U.S. DEPARTMENT OF THE INTERIOR GEOLOGIC INVESTIGATIONS SERIES U.S. GEOLOGICAL SURVEY I–2697

Qtl Ta Ktl Ta CORRELATION OF MAP UNITS microcline phenocrysts as much as 10 cm long making up 2 to 10 The pre-Tertiary rocks of the Tower Peak quadrangle fall into two groups: (1) an here has burst its shell of more mafic differentiates and intrudes older granitic and Qng Qtl

Qg a c percent of the rock. Quartz typically occurs in 1/2-cm clots. Mafic L-shaped area of older plutonic and metamorphic rocks, 3 to 10 km wide, that metamorphic rocks, and (2) the Half Dome Granodiorite, which is interpreted as an Qal Qng Tvs Qg 70 Tr p SURFICIAL DEPOSITS Qtl 75 c

Qtl Ktl Qga mineral content about 10 percent. Asymmetric schlieren locally extends diagonally both northeast and southeast from near the center of the quadran- earlier, more mafic differentiate of the same magmatic pulse as that for the Ta c Kfl Qal Qtl Qls Qng Holocene Ktl Qtl abundant gle; and (2) a younger group of large, probably composite intrusions that cover large Cathedral Peak Granodiorite.

Qtl Ta 70 QUATERNARY a Qal c areas in adjacent quadrangles and extend into the Tower Peak quadrangle from the The northern composite intrusion of the younger group includes the Qal c Kfl Granodiorite of Fremont Lake (Cretaceous)—Medium-dark-gray, Qng Tvs Qg Late Qtl Qtl 65 Tr p Qg medium-grained, hornblende-biotite granodiorite. Where horn- east, north, and southwest. granodiorite of Topaz Lake, a rock almost identical in appearance and age to the Qtl Qtl Pleistocene Tr p Qng Qng 70 a Cathedral Peak Granodiorite, but separated from the latter by a 6- to 7-km septum of Ktl Ta Qg VOLCANIC ROCKS blende-rich, contains abundant lenticular or elongate mafic inclu-

Qng Qtl Qtl 70 65 OLDER PLUTONIC AND METAMORPHIC ROCKS older rocks. The Topaz Lake pluton is bordered on the south by the granodiorite of c sions, commonly uniformly distributed, but locally in clusters. In the

a a a

Qal a Qg 60 Ta southwest part of its occurrence in this quadrangle, it is largely The L-shaped remnant of older plutonic and metamorphic rocks that extends Fremont Lake. The Fremont Lake pluton appears to bear the same relationship to the Tvs 55 c 70 75 northeast and southeast from the center of the quadrangle contains ten plutons with granodiorite of Topaz Lake that the Half Dome Granodiorite does to the Cathedral Kfl a Tr p Miocene mafic free, lacking in inclusions, and tending toward granitic com- Tr p contiguous areas of at least 2.5 sq. km and several complexes of dikes and small Peak Granodiorite.

Qal Qtl 65 a a TERTIARY position. Map unit is named for exposures near Fremont Lake where

c Qal Qng

Ta Tvs Tbb irregular masses. These plutons and dikes intruded silicic and mafic metavolcanic The southwestern composite intrusion of the younger group includes four large a it was mapped by Giusso (1981) in the Sonora Pass quadrangle to Qng 35 c 65 a 50 Kfl a Qal 65 rocks and miogeoclinal metasedimentary rocks. Mutual age relations between the plutons in the southwest corner of the Tower Peak quadrangle and in adjacent Tvs 55 Qng Miocene to the north. The unit extends west into the Pinecrest quadrangle where Ktl Qtl Qal 50 65 a a65 Tvs plutonic rocks are incompletely determined, either because some of the rocks are not a 60 a a Oligocene it has been called the granodiorite of Kinney Lakes (Huber, 1983) quadrangles. These plutons show some evidence of being consanguineous, yet other Tbb Qtl a 80 a in geographically contiguous sequences or because the contacts have ambiguous age evidence suggests a significant hiatus in the sequence. The complex includes, from Qtl Tbb Qg Klc Granodiorite of Long Canyon (Cretaceous)—Dark hornblende-biotite

Qal aa85 75 Klc mvr PLUTONIC ROCKS criteria. Structures in this remnant are generally steep, trend northwesterly, and are oldest to youngest, the quartz diorite of Mt. Gibson, the granodiorite of Bearup Tr p 70 [Lines and arrows indicate intrusive relations] granodiorite and quartz-diorite with mafic mineral content of about c c a c cut off sharply by the younger plutons. Lineations, foliations, and zones of recrystal- Lake, the granodiorite of Lake Vernon, and the granodiorite of Boundary Lake. A Tvs a c Qg South and 30 percent and with abundant mafic inclusions aa70 80 lization and shearing, all of supposed metamorphic or tectonic origin, are present in swarm of fine-grained diorite dikes cuts the Mt. Gibson and Bearup Lake, but is 75 msm msq southwestern Northern Eastern Qal 70 gb a75 Klc a 80 a Eastern area some plutons and suggest at least one period of dynamic metamorphism during or apparently cut off by the granodiorite of Lake Vernon. This succession of events Tr p 70 a Qtl area area area a apa a a 75 c Qal 80 70 a Qg Tr p Kcp Cathedral Peak Granodiorite (Cretaceous)—Medium- to coarse- after the period of emplacement of these plutons. The metamorphic and early mafic suggests a time break and interval of cooling. However, the granodiorite of Bearup msh 60 a70

80 Kbl Ktl Kcp rocks are described first below, followed by the plutonic rocks of the northeast arm Lake grades in color index from very near that of the Mt. Gibson where it is in Qg mvr c c grained, hornblende-biotite granodiorite that contains conspicuous 70 a70 85 of the "L", and then the rocks of the southeast arm.

Klh Qg a 85 Klv Kfl Khd blocky phenocrysts of microcline as much as 10 cm long. The intrusive contact with the Mt. Gibson to very near that of the Lake Vernon where the

a Metamorphosed sedimentary rocks appear to be the oldest rocks. They include latter intrudes the Bearup Lake. This suggests a genetic relationship extending a a aa phenocrysts commonly occur in aligned swarms and asymmetric 80

mvb Qal 75 Kbu Klc Kgm Ktl di ap schlieren are locally abundant pure white orthoquartzite, in beds a few meters thick, that display thin partings bear- across the time gap.

80 80 Kmgc

a a mvr i Kut Khd Half Dome Granodiorite (Cretaceous)—Medium- to coarse-grained, ing andalusite and biotite and common internal crossbedding. These are interbedded

80 Tvs a Kmgf CRETACEOUS

c 80 a DIORITE DIKES

Qtl a 85 equigranular hornblende-biotite granodiorite with abundant elongate with thick (10 to 50 m) units of biotite-andalusite-sillimanite(?) schist, coarsely

c Kdl 80 Qg

c Kpm Kt Kmp Kbp c a

a 75 crystalline marble, and fine to coarse beds of pale-green, calc-silicate hornfels. Sets of diorite dikes (not shown on the geologic map) with at least three 65 c a or flattened mafic inclusions. Characterized by euhedral hornblende

80

c 80 a These metasediments are complexly deformed. The southern body around Benson orientations intrude the granite of Avonelle Lake, and at least one set also intrudes a

c g Klh Kal ap Kdl prisms as much as 1 cm long, biotite books as much as 1 cm across,

Kfl 85 Lake is mainly quartzite, with some thick biotite-andalusite schist bodies near the the quartz diorite of Mt. Gibson and granodiorite of Bearup Lake. These dikes are a

a c and conspicuous sphene. Near Tilden Lake it is mafic-poor and has

80 c Klh c msh a top and marble at the base, folded into a large anticline with a horizontal crest and confined to the southwest part of the quadrangle and do not appear to occur in the 80 i Klh large microcline phenocrysts

Qal c

80 vertical limbs. The minimum stratigraphic thickness exposed in this body is 750 m. northeastern part of the Avonelle Lake pluton. One set trends due north and is about 75 c 75 ap c CRETACEOUS Kgm Alaskite of Grace Meadow (Cretaceous)—Sugary, medium- to fine-

di gb The northern body, around Bigelow and Snow Lakes, contains abundant marble bod- vertical, another set trends northwest and is about vertical, and the third strikes

a a msq Qtl c OR OLDER grained, light-pink to white alaskite with rare dark minerals.

ies and about equal amounts of quartzite, biotite schist, and calc-silicate hornfels. It roughly east-west and dips 30 to 45 north. The first two sets appear to predate the

80 ° °

a c Contains abundant inclusions of diorite, gabbro, quartzite, biotite

Qal METAMORPHIC ROCKS has been folded at least twice, the first time isoclinally. The latest deformation was formation of the Mahan Peak complex and the intrusion of the Mt. Gibson pluton

c schist, and marble a

a Qng into a flat-topped dome with nearly vertical flanks along the intrusive contacts. because they are found as inclusions in the former. The diorite dikes probably

c CRETACEOUS

c a Kut

80 c i mvb mvr Granite of Upper Twin Lake (Cretaceous)—Coarse, equigranular, a Small bodies and inclusions of metasedimentary rocks in several of the plutons indi- represent periods of crustal extension, although it is not clear how extension alone

70 di ms msq msm OR OLDER a 60 Qg 85 pink biotite granite. Locally has a very strong vertical lineation,

a Qal Kcp cate that this terrane was once more widespread. In the extreme northeast part of the would produce a dike-swarm dipping 30 north.

Qng °

80 45 Kbp msq probably of metamorphic origin

75 Qg quadrangle, metasedimentary rocks, which may be in depositional sequence with the Where the diorite dikes intrude granite, they are bordered by thin, discontinuous 60 g

a g Kfl 70

a Kbp Granite of Bond Pass (Cretaceous)—Gray, moderately foliated,

a msq

60 g ms msm metavolcanic rocks, include quartzite and stretched conglomerate. selvages of fine-grained felsic rock, generally of granitic composition, but ranging a

g PRE-CRETACEOUS

70 50 g

Kbl 60 c hornblende-biotite granite and granodiorite with moderately large, toward diorite. In addition, the dikes are cut by thin, closely spaced, and exceedingly g c a [The metamorphic rocks in the Snow Lake region (Snow Lake pendant) have been

a 60

a 75 55 a 70 65

Kbl a 55 msh slightly pinkish, K-feldspar phenocrysts. Locally intensely sheared.

g msm irregular veins of the same material, which are continuous with the selvages. The

g apa extensively studied by Mary M. Lahren, who has correlated them with Precambrian 60 c

60 c 75

a ms Kgm Includes bodies of aplite or fine-grained sugary alaskite containing 50 Qg Qg to Triassic formations exposed in southeastern California (Lahren, 1989; 1991; Lah- selvages are probably the product of melting of the granitic wall-rock by the diorite c a c msq

Kfl 65 i

Qal Kut Qg tourmaline rosettes and mapped separately ren and Schweickert, 1989). No attempt has been made here to reconcile Wahrhaf- magma, which was probably intruded at a temperature well above the melting

70 di

msq Kdl c Qal Granite of Dorothy Lake (Cretaceous)—Light-pink, fine- to coarse- temperature of the more felsic rocks.

a Qg Qng

75 i 75 tig's earlier mapping with her later interpretations.]

a Kgm Qtl DESCRIPTION OF MAP UNITS

a di gb

gb gb grained tourmaline-bearing granite. Contains rare miarolitic

55 c Qal Qng c SURFICIAL DEPOSITS Bodies of diorite and hornblende-gabbro appear to be the oldest intrusions in 55 c MAFIC INCLUSIONS

a ms cavities. Locally intensely sheared, with tourmaline on shear the metasedimentary sequence. The gabbro contains bodies of pure hornblendite or

Qal gb Alluvium (Holocene)—Chiefly sand and gravel underlying meadows

a Qal a a Most of the hornblende-bearing plutonic rocks have crudely lenticular or rod- di 80 surfaces a c

a hornblende-pyroxene rock as much as 300 m across. Hornblende crystals in these

80 ms 80 85 like inclusions, a few centimeters to a meter or more thick and as much as 5 meters

65 a msq Klh Granodiorite of Lake Harriet (Cretaceous)—Dark-gray, moderately a Qng

65 a Qtl Talus (Holocene)—Rock waste derived from cliffs. Only especially pods are as much as 3 cm across and are generally stubby or equant. Some of the

85 80

a Kut Qtl long, of relatively fine-grained predominantly mafic minerals. These are distributed

85 a Qal foliated granodiorite characterized by shreddy clots of biotite and gabbro in the large body near the center of the quadrangle shows tilted but right-

Klh extensive areas shown

85 80 c hornblende. Aplitic border facies along northeastern margin mapped moderately uniformly through the plutons, although in a few localities the inclusions

c Qg side-up cumulate layering. All the mafic and ultramafic rocks have been metamor-

a a di Qls c Landslide deposits (Holocene)—Unsorted debris deposits resulting

c 85 form clusters resembling schools of fish. In some plutons, especially the

c separately a phosed.

c c ap

c 80 from mass movement granodiorite of Fremont Lake and Half Dome Granodiorite, the concentration of

a c 75 a ap a Aplite (Cretaceous)—In granodiorite of Bond Pass (Kbp) occurs as Next younger seems to be a differentiated plutonic complex that includes the

75 a a di Qng Neoglacial and periglacial deposits (Holocene)—Includes cirque mor- inclusions varies greatly from place to place. The mafic inclusions are composed of

85 Kbp 70 75 dike-like bodies of aplite or fine-grained sugary alaskite containing granodiorite of Lake Harriet, with an aplitic border facies, and the granite of Doro-

c di 65 ap aines and rock glaciers the same minerals as the enclosing granitic rock, but in different proportions. Their

c Qg

di tourmaline rosettes. Includes aplitic border facies of granodiorite of thy Lake. The Lake Harriet and its aplitic border facies intrude the metarhyolite,

65

a a Qg Glacial deposits (late Pleistocene)—Chiefly morainal deposits from origin remains an enigma. Current evidence favors most of the inclusions having c

c 35 Klh c Lake Harriet ( ) mapped along the northeastern margin of that which is interpreted to be an ignimbrite because the outlines of flattened pumice

Kbl a 60 Tioga-age glaciation, but includes some of probable Tahoe age in originated as blobs of basaltic magma that were incorporated into the more felsic

di a pluton fragments can be seen on weathered outcrops. The Dorothy Lake appears to be a

a a a c

80 a

a southwestern corner of quadrangle magma from which the granitic rocks crystallized (Bateman, 1992). Qal 80 Qg 40 Kgm di Diorite and gabbro (Cretaceous or older)—Occurs as generally small, siliceous core to the Lake Harriet pluton.

a a

50 a Kgm

70 55 Khd di irregularly shaped bodies throughout the map area. Extremely Intrusive into the Lake Harriet complex is the granite of Bond Pass, which was

Klv di 55 Qg VOLCANIC ROCKS gb

c ms

Qls c REFERENCES CITED

a intruded in turn by the granite of Upper Twin Lake, and that by the alaskite of Grace a

70 c variable in grain size, texture, and composition. Some bodies are 20 c

a Ta Hornblende andesite and basalt (Miocene) a —Dark gray andesite, with

Kal a 50 Bateman, P.C., 1992, Plutonism in the central part of the Sierra Nevada batholith,

65 a older and some younger than the plutonic rocks with which they are Meadow. The Bond Pass is cut by northwest-trending, dike-like bodies of aplite that

c 40 25

c conspicuous hornblende needles, and basalt; occurs as dikes, sills,

80 75 contain spherical rosette-like intergrowths of tourmaline, quartz, and feldspar. The California: U.S. Geological Survey Professional Paper 1483, 186 p.

a di in contact, but most appear to be xenoliths. Two larger bodies of a a

c a

70 a c a 20 a Qg and irregular masses intrusive into and probably related to the Relief

Qal c Qtl granite of Upper Twin Lake has in places an intense vertical lineation expressed as a Dalrymple, G.B., 1964, Cenozoic chronology of the Sierra Nevada, California: Cali-

65 55 50 coarse-grained hornblende gabbro (gb), near the center of the

30 c 80 80 Peak Formation

c Qg Qal a 70 fornia University Publications in Geological Sciences, v. 47, 41 p. c a Kcp lengthening of quartz and feldspar grains, which is probably metamorphic in origin. di a55 75 quadrangle, intrude the metasedimentary sequence and in turn also a a

a Trp Relief Peak Formation (Miocene)—Mainly lahars with porphyritic

Kmp c Kal di have been metamorphosed. This coarse-grained gabbro has a U/Pb The Grace Meadow lacks these metamorphic structures, at least on the mesoscopic Dodge, F.C.W., and Calk, L.C., 1987, Geologic map of the Lake Eleanor quadran-

c c 80 35 hornblende andesite clasts and some lava flows. Includes interbed-

80 zircon age of about 148 Ma (Lahren and others, 1990) scale. This implies a period of tectonism affected the above sequence just prior to gle, central Sierra Nevada, California: U.S. Geological Survey Geologic Quad-

a

25 c c

a

di a Qg a Kcp ded stream deposits. In quadrangles to the west and northwest, unit the Grace Meadow intrusion. rangle Map GQ–1639, scale 1:62,500.

a 35

a 40 Qal underlies Table Mountain Latite, whose K-Ar age is about 9.5 Ma METAMORPHIC ROCKS The alaskite of Grace Meadow has the geographic pattern of a sheath enclosing Giusso, J.R., 1981, Preliminary geologic map of the Sonora Pass 15-minute quad- c c 75 c 15 a 40 40

c (Dalrymple, 1964) mvb

di Qg Basaltic metavolcanic rocks (Cretaceous or older)—Basaltic and the northwest end of the Half Dome Granodiorite pluton, suggesting that the Half rangle, California: U.S. Geological Survey Open-File Report 81–1170, scale

c Qg c

a Tbb Basalt of Brown Bear Pass (Miocene)—Light- to dark-gray, massive andesitic metavolcanic rocks derived from lava flows and tuffs. Dome was emplaced by stoping the core of the Grace Meadow. The Grace Meadow 1:62,500.

a Includes associated dark metasedimentary rocks Huber, N.K., 1983, Preliminary geologic map of the Pinecrest quadrangle, central 50 basalt with vertical columnar jointing. Highly vesicular facies and has the peculiarity that although it is relatively uniformly leucocratic in color index, Khd c

Qg 55 a 65 Kgm purplish autobrecciated facies also present. Overlies Valley Springs mvr Rhyolitic metavolcanic rocks (Cretaceous or older)—Rhyolitic and it contains abundant, irregularly distributed, large and small inclusions of gabbro, Sierra Nevada, California: U.S. Geological Survey Miscellaneous Field Studies c

a

a a Formation, but relationship to Relief Peak Formation is unclear. diorite, and metasedimentary rocks, many large enough to show on the geologic Map MF–1437, scale 1:62,500.

a dacitic metavolcanic rocks derived from tuffs, some probably

a a Qg 85 di

c

75 85 a c

65 70 35 70 60 Unit has K-Ar ages of 19 to 20 Ma (Robinson and Kistler, 1986) ignimbrites. Includes metarhyolite breccia and possibly some map. These inclusions appear to define belts through the Grace Meadow that before Huber, N.K., Bateman, P.C., and Wahrhaftig, Clyde, 1989, Geologic map of Yosem- 50 a

a a a c

a a ite National Park and vicinity, California: U.S. Geological Survey Miscellane-

c 55 Tvs Valley Springs Formation (Miocene to Oligocene)—Rhyolite tuff, metamorphosed intrusive rocks the intrusion might have been largely metasedimentary or largely mafic intrusive 80 60 c

Kbl di a ms rocks. Although the contacts of the Grace Meadow with all older rocks are clearly ous Investigations Series Map I–1874, scale 1:125,000.

a c partly to densely welded, and bedded ash deposits. Locally includes Metasedimentary rocks (pre-Cretaceous)—Includes quartzite, marble,

55 a 50 a c 75 c

85 rhyolitic sedimentary deposits. Unit has K-Ar ages of 24 to 27 Ma biotite-andalusite schist, meta-conglomerate, and calc-silicate intrusive, suggesting magmatic stoping, the impression given by the abundant inclu- Kistler, R.W., 1973, Geologic map of the Hetch Hetchy Reservoir quadrangle,

65 msq a c a c Yosemite National Park, California: U.S. Geological Survey Geologic Quadran- a sions is one of relatively passive emplacement with little large-scale fluid flow a in Dardanelles Cone quadrangle to northwest (Robinson and Kistler,

c 85 hornfels. Predominate rock type indicated in local areas: msq,

a Qtl gle Map GQ–1112, scale 1:62,500.

a c Qal di 65 c 1986) msm commonly pure, white, crossbedded quartzite; msm, white to gray, within the pluton. Perhaps the magma was injected initially as a dike complex along

a 60 70 a

50 75 70 70 fractures in a shattered mafic and metamorphic complex, and the dikes simply wid- Lahren, M.M., 1989, Tectonic studies of the Sierra Nevada: structure and stratigra-

a

c a medium- to coarse-grained marble; msh, fine-grained calc-silicate

45 msh

c c PLUTONIC ROCKS phy of miogeoclinal rocks in Snow Lake pendant, Yosemite-Emigrant Wilder- a

c hornfels ened out to form the present pluton as the fragments of older rocks drifted apart and c c 55 Qal c a

c a 85 South and southwestern area downward. The inclusions also indicate that if the older plutons, such as the granite ness; and TIMS analysis of the northern Sierra terrane: Reno, NV, University of

c c 70

a 45 Klv Qg a c Nevada, Ph.D. dissertation, 260 p. 35 Kbl Granodiorite of Boundary Lake (Cretaceous)—Light-colored, Contact of Bond Pass and granite of Upper Twin Lake, were present where the Grace

a65 a Kmp c

75 a 70 c medium-grained biotite granodiorite and granite characterized by Meadow now is, they were completely dissolved in the new magma. Lahren, M.M., 1991, Snow Lake pendant, Yosemite-Emigrant Wilderness; Evidence Qal a

Fault

75 Qls a c discrete anhedral quartz grains. Locally porphyritic with varying The granodiorite of Long Canyon, in the northeast corner of the quadrangle, is a for a major strike-slip fault within the Sierra Nevada, California: California c 50 di c 45

a proportions of plagioclase and small tabular K-feldspar phenocrysts mafic granodiorite that intrudes metavolcanic rocks and is intruded in turn by the Geology, v. 44, p. 267–274.

a di Qal Qal Strike and dip of bedding

85 35 Kal Qg a Klv granodiorite of Fremont Lake. Its geographic position suggests that it might be an Lahren, M.M., and Schweickert, R.A., 1989, Proterozoic and Lower Cambrian mio- c a c 80 Granodiorite of Lake Vernon (Cretaceous)—Hornblende-biotite gran- 65 c c 85 Inclined a a a

Kbu di 70 odiorite characterized by bimodal grain-size distribution of mafic early mafic member of the Fremont Lake-Topaz Lake intrusive sequence, but it geoclinal rocks of the Snow Lake pendant, Yosemite-Emigrant Wilderness,

80 c Kmp Qg g

70 75 appears to have been affected by a period of deformation that predates the intrusion Sierra Nevada, California; Evidence for major Early Cretaceous dextral transla- c 80 a di minerals, with scattered grains 5 mm to 1 cm in size, and abundant c 55 Vertical a a i of the Fremont Lake. This deformation has produced boudinage of dikes and min- tion: Geology, v. 17, p. 156–160. c di a Kpm Qtl grains 1 mm in size and smaller, giving the rock a "spotted" appear-

c Khd Lahren, M.M., Schweickert, R.A., Mattinson, J.M., and Walker, J.D., 1990, Evi- a eral foliation at considerable angles to intrusive contacts. Hence the Long Canyon

80 a c Qg Kbu 60 ance. Contains numerous flattened mafic inclusions. Equivalent to Strike and dip of foliation

65 a a 75 a c c granodiorite of Tueeulala Falls of Dodge and Calk (1987), part of 65 pluton may be much older than the above intrusive sequence. dence of uppermost Proterozoic to Lower Cambrian miogeoclinal rocks and the a Inclined

a c 55 c a Mojave-Snow Lake fault; Snow Lake pendant, central Sierra Nevada, Califor-

70 c granodiorite of Boundary Lake of Huber (1983), and part of the The southeast branch of the L-shaped area of older rocks is dominated by the 80 Qg c 85 gg

80

80 a Vertical granite of Avonelle Lake, which contains abundant euhedral to subhedral, tabular- nia: Tectonics, v. 9, p. 1585–1608. a 80 65 quartz diorite of Mount Gibson of Kistler (1973) a

Qal c a c a c 70

a shaped K-feldspar phenocrysts as much as 3 cm in maximum dimension. The Avo- Robinson, A.C., and Kistler, R.W., 1986, Maps showing isotopic dating in the

Klv c 85 70 Kbu Granodiorite of Bearup Lake (Cretaceous)—Even-grained granodior- a

50 65 a Qtl nelle Lake pluton extends south into the Hetch Hetchy Reservoir quadrangle, where Walker Lake 1° by 2° quadrangle, California and Nevada: U.S. Geological Sur-

c

a 55 PREFACE

g g i 55 ite characterized by euhedral hornblende and biotite crystals and a

c 50 75 ms Klv di 55 it is probably equivalent to the granodiorite of Double Rock (Kistler, 1973). How- vey Miscellaneous Field Studies Map MF–1382–N, scale 1:250,000.

c di g55 Qal g70 with a wide range in mafic mineral content. Equivalent to part of Clyde Wahrhaftig mapped the geology of the Tower Peak quadrangle in great

c c

Qg Kmp detail (scale 1:24,000) over a period of many years from 1955 to 1980. For use in ever, difficulties in matching contacts and lithologic descriptions across the quadran- a c quartz diorite of Mount Gibson and part of granodiorite of Double

Klv 80

Qg g i

60 45 gle boundary make this correlation tentative and require a separate rock-unit name to 70 70 g g a

a a 45 c Qal Rock of Kistler (1973) preparing a geologic map of Yosemite National Park (Huber and others, 1989), he

75 75 35

Qal c a di c reduced and generalized his geology to a scale of 1:48,000. Clyde died before he avoid future confusion. The contact of the Avonelle Lake with the granite of Upper

Qalc Qala Quartz diorite of Mount Gibson (Cretaceous)—Dark-gray, pyroxene- 60

a 75 Twin Lake has given conflicting evidence for their relative ages, but there is a strong

c di a could complete a 1:62,500 version to match other published 15-minute geologic

Kmgf a g bearing quartz diorite, commonly with large poikilitic biotite crys-

a c Qg 60 i indication that the Upper Twin Lake is younger.

75 Kmgc Kbu a55 tals and locally with rare orbicules. Composed of two facies. The quadrangles in the park. Consequently, the present version was compiled by N. King a c The granite of Avonelle Lake is intruded on the northeast by two relatively Kmgc a Huber from materials left by Clyde and from geologic information from adjacent Kmgc 80 contact between the facies is sharp, with the coarse-grained facies 75 Klv Tr p Qal small plutons. The granite of Piute Mountain contains much more abundant, but Kbu Kt quadrangles. It is hoped that the result does not seriously compromise Clyde's inter- Kmgf 85 80 intruding the fine-grained facies Qg Qg c 75 smaller, flattened K-feldspar phenocrysts and has sharp intrusive contacts with a

80 di 45 Kmgc Coarse-grained facies pretations. Publication of the map was supported by a contribution from the Clyde a a a fine-grained gray selvage against the Avonelle Lake. The leucogranite of Ten Lakes a Wahrhaftig Trust. c INTERIOR—GEOLOGICAL SURVEY, RESTON RESTON, VA—2000 Kmgf Fine-grained facies (termed alaskite by Kistler, 1973, in the adjacent Hetch Hetchy Reservoir quadran- PLUTONIC AND METAMORPHIC ROCKS OF THE gle) is coarse grained and mottled by gray anhedral quartz crystals. Both of these Base from U.S. Geological Survey, 1956 SCALE 1:62 500 Geology by Clyde Wahrhaftig, 1955-80; compiled Kpm Granite of Piute Mountain (Cretaceous)—Light-pink to orange, TOWER PEAK QUADRANGLE latter plutons are intruded by rocks of the Tuolumne Intrusive Suite, part of the 10,000-foot grid based on California coordinate 1 1/2 012345 MILES by N. King Huber, 1998 medium- to coarse-grained granite containing abundant, closely younger group of plutons. system, zone 3 Edited by Jane S. Ciener; digital cartography by [The following text is from a draft prepared by Wahrhaftig and all of the interpretations are his. It has 1000-meter Universal Transverse Mercator grid On its southwest margin the granite of Avonelle Lake is intruded by a strongly 1 .501234567 KILOMETERS Hugh F. Thomas and Darlene A. Casebier packed, tabular microcline crystals been slightly rearranged and edited by N. King Huber.] ticks, zone 11 15° Kt Leucogranite of Ten Lakes (Cretaceous)—White, coarse-grained leu- foliated complex of leucogranite containing abundant diorite inclusions and cut by Manuscript approved for publication July 7, 1999 INTRODUCTION CONTOUR INTERVAL 80 FEET cogranite mottled by gray anhedral quartz crystals. Quartz, micro- unfoliated, fine-grained granite dikes and irregular masses. This complex is mapped NATIONAL GEODETIC VERTICAL DATUM OF 1929 cline, and plagioclase in equal proportions; mafic mineral content The Tower Peak quadrangle, which includes northernmost Yosemite National as the complex of Mahan Peak. It is continuous with the granodiorite of Rancheria about 4 percent Park, is located astride the glaciated crest of the central Sierra Nevada and covers an Mountain of Kistler (1973). The complex is clearly intruded by the granodiorite of CALIF exceptionally well-exposed part of the Sierra Nevada batholith. Granitic plutonic Lake Vernon (the "spotted rock"). Its contact relations with the quartz diorite of Mt. TRUE NORTH Kmp Complex of Mahan Peak (Cretaceous)—Strongly foliated and migma- MAGNETIC NORTH rocks of the batholith dominate the geology of the Tower Peak quadrangle, and at Gibson and the granodiorite of Bearup Lake are equivocal, but a locality near the APPROXIMATE MEAN titic complex of fine-grained leucogranite with abundant diorite DECLINATION, 2000 QUADRANGLE LOCATION least 18 separate pre-Tertiary intrusive events have been identified. trail from Jack Main Canyon (Paradise Valley) to Tiltill Mountain has inclusions of inclusions and cut by unfoliated, fine-grained granitic dikes and Pre-Cretaceous metamorphic rocks crop out in the quadrangle in isolated roof the Mahan Peak complex in the Mt. Gibson pluton. The simplest, but not completely irregular masses. Equivalent to part of granodiorite of Double Rock pendants and septa. Tertiary volcanic rocks cover granitic rocks in the northern part satisfactory, explanation for the Mahan Peak complex is that it represents granite of of Kistler (1973) GEOLOGIC MAP OF THE TOWER PEAK QUADRANGLE, Kal of the quadrangle, but are not considered in this brief summary. Potassium-argon (K- Avonelle Lake together with contained diorite dikes that were remobilized and Granite of Avonelle Lake (Cretaceous)—Coarse-grained biotite gran- Ar) age determinations for plutonic rocks in the quadrangle range from 83 to 96 mil- partly melted by the intrusion of the quartz diorite of Mt. Gibson, whose emplace- ite, commonly with abundant tabular phenocrysts of microcline as CENTRAL SIERRA NEVADA,CALIFORNIA lion years (Ma), including one of 86 Ma for the granodiorite of Lake Harriet (Robin- ment temperature would have been considerably higher than that of the granite of Any use of trade, product, or firm names in this publication is for much as 3 cm in maximum dimension. Equivalent to granodiorite of son and Kistler, 1986). However, a rubidium-strontium whole-rock isochron age of Avonelle Lake. descriptive purposes only and does not imply endorsement by the U.S. Government. Rancheria Mountain and part of granodiorite of Double Rock of 129 Ma has been obtained for the Lake Harriet pluton (Robinson and Kistler, 1986), By Kistler (1973) For sale by U.S. Geological Survey, Information Services, Box 25286, which field evidence indicates is the oldest plutonic body within the quadrangle. YOUNGER PLUTONIC ROCKS Federal Center, CO 80225, 1–800–ASK–USGS Clyde Wahrhaftig Northern area This suggests that some of the K-Ar ages record resetting during later thermal events The eastern composite intrusion of the younger group is the Tuolumne Intrusive Available on World Wide Web at http://geopubs.wr.usgs.gov/data.html Ktl Granodiorite of Topaz Lake (Cretaceous)—Light-gray, coarse-grained and are too young. The evidence indicates that all the plutonic rocks are of Creta- Suite. In the Tower Peak quadrangle, the Tuolumne Suite includes (1) the 2000 biotite granodiorite and granite with roughly equant, well-formed ceous age, with the youngest being the Cathedral Peak Granodiorite at about 83 Ma. northernmost and westernmost extent of the Cathedral Peak Granodiorite, which Printed on recycled paper