomatism of the enclosing granodiorite. Emplacement on marginal thrusts is also suggested for the 53

. # iiiaiEI : y # - - /

Figure 22. Drag Folds in a Schlieren Dike Looking along a north-striking schlieren dike, drag folds reveal the relative upward motion of the hanging wall. 54

Figure 23. Crosscutting Schlieren Dikes An earlier dike has been faulted, offset, and rehealed. View looking S. 10° W. , near crest of Serene Ridge. 55 schlieren dikes by occasional feather fractures and the geometric iden­ tity of the orientations of schlieren dikes and low-angle joints revealed by equal-area plots (Figs. 19, 20, and 21).

A few felsic dikes in the metagabbro dip southward and were derived from the Lamarck Granodiorite pluton on the south. Equivalent marginal dikes in the metagabbro mass .derived from the Round Valley

Peak Granodiorite do not exist; instead that contact is marked by a wide band of intrusive breccia.

In the Serene Ridge area both schlieren dikes and felsic dikes dip westward generally at 30 to 40 degrees. Closer to the parent pluton, on the flanks of Mount Starr, the dips are much shallower, and near the summit of Mount Starr they are eastward. Similar flattening of the dips of the felsic dikes toward the Cathedral Peak pluton is observed in the dike swarms south and southwest of Long Lake. Presumably, the flat­ tening is due to bending by the upward motion of the Cathedral Peak

G ran ite.

The set of joints which strike about north-northeast and dip westward from 20 to 40 degrees have approximately the same special

geometry as the schlieren dikes and the felsic dikes (Figs. 19, 20, and

21). These joints, the schlieren dikes, and the felsic dikes are con­

sidered to be structural features formed during emplacement along the

margin of the rising Cathedral Peak Granite pluton. Geometrical rela­

tions of the structures within and along the schlieren dikes, discussed

previously, indicate that many of the dikes have been emplaced along

thrusts marginal to the rising granite. Probably the schlieren dikes and

the felsic dikes were emplaced along somewhat earlier formed marginal 56 joints and thrusts, with the low-angle barren joints forming after the consolidation of marginal portions of the Cathedral Peak Granite.


Emplacement of the Cathedral Peak Granite

Most of the examples cited in the literature describing the de­ formation of wall rocks by the emplacement of plutons involve metamor- phic wall rocks. The lack of descriptions of the deformation of granitic wall rocks is understandable if the subtle nature of the adjustments shown by the Round Valley Peak Granodiorite and the transition rocks are representative. Part of the contact between the Cathedral Peak Gran­ ite and its walls is dynamic and sharp where it is marked by a band of mafic schlieren and aligned K-feldspar phenocrysts. But detailed struc­ tural mapping along most of the contact discloses that the plutonic wall rocks have yielded by a combination of brittle and plastic adjustments.

Compositional variations across the contact zone (Figs. 10 and 11) in­ dicate that chemical activity caused potash feldspathization along the contact between the Cathedral Peak Granite and its wall rocks, forming the wide transition zone. Presumably the heat and feldspathization softened the wall rocks and lowered their rheidity, promoting plastic adjustments.

Reality of Interpenetrating Foliations

The structural map (Fig. 4) alone leaves no reasonable doubt of the reality of the east-west and north-south foliations in the valley of upper Rock Creek, and the inference follows that a similar condition may exist elsewhere. In addition to structures that result from emplacement

57 58 of the plutons, an orthogonal network of foliation has therefore been

imprinted on, or preserved in (?), the several granitoid plutons, and at least one of the directions is present in the metagabbro. Comparison of

Figures 4 and 5 (in pocket) and Figure 20 reemphasizes the above state­ m ent. REGIONAL CONSIDERATIONS

Structural Mosaic of Rock Creek Salient

Measurements accumulated from 1933 to the present in a region which includes the upper Rock Creek valley are plotted on Figure 16 (in pocket). This region, which forms a northeasterly bulge in the eastern front of the Sierra Nevada, was named the Rock Creek Salient by Mayo

(1937, p. 172-173). The upper Rock Creek valley with its orthogonal foliation network is located easily (Fig. 16), but in the region are sever-, al important features that are not obvious in the smaller area.

In the southeatern corner of the map (Fig. 16) a narrow septum of metamorphosed sedimentary rocks is on strike with a wider belt of the same rocks in the northwestern corner. Between these two groups of metamorphic rocks, however, the metasediments are turned aside into a great northeastwardly convex loop, which has a rather straight-sided, boxlike form. Nested within this loop, the contact between the Cathedral

Peak Granite and the Round Valley Peak Granodiorite forms a comparable loop, the two structures having a common northeast-trending axis. The septum on the southeast margin of the salient, the generalized contact between metasediments and Round Valley Peak Granodiorite near Big

McGee Lake, and the prong of Cathedral Peak Granite near Ruby Lake all trend in the northeast direction. Many measurements of foliation in the granitoid rocks likewise reveal the northeast trend.

The east-west trend, so obvious in the upper Rock Creek valley, appears to control the course of the northern border of the salient, which

59 60 terminates abruptly the northwest-trending bedding of the broad septum of metasediments. Somewhat surprisingly, however, numerous measure­ ments of foliation in the granodiorite along the discordant contact depart considerably from the trend of the contact and appear to carry through the northwest direction of bedding southeastward into the granodiorite. This same condition exists along the generally northeast-trending contact near Big McGee Lake. These observations suggest that at least some of the foliation in the granodiorite was "inherited" by metasomatism from the bedding in the sedimentary rocks. The metagabbro also appears to have been influenced in part by an east-west trend along which it broke across the narrow metasedimentary septum. Later, the belt of metagabbro was transected by the north-south-trending pluton of Tungsten Hills

Quartz Monzonite which still contains traces of the east-west structures preserved within it.

The septum along the eastern margin of the salient is turned only slightly clockwise from the average northwest trend of the metamor- phic rocks, thus it does not seem correct to regard this septum as a north-south element. About a mile southeastward, however, the narrow strips of metagabbro and the northern half of the dikelike body of aplite reveal north-south elements. Unfortunately, most of the Hilton Lakes valley has not been investigated structurally, but, by analogy with the similar trend of Rock Creek valley, north-south foliation would be ex­ pected here. On the other hand, the east-west foliation, measured on the southeast edge of the valley, should continue westward.

At first glance the Rock Creek Salient appears to be a structural knot developed where a broad northwest-trending band of metasediments 61 is crossed by a wide northeast-trending buckle. Further examination suggests that the north-south and east-west trends have also determined the shape and influenced the internal structure of the salient. The plu- tons in this region, rather than having forcefully thrust the metamor­ phosed septum aside, appear to have been molded to the structural framework and to have somehow received as a foliation network the im­ print of a structural mosaic, or perhaps to have preserved within them­ selves an interpenetrating pattern inherited by metasomatism. Many more details of the structure of the metamorphic rocks are needed in order to evaluate these possibilities.

It is now necessary to see whether the foliation network, to­ gether with the related joint system, can be recognized at more widely separated localities in the central Sierra Nevada.

Observations in Yosemite National Park

A 5-mile traverse made across part of the Tuolumne plutonic complex from Lembert Dome in Tuolumne Meadows to Glen Aulin (Fig. 3, in pocket) permitted structural observations in the Johnson Granite Por­ phyry, Cathedral Peak Granite, Half Dome Quartz Monzonite, and the Sentinel Granodiorite.

At the northwest end of the traverse, the foliation of mafic minerals and inclusions in the Sentinel Granodiorite strikes northeast and dips moderately to the southeast; the strike parallels the contact with the Half Dome Quartz Monzonite. No interpenetrating foliation was found. 62

Steeply dipping, northwest and northeast foliations are present in the Half Dome Quartz Monzonite and the Cathedral Peak Granite, and these agree with the peaks shown in rose diagrams ( and

Lembert Dome; Fig. 3) made from measurements in these formations.

Near the contact of the Half Dome Quartz Monzonite and the

Cathedral Peak Granite at Lake, a moderately to steeply dipping foliation is obvious striking north-south parallel to the contact. How­ ever, within a quarter of a mile on either side of the contact, both the

Cathedral Peak Granite and the Half Dome Quartz Monzonite contain

steep interpenetrating foliations with northwest and northeast strikes.

The maxima on a rose diagram made at Tenaya Lake from the orientations of mafic minerals in the Half Dome Quartz Monzonite (Fig. 3) also show these two directions. The north-south and east-west foliations were not

observed in the Tuolumne and Tenaya Lake areas, but the north-south

trend is shown by the direction of elongation in the shapes of the plutons

'of Cathedral Peak Granite and the Johnson Granite (E. Cloos,

1936, Plate 1; Bateman and others, 1963, Plate 1).

The north-south direction is also present at near

Glacier Point in the western main mass (E. Cloos, 1936) of the Sierra

Nevada pluton. Here several schlieren strike approximately north-south

with steep dips and are nearly orthogonal to a strongly developed, steep­

ly dipping, N. 85° E. primary foliation of mafic minerals and inclusions.

Further evidence of the north-south direction is present three-quarters of

a mile northeast at as the trend of a thin and discontinuous

septum that separates the Sentinel Granodiorite from the Half Dome

Quartz Monzonite. This septum is not shown on published maps, but a 63 small piece of it was pointed out to E. B. Mayo in 1938 by Francois

Matthes of the U.S. Geological Survey (E. B. Mayo, personal communi­ cation , 1970). Additional evidence for the north-south structural trend comes from maps outlining the plutons of the Yosemite region (Calkins,

1930, Plate 51; Bateman and others, 1963, Plate 1). Numerous small masses of Granite included within the younger Sentinel Grano- diorite are elongated in the north-south direction, and the general trend of the Sentinel Granodiorite itself is north-south.

Joints are sparse in the Cathedral Peak Granite and only a few were measured. Nevertheless, a steep set striking N. 20° E. to N. 30°

E. seems to dominate. A second set of apparently lesser importance strikes about N. 80° W. with moderate to steep dips. The system of joints in the Half Dome Quartz Monzonite and the Sentinel Granodiorite is more closely spaced than in the Cathedral Peak Granite. The joints striking northeast subparallel to the northeast foliations seem to con­ sist of two sets, one with steep dips and the other with moderate dips.

The relationships of the moderately dipping set to the contact of the plutons suggests that they are marginal joints. A second set of steep northwest-trending joints is present in the Half Dome Quartz Monzonite.

Even though only cursory attention was given to joints in the Tuolumne and Tenaya Lake area, there is the distinct impression that two sets pre­ vail that are subparallel to the northwest and northeast foliations.

Interpenetrating Foliations on the Middle Fork of the San Joaquin River

Several square miles of plutonic rock were traversed along the

Middle Fork of the San Joaquin River near the Devils Postpile National 64

Monument. Foliations in the north-south and east-west directions were observed in outcrops of three plutonic rocks of the area: Cathedral Peak

Granite, Half Dome Quartz Monzonite, and Mount Givens Granodiorite.

The most obvious foliation is steeply dipping and strikes N. 80° W ., thus corresponding to the east-west direction observed elsewhere in the

Sierra Nevada. A second foliation has strikes varying from N. 10° W. to about N. 5° E. and is also steep. 1

A rose diagram made from measurements on phenocrysts in the pluton of Cathedral Peak Granite at Pumice Flat (Middle Fork, San Joa­ quin River; Fig. 3) reveals the four interpenetrating directions observed in other areas of the Sierra Nevada, although the directions appear to be rotated slightly counterclockwise.

A set of very obvious steep joints parallels the foliation that varies from N. 10° W. to N. 5° E. A few joints were measured that strike approximately east-w est, but so few measurements were made that no generalization seems warranted.

The general outlines of the plutons in this area were originally reported by Erwin (1937) as showing elongations and boundaries in three of the "framework" directions. He recognized northeast, northwest, and north-south trends. The northeast trend is shown by the southeastern edge of the metavolcanic rocks west of Mammoth Mountain (Fig. 3) which are terminated southeastward by a pluton of Half Dome Quartz Monzonite.

The northwest direction is followed by two elongated prongs of plutonic rocks that extend into the metavolcanics. These are located, respective­ ly, about 5 and 7 miles due west of Mammoth Mountain. The north-south 65 direction is followed by an extension of a pluton of Cathedral Peak Gran­ ite which is centered about 2 miles northwest of Mammoth Mountain.

Interpenetrating Foliations on the South Fork of Bishop Creek

A reconnaissance of exposures of a pluton of the Lamarck Grano- diorite, mapped and named by Bateman (1961), near South Lake reveals the presence of the interpenetrating foliations. Mesoscopic observations show two steep foliations: one striking north-northwest, the other strik­ ing approximately east-w est. A rose diagram (South Fork Bishop Creek;

Fig. 3) made near South Lake indicates the dominance of the north- . northwest direction but also distinctly reveals the east-west direction and two lesser maxima to the northeast and northwest.

Two steep joint sets are also developed which are subparallel to the two directions of the foliation: one striking north-northwest and

the other striking N. 60° W.

Reconnaissance in Lone Pine Canyon

The Mount Whitney trail was followed for about 4 miles from

the road head at Whitney Portal across part of a pluton of Cathedral Peak

Granite to . Observations were made of the orientations of

phenocrysts and joints in exposures along the trail. Two steeply dipping,

interpenetrating foliations striking northwest and northeast are common,

and the attitudes of the joints show two steep sets striking northeast and

slightly west of north.

A rose diagram constructed from measurements of phenocryst

orientation at Mirror Lake (Fig. 3) indicates two maxima trending 66 northeast and north-south, respectively, which coincide with the measured

strikes of foliations. Further indication of the northwest direction is

shown by (1) the overall elongation of the Cathedral Peak pluton (Broder-

son, 1962, Plate 1), (2) the N. 50° W. strike of the eastern contact of the Cathedral Peak granite with an unnamed granodiorite (Mayo, 1941,

Plate 1; Broderson, 1962, Plate 1), and (3) the steep foliation striking

N. 55° W. in a large dioritic xenolith in the unnamed granodiorite along

the Whitney Portal road. This dioritic mass aligns with and may be re­

lated to several large disconnected metamorphic xenoliths north of

Mount Whitney (Fig. 3) that trend N. 50° W. and string out for 8 miles

across the crest of the Sierra Nevada.

The east-west trend is found along the road near the contact of

the granodiorite and the Cathedral Peak Granite. Here, a large schlieren

bundle (Fig. 24) that strikes N. 40° W. is terminated by a steep N. 80°

W. foliation of mafic minerals and inclusions as though the schlieren

were cut off by movements in the plane of the N. 80° W. foliation.

The joint system in Lone Pine Canyon comprises two steep sets.

The dominant set strikes about N. 60° E ., the same direction as the

trend of the canyon, and the second set strikes slightly east of north,

the same preferred direction shown by phenocrysts on the rose diagram

from Lone Pine Lake (Fig. 3).

Relation of Interpenetrating Foliations to Regional Joints

Although the data are by no means as complete as could be de­

sired, the probability seems very good that the foliation and fracture

network demonstrated on upper Rock Creek and reasonably inferred in the 67

Figure 24. Schlieren Bundle Terminated by Steep Foliation Re­ vealed by the Parallel Orientations of Dark Inclusions Photograph taken along Whitney Portal road. The schlieren strike N. 40° W ., and the foliation strikes N. 80° W. 68 larger Rock Creek Salient is present throughout the central Sierra Nevada.

Indeed, my reconnaissance suggests that one of two principal systems of steep joints may be everywhere present in the Sierra Nevada: (1) approx­ imately northwest and northeast or (2) approximately north-south and east-west; and, as discussed above, each of these systems parallels two directions of interpenetrating foliations. Several rose diagrams in­ dicate the presence of all four directions of foliation. Apparently, which of the two systems of foliations is to be followed by joints is determined by conditions of stress that favor fracturing along those certain directions.


Suggested Tectonic Plan of the Sierra Nevada

Four trends that are followed by both small structures and large tectonic units have been recognized in the Sierra Nevada. Of these the most obvious is the northwest, inasmuch as it is generally followed by the shapes and foliation or bedding of the metamorphic masses (Fig. 3) and by the elongation of the range itself. At angles to the dominant northwest trend are the northeast, north-south, and west-northwest to east-west structures. Structures following these trends were recognized by E. Cloos (1936), Erwin (1937), and Mayo (1937, 1941, 1947) and at­ tributed to large-scale tectonic control. The importance of these region­ al, or 11 framework," trends can be further realized by a careful study of the sheets of published geologic maps of California which pertain to the Sierra Nevada. My work has confirmed that the above four struc­ tural directions are also followed by the interpenetrating foliations and by the steep joint systems in the plutonic rocks of the Sierra Nevada.

Thus, the coarse regional framework is filled in by the finer foliation and joint network. From this it should follow that the network of inter­ penetrating cross foliations is a result of some regional condition.

Suggested Origin of Interpenetrating Foliations

At this writing there appear to be three hypotheses or some

combination of these hypotheses that may explain the regional network of

interpenetrating foliations. The network may be a relic of the structures

69 70 of preintrusive rocks that have been preserved by metasomatism. The evidence for this suggestion was presented above, but the idea has only limited appeal until a comparison is possible of the fabric of plutonic rocks with that in the metasedimentary and metavolcanic remnants in many areas of the Sierra Nevada. For the present it seems unproductive to discuss the origin of the supposedly pre intrusive structures.

If the interpenetrating foliations are not relics, perhaps they originated by regional horizontal compression during the long cooling history of the Sierra Nevada composite pluton. For example, compression from the southwest or northeast may have folded the metamorphic rocks and at a later time brought about the northwest-trending foliation in the plutonic rocks. The same compression may have opened northeast- trending cracks and fissures parallel to which inclusions and crystals became oriented. The north-south and east-west directions of the shears would be the directions into which the solid particles were rotated.

Experiments by Ekkernkamp (1939, p. 732-733) suggest that a pattern of four directions of fracturing could originate by the vertical up­ lift of an elongate dome. In the case of the Sierra Nevada, the dome axis would lie along the length of the range, the transverse fractures would trend northeast, and the diagonal shears would lie on either side of the dome axis. However, with this model it is difficult to account for the folding of the metamorphic rocks unless they were squeezed between rising plutons. This model may also fit with ideas of the new global tec­ tonics , the elongate dome being engendered above the inferred Mesozoic

subduction zone that dipped under the continent. 71

Finally, some combination of the above hypotheses may explain the regional network of interpenetrating foliations and, in view of the complications that seem to prevail in nature, seems to be the best pos­ sibility. A more definite statement will only become possible on the basis of more complete data. CONCLUSIONS

Previous studies of granite tectonics in the Sierra Nevada have emphasized the autonomous internal structures that disclose the history of emplacement of each pluton. These autonomous structures are ar­ ranged according to the external shape of each pluton, and they are developed best on and near intrusive contacts. Marginal structures were mapped and described in the upper Rock Creek valley, and they have been interpreted as the evidence of the forcible emplacement of the p lu to n s.

More important in my investigation, however, is the recogni­ tion of an "anomalous" network of steep interpenetrating foliations that may follow some, or all, of the four framework directions reported by previous workers in the Sierra Nevada. Preservation of relic structures and orientation of mineral grains by regional compression are appealed to as possible origins of the interpenetrating foliations. However, other than that the interpenetrating foliations are regional in extent and thus must result from some regional cause, no definite conclusion on their origin seems warranted at present.

The four directions taken by the interpenetrating foliations that

have been disclosed in this study are the same as those shown by Mayo

(1958) to be present in the structure of the entire southwestern United

States. A careful study of the "Tectonic Map of North America" (King,

1969) yields the impression that the four directions form a structural

framework throughout the entire Cordillera and perhaps through the

72 continent. Thus, it seems that a pluton, in common with the entire

Sierra Nevada, is branded with the Cordilleran and continental pattern regardless of the independent motion of that pluton during its emplace­ ment in the Sierra Nevada. APPENDIX A


Rose Diagrams

Apparently the first use of rose diagrams for representing the spacial orientations of mineral grains on a surface was by Schmidt

(1918). He grouped the measurements of the trends of mineral orienta­ tions into class intervals of five degrees and plotted the midpoints of these intervals against the class frequencies. The class frequencies were plotted as radii against the direction of the interval midpoint on polar coordinates, and the radii were extended in both directions through the origin. The ends of the radii of each of these sectors were con­ nected by straight line segments. Although Schmidt was representing the fabric of thin sections measured with a microscope, the same basic pro­ cess has been used by other workers on a mesoscopic and macroscopic scale to represent semistatistically preferred orientations of elongate minerals in igneous rocks (Mayo, 1941, p. 1025, 1961, p. 9; McCul­ lough, 1963, p. 24; Yeatts, 1964, p. 17-31) and to analyze regional joint patterns (Badgeley, 1965, p. 497; Balk, 1932, p. 59).

The following procedure was used in this study for obtaining a semistatistical impression of the directions of preferred orientation of elongate mineral grains in igneous rocks. A flat or nearly flat surface is selected on an outcrop that is nearly horizontal which must also be free of lichen and be relatively unsweathered. From an initial point as center.

74 75 the orientations of all mafic minerals which have length-width ratios of at least 5:1 or, if a porphyry, phenocrysts with a ratio of at least 1.5:1 are measured with a Brunton compass until the desired number of miner­ als has been measured. Each measured crystal is marked to avoid du­ plicating measurements. The data are then converted to percentages, tabulated, and plotted on polar coordinate paper, much as done by

Schmidt (1918), except that the sectors subtend 10 degrees.

Two computer programs were written to expedite handling the data. One program converted the raw data to percentages and tabulated the percentages into histograms from which the rose diagrams were con­ structed. The second program, to be discussed in detail below, elimi­ nated the "noise" from the histogram by overlapping the frequencies of adjacent sectors. The interpretation and significance of the preferred directions of orientation represented on the rose diagrams are discussed in the section on structural elements.

Consideration of the patterns of preferred mineral orientations shown on the rose diagrams made in the early phases of this study raised some important and very fundamental questions:

1. Occasional sharp, narrow peaks on rose diagrams may give

superficial impressions of preferred directions which actually

confuse the overall pattern. Could a smoothing process elimi­

nate this "noise" and produce a more conservative pattern?

2. What kind of patterns would result on rose diagrams constructed

from measurements of minerals that are oriented in a statistical­

ly random manner, and how would these compare to the diagrams

obtained from the field measurements? 76

3. What minimum number of measurements is necessary to estab­

lish the major trend or trends of preferred mineral orientations

(a) near the margins of plutons and (b) at some distance inward from the margins?

4. Can different workers independently duplicate each other's

measurements at the same site?

5. Will replication occur at two or more sites that are in close

proxim ity?

6. Previous workers have interpreted rose diagrams visually; can

they be interpreted statistically?

Eliminating "Noise" from Rose Diagrams

In the standard method of preparing rose diagrams, the measure­ ments are classed into 18 intervals or sectors that subtend 10 degrees of arc each, and the frequencies of each interval are plotted on the bisec­ tors of the interval with the bisectors spaced on 10-degree centers. The resulting rose diagrams may have one or more clearly defined maxima, but they also have numerous minor peaks that may or may not be signifi­ cant. Visual interpretation can become dubious. If each of the major and minor maxima is considered to represent a normal distribution of pre­ ferred directions about the midpoint of each section, one can conceive that the tails of the distributions in adjacent sectors should overlap.

Thus, the distribution in one sector should have an influence on the am­ plitude in adjacent sectors. But in the standard method of constructing rose diagrams the data are rigidly compartmentalized into 18 sectors and each sector exerts no influence on neighboring sectors. 77

With rose diagrams which represent a pronounced unimodal fabric, e .g ., along the contact of a pluton, the independence of each sector is of no consequence. However, in the interior of a pluton where the stress field at the time minerals were being oriented was different than at the margins, a method of enhancing the dominant preferred direc­ tions and subduing the "noise" would result in a less equivocal visual interpretation. An attempt to meet these ends led to experimenting with different methods of overlapping adjacent sectors and culminated in writing computer program Twenfiv.

Program Twenfiv makes a histogram of the amplitudes of 36 sec­ tors , each of which subtends 20 degrees and overlaps other equivalent sectors spaced on 5-degree centers. The rose diagrams in Figures 3 and

4 (in pocket) have been prepared with histograms from Program Twenfiv.

The rose diagrams included in the sections on testing and replication are of both the standard and smoothed forms to give the reader the oppor­ tunity to evaluate the relative merits of the two constructions.

Random v s. Preferred Orientations

Random3 numbers may cluster, consequently, if elongate min­ erals should be oriented in a statistically random pattern they also could tend to cluster. For example, if 60 or 70 percent of a small sample of about 50 minerals randomly oriented in a field of 18 sectors should fall within 3 or 4 sectors, 30 or 40 percent of the measurements would be distributed over the remaining 14 or 15 sectors. Consequently, the

3. The word "random" is used here in the proper statistical sense in which all members of the sampled population have an equal probability of being selected. 78 frequencies in the remaining sectors would be much lower than in the three or four sectors simply as a function of randomness. If, however, a sample of sufficient size of randomly oriented minerals is collected, the clustering would be distributed more evenly throughout the sample.

Therefore, an optimum sampling size should exist that will offset the conditions imposed by randomness and by the technique of constructing rose diagrams. An optimum sampling size of randomly oriented grains

should produce a nearly circular rose diagram.

A total of 15 sets of random numbers was drawn from the random

number generator of the University of Arizona GDC 6400 computer and

converted to compass bearings by a subroutine of Program Rosekol. The

results are illustrated in Figures A-l and A-2. Five sets each were

drawn of samples of 100, 200, and 300 random numbers. Rose diagrams

from the five sets of 100 random numbers show apparent preferred direc­

tions which are disconcertingly similar to some of the rose diagrams

constructed from field measurements of 100 mineral orientations. The

samples of 200 random numbers give an impression of more uniformly

random orientations, and there is little change in the patterns if an ad­

ditional 100 random measurements are plotted. If with additional data a

preferred maximum becomes more accentuated, it is significant, but if

the maximum becomes more subdued it is probably the result of the

chance clustering of random values.

Minimum Number of Measurements

A second experiment was conducted to determine the minimum

number of field measurements necessary to establish the directions of o i. c i Standard Rose Diagrams Constructed from Five Sets of 100, 200, and 300 Random Numbers 100 Random 200 Random 300 Random

Set I

Set 2

Set 4

Set 5

Figure A-2. Smoothed Rose Diagrams Constructed from Five Sets of 100, 200, and 300 Random Numbers 81 preferred orientation. This test was made with the help of John Hoelle, a fellow graduate student in the Department of Geosciences, The Uni­ versity of Arizona, on exposures of the Catalina granite in the Santa

Catalina Mountains near Tucson, Arizona. The site was selected be­ cause of its accessibility, its remoteness from the contact of the pluton with its wall rocks, and the similarity of the Catalina granite to the composition, texture, and structure of the Cathedral Peak Granite of the

Sierra Nevada, both plutons being porphyritic quartz monzonites. Three sets of measurements were taken on the orientations of the longest di­ mension of phenocrysts of orthoclase; one set of 100 was measured by me, and two sets, one of 100 and one of 90, were measured by Hoelle.

Only phenocrysts with a length to width ratio of 1.5:1 or greater were considered, and the total area of rock exposure covered was 24 square fe e t.

Rose diagrams were drawn to represent the directions of pre­ ferred orientation of 50, 100, 150, 200, 250, and 290 measurements

(Fig.A-3). At least four preferred trends are suggested by plotting the first 50 measurements of feldspar orientations; adding the next 50 mea­ surements does not alter the impression of these preferred directions. If all of the maxima from 100 measurements do exist in fact, they should persist with additional measurements. It is evident that two directions about 30 degrees apart become dominant after 150 measurements and the other two directions become relatively subdued. This condition becomes increasingly definite as more measurements are added. The visual im­ pression is that the dominant directions are established with about 150 82

standard smoothed

Set I 5 0 measurements

Set 2 ^ 100 measurements

Set 150 measurements

S e t 4 / ' 200 measurements

Set 5 250 measurements

Set 6 ^ 290 measurements x

Figure A-3. Standard and Smoothed Rose Diagrams Used to Determine the Minimum Number of Measurements Necessary to Establish the Directions of Preferred Orientations of K-feldspar Phenocrysts in the Catalina Granite 83 to 200 readings, which is in accord with results of the analysis of pat­ terns based on random numbers.

Further testing was done in the upper Rock Creek area to deter­ mine the minimum number of measurements of mafic minerals necessary to establish preferred mineral orientation. The locations of these sites are shown on Figure 4 (in pocket). Figures A-4, A-5, andA-6 illustrate the results. In Figure A-4, the pattern of 100 measurements at the north end of Serene Ridge could be interpreted as random, but it does indicate higher frequencies around the north-south and east-northeast directions.

The second 100 measurements were taken at a site about 200 feet from the first site. Combining the 200 measurements subdues the scatter, and three maxima become distinct. The last 100 measurements, taken two feet from the second 100, when combined with the previous 200, cause no significant change in the pattern.

The results are much the same with data collected on the east side of the largest Eastern Brook lake (Fig. A-4). The first 100 measure­ ments have a pattern that appears basically random with a suggestion of three possible maxima. The last 200 measurements, collected about four feet from the first 100, do not alter the basically random appearance, but the maxima become more clearly defined with 200 and 300 measurements.

The N. 5° to 10° W. and northeast maxima are closely similar to maxima obtained at the north end of Serene Ridge, 3,500 feet away (Fig. A-4).

The data from Starr Flank (Fig. A-5) were taken in two circular areas, three and four inches in diameter, respectively. Clearly, in this case, the last 100 measurements were not needed as there is virtually no change in the pattern between 100 and 200 measurements. 84

North end of Serene

lOOmafics 200 mafias 300 mafias

East side of the largest Eastern Brook Lake

lOOmafics 20 0 mafias 3 0 0 mafias r= 10%


Figure A-4. Smoothed Rose Diagrams of 100, 200, and 300 Measurements at Two Different Sites 85

Starr Flank

100 m afics


Figure A-5. Smoothed Rose Diagrams of 100 and 200 Measure­ ments at Starr Flank smoothed

set B

set C

set D

Figure A-6. Standard and Smoothed Rose Diagrams to Test Replication by Different Workers 87

Similar testing was done by E. J. McCullough (personal com­ munication, 1970) to determine the minimum number of measurements required to establish the direction of preferred orientation along the con­ tact of the Catalina granite in the Santa Catalina Mountains, Arizona.

His study showed that a preferred orientation was evident with only 10 measurements. The difference in our findings may be accounted for by a greater stress gradient existing along the contact at the time the gran­ ite was mobile than existed at localities in the more central parts of the pluton.

From the above tests the conclusion seems to follow that in the more central parts of a pluton, a sample of 100 orientation measure­ ments of elongate minerals may result in anomalous trends that are not necessarily structurally significant and may not be sustained with sub­ sequent measurements. One hundred measurements may only reflect a random clustering. At such locations, in order to override a possible random distribution, approximately 200 measurements of mineral orien­ tation are necessary to indicate the directions of preferred maxima. At most sample sites in the Sierra Nevada only 100 measurements were made. From what was said above, this would seem to be very poor prac­ tice unless some additional criteria indicate that the results are valid.

Replication by Different Workers

Because of possible effects of measurement errors, limits of precision in the use of the Brunton compass, and site-to-site and exposure-to-exposure variation, experiments were made in an attempt to test the ability of different workers to replicate one another. 88

Replication, according to Krumbe in and Gray bill (1965, p. 218) " tends to reduce bias by providing opportunity for effects of uncontrolled fac­ tors to balance out . . . replication assures that the experiment is self- contained; that is, the experiment provides for evaluation of its own results." Although limited aspects of replication are implicit in the testing discussed in the preceding section, more explicit testing was n e c e ssa ry . The data from the Catalina granite, considered in the previous section, were used for one test by plotting them in three sets in exactly the order in which they were taken in the field. A fourth rose diagram was plotted from data collected some years earlier about a quarter of a mile to the east by a third worker, Jeffrey Bushnell, another graduate student at The University of Arizona. The four diagrams (Fig. A-6) have similar frequencies and directions of preferred maxima, even though the samples consisted of only 100, or fewer, measurements. Smoothing these diagrams results in even closer similarities. If the smoothed rose diagrams based on random numbers (Fig. A- 2 , left-hand column) are compared with the smoothed diagrams resulting from the replication test (Fig. A-6), it appears that the diagrams obtained from the replication test resemble on another much more closely than do those constructed from random numbers. Accordingly, it should follow that reasonably good replication is a dependable criterion of significance even where only 100 measurements, or fewer, are available.

Replication at Different Sites That Are in Close Proximity Replication at two sites is illustrated in Figure A-6 where rose diagrams illustrate that three different investigators, two collecting data at one site (sets A, B, and C) and the third collecting data a quarter of a mile away (Set D), all record a dominant northwest direction of preferred orientation. Set B shows an east-west maximum that is weakly percep­ tible a quarter of a mile away. Set A indicates the east-west maximum and two additional narrow maxima, the nearly north-south and the north­ east that are not evident in set D; the last two directions are probably spurious and help strengthen the correlation. Further support for repli­ cation over short distances comes from testing these data with the Kolmogorov-Smirnov statistic, to be discussed in the next section, which illustrates that all of these rose diagrams could be drawn from the

same population. Another example of site-to-site replication is illustrated by

data collected at Lembert Dome in Yosemite National Park, along the Tuolumne River, and at Tenaya Lake (Fig, 3, in pocket). Even though

the frequencies vary and there is considerable scatter in the Tenaya Lake

' diagram, the three diagrams indicate two maxima in common, the north­ west and the northeast.

Care and judgment based on geological experience must be exercised in making semistatistical correlations based on replication of rose diagrams from site to site and even more so when using the Kolmogorov-Smirnov statistic. For example, the data from the Tuolumne River rose diagram were collected in the Half Dome Quartz Monzonite about 600 yards from its northeast-trending contact with the Sentinel Granodiorite. It could be argued that the replication is coincident and the northeast trend in the Tuolumne River data merely reflects local stresses generated by the emplacement of the Half Dome Quartz Mon­ zonite. However, this trend is found repeatedly throughout the Sierra Nevada, and it may be that the northeast trend of the contact and the

foliations in the Lembert Dome, Tuolumne River, and Tenaya Lake dia­

grams are due to a common factor. Moreover, all three diagrams also

show a northwest trend which is difficult to explain in the Tuolumne 90

River diagram if the foliation is due solely to stresses along a contact.

Thus, factors other than local stresses must be responsible for the pre­ ferred orientations.

The Kolmoqorov-Smirnov Statistic

In the previous sections the interpretations of the graphic pat­ terns of preferred mineral orientations have been visual. A search of the literature for a method of statistical interpretation reveals the compara­ tively little attention which has been given to the statistical analysis of structural geologic data. Two recent books (Miller and Kahn, 1962,

Krumbein and Graybill, 1965) on the application of statistics to geology refer only briefly to the analysis of directional data. Watson (1966, p.

786), in a rigorous paper on the statistical analysis of orientation data, states: "Geologists have suggested one statistical problem that is novel to statistics—the problem of how to handle data in which the basic ob­ servation is a direction." He defines a direction as a unit vector, which is a different condition than the directions, which lack sense, that are recorded on rose diagrams. Watson develops the mathematics for the analysis of unimodal distributions of preferred directions in both two- and three-dimensional cases by using the "circular normal" or " von

Mises" distribution. He (p. 787) explains, however, when data indicate several modes—as on my rose diagrams—that "the case for using the circular distribution is slight and the geologist should be content to show his data graphically."

Because most of my rose diagrams represent sample populations that are polymodal, such basic statistical methods as Student's t_ test for significant differences in sample means and Snedecor's F test for 91 analyzing sample variances are not applicable; these tests require that the samples be compared to a normally distributed standard distribution.

Consequently, only nonparametric tests can be considered for analysis of my data, inasmuch as no assumptions can be made about the form of the population distribution from which my samples were taken.

In spite of the gloomy prospects for a statistical evaluation of the data, a test was found that could be adopted; the Kolmogorov-

Smirnov statistic (Siegel, 1956, p. 127-136; Miller and Kahn, 1962,

Appendix G). This test is ideally suited for evaluating polymodal distri­ butions to determine whether or not the two samples could have been drawn from the same population. I have used this test for comparing (1) the experimental field samples with each other and (2) the field samples with the theoretically random samples.


The Kolmogorov-Smimov statistic is a test of whether or not

independent samples have been drawn from the same population. The

test is concerned with the agreement between cumulative frequency dis­

tributions. If two samples have been selected from the same population

distribution, their cumulative frequency distributions will be similar and

they should show only random deviations from the population distribution.

The test is sensitive to any kind of difference in the distributions from

which the samples have been drawn—differences in dispersion, in skew­

ness, in direction of modes, etc. A large enough difference between the

cumulative distributions of two samples is considered to be evidence

that the two samples have been drawn from different populations. 92 M ethod

Siegel (1956, p, 127-136) explains that to apply the Kolmogorov-

Smimov statistic cumulative frequency distributions are made for each sample. The "null hypothesis" is that the two continuous cumulative frequency distributions, from which the samples are drawn, are the same.

Consequently, if the maximum difference D between the two frequency distributions is sufficiently large, the null hypothesis is rejected. D is defined as

D = maximum where Sn^(X) is the observed cumulative step function of one sample and

8^2(%) is the observed cumulative step function of the other sample. The

values of D so large as to call for the rejection of the null hypothesis

the usual levels of significance are:

for the 0.01 level of significance

for the 0.05 level of significance


for the 0.10 level of significance


where nj and ng are the number of observations in each sample.

To use the test with a small number of samples, a graphical

method can be followed (Miller and Kahn, 1962, Appendix G) to obtain D,

the value of which is compared to tables of critical values. Because of 93 the large number of samples to be compared in this study, program Rose- kol was written for use on the CDC 6400 computer.

The test was programmed to reject the null hypothesis at a sig­ nificance level of 0.05. In interpreting the comparisons of field samples, the null hypothesis was rejected if the value of D for the largest step function difference is so large that the probability of its occurrence under the null hypothesis is equal to or less than 0.05. In other words, the two samples are considered to be drawn from different populations with a sufficiently large D, because the chances are 5 or fewer in 100 that a rare or unlikely event has occurred and the two samples are drawn from the same population. Rejection of the null hypothesis at p = 0.05 or less seems sufficiently conservative.

Applying the Kolmogorov-Smirnov statistic to the experiments discussed in the section on rose diagrams illustrates its usefulness. A tew samples are shown in Table A-l to illustrate the results.

Table A -l. Results of the Application of the Kolmogorov-Smirnov Statistic to the Comparison of Some Distributions of Preferred Mineral Orientations from the Catalina Granite

No. 1 vs. No. 2 No. 6 vs. Set A No. 6 vs. Random 1 (Fig. A-3) (Figs. A-3, A-6) (Figs. A-2, A-6)

D = 0.07000 D = 0.04655 D = 0.13017

Signifg Qg = 0.23556 Signif0i05 = 0.15771 Signlfg Qg = 0.12500 Conclusion: Conclusion: Conclusion: same population same population different populations 94

The comparison of all of the samples collected in the Santa

Catalina granite is given in Table A-2. The samples, which were com­ pared in increasing increments of 50 measurements, could have been drawn statistically from the same population distribution. Comparing these field samples with the theoretical distributions obtained from 200 random numbers reveals that most of the field samples of 150 or fewer measurements could have come from populations with random distribu­ tions. Beginning with field samples of about 200 measurements, how-, ever, the distributions in the Catalina granite are significantly different from those generated from random numbers.

Similar findings result by applying the Kolmogorov-Smirnov statistic to the test data from the Rock Creek area in the Sierra Nevada.

The three samples of 100, 200, and 300 measurements from the north end of Serene Ridge all represent sample populations of the same dis­ tribution. Compaing the test samples to theoretically random samples reveals that most of the five random samples and the test samples could be derived from the same population. The three samples of 100, 200, and 300 measurements on the eastern side of Eastern Brook Lakes yield the same results.

Although the Kolmogorov-Smirnov statistic is useful in compar­ ing field samples to theoretically random samples, the test does not seem valid in comparing rose diagrams taken in greatly separated areas.

In the work presented above, it has been shown that up to four directions of foliation are found in the plutonic rocks of the Sierra Nevada The number of directions of foliation and the relative frequencies of these directions vary from place to place. For this reason the cumulative 95 Table A-2. Results of Applying theKolmogorov-Smirnov Statistic to the Preferred Mineral Orientation Data from Measurements in the Catalina G ranite (S = significantly different sets of data at the 0.05 level.) Santa Catalina No. 2 Santa Catalina Set D | Santa Catalina No. 1 Santa Catalina No. 3 Santa Catalina No. 4 Santa Catalina No. 6 Santa Catalina Set A Santa Catalina Set C Santa Catalina No. 5 Santa Catalina Set B

Santa Catalina No. 2 -

Santa Catalina No. 3

Santa Catalina No. 4

Santa Catalina No. 5

Santa Catalina No. 6

Santa Catalina Set A

Santa Catalina Set B '

Santa Catalina Set C

Random 1 S S S

Random 2 S S SS

Random 3 s S S S

Random 4 s SS

Random 5 s SS 96 frequency diagrams of two or more rose diagrams might test significantly different with the Kolmogorov-Smirnov statistic even though the rose diagrams have two or more common directions of preferred mineral ori­ entation but differ only in relative magnitudes. Another limitation of the test is that in some instances, such as the samples from the north end of Serene Ridge, the samples measured in the field could have been drawn from a statistically random distribution. But that the distributions cannot be entirely random is indicated by certain preferred directions that reappear throughout the Sierra Nevada; therefore, it seems that the

semistatistical rose diagrams do provide a reliable and independent check on the results of the field mapping. APPENDIX B


Numerous hand specimens were collected from which 44 thin

sections were made. These were studied with a petrographic microscope, and data were obtained on textures and mineralogical composition. Modal percentages of minerals in the plutonic rocks were made using oversize

(22 x 35 mm) thin sections. Many specimens are too coarse grained to yield statistically accurate modes, even from oversize thin sections.

Modes for these coarse-grained rocks were counted by using slabs that

ranged in size from 4 to 12 square inches. The surfaces of the slabs

were etched and stained following a method of Laniz, Stevens, and Nor­

man (1964) that produces a surface on which K-feldspar is yellow,

plagioclase is red, and quartz and mafic minerals remain unchanged. In

this procedure the plagioclase is stained with F.D. and C. Red No. 2

(amaranth), which reacts with previously introduced barium, and the

K-feldspar is stained with cobaltinitrate. The actual counting

was done by projecting color photographic transparencies of the stained

slabs on a grid of about a thousand dots. Percentages of the individual

mafic minerals cannot be obtained from stained slabs; consequently,

the percentages of hornblende, biotite, and opaque minerals could only

be determined from thin sections. Stained slabs of rocks from the upper

Rock Creek area are illustrated in Figures B-l, B-2, and B-3.

97 98

Figure B-2. Stained Slab of Transition Rock 99

Figure B-3. Stained Slab of Cathedral Peak Granite 100 The composition of the plagioclase was determined optically,

using two methods: (1) the Michel-Levy method of recording the maxi­

mum extinction angle normal to (010) for plagioclase grains twinned ac­

cording to the albite law, the extinction angles being converted to the

percentage of An by using a curve determined by Wahlstrom (1955, p.

121), and (2) measurement of the extinction angles of combined albite

and carlsbad twins in sections normal to (010) (Rogers and Kerr, 1942,

p. 242-243). These methods have the advantage of rapidity, thus per­

mitting the determination of the composition of a large number of rock

samples, and they are also useful in obtaining the compositional range

of zoned plagioclase grains.

The modal data for the plutons are given in Tables B-l, B-2, s B-3, and B-4. The values of plagioclase, K-feldspar, and quartz are

recalculated to 100 percent and plotted on quaternary diagrams (Figs. 9,

12, and 13) in a manner similar to that described by Johannsen (1939,

p. 152) and contoured in the fashion common in petrofabric studies,

using a counting circle that is one percent of the total area of the tri­

angle. Diagrams of the compositional and textural variations of the

rocks are shown in Figures 10 and 11. Table B -l. Mineralogical Composition of the Round Valley Peak Granodiorite

Number Plagloclase Accessory Sample of points K- Total Horn­ and Number counted Quartz feldspar Amount Composition mafic blende Blotlte secondary Rock type

70A0 813 22.8 21.4 45.6 An25-36 10.1 7.6 2.5 0.1 Hornblende granodiorite 69C4 492 33.6 17.3 36.5 12.6 Hornblende blotlte granodiorite 69C5 1815 20.5 18.8 44.5 Anas 15.7 7.3 6.6 0.5 •1 M M 69A2 267 21.3 8.2 54.6 Anas 13.9 3.9 9.4 3.0 Blotlte granodiorite 70-B1 242 20.6 20.3 45.0 Anao-39 13.2 8.3 3.7 2.0 Hornblende granodiorite 691-1 246 28.0 16.6 47.0 An24-37 8.5 1.6 6.9 2.0 Blotlte granodiorite 70G5 259 25.5 15.9 43.8 Anag-aa 14.0 5.8 7.4 1.5 69J5 425 16.7 16.5 45.6 An26-35 20.8 6.8 12.2 2.2 69B2 207 26.5 16.4 48.8 An23-28 7.5 3.7 3.8 0.8 Hornblende blotlte granodiorite 70E2 260 20.0 18.0 47.4 14.6 M H i i 70E5 358 19.0 19.3 46.4 15.3 I I I I M 70F5 257 20.2 18.7 46.7 14.4 I I I I I I 70-EO 768 25.0 17.2 46.5 Ana7-36 11.3 2.6 7.6 1.0 Blotlte granodiorite

69J2 443 15.6 12.4 51.4 20.6 • e • • • • • e • Hornblende blotlte granodiorite 68-H-10 340 41.6 10.6 40.3 Ani8-31 7.1 0.6 5.9 0.9 Blotlte granodiorite

Average 23.8 16.5 46.0 13.3 4.8 6.6 Standard deviation 6.8 3.6 4.2 4.1 2.7 2.9

o Table B-2. Mlneraloglcal Composition of the Transition Rocks

Number Plagioclase Accessory Sample of points K- Total Horn­ and number counted feldspar Amount Compositionmafic blende Biotite secondaryQuartz Rock type 70A-5 325 25.0 23.0 40.3 11.7 ... Borderline; quartz monzonite and granodiorite 70A-8 447 15.2 24.6 46.5 13.7 ... Same as 69A-5; some K-feld- spar phenocrysts 69G-2 553 20.6 16.6 55.2 An25-34 7.1 2.2 4.0 1.3 Biotite granodiorite 69H-2 340 18.8 23.8 48.6 8.8 ...... Borderline; quartz monzonite and granodiorite 69-H1 232 34.0 27.6 25.9 A"29 11.6 2.6 9.0 <1 Biotite quartz monzonite 69E5a 274 24.1 26.0 37.3 An30-40 10.8 5.4 5.4 1.8 Biotite hornblende quartz monzonite 69-J-3 811 29.0 26.0 33.5 ' An39 11.2 8.2 3.0 0.3 Hornblende quartz monzonite 69-10 279 26.1 27.5 31.9 An35 14.2 6.5 4.7 3.3 " " " 70-A-4 381 27.4 21.2 41.0 Anai 9.4 . 1-8 7.1 1.5 Borderline; quartz monzonite and granodiorite 70C4 179 20.5 17.0 45.6 An28-30 16.7 1.7 11.7 3.4 Biotite granodiorite; intense alteration of biotite and plagioclase 70A4 230 25.0 11.0 47.0 An25-31 15.5 2.6 11.0 2.4 Biotite granodiorite 70F-4 393 27.0 20.5 40.0 An31 9.6 1.8 6.0 3.2 Borderline; quartz monzonite and granodiorite 70A-3b 213 32.5 16.0 42.0 An32 8.1 1.4 6.6 0.5 Biotite quartz monzonite Average 25.0 21.7 40.6 11.4 3.4 6.9 Standard deviation 5.3 5.2 7.7 2.9 2.4 2.9 102 Table B-3. Mineralogical Composition of the Cathedral Peak Granite

Number Plagioclase Accessory Sample of points K- • Total Horn­ and number counted Quartzr feldspar Amount Composition mafic blende Biotite secondary Rock type

69-G-5 343 25.1 29.2 39.9 An30 5.8 0.0 5.8 0.0 Porphyritic quartz monzonite n n ii 70E-6 423 24.8 26.2 37.3 11.7 e • • • • • 70-G-8 212 27.5 25.0 40.5 An32 6.6 1.9 3.3 1.8 Quartz monzonite

Average 26.5 27.8 40.3 8.1 1.0 4.6 Standard deviation 2.6 1.6 3.1 3.2 1.3 1.8

Table B-4. Mineralogical Composition of Other Rocks of the Upper Rock Creek Valley

Number Plagioclase Accessory Sample of points Total Horn­ and number counted Quartz feldspar Amount Compositionmafic blende Biotite Auglte.. secondary Rock type

69-H-9 683 6.3 16.1 44.1 An38 32.0 18.2 14.0 0.0 1.3 Hornblende diorite HM69C6e 251 23.1 5.2 54.0 An30-36 15.2 6.8 7.6 0.0 3.3 Biotite hornblende quartz diorite 69-EO • • • 90+ ...... Very fine grained meta- quartzite 680-3 500 1.6 0.0 58.6 An52 39.8 3.8 13.0 20.0 3.0 Augite metadiorite 68-P-5 400 0.5 0.5 46.0 An48 ' 52.5 42.0 0.0 2.5 8.5 Hornblende metadiorite 69E7a 400 4.0 7.2 48.0 40.6 14.2 25.0 0.0 1.5 Quartz diorite inclusion REFERENCES

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) IO z Alluvium, talus, UJ colluvium and till o

Cathedral Peak Granite

(/) 3 O LlI O < P- Transition rocks LU cr m, main moss, u s, small mass

Lamarck Round Volley Peak Granodiorite Granodiorite CO 3 O O UJ JKmg co

Contact Gabbro dike Dashed where approximately Dashed where approximately located; dotted where covered located; dotted where covered.

::::::::::::::::::::::::::::::::::::::::::::::::: X 6 9 -G 2 Gradational contact Location of modally analyzed specimen.

Strike and dip of steep joint Strike and dip of vertical joint

-3 7 * 2 5 — 37*25

IOOO 1000 2000 3000 4000 1— 1 I— I t— I t— I M feet

contour intervol 80 feet Bose mop prepored from U.S.G.S. Mt. Abbott, 1953, ond Geology by D. D. Trent Mt. Tom, 1949, Quadrangles. Streams ond trails revised.


FIGURE 5. HIGH ANGLE JOINT MAP, UPPER ROCK CREEK, FRESNO AND INYO COUNTIES, CALIFORNIA. D. D.Trent Ph.D. Dissertation Geosciences 1973 / /<»/ Mt. Abbott Quadrangle * Mt. Tom Quadrangle 118*45' HALF MOON PASS VALLEY OUTLET GOLDEN LAKE 1 100 Mafics . IOO K-feldspars



U O NORTHEAST OF SERENE LAKE IN O Z LU 100 Mafics lA Alluvium, talus, O colluvium and till

Cathedral Peak Granite

V) ZD O LU O < I- Transition rocks LU o: m, main mass, o s, small mass

Round Volley Peak Gronodiorite co 3 <-> O




200 Mafics

Gabbro dike Dashed where approximately Dashed where approximately located; dotted where covered located; dotted where covered.

X 6 9 -G 2 RUBY LAKE TRAIL Location of modally analyzed specimen. 200 Mafics x bj Strike and dip of foliation in metamorphic inclusion

Vertical and inclined foliation shown by mafic minerals

Vertical and inclined foliation shown by inclusions

Vertical and inclined foliation -3 7 * 2 5 shown by mafic minerals and inclusions

Foliation shown by K-feldspar phenocrysts

Vertical foliation and trend and plunge of lineation shown by mafic minerals

Inclined foliation and trend and plunge of lineation shown by mafic minerals

Trend shown by inclusions '''P

- * r Synform in schlieren


contour interval 80 feet Base mop prepared from U.S.G.S. Mt. Abbott, 1953, and Geology by D. D. Trent Mt. Tom, 1949, Quadrangles. Streams and trails revised.



/=y Mt. Abbott Quadrangle * Mt. Tom Quadrangle I ISMS'

/ / f -ZZ/ / / j K f ^ m Z / ------

X HM69C6

/ y / 1 \ ) l v l J/) i M i l z X U z V 1 X \ v Jr ^ \ \ \ l\v \ / LOCATION /

x V \ EXPLANATION \ j> V / «;(°38yV i U u u \ \ O N O Z "z V Alluvium, talus, Ixl O Krv colluvium and till /■ iiiiifflto" v vt J Kcp W h > } i i / w Cathedral Peak Granite y ?ll' Mliiiirr/if \ 1 // I d co x 3 1 1 1 1 1 O Ixl O # 8 4 O l2 i < I- f / v L Transition rocks Lxl m, main mass, tr u r, s, small mass / \ M 7 \ i/ y» Granodiorite Granodiorite 5 / > -1 va cn i r r r W / / i 4 > 69 C 6 3 / // / O / Ixl )()(// (TV si, JKmg z .eg / o < / / A I- v'//f Ixl / / / / Metagabbro GC ( ; m j / j Ktt| i//// y J U f X- 70A-9 # / # / z l ! Mt.fStorr //V >7777/// / / / X 69 A? X 70 *- A— 4 / A / Z4' , 3/ m / / / ; Contact Gobbro dike Krv / / z v - f / y Dashed where approximately Dashed where approximately locatedi dotted where covered. located^ dotted where covered. X i-'3/ y) / , ^ / / w v b , W z / X 6 9 - 6 2 1 * 7 / •A; y // Gradational contact Location of modally A y If c n X / z analyzed specimen. va i • ii y . Kcp r> A Tf e- f i

Krv A \ / Strike and dip of inclined joint Horizontal joint 9-i^e - s ^ c u . 7 / X \ \ zv A - 6^-H-UD X -3 7 * 2 5 — 37° 25 \ * - r Z\ 6 9-10 X 6-^ -v -3 J Y ? N . X/ X770-J1 o V I

7 ,; /)// y / U6 ' ___y

) / / z' i M ^>57 / //// z I | 1 y E Z ''' % 684~3 y / / / /


Scale 112000

1000 1000 2000 3000 4000 i i—i t—i i—i t—< i—r feet

contour interval 80 feet Base map prepared from U.S.G.S. Mt. Abbott, 1953, and Geology by D. D. Trent Mt. Tom, 1949, Quadrangles. Streams and trails revised.


FIGURE 6. LOW ANGLE JOINT MAP, UPPER ROCK CREEK, FRESNO AND INYO COUNTIES, CALIFORNIA. D. D.Trent Ph.D. Dissertation Geosciences 1973 ^ f / /4)3 /*/ Mt. Abbott Quadrangle ^ Mt. Tom Quadrangle II8"45'



U O N O Z LU Alluvium, talus, O colluvium and till

Cathedral Peak Granite

C/3 ZD O LU Ktr O < H Transition rocks LU

Lamarck Round Volley Peak Granodiorite Granodiorite co 3 u O CO LU JKmg <" 5 % CL Metagobbro


Contact Gabbro dike Dashed where approximately Dashed where approximately located; dotted where covered located; dotted where covered.

X 6 9 -6 2 Gradational contact Location of modally analyzed specimen.

27 y strike and dip of antiform -synform pair of schlieren dike recumbent folds of a schlieren dike with trend and plunge of axis; small arrow indicates /5 „6 same with trend direction of movement of upper and plunge of lineation fold

same with trend of antiform in schlieren dike horizontal lineation — 37° 25 - 3 7 ° 2 5 \_ same with trend and plunge "y approximate strike of axis y and dip of curviplanar schlieren dike synform in schlieren dike

\ horizontal schlieren dike y strike and dip of aplite or pegmatite dike antiforma I and synformal fold of schlieren dike with axial trend r\ direction of movement of ^ I) the upper part of an offset inclusion, or 2) the upper block yQ overturned synformal fold of a marginal fault as shown within schlieren dike by drag folds in a schlieren showing axis and direction dike or by fiederspatte of dip of limbs

D/, fault; U, upthrown side, ^ overturned antiformal fold w D, downthrown side within schlieren dike showing axis and direction of dip of limbs

Scale 112000

1000 1000 2000 3000 4000 I—I I—I >—1 I—I kT feet

contour interval 80 feet Base map prepared from U.S.G.S. Mt. Abbott, 1953, and Geology by D. D. Trent Mt. Tom, 1949, Quadrangles. Streams and trails revised.



/ b i b ?

D 0° * 1° 11600-'

d no 0

12000 - — 10800

0 00 onut! On 11600 l— 10400 H \Y/

Krv.'j 12000 CPnCo 0 1j0dd0 — loeoo

11600 1 0 4 0 0

12000 - ™ t\' I,'1 \ '« : 11200

11600 loeoo

11200 -1 11200


— 10400

1000 2 0 0 0 3000 1 M M M M M


schlieren dike gabbro or diorite dike

felsic dike

See Figure 4 for additional explanation.

FIGURE 8. CROSS SECTIONS, UPPER ROCK CREEK, FRESNO AND INYO COUNTIES, CALIFORNIA. D. D.Trent Ph.D. Dissertation Geosciences 1973 f 1 1 8 * 5 0 / 118° 4 5 ' / Z 118° 4 o ' LAKE CROWLEY \ / ' / z X RIVER V x;;vv OWENS __ _

- 3 7 ° 3 5 — 3 7 3 5 \ \ z / \ \ /

\ X J v - /

/ *♦' > 58 v \ V LOCATION 11,108 McGEE MTN 7 2 0 8 \ — ' \ 10,871 G s 76 X z S MT MORRISON P z m 12,268 7 0 0 8 1 \ 5? ; 7 0 0 4 6 9 4 3 \ ^4' / 83 V 65 \ 68|| f 68 / V J ) A 73 62^ ^ \ 65 X KWC 82 11,385 X 6 2 / \ / V X K w c 72 v V *44 MT AGGIE •57 J 7 6 > X X . X 64 11,561 60 8 0 4 9 78 Y 52 # 49 V

8 2 9 5 4 4 i 6 5 6 0

60 37 \ MT. BALDWIN / 7 6 10,840 7017 X, 12,614 : \ ,8 8 11,328 BIRCH

i \ P z m > 7 5 ^ ^ KWC 80 ^ 82 X

60 X X > -V . 80 \ X i X ' - x _ .7 7 7 6 ‘•jr. •; :.x: ^ s \ > 71 71 72 62 h 8 5 . 73 ' V70 X X L ^ 72 87 V ^ X RED MTN. v K w c > ^ XA'X 12,553 X' \\ . 70 .X\ 52- >5*

Pzm S is Z Z 'i:" 70 V EXPLANATION K wc X 40 10,943 I v> v X 52 . Vt 56 \r. :•••. V 5c. - vV .-'.V - X - 50 V X 12,984 Krv "< '*'76 Ka X' 55 e i t # # # # 70*' 10,793 : 40 x 1 . • • • 7 r < 1- T • • • ,6° 1 ; - ! 83 Av* ’ Krv • 75 /• 4 0 / ' v alaskite Cathedral Peak Granite ' ‘. X e e is V. • * . * 45 X. X V v« Krv . ": • • • 4 5 62. ^ 42 • Y , .• ' 1

'9801 M v ' y ••• \ i f 11,461 .“ •.7 • : • •• . Krv V • • •. • 47 • *♦ . . • x 6 e . y — 3 7 * 3 0 v ■ 88 Fine-grained granite

'V. y 60 4° : : % . . 8 5 ^ • •. 70 Vt )" • 11,336 ■ ' v / * • 4 5; . Y z • ' . 50VV*65 ••V .'.V :/. • U r : / \ ^ Kwc V74 12,522 / v .•. - • . ..Z. ; t,; :• MT. STANFORD f Z U 4 : ••• Tungsten Hills • , * / • * 47 Quartz Monzonite v ' ™ . : • X 75 / 7 • 'V 72 ' • .

f 80 > i J m v •:"X; : . / Z f l 'Vrc : v ,; 2 MT CROCKER • z •*. Krv . . ' V ; - ' ' ' ?2,457 * 11,498 RED AND WHITE MTN.,' •; * T \/:‘* • Krv . 12,318 v X Round Valley Peak \ ^ > r e . •. J ; * • so *, ' • Lamarck *2,850 • • • 68 4 - f :; • .* • • Granodiorite Granodiorite \ . 75 11,962 > V x*. •• • . X. \ * x .. V. •

Wheeler Crest MT. HUNTINGTON Quartz Monzonite 12,405 / ^y:V>:\;Sv Kcp MT. HOPKINS 87 \Q * • ; 5 7 / y i - i Kwc m m m i 12,302 // 4 ' ) Gabbro,diorite,and .e P ' o o 12,2 52 . h7° hybrid mafic rocks \ 0 f ::vj 65 y " A u u tn tn o / % J t> 82 ^ £ c - 5 Metavolcanic rocks £ i 50 . , 1 ■ M - 12,067 • 'x , ' % ROUND VALLEY PEAK 8 8 ./ ) . / KO ; % / 78 X* ^ X L / —^ ^ ' \ zX' •;•.•: , * 9 4 3 z z z / ' 40 V '.' • * . v • - 63 c j \ o ^ ^ ^ ■ 70 = Krv 12,098 i : X «» / o ° 80 ^ » o O <7 Metasedimentary rocks c r e e k X <3/ O o 1 • o ^ X JT • V f 1 Kcp » • 1 V V ^ o 1 M ^ 82' . -. -ZOsfZ, g2// 77

MONO ROCK W ^ • 8 5 1 a L t;, o 11,555 0 X strike and dip of steep(>45°) strike and dip (>45°) of foliation Krv X 8V foliation shown by inclusions 0 ° o shown by feldspar phenocrysts h 8 6 and mafic minerals OL-o, 088 ' D A0^ «=> c3 vertical foliation shown by 6 8 ' es same with trend and plunge ^ * cp feldspar phenocrysts : 7 / eT of lineation 80 » .47 i & ■ 86 4 z/ / • *. 11,960 do Kwc axis of syncline 0 02° W . tv- / y , vertical foliation shown by X V 80 r f w z r 60 • ' • ; . z :.TT / inclusions and mafic minerals . 8 2 6 8IA - 4 5 . 3I strike and dip(<45°) of o' W m Krv A ■ m o n o 79 . • x foliation shown by inclusions ^ trend and plunge of lineation and mafic minerals .x c = fl 0 / Kcp 42, r 8'. 12,406 :V; trend of foliation >81 1 81 strike and dip of bedding y .y .y S i 7 7 ::::: -37*25 82 vx z V i!: - 3 7 * 2 5 n contact; dashed where approximately glacier VvzXV/ 12,145 \ located, dotted where uncertain 2XZI .58 > v r i m # # # X SB pvrf:? Zv.’ i t w

0 \ x XZ X 47 x" L70 V

^ y o 84X ..83

MT. MILLS . 75 13,468

12,975 ‘A.i Scale h3l,250 MT ABBOT v 80 • . . • Y67 13,715 X " 72 '«» -7' 0 miles RECESS PEAK MT. DADE 12,743' 12,836

iX70 Base map prepared from U. S. G. S. Mt. MT. GABB X Geology by D. D. Trent, P. C. Batem an(l965), Abbot, 1953, Mt. Tom, 1949, Casa Diablo Mtn., x, and from field notes of J. R. Chelikowsky, 13,711 Kwc L. C. Cononf, E. B. Mayo, and J. M. Parker,HI. 1953, and Mt. Morrison, 1953, quadrangles. G \ \ 70 c% #5, 1 2 , 8 6 6 <\ \

-17% BEAR CREEK SPIRE 0 13,713 )

MT. HILGARD F- A 12,571 x 13,361 LAKE a ALT \ 118*50 1






80 K-feldspars

Geology is generalized from the Geologic Map of California, Fresno (1966), Mariposa (1967), and Walker Lake (1963) sheets.


36o30' 36*30'

118*15' 118*00'


D. D.Trent Ph D. Dissertation Geosciences 197 3 £ 4 7 9 /

/ O j