120°00' 1 19°45' 119°30' 119°15' 1 19°00' 

37°30' 

YOSEMITE NATIONAL PARK AND VICINITY -index map showing key localities and geographic features. 
_) 

7kG~S~-~ 

YOSEMITE 

NATIONAL PARK 
37°30' 

0 10 KILOMETERS 

Generalized from geologic map of Yosemite 

National Park and vicinity (Huber and others, 

in press) 

GEOLOGIC MAP OF YOSEMITE NATIONAL PARK AND VICINITY 
EXPLANATION 

D 

Alluvium and glacial till 

Shown only east of Sierran Crest 

and in Yosemite Valley 

Volcanic rocks 

Tuolumne Intrusive Suite 1 

Intrusive suite of Sonora Pass 

} QUATI'RNARY 

} TERTIARY 

Intrusive suite of Jack Main Canyon 

Intrusive suite of Washburn Lake 

CRETACEOUS 

Intrusive suite of Buena Vista Crest 

Intrusive suite of Merced Peak 

'"""'''' '"'i~mi<e Volley J 

Fine Gold Intrusive Suite 2 

Granitic rocks, unassigned to suites 

Diorite and gabbro 

Scheelite Intrusive Suite 

Mostly metamorphosed 

sedimentary rocks 

Mostly metamorphosed 

volcanic rocks 

Contact 

Fault 

Symbol on side that moved down 

1 An intrusive suite is a grouping of 

genetically related plutonic rocks 

2 Bateman (in press a) 

) 

CRETACEOUS 

AND JURASSIC 

} TRIASSIC 

1 MESOZOIC 

) 

} PALEOWIC 

GEOLOGIC MAPS OF YOSEMITE 

A geologic map shows the distribution of different 

types of rocks at the Earth's surface. Construction of 

such a map is usually prerequisite to understanding 

the geology of any given area. Geologic quadrangle 

maps at the same scale as topographic quadrangle 

maps of the U.S. Geological Survey's IS-minute 

series (l in. to l mi) currently are available for only a 

little more than half of the park area. Two other 

geologic maps are especially suitable to this volume 

because they show details of Yosemite geology not 

possible to show at the small scale of the geologic 

maps herein. A new geologic map of Yosemite 

National Park and vicinity, at a scale of l in. to about 

2 mi, has recently been compiled from both published and unpublished geologic mapping by many 

individuals (Huber and others, in press). A more 

detailed geologic map of Yosemite Valley is also 

available (Calkins and others, 1985). The fieldwork 

for this latter map was carried out by Frank Calkins 

between 1913 and 1916, but Calkins, the consummate 

perfectionist, was never completely satisfied with 

his map and would not let it be published during his 

lifetime. Though now belatedly published as a historical document, it is still the best geologic map of 

Yosemite Valley available. These two geologic maps, 

reduced and generalized, are the basis for the geologic maps in this volume (pls. l. 2). 

---------------------------------------------PLATEl 

c~oo) 

£ 

95 0 S E M I T E :e:~;tcr:~::si:; the natural processes 

that have created-

~~~~~~~~~~~~~~~~~~ and are still creating -

NAT I 0 N A L PARK thestunningterrain 

we know as Yosemzte 

B y N. K in g Huber 

U.S. GEOLOGICAL 
... · ... 

HALF DOME AT SUNSET 

"On the south-east stands the majestic Mount Tis-sa-ack, or 'South Dome' * * *. Almost one-half of this 

immense mass, either from some convulsion of nature, or 'Time's effacing fingers,' has fallen over* * *. 

Yet proudly, aye, defiantly erect, it still holds its noble head, and is not only the highest of all those around, 

but is the greatest attraction of the valley." - ]. M. Hutchings, "Scenes of Wonder and Curiosity in California," 1870. 
FOREWORD 

Within 150 years, Yosemite has moved from great obscurity to 

worldwide fame as one of the most visited of our national parks. As 

a remarkable place where people can enjoy unparalleled scenes of 

natural beauty and where many easily observed geologic features are 

concentrated, the park is rivaled by few other areas on the planet. 

The majesty and immense variety of these features have inspired 

artists and photographers, intrigued tourists, and stirred 

controversy among geologists. 

Field studies in the Yosemite area have contributed to the 

development of our ideas about geologic processes, including the 

different actions of streams and glaciers in the evolution of the 

landscape, and the formation of granite, the basic bedrock of much 

of the Earth's continents. The park's role as a natural laboratory for 

geologic research cannot be overemphasized, and its investigation 

has led to many landmark studies by U.S. Geological Survey 

geologists over the past 70 years. In 1913, the first detailed program 

of research on the geology of the park and the origin ofYosemite 

Valley was begun by Fran<;ois Matthes and Frank Calkins. Their 

work, along with that of later generations of Survey geologists, 

myself included, serves as the basis for our present understanding 

of the geologic history of Yosemite and of the processes that formed 

and continue to mold its landscape. 

This book, which makes available in one volume a comprehensive 

summary of the current geologic knowledge of Yosemite National 

Park, is an excellent example of the Survey's continuing effort to 

provide earth-science information in the public service. 

Dallas L. Peck 

Director, U.S. Geological Survey 
VIII 

CONTENTS 

Page 

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII 

Yosemite country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

• Creation of a park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

• Years of exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

A view from the top-Mount Hoffmann . . . . . . . . . . . . . . . . . . . . . 5 

Geologic overview ....................................... 10 

Rocks, the building materials .............................. 11 

• Granite, granite everywhere ........................... 11 

• Granitic rocks of Yosemite ............................. 17 

c Yosemite Valley area ............................. 18 

c Tuolumne Meadows area .......................... 19 

• Metamorphic rocks-ancient sediment and lavas .......... 22 

• Late Cenozoic volcanic rocks-born of fire ............... 23 

Genesis of Yosemite's rocks ................................ 26 

• A single quiet plate-the Paleozoic ..................... 26 

• A time of fire and upheaval-the Mesozoic . . . . . . . . . . . . . . . 26 

• The Sierra grows again-the late Cenozoic . . . . . . . . . . . . . . . 2 7 

Final evolution of the landscape ............................ 30 

• The role of joints .................................... 30 

• Weathering and erosion ............................... 36 

c Influence of the rocks on weathering ................ 36 

c Agents of erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

·The role of flowing water ...................... 39 

· The role of glaciers .......................... 40 

Glacial erosion .......................... 41 

Glacial deposition ....................... 44 

• The record of Pleistocene glaciation ..................... 45 

• The glacial geology of Yosemite ........................ 46 

• What the glaciers missed .............................. 52 

• Modern glaciers ..................................... 54 

• After the glaciers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 
Page 

Definition of terms ....................................... 58 

References and additional reading .......................... 60 

• History ............................................ 60 

• Geology ........................................... 60 

• Geologic maps ...................................... 61 

A word of thanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 

Index ................................................. 64 

Special topics :: 

Geologic maps of Yosemite ................................ III 

Common minerals in granite ............................... 10 

Classification of plutonic rocks ............................. 12 

Plate tectonics-a dynamic globe .......................... 24 

IX 
ILLUSTRATIONS 

Page 

Frontispiece. Half Dome at sunset 

PLATE 1. Geologic map of Yosemite National Park and vicinity . . . . . . . . . . . . . . . . . . . . . . II 

2. Geologic map of the Yosemite Valley area ................................ 66 

FtGURE 1. Yosemite National Park area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

2. The Sierra Nevada, an asymmetric mountain range . . . . . . . . . . . . . . . . . . . . . . . . 2 

3. Summit of Mount Hoffmann, with Charles F. Hoffmann at the transit . . . . . . . . . 3 

4. Views from Mount Hoffmann .......................................... 4 

5. Panorama from Mount Hoffmann ...................................... 6 

6. Physiographic diagram of Yosemite National Park . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

7. Geologic time scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

8. Hornblende and biotite crystals ........................................ 10 

9. Plutonic-rock classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

10. El Capitan Granite .................................................. 13 

11. Varieties of granodiorite .............................................. 14 

12. Diorite ............................................................ 14 

13. Dike of aplite crosscutting granodiorite .................................. 15 

14. Porphyritic texture in the Cathedral Peak Granodiorite ..................... 15 

15. Aligned dark inclusions in granodiorite .................................. 16 

16. Schlieren, layered concentrations of dark minerals ......................... 16 

17. Features that determine the relative ages of plutonic rocks ................... 17 

18. Bird's-eye view of Yosemite Valley ...................................... 18 

19. Diorite dikes on the face of El Capitan .................................. 19 

20. Evolution of the Tuolumne Intrusive Suite ............................... 20 

21. Johnson Granite Porphyry ............................................ 21 

22. Final stages in the evolution of the Tuolumne Intrusive Suite ................ 21 

23. Contorted chert beds along the M~rced River ............................ 22 

24. Metamorphic rocks with relict sedimentary bedding ........................ 23 

25. Interior of the Earth ................................................. 24 

26. Major plates of the world today ........................................ 25 

27. Three principle kinds of plate motion ................................... 25 

28. Oceanic plate subducted beneath continental plate ........................ 2 7 

29. Uplift and tilt of the Sierran block ..................................... 28 

30. Ancient channel of the Tuolumne River ................................. 29 

31. Volcanic mudtlow deposit ............................................. 29 

32. Columnar joints in basalt at the "Little Devils Postpile" ..................... 29 

33. Regional joints shown on aerial photograph .............................. 30 

34. Inclined joints determine the slope of Three Brothers ...................... 31 

35. Staircase Falls follow inclined joints .................................... 31 

36. Rectangular blocks formed in the EI Capitan Granite ....................... 32 

37. The Rockslides and El Capitan ........................................ 32 

38. Bold exposure of the Half Dome Grandiorite beneath Glacier Point ........... 33 

39. Progressive rounding of massive granite by exfoliation ...................... 34 

40. Sheet joints follow topographic surfaces .................................. 34 

X 
Page 

41. Undulating surface below Clouds Rest ................................... 35 

42. Royal Arches, a gigantic expression of sheet jointing ....................... 35 

43. Weathering of joint blocks and formation of corestones ..................... 36 

44. Spheroidal weathering around corestones ................................. 36 

45. Weather pans formed on the summit of North Dome ....................... 37 

46. Resistant potassium feldspar phenocrysts ................................. 3 7 

4 7. Knobs of resistant diorite protrude from weathered rock surface ............... 38 

48. Natural bridge formed from resistant aplite ............................... 38 

49. Rockfall that blocked the El Portal Road ................................. 38 

50. Deeply incised canyon of the Merced River .............................. 39 

51. Uplift and stream incision over time .................................... 39 

52. Maclure Glacier, showing annual layers of ice accumulation ................. 40 

53. Valley glacier, showing accumulation and wastage areas. . ................... 40 

54. Roche moutonnee, showing the influence of jointing on its development ....... 41 

55. Imprints on the rock left by passing debris-laden ice ....................... 41 

56. Mountain crest, showing glacial sculpture ................................ 42 

57. Jagged unglaciated spires of Unicorn Peak ................................ 43 

58. Valley modification by glacial erosion ................................... 42 

59. Bridalveil Fall, issuing from a hanging valley .............................. 43 

60. Glacial till, an unsorted mixture of debris ................................ 44 

61. Glacial erratic left behind as the ice melted .............................. 44 

62. Moraines formed by valley glacier ...................................... 45 

63. Moraines in Lee Vining Canyon ....................................... 45 

64. Tioga moraine with sharp crest and abundant boulders ..................... 46 

65. Tahoe moraine with subdued crest and scattered boulders ................... 46 

66. Perched erratic from pre-Tahoe glaciation ................................ 4 7 

67. Tioga icefield and valley glaciers ....................................... 47 

68. U-shaped glaciated valley ............................................. 48 

69. Glacial polish high on Fairview Dome. . ................................. 49 

70. Pothole Dome, a large roche moutonnee ................................. 49 

71. Potholes angling up the side of Pothole Dome ............................. 49 

72. Subglacial water polish on Pothole Dome ................................ 49 

73. Kettles, small lake-filled depressions .................................... SO 

74. Glacial moraines in Yosemite Valley .................................... 51 

75. Glaciers come and go in the Yosemite Valley area .......................... 51 

76. Pre-Tahoe glaciation, its extent in the Yosemite Valley area .................. 52 

77. Dana Plateau, unglaciated remnant of an ancient land surface ................ 53 

78. Boulder-strewn upland surface on Dana Plateau ........................... 53 

79. West shoulder of Mount Hoffmann ..................................... 54 

80. Lyell and Maclure Glaciers, 1972 ....................................... 55 

81. Lyell and Maclure Glaciers, 1883 ....................................... 55 

82. Dana Glacier, 1975 .................................................. 56 

83. Dana Glacier, 1908 .................................................. 56 

84. Avalanche chutes and talus cones in Lee Vining Canyon .................... 57 

85. The Slide on Slide Mountain .......................................... 57 

XI 

-rkG~~~-~ 

YOSEMITE 

NATIONAL PAR K 

By N. King Huber 

YOSEMITE COUNTRY 

CREATION OF A PARK 

For its towering cliffs, spectacular waterfalls, granite 

domes and spires, glacially polished rock, and groves of 

Big Trees, Yosemite is world famous. Nowhere else are 

all these exceptional features so well displayed and so 

easily accessible. Artists, writers, tourists, and 

geologists have flocked to Yosemite- and marveled. 

120°00' , 19°00' 

Although there are other valleys with similarities to 

Yosemite, there is but one Yosemite Valley, the "Incomparable Valley" of John Muir. Appreciation of Yosemite 

Valley came early, and in 1864, less than 15 years after 

the general public became aware of the area's existence, 

President Abraham Lincoln signed a bill that granted 

Yosemite Valley- "the 'Cleft' or 'Gorge' in the granite 

peak of the Sierra Nevada"- to the State of California. 

The act stipulated that "the premises shall be held for 

public use, resort, and recreation; shall be inalienable 

for all time." Also included in the grant was the 

"Mariposa Big Tree Grove." Though not the first 

official national park, Yosemite established the 

national-park concept and eventually evolved into a 

national park itself. An area larger than the present 

park, surrounding but not including Yosemite Valley, 

was set aside as a national park in 1890. In 1906, the 

boundaries were adjusted, and Yosemite Valley and the 

Mariposa Grove were re-ceded to the Federal Government by California to create a unified national park 

(fig. 1). 

YEARS OF EXPLORATION 

From the earliest days, the Sierra Nevada (Spanish 

for "snowy mountain range") was a formidable barrier 

to westward exploration (fig. 2). Running half the 

length of California, it is the longest, the highest, and 

the grandest continuous mountain range in the United 

YOSEMITE NATIONAL PARK and the original grants to 

the State of California. (Fig. 1) 

1 
THE SIERRA NEVADA, a strongly 

asymmetric mountain range with a steep east 

escarpment and a gentle westward slope 

toward the broad Central Valley of California. Physiography from landform map by 

Erwin Raisz; used with permission. 

(Fig. 2) 

States, outside of Alaska. The central Sierra with its 

steep east escarpment is particularly awesome. Nevertheless, in 1833, Joseph Walker led a party up the 

east escarpment and westward across the range through 

Yosemite country. His route traversed the upland 

between the Tuolumne and Merced Rivers, a route 

later followed by the western part of the Tioga Road. 

Walker and his men were probably the first of European 

descent to view Yosemite Valley and the Big Trees, now 

known as giant sequoias. 

The Walker party's journal, recorded by Zenas 

Leonard, refers to "many small streams which would 

shoot out from under these high snow-banks, and after 

running a short distance in deep chasms which they 

have through ages cut in the rocks, precipitate themselves from one lofty precipice to another, until they 

are exhausted in rain below. Some of these precipices 

appear to be more than a mile high. • • • we found it 

utterly impossible to descend, to say nothing of the 

2 

horses. [Continuing westward] • • • we have found 

some trees of the redwood species, incredibly largesome of which would measure from 16 to 18 fathoms 

[96 to 108 ft] around the trunk at the height of a man's 

head from the ground." The trees Leonard described 

could be those either of the Tuolumne Grove or of the 

Merced Grove, possibly both. The journal was printed 

in Pennsylvania in 1839, but only a few copies survived 

a printshop fire, and so this account went unread for 

many years. 

Yosemite Valley and the giant sequoias remained 

unknown to the world at large for nearly another 20 

years after the Walker party's discovery, until Maj. 

James Savage and the Mariposa Battalion of militia 

entered the valley in pursuit of Indians in 1851. Overwhelmed by the majesty of the valley, one member of 

the battalion, Dr. Lafayette Bunnell, remarked that it 

needed an appropriate name. He suggested Yo-sem-i-ty, 

the name of the Indian tribe that inhabited it, and also 
the Indian word for grizzly bear. A year later, giant 

sequoias were discovered anew in the Mariposa Grove 

and in the Calaveras Grove north of Yosemite. 

The history of further exploration of the Yosemite 

area, and of the creation of the park itself, were well 

described by Carl P. Russell (1957). Of particular 

geologic interest was the excursion of the Geological 

Survey of California to Yosemite in 1863. After visiting 

Yosemite Valley, Josiah Whitney, the Director of the 

Survey, accompanied by William Brewer and Charles 

Hoffmann, explored the headwaters of the Tuolumne 

River and named Mounts Dana, Lyell, and Maclure for 

famous geologists and Mount Hoffmann for one of their 

own party. In 1867, another party from the Geological 

Survey of California again ascended Mount Hoffmann, 

accompanied by photographer W. Harris, who documented the scene with Hoffmann himself at the transit 

(fig. 3). Observations from these excursions, and additional topographic mapping by Geological Survey of 

California colleagues Clarence King and James Gardiner, provided the first description of Yosemite Valley 

and the High Sierra that not only contained reasonably 

accurate topographic information but also was relatively 

free from the romantic exaggeration characteristic of 

the times. The term "High Sierra," coined by Whitney 

to include the higher region of the Sierra Nevada, 

much of it above timberline, has been used by writers 

and hikers ever since. Whitney and his party recognized abundant evidence for past glaciation in the High 

Sierra but failed to recognize the degree to which 

glaciers had modified the topography, and Whitney 

SUMMIT OF MOUNT 

HOFFMANN. Charles F. 

Hoffmann, cartographer with the 

Geological Survey of California, at 

the transit. Photograph by W. Harris, 1867; first published in ].D. 

Whitney's "The Yosemite Book" 

in 1868. (Fig. 3) 

ascribed the ongm of Yosemite Valley to a "grand 

cataclysm" in which the bottom simply dropped down. 

Indeed, most geologic processes were poorly understood in Whitney's day, and so numerous conflicting 

interpretations soon developed regarding the origin of 

many of Yosemite's scenic features. The controversy 

that arose between Josiah Whitney and John Muir 

regarding the origin of Yosemite Valley reflects this 

situation. Muir's observations in the Yosemite Sierra led 

him to propose that Yosemite Valley was entirely carved 

by a glacier. However, he overestimated both the work 

of glaciers and the extent of glaciation, because he 

believed that ice once completely covered the Sierra to 

the Central Valley and beyond. Thus, Whitney and 

Muir held opposing views that were both too extreme, 

although Muir's ultimately proved more durable. Finally, 

partly in response to this controversy, a study of the 

geology of the Yosemite area was initiated in 1913 by 

the U.S. Geological Survey, with Fran<;ois E. Matthes 

studying the geomorphology and glacial geology and 

Frank C. Calkins the bedrock geology. Matthes' conclusions, particularly with respect to the relative roles 

of rivers and glaciers in sculpting the landscape, have 

held up well, and his lucid descriptions and interpretations have enlightened many a park visitor. In the 50-

odd years since Matthes and Calkins completed their 

studies, we have gained considerably more geologic 

knowledge of the Sierra Nevada; we have abandoned 

some of their ideas, but we still build on their pioneering efforts. 

3 
VIEWS FROM MOUNT HOFFMANN. A, Westerly 

view down wooded slopes toward California's Central Valley. B, 

Northerly view including snow-patched Sawtooth Ridge and 

Matterhorn Peak on Skyline at north edge of the park. Photograph by Tau Rho Alpha. C, Easterly view, with May Lake in 

foreground and Tenaya Lake to right in middle distance. 

A 

4 

Tuolumne Meadows is in wooded area to left, and Mount Dana is 

highest summit on skyline beyond. D, Southerly view toward 

Clouds Rest in late spring, with Mount Clark on left skyline. Half 

Dome at far right center displays its northeast shoulder, in contrast 

to its oft-pictured profile from Yosemite Valley's floor. Photograph 

from National Park Service collection. (Fig. 4) 

B 

D 
A VIEW FROM THE TOPMOUNT HOFFMANN 

Of Mount Hoffmann, William Brewer noted in his 

journal under the date June 24, 1863, that "It commanded a sublime view and the scene is one to be 

remembered for a lifetime." In his tum, Josiah Whitney 

stated that "The view from the summit of Mount 

Hoffmann is remarkably fine." 

The view from Mount Hoffmann is, indeed, 

remarkably fine. This peak is in almost the exact center 

of Yosemite Park (fig. 4 ), and from its 10,850-ft summit 

we can see much of the perimeter of the park, for much 

of that perimeter consists of high ridges. 

Looking westward from Mount Hoffmann, we see 

timbered foothills disappearing into the haze of the 

Central Valley of California. As we shift our view 

northward, we see the smooth contours of the foothills 

give way along the skyline to pointed and jagged peaks 

of bare rock in shades of white, red, and gray. A lakestrewn cirque, which fed the Hoffmann Glacier that 

moved down Yosemite Creek, forms the precipitous 

north face of Mount Hoffmann itsel£ 

To the east, May Lake-named for Hoffmann's 

wife-is directly below and Tenaya Lake is in the 

middle distance, surrounded by sheeted granite walls, 

5 
Whorl · Mountain · 

which lead to a series of monolithic granite domes 

between Tenaya Lake and Tuolumne Meadows-domes 

that are among the most striking features of the 

Yosemite landscape. On the eastern segment of the 

skyline rise the highest peaks in the park: Conness, 

Dana, Gibbs, Koip, and Lyell-all but Gibbs with 

living glaciers. The vista to the south past Clouds Rest, 

Half Dome, and Yosemite Valley has the Clark Range 

and Buena Vista Crest as the skyline backdrop. From 

Mount Hoffmann we see the northeast shoulder of Half 

Dome, a striking contrast to the view from Yosemite 

Valley (figs. 5, 6). 

The scenic panorama from Mount Hoffmann is a 

grand introduction to much of the geology of Yosemite. 

The landforms of Yosemite, like landforms everywhere, 

reflect the type, structure, and erosional history of the 

underlying rocks. The different colors- white, red, 

shades of gray-reflect different rock types. The different topographic shapes- spires, domes, cliffsreflect different rock structures and erosional histories, 

especially erosion caused by glaciers. In discussing "how 

best to spend one's Yosemite time," John Muir suggested 

"go straight to Mount Hoffmann. From the summit 

nearly all the Yosemite Park is displayed like a map." 

For those who wish to take his advice, the summit is 

about 3 mi from the trailhead south of May Lake, and 

the elevation gain is about 2,000 ft. 

The landscape we see today is largely the result of 

geologic processes operating in the past few tens of 

millions of years on the parent rock. But to gain a full 

understanding of the present landscape, we must go 

back many tens of millions of years more-to the 

creation of the rocks themselves. Fragments of geologic 

history going back hundreds of millions of years can be 

read from the rocks of the park, and with additional 

data from elsewhere in the Sierra Nevada and beyond, 

we can reconstruct much of the geologic story of 

Yosemite. After more than a hundred years of study, 

the story is still incomplete. But then, geologic stories 

are seldom complete, and what we do know whets our 

curiosity about the missing pieces and allows a deeper 

appreciation for one of our most spectacular national 

parks. This volume is an attempt to describe the 

geology of Yosemite and to explain how this splendid 

landscape, centered on Mount Hoffmann, came into 

being. 

PANORAMA FROM MOUNT HOFFMANN, encompassing an easterly-facing arc between Whorl Mountain on left and Half 

Dome on right. (Fig. S) 

6 
Mt Gibbs 

N 

l 

PHYSIOGRAPHIC DIAGRAM of 

Yosemite National Park and vicinity. Red 

dot, centrally located Mount Hoffmann. 

(Fig. 6) 

Direction of view from Mount Hoffmann 

for panorama . (Fig. 5) 

Koip Peak 

Johnson Peakl 

Unicorn Peak Cockscomb 

Lower 

Blacktop 

Peak 

Donohue 

Rafferty Peak 

Peak 

Cathedral Peak Cathedral Lake 

7 

Mt Lyell 

Simmons Peak 1 

Vogelsang Peak 

Mt Maclure 

Mt Ansel Adams 

Mt Florence 

Post Peak 

Vertical scale ts 

twtce the left-nght 

horiZontal scale 

Divide Peak 

Gray Peak 

Mt Clark Buena Vista Crest 

Clouds Rest 

Buena VIsta Peak 

Mt 

Starr 

King 

Horse Ridge 

8 
8 
Early man ~~~~~~~----- ~~~~oloc ~~-, Pleistocene J Multiple glaciations 

PRECAMBRIAN 

Emplacement of granite 

and formation of ancestral 

Sierra Nevada 

~ 

Deposition of sediment in 

sea adjacent to continent 

Oldest rocks in the 

Yosemite area 

Beginning of the Earth 

THE GEOLOGIC TIME SCALE-the "calendar" used by 

geologists in interpreting Earth history. Column A, graduated in 

billions of years (b.y.) and subdivided into the four major geologic 

eras (Precambrian, for example), represents the time elapsed since 

the beginning of the Earth, which is believed to have been about 

4.5 b.y. ago. Column B is an expansion of part of the time scale in 

millions of years (m.y.), to show the subdivisions (periodsCambrian, for example) of the Paleozoic, Mesozoic, and 

Cenozoic Eras; column C is a further expansion to show particularly the subdivisions (epochs- Paleocene, for example) of the 

Tertiary and Quaternary Periods. Some key events in the geologic 

history of Yosemite National Park are listed alongside the columns, opposite the time intervals in which they occurred. 

The subdivisions of geologic time are based largely on the fossil 

~ THIS PAGE FOLDS OUT 

Pliocene 

Miocene 

Oligocene 

Eocene 

c 

Mountain uplift and can· 

yon cutting creates present 

Sierra Nevada with great 

topographi c relief 

Erosion reduces ancestral Sierra Nevada to 

rolling upland with low 

topographic relief 

Emplacement of youngest 

granite 

record; rocks of the Cambrian Period contain the earliest evidence 

of complex forms of life, which evolved through subsequent periods 

into the life of the modern world. The ages (in years) are based on 

radiometric dating. Many rocks contain radioactive elements that 

begin to decay at a very slow but measurable rate as soon as the 

parent rock is formed. The most common radioactive elements are 

uranium, rubidium, and potassium, and their decay ("daughter") 

products are lead, strontium, and argon, respectively. By measuring both the amount of a given daughter product and the amount of 

the original radioactive element still remaining in the parent rock, 

and then relating these measurements to the known rates of radioactive decay, the age of the rock in actual numbers of years can be 

calculated. (Fig. 7) 

9 
GEOLOGIC OVERVIEW 

Topographically, the Sierra Nevada is an asymmetric 

mountain range with a long, gentle west slope and a 

short, steep east escarpment that culminates in the 

highest peaks (fig. 2). It is 50 to 80 mi wide and 

extends in altitude from near sea level along its west 

edge to more than 13,000 ft along the crest in the 

Yosemite area. Geologically, the Sierra Nevada is a 

huge block of the Earth's crust that has broken free on 

the east along a bounding fault system and has been 

uplifted and tilted westward. This combination of uplift 

and tilt, which is the underlying geologic process that 

created the present range, is still going on today. 

Massive granite dominates the Yosemite area and 

much of the Sierra Nevada as well. Mount Hoffmann 

and most of the terrane visible from it are composed of 

granite, formed deep within the Earth by solidification 

of formerly molten rock material and subsequently 

exposed by erosion of the overlying rocks. Because of its 

massiveness and durability, granite is shaped into bold 

forms: the cliffs of Yosemite and Hetch Hetchy Valleys, 

Five minerals compose the bulk of the plutonic 

rocks of Yosemite: quartz, potassium feldspar, plagioclase feldspar, biotite, and hornblende. Quartz 

and both varieties of feldspar are translucent and 

appear light gray on fresh surfaces. On a weathered 

surface, the feldspars turn chalky white, whereas 

the quartz remains clear gray. Feldspar crystals have 

good cleavage, a property of breaking along planar 

surfaces that reflect sunlight when properly oriented; quartz has no cleavage but breaks randomly 

along curved surfaces. Biotite crystals commonly 

appear hexagonal. and their dark. brown to black 

plates can be split with a knife into thin flakes along 

one perfect cleavage direction (fig. 8). Hornblende is 

much harder than biotite, appears very dark green to 

almost black, and commonly occurs as elongate, 

rod-shaped crystals. It has good cleavages in two 

directions that intersect to form fine striations along 

the length of the rods, making them look like bits of 

charcoal. Other minerals are present in small 

amounts; the most distinctive is sphene (calcium and 

titanium silicate), which occurs in small, amber, 

wedge-shaped crystals. With a little practice, all 

these minerals can be identified with a small magnifying glass. 

10 

many of the higher peaks in the park, and the striking 

sheeted domes that can form only in massive, unlayered 

rock. Although granite dominates nearly the entire 

length of the Sierra, the granite is not monolithic. 

Instead, it is a composite of hundreds of smaller bodies 

of granitic rock that, as magma (molten material), 

individually intruded one another over a timespan of 

more than 100 million years (fig. 7). This multiplicity 

of intrusions is one of the reasons why there are so 

many varieties of granitic rock in Yosemite and the rest 

of the Sierra. The differences are not always apparent 

to the casual observer, but they are reflected in sometimes subi:le differences in appearance and in differences in response to weathering and erosion acting 

on the rocks. 

Layered metamorphic rocks in the foothills at the 

west edge of the park and along the eastern margin in 

the summit area are remnants of ancient sedimentary 

and volcanic rocks that were deformed and metamorphosed in part by the invading granitic intrusions. 

Other metamorphic rocks that once formed the roof 

beneath which the granitic rocks solidified were long 

ago eroded away to expose the granitic core of the 

range, and only small isolated remnants are left. 

COMMON MINERALS 

IN GRANITE 

~' ••• 

·-

• • • • 

HORNBLENDE AND BIOTITE. Rod-shaped crystals of 

hornblende and hexagonal crystals of biotite. These large and 

exceptionally well formed crystals are from Half Dome Granodiorite. (Fig. 8) 
Because Yosemite is centered on this deeply dissected 

body of granite, metamorphic rocks are sparse; they 

occupy less than 5 percent of the area of the park. 

Evolution of the landscape is as much a part of the 

geologic story as the rocks themselves, and Yosemite is 

a place where the dynamism of geologic processes is 

well displayed. By the end of Cretaceous time (see fig. 

7), about 65 million years ago, after the granite core of 

the range had been exposed, the area had a low relief 

in comparison with the mountains of today. Then, 

about 25 million years ago, this lowland area began to 

be uplifted and tilted toward the southwest, a construction that would eventually lead to the present 

Sierra Nevada. As the rate and degree of southwestward tilt increased, the gradients of streams flowing 

southwestward to California's Central Valley also 

increased, and the faster flowing streams cut deeper and 

deeper canyons into the mountain block. About 10 

million years ago, from the Tuolumne River northward, 

. these canyons were inundated and buried by volcanic 

lava flows and mudflows, and the streams were forced to 

begin their downcutting anew, in may places shifting 

laterally to find a new route to the Central Valley. The 

streams were equal to the task, however, and the 

present river courses and drainage patterns throughout 

the Sierra became well established. 

As the world grew colder, beginning about 2 or 3 

million years ago, the Sierra Nevada had risen high 

enough for glaciers and a mountain icefield to form 

periodically along the range crest. When extensive, the 

icefield covered much of the higher Yosemite area and 

sent glaciers down many of the valleys. Glacial ice 

quarried loose and transported vast volumes of rubble, 

and used it to help scour and modify the landscape. 

Much of this debris eventually accumulated along the 

margins of the glaciers and in widely distributed, hummocky piles. The greatest bulk of this debris, however, 

was flushed out of the Sierra to the Central Valley by 

streams swollen with meltwater formerly stored in the 

glaciers as ice and released as the glaciers melted away. 

Although many of today's general landforms existed 

before modification by glacial action, some of them 

surely did not. Can you imagine the Yosemite landscape with no lakes? Virtually all the innumerable 

natural lakes in the park are the result of glacial 

activity. But even these lakes are transitory, doomed to 

be filled with sediment and become meadows; many 

lakes already have undergone this transformation. 

Yosemite Valley itself once contained a lake. 

The geologic story of Yosemite National Park can be 

considered in two parts: ( 1) deposition and deformation 

of the metamorphic rocks and emplacement of the 

granitic rocks during the Paleozoic and Mesozoic; and 

(2) later uplift, erosion, and glaciation of the rocks 

during the Cenozoic to form today's landscape. 

The paragraphs that follow start with a description of 

the rocks-what can be seen on excursions through the 

park-granite first and in the most detail, because it 

dominates the Yosemite scene. The rocks will then be 

fitted into the context of a geologic history through 

which today's Yosemite evolved. 

ROCKS, THE BUILDING 

MATERIALS 

Yosemite is renowned for its magnificent rock 

exposures. Although granitic rocks dominate the 

Yosemite scene, various metamorphic and volcanic 

rocks are also present. Together, these rocks form 

Yosemite's foundation. 

GRANITE, GRANITE EVERYWHERE 

Granite, in the broad sense of the term, is a massive 

rock with a salt-and-pepper appearance due to random 

distribution of light and dark minerals. The mineral 

grains are coarse enough to be individually visible to 

the naked eye. 

Granite is a plutonic igneous rock. There are two 

types of igneous rock-plutonic and volcanic. Both 

types result from the cooling and solidification of molten rock, or magma. Magma originates deep within 

the Earth and rises toward the Earth's surface at 

temperatures of about 1,000 °C if granitic in composition and of as high as 1,200 °C if basaltic-by 

comparison, steel melts at about 1,430 oc. Magma 

that cools and solidifies within the Earth's crust forms 

plutonic rock (named for Pluto, the Roman god of 

the underworld). The slow cooling of plutonic 

magma fosters the growth of individual crystals visible to the naked eye. In contrast, magma that erupts 

at the Earth's surface, where it is known as lava, 

quickly cools into volcanic rock. Thus, having insufficient time to grow, most mineral grains in volcanic 

rock are so small that a microscope is needed to 

distinguish them. 

The plutonic terrane in the Sierra, once thought 

simply to represent local variations in one huge mass 

11 
12 

100 PERCENT 

QUARTZ 

1 00 PERCENT 100 PERCENT 

POTASSIUM FELDSPAR PLAGIOCLA SE 

CLASSIFICATION COMPONENTS 

QUARTZ 

POTASSIUM FELDSPAR 

QUARTZ 

PLAGIOCLASE 

PLUTONIC-ROCK CLASSIFICATION, showing classification components, the formerly used system, and the one now 

used worldwide. Red area indicates general range in composition 

of plutonic rocks, exclusive of dikes and other small bodies, in the 

Yosemite area; names for rock types not occurring in the area are 

omitted. Star in center of triangle indicates composition of a rock 

containing equal proportions of quartz, potassium feldspar, and 

plagioclase. (Fig. 9) 

POTASSIUM FELDSPAR PLAGIOCLASE 

FORMER CLASSIFICATION SYSTEM 

-CLASSIFICATION OF PLUTONIC ROCKSNames for the more common varieties of plutonic 

rocks are based on the relative proportions of quartz, 

potassium feldspar. and plagioclase, as plotted on a 

triangular diagram, with each corner representing 

100 percent of that constituent (fig. 9); other minerals 

present are ignored. The greater the percentage of 

any one of these three minerals in the rock, the 

closer the rock's composition would plot to the corner 

for that mineral. A rock with equal percentages of 

the three minerals would plot in the center of the 

diagram (*), and the rock would be called a granite. 

Increasing the percentage of plagioclase at the 

expense of potassium feldspar would move the composition toward the granodiorite compartment on the 

triangular diagram. "Granitic rocks" are those that 

lie within the heavy-lined boundary. 

The rock classification used in this volume was 

adopted by an international commission in 1972 and 

is now used worldwide. This classification differs 

from the one previously in use and thus results in 

many contradictions with the rock names in earlier 

geologic writings on the Sierra Nevada. Nearly all 

the granitic rocks in the Sierra previously called 

quartz monzonite fall within the granite classification of the present system, and quartz monzonite is 

relegated to a small compartment below granite on 

the triangular diagram; the old system is shown for 

comparison. In some cases, rocks previously called 

quartz monzonite are now called granodiorite 

because of better know ledge of their actual mineral 

composition. 
of granite, is actually made up of many individual 

bodies of plutonic rock- plutons-that formed from 

repeated intrusions of magma into older host rocks 

beneath the surface of the Earth. These plutonic 

rocks, formerly deep within the Earth, are now 

exposed at the surface, owing to deep erosion and 

removal of the formerly overlying rocks; they form 

the monoliths and domes of Yosemite within the 

lofty Sierra Nevada. 

The collection of plutons in the park is part of a 

larger mass of plutonic rock called the Sierra Nevada 

batholith (from the Greek words bathos, deep, and 

lithos, rock). Although this large mass of granite 

forms the bedrock of much of the Sierra Nevada, it is 

different from the range itself and originated many 

tens of millions of years before uplift, weathering, 

and erosion shaped the present range. It needs to be 

emphasized that the batholith is composite, a fact 

not perceived by the earliest geologic studies. Distinguishing between individual plutons that represent 

separate episodes of intrusion and solidification of 

magma is the key to understanding the origin and 

complex geologic history of the batholith. Geologists 

have mapped more than a hundred discrete masses of 

plutonic rock in the vicinity of Yosemite National 

Park alone, attesting to the complexity of what was 

once thought to be a relatively simple batholithic 

setting. Emplacement of the Sierra Nevada batholith 

at depth may have taken as long as 130 million years. 

Five minerals compose the bulk of the plutonic 

rocks of the batholith: quartz, two varieties of feldspar (potassium feldspar and plagioclase), biotite, and 

hornblende. All contain the elements silicon and 

oxygen, and all except quartz contain aluminum as 

well. Other constituents of the feldspars include 

potassium, sodium, and calcium; greenish-black 

hornblende and the black mica, biotite, also contain 

magnesium and iron. The section on common minerals in granite provides clues on how to identify 

these minerals. 

Plutonic rocks consisting chiefly of quartz and feldspar, with only a minor amount of dark minerals, are 

loosely called granitic rocks. Granitic rocks, such as 

granite, granodiorite, and tonalite, differ primarily in 

the relative proportions of these minerals (fig. 9). For 

example, granite, in the technical sense of the term, 

contains much quartz and both potassium feldspar and 

calcium-rich feldspar (plagioclase). In outcrop, it is 

generally difficult to distinguish the relative percentages 

of potassium feldspar and plagioclase. In the laboratory, 

the feldspars can be distinguished by applying chemicals 

that stain potassium feldspar yellow, plagioclase red, 

and leave quartz uncolored (fig. 10). By this means, the 

relative percentages of the three minerals can be determined easily. 

Granodiorite (fig. 11) is similar to granite but contains about twice as much plagioclase as potassium 

feldspar. Tonalite contains even less potassium feldspar. 

In addition to quartz and feldspar, dark minerals, such 

as hornblende and biotite, further characterize individual plutonic-rock types, as is commonly indicated with 

modified names, such as hornblende granodiorite and 

biotite granodiorite. Dark minerals are generally more 

abundant where potassium feldspar is scarce, and thus 

granodiorite tends to be darker than granite, and most 

tonalite even darker. 

A 

B 

EL CAPITAN GRANITE. A, Freshly broken surface of the 

rock. B, Rock surface chemically etched and stained to differentiate potassium feldspar (orange yellow), plagioclase (red), and 

quartz (uncolored). (Fig. 1 0) 

13 
A 

c 

VARIETIES OF GRANODIORITE. All these granodiorites have about the same mineral composition but differ in texture: 

Half Dome Granodiorite (A) contains large, well-formed 

hornblende crystals; Sentinel Granodiorite (B) contains both 

biotite and hornblende in poorly formed crystals; Leaning Tower 

DIORITE is mostly plagioclase and dark minerals, with little 

quartz and potassium feldspar. (Fig. 12) ___ ___ _ 

14 

B 

D 

Granodiorite (C) has a spotted appearance from rounded clots of 

dark minerals; and Bridalveil Granodiorite (D) has a salt-andpepper appearance from fine, evenly distributed light and dark 

minerals. (Fig. II) 

In contrast to granitic rocks, quartz diorite, diorite, 

and gabbro contain mostly plagioclase and dark minerals, with little or no quartz or potassium feldspar (figs. 

9, 12). In addition, the plagioclase in gabbro contains 

more calcium than the plagioclase in diorite. Such 

plutonic rocks poor in quartz are sparse in the Yosemite 

area and generally occur as small, irregular masses and 

dikes- sheetlike masses- of quartz diorite or diorite; 

they generally are dark gray and commonly are fine 

grained, with few minerals readily recognizable to the 

naked eye. 

Light-colored rock, composed chiefly of quartz and 

potassium feldspar, also forms irregular masses and 

dikes. This rock occurs both with a fine-grained texture-aplite (fig. 13)-and with a very coarse grained 

texture-pegmatite-displaying large, intergrown 
quartz and potassium feldspar crystals. A fine example of pegmatite is visible a short distance down the 

Pohono Trail to Taft Point from the Glacier Point 

Road. 

Most granitic rocks contain mineral grains of 

about equal size and are said to have a granular 

texture. Some granites, however, and many volcanic 

rocks have crystals of one mineral considerably larger 

than the others; these oversized crystals are called 

phenocrysts (from the Greek words meaning "to 

appear" and "crystal"), and the texture of such a rock 

is described as porphyritic. In Sierran granites, the 

most common mineral to occur as phenocrysts is 

potassium feldspar, in crystals commonly as much as 

2 to 3 in. long (fig. 14 ). 

Rounded inclusions of dark, fine-grained dioritic 

material are common in granitic rocks, most commonly in granodiorites and tonalites. Generally pancake or football shaped, the inclusions range in size 

from a few inches to many feet across. It is not 

uncommon for all the inclusions within an area to 

have their long dimensions arranged in the same 

direction, like a school of fish (fig. 15). An excellent 

example occurs at the Yosemite Falls overlook on the 

north rim of the valley. The origin of these inclusions is uncertain. Some probably were derived from 

preexisting rock; others may be derived from globules 

of darker magma that because of their high melting 

temperature were chilled by the granitic magma 

rather than being digested into it. However, the 

shape of the inclusions suggests that, whatever their 

origin, they were at least partially plastic while suspended in the magma and that they were stretched 

and given their parallelism by movement within the 

magma. 

Concentrations of dark minerals sometimes form 

wavy, discontinuous streaks and layers, especially 

near the outer margins of individual plutons. These 

layers, called schlieren (German for streaks), probably 

represent clustering of dark minerals early during the 

crystallization of the magma, with alignment in 

streaks caused by movement within the partially 

solidified magma (fig. 16). The commonly abrupt 

termination of one set of layers by another set suggests repeated pulses of movement in a magma mush. 

Individual bodies of granitic rock, particularly large 

ones, generally vary in mineral makeup and commonly 

overlap the boundaries between specific rock classifications. Bodies of granitic rock may also overlap each 

other's compositional ranges, and so composition is 

only one factor in the recognition of separate rock 

DIKE of light-colored, fine-grained aplite crosscutting granodiorite. Aplite is a silica-rich rock composed chiefly of quartz and 

potassium feldspar. (Fig. 13) 

PORPHYRITIC TEXTURE in Cathedral Peak Granodiorite, with potassium feldspar phenocrysts much larger than the 

other minerals in the rock matrix. (Fig. 14) 

15 
bodies. The chief distinguishing property may be the 

presence or absence of specific minerals, such as biotite, 

hornblende, or sphene. Or it may be the general 

physical appearance defined by the texture of the 

rock- the size, shape, and arrangement (random or 

oriented) of the minerals (fig. 11). A porphyritic texture is particularly useful because it is prevalent in only 

a few plutons in the Yosemite area. The presence or 

absence of dark inclusions may also characterize a rock 

body. 

Knowledge of the age relations among plutons is 

essential to understanding the geologic history of the 

16 

ALIGNED DARK DIORITIC 

INCLUSIONS in granodiorite. 

Photograph by Dallas L. Peck. 

(Fig. 15) 

SCHLIEREN-streaks or layers 

formed by clustering of dark minerals during differential flow within the 

partially solidified magma. Note 

parallel alignment of potassium feldspar phenocrysts by the same process; larger phenocrysts are about 2 

in. long. (Fig. 16) 

Sierra Nevada batholith. Certain features observed in 

outcrop help determine the relative ages of individual 

rock bodies. For example, younger magma commonly 

shoots thin sheets, or dikes, into cracks in the older 

rocks (fig. 17 A). Additionally, some of the younger 

plutons contain inclusions, or fragments of older 

rock, which were embedded in the younger rock 

while it was still molten (fig. 178). Where dark 

inclusions or other oriented structures are present, 

the contact between two rock bodies may truncate 

structures in the older body, while similar features in 

the younger rock may parallel the contact (fig. 17C). 
Determining the absolute age of a given gramttc 

rock, in millions of years, requires measurement of 

the extent of radioactive decay of certain elements, 

such as uranium, potassium, and rubidium. From 

such measurements and the known rates of decay, we 

can approximately determine the time elapsed since 

the rock crystallized or cooled enough to stop escape 

of the daughter decay products from the rock (see fig. 

7). 

In their studies of plutonic rocks, geologists have 

devised ways to separate individual bodies of such 

rock and to depict them on geologic maps so as to 

show their relations to each other and to nonplutonic 

rocks with which they are in contact. Once established by field study, the boundaries of these individual plutonic-rock bodies-plutons-can be plotted 

on a map, and these rock bodies become geologic 

map units. After further study, the geologist may 

decide that two or more nearby bodies of plutonic 

rock exposed on the Earth's surface are similar in all 

essential respects, including known or inferred age. 

Even though they may not be connected at the 

Earth's surface, the geologist may thus combine several masses of similar plutonic rock into a single 

geologic map unit, inferring that they are somehow 

connected below the surface and represent a single 

intrusive episode. This grouping of isolated bodies of 

related plutonic rock into a single geologic map unit 

is analogous to the grouping of discontinuous 

exposures of similar sedimentary rock into formations, such as the Coconino Sandstone and the 

Kaibab Limestone, which are well exposed in the 

Grand Canyon region. For ease of reference, the 

plutonic-rock units likewise are generally named for 

an appropriate geographic feature, plus a compositional term: for example, the El Capitan Granite, the 

Half Dome Granodiorite, and the granodiorite of 

Kuna Crest. 

A 

y 

Dikes of younger 

rock intrude 

older rock 

Inclusions of older 

rock in younger 

rock 

c 

Younger rock trun· 

cates linear features 

in older rock 

FEATURES SEEN IN OUTCROP that help determine the 

relative ages of plutonic rocks: 0, older pluton; Y, younger pluton. 

(Fig. 17) ---------------

GRANITIC RocKs oF YosEMITE 

The plutonic rocks of Yosemite have been mapped 

and studied in considerable detail. Few of those details 

can be shown on the generalized geologic map in this 

volume (pl. 1 ), but a geologic map at a much larger 

scale is available (Huber and others, in press). On that 

map, the granitic rocks of the Yosemite area are separated into nearly 50 different plutonic-rock units, each 

consisting of one or more individual bodies of rock. An 

even larger scale geologic map is available for Yosemite 

Valley (Calkins, 1985; see section above entitled "Geologic Maps of Yosemite"). 

Some plutonic-rock units are further grouped into 

intrusive suites. The concept underlying an intrusive 

suite is that all the rocks in the suite resulted from the 

same magma-producing event. Geologists are most sure 

of a common ancestry if the rocks in a suite grade into 

each other. Such suites commonly are zoned, both 

compositionally and texturally, and generally exhibit 

partial or complete nested patterns in which relatively 

dark rock in the margins gives way inward to younger, 

lighter colored rock in the interior. The units that 

compose this ideal kind of intrusive suite are believed to 

result from modifications of a common parent magma. 

Examples include the Tuolumne Intrusive Suite, the 

first intrusive suite to be identified in the Sierra 

Nevada, and the intrusive suite of Buena Vista Crest. 

The geologic map (pl. 1) groups most plutonic-rock 

units into intrusive suites and thus provides a broader 

picture of the major pulses of plutonic activity that 

contributed to the construction of the Sierra Nevada 

batholith. The more detailed geologic map of Yosemite 

Valley (pl. 2) delineates not only intrusive suites but 

also component units of the suites. 

All the plutonic rocks within Yosemite National 

Park proper are believed to be of Cretaceous age, with 

the possible exception of some small bodies of diorite 

and gabbro that may be somewhat older. Some Jurassic 

plutonic rock does occur just west of the park, west of 

the Big Oak Flat entrance, and some Triassic plutonic 

rock occurs east of the park in Lee Vining and Lundy 

Canyons. These rocks are included with "Plutonic 

rocks, unassigned to suites" on plate 1 and are shown 

individually only on the larger scale geologic map 

published separately (Huber and others, in press). 

Examples of many of the named rock types in 

Yosemite are displayed at the Valley Visitor Center, 

where they may easily be compared; they are next 

described for two readily accessible areas in the park, 

Yosemite Valley and the Tuolumne Meadows area. 

17 
AS Rockslides 

AF Ribbon Fall 

EC El Capitan 

TB Three Brothers 

EP Eagle Peak 

YF Top of Yosemite Falls 

YV Yosmite Village 

IC Indian Canyon Creek 

A Royal Arches 

W Washington Column 

TC Tenaya Canyon 

ML Mirror Lake 

NO North Dome 

BD Basket Dome 

MW Mount Watkins 

E Echo Peaks 

C Clouds Rest 

SM Sunrise Mountain 

0 Quarter Domes 

HD Half Dome 

M Mount Maclure 

L Mount Lyell 

F Mount Florence 

CC Cascade Cliffs 

L Y Little Yosemite 

LC Liberty Cap 

8 Mount Broderick 

SO Sentinel Dome 

G Glacier Point 

SR Sentinel Rock 

FS Fissures 

T Taft Point 

CS Cathedral Spires 

CR Cathedral Rocks 

BV Bridalveil Fall 

LT Leaning Tower 

DP Dewey Point 

MR Merced River 

YOSEMITE VALLEY AREA 

The oldest plutonic rocks of the Yosemite Valley area 

compose the walls of Merced Gorge and the west end 

of the valley. They include the diorite of the Rockslides, the granodiorite of Arch Rock, and the tonalite 

of the Gateway (pl. 2). The largest outcrop of diorite is 

just west of the Rockslides (fig. 18), but the talus slopes 

below, composed of broken blocks of diorite, are more 

accessible. A good exposure of the granodiorite of Arch 

Rock can be seen immediately east of the Arch Rock 

Entrance Station on the El Portal Road (Route 140), 

where the road passes under two large fallen blocks of 

the granodiorite (park vehicles near the entrance station). The tonalite of the Gateway can be seen along 

the El Portal Road across from the first turnout after the 

road starts climbing up the Merced Gorge eastward 

from El Portal; these last two locations are west of the 

map area shown in plate 2. Studies of radiometric decay 

indicate that the tonalite of the Gateway is about 114 

million years old. The radiometric age of the granodiorite of Arch Rock has not been determined, but it 

probably is only a little younger than that of the 

Gateway. 

The El Capitan Granite subsequently intruded these 

older plutonic rocks about 108 million years ago and 

18 

BIRD'S-EYE VIEW 

OF YOSEMITE 

VALLEY, with selected 

landforms identified . 

(Fig. 18) 

now makes up the bulk of the west half of the valley 

area. About 4 km east of the Arch Rock Entrance 

Station, the El Portal Road cuts through blocks of El 

Capitan Granite dislodged in a 1982 rockfall. These 

blocks, some the size of a small house, display fresh 

surfaces of the granite (fig. 10; see fig. 48), as well as 

numerous inclusions of dark-colored rock. The imposing monoliths of Turtleback Dome, El Capitan, Three 

Brothers, and Cathedral Rocks also are hewn chiefly 

from massive El Capitan Granite. 

After the El Capitan Granite was emplaced, the Taft 

Granite welled up and intruded the El Capitan. Dikes 

of Taft Granite invading El Capitan Granite and inclusions of El Capitan in Taft establish the Taft as 

younger. The two rocks are similar, but Taft Granite is 

lighter in color and commonly finer grained than El 

Capitan Granite and, unlike El Capitan Granite, generally does not contain phenocrysts. Taft Granite forms 

the brow of El Capitan and part of the upland between 

El Capitan and Fireplace Bluffs. On the south side of 

the valley, Taft Granite can be seen at Dewey Point and 

near The Fissures, just east of Taft Point. 

In the vicinity of Leaning Tower and Cathedral 

Rocks, dikes and irregular masses of several fine-grained 

rocks cut the Taft and El Capitan Granites. Examples 

of these fine-grained rocks can be seen in blocky rubble 
near the base of Bridalveil Fall. The Leaning Tower 

Granodiorite characteristically contains rounded clots 

of dark minerals that give it a spotted appearance (fig. 

llC). The Bridalveil Granodiorite, which contains 

fine, evenly distributed, light and dark minerals, has 

a salt-and-pepper appearance (fig. llD); features seen 

in outcrop show that it intruded nearly all the rocks 

which it now contacts. 

Dark, fine-grained diorite also intrudes the El 

Capitan and Taft Granites. A striking example is 

exposed on the east face of El Capitan, where dikes 

of diorite form an irregular pattern that, in part, very 

crudely resembles a map of North America (fig. 19). 

The Sentinel Granodiorite fomts a north-south band 

that crosses the valley between Taft Point and Glacier 

Point. The rock varies in appearance but is generally 

medium gray and medium grained (fig. llB). Giant 

inclusions of El Capitan Granite are embedded 

within Sentinel Granodiorite in a zone that extends 

along Yosemite Creek and down the face of the cliff 

near Yosemite Falls. The Sentinel Granodiorite reappears on the south valley wall west of Union Point 

and then extends southward through Sentinel Dome 

to Illilouette Ridge. Dikes of Sentinel Granodiorite 

DIORITE DIKES on the face of El Capitan; dark patch is 

thought by some to resemble a crude map of North America. 

Some lighter colored dikes are also present. (Fig. 19) 

that cut inclusions of El Capitan Granite can be seen 

in the roadcut along the Glacier Point Road near the 

trailhead to Taft Point. 

The rock at Glacier and Washburn Points is darker 

than Sentinel Granodiorite and has a streaky 

appearance from parallel-oriented flakes of biotite 

and rods of hornblende. This darker rock, once 

thought to be part of the Sentinel and shown as such 

on earlier geologic maps, is now assigned to the 

granodiorite of Kuna Crest. 

The Half Dome Granodiorite dominates the valley 

area east of Royal Arches and Glacier Point. It is 

medium to coarse grained and contains well-formed 

plates of biotite and rods of hornblende (fig. 11A). 

At Church Bowl and in the cliff west of Royal 

Arches, horizontal dikes of Half Dome Granodiorite 

cut the older granodiorite of Kuna Crest. Half Dome 

Granodiorite forms the sheer cliffs to the north of 

the trail between the Ahwahnee Hotel and Mirror 

Lake. The trail to Vernal and Nevada Falls also 

crosses through Half Dome Granodiorite. Except for 

minor dikes, the Half Dome Granodiorite, about 87 

million years old, is the youngest plutonic rock in 

the valley area. 

TUOLUMNE MEADOWS AREA 

The granodiorite of Kuna Crest and the Half Dome 

Granodiorite exposed at the east end of Yosemite Valley 

are two plutonic-rock units that make up the western 

margin of the Tuolumne Intrusive Suite. This suite 

underlies a large part of eastern Yosemite National Park 

from upper Yosemite Valley, across Tuolumne Meadows 

eastward to the crest of the Sierra, and northward 

beyond the park boundary (pl. 1). The Tuolumne 

Intrusive Suite, one of the best studied groups of 

granitic rocks in the Sierra, consists of four bodies of 

plutonic rock, sequentially emplaced and partly nested 

one within the other (fig. 20). The suite is well exposed 

in the area centered on Tuolumne Meadows, and the 

Tioga Road (Route 120) provides access to many conspicuous outcrops of the suite's components. 

The oldest and darkest plutonic rock generally forms 

the margin of the suite, and the youngest rock is in its 

core. The rocks are, from oldest to youngest: the 

granodiorite of Kuna Crest (about 91 million years old), 

the Half Dome Granodiorite, the Cathedral Peak 

Granodiorite (about 86 million years old), and the 

Johnson Granite Porphyry. Field relations indicate that 

the Johnson Granite Porphyry is the youngest granitic 

rock in the park, although a radiometric age has not 

19 
N 

0 

0 

20 

Initial intrusion and 

solidification of marginal 

granodiorite of Kuna Crest 

Surge of fresh magma 

locally breaches the Kuna 

Crest and solidifies as the 

equigranular phase of the 

Half Dome Granodiorite 

New surge of magma 

followed by solidification 

of porphyritic phase of Half 

Dome Granodiorite 

Third surge of magma 

followed by solidification 

of Cathedral Peak Granodiorite 

and emplacement of 

Johnson Granite Porphyry 

as final stage 

15 MILES 

yet been determined. The granodiorite of Kuna Crest 

normally occupies the margin of the suite, but on much 

of the perimeter the Half Dome Granodiorite and the 

Cathedral Peak Granodiorite have broken through the 

granodiorite of Kuna Crest to form the marginal units 

(fig. 20). 

The overall concentric zonation of rock bodies 

within the suite, as well as the overall chemical similarities among the rocks, suggests that these rocks 

originated from the same magma chamber. This inferred common parentage provides the rationale for grouping these rocks into an intrusive suite. The composition 

of the magma, however, changed over time: the older, 

hornblende- and biotite-rich rocks at the margins give 

way to quartz- and potassium feldspar-rich rocks toward 

the center. Hornblende and biotite crystallize at higher 

temperatures than quartz and feldspar, and so during 

cooling of a magma, these dark minerals generally 

crystallize earlier than the light-colored ones. This 

relation suggests that cooling of the magma started at 

the margins and progressed inward over time. 

North of the Tioga Pass Entrance Station, the trail 

to Gaylor Lakes crosses over the granodiorite of Kuna 

Crest, the oldest and darkest rock in the Tuolumne 

Intrusive Suite. This trail weaves back and forth near 

the contact between the granodiorite and the metamorphic rocks that it intruded. The granodiorite also 

contains many disc-shaped inclusions that are oriented 

parallel to its contact with the older metamorphic 

rocks. These inclusions were probably stretched and 

oriented by movement within the magma during intrusion and cooling. 

The Half Dome Granodiorite, the next youngest 

rock in the suite, is in contact with the granodiorite of 

Kuna Crest to the west along the ridge crossed by the 

Gaylor Lakes Trail. The best exposures of the Half 

Dome, however, are surrounding the turnout at 

Olmsted Point west of Tenaya Lake. Fresh, clean outcrops of the rock abound at and across from the 

turnout. Half Dome Granodiorite makes up much of 

the southwestern part of the Tuolumne Intrusive Suite 

and in several areas is the marginal rock. 

Heading east toward Tuolumne Meadows, the Tioga 

Road crosses the contact between the Half Dome 

Granodiorite and the Cathedral Peak Granodiorite just 

east of Tenaya Lake. The contact is obscure, however, 

because here the Half Dome contains nearly as many 

potassium feldspar phenocrysts as does the younger 

EVOLUTION OF THE TUOLUMNE INTRUSIVE 

SUITE- a map view. (Fig. 20) 
Cathedral Peak. Pothole and Lembert Domes, both 

marginal to the meadows, are composed entirely of 

Cathedral Peak Granodiorite. The rock of these domes 

clearly displays potassium feldspar phenocrysts, commonly as much as 2 to 3 in. long (fig. 14). These 

impressive crystals stand out against a medium-grained 

background. The Cathedral Peak Granodiorite forms 

the largest pluton of the Tuolumne Intrusive Suite, 

extending long distances to the north and south of 

Tuolumne Meadows. 

The youngest, smallest, and most central rock body 

of the suite is composed of the Johnson Granite Porphyry. In a porphyry, the conspicuous phenocrysts are 

set in a finer grained matrix than in such porphyritic 

rocks as the Cathedral Peak Granodiorite, and so 

individual mineral grains in the matrix are difficult to 

identify without a microscope. Low outcrops of the 

porphyry can be seen in Tuolumne Meadows along 

the Tuolumne River, across from the store, and east 

of Soda Springs on the north side of the river. The 

rock is very light colored, with only a few scattered 

potassium feldspar phenocrysts within a fine-grained 

matrix (fig. 21). Dikes of Johnson Granite Porphyry 

intrude Cathedral Peak Granodiorite, and the porphyry itself is cut by light, fine-grained aplite dikes. 

The fine-grained matrix of a porphyry requires that 

Rocks removed 

JOHNSON GRANITE PORPHYRY, showing potassium 

feldspar phenocrysts set in a fine-grained matrix. (Fig. 21) 

partially crystallized magma be quenched or cool relatively quickly. Such conditions would result from a 

sudden release of pressure, as would occur if some of 

the magma were erupted at the Earth's surface. Thus, 

volcanic eruptions probably accompanied final 

emplacement of the Tuolumne Intrusive Suite-a volcanic caldera may once have existed far above what is 

now Johnson Peak (fig. 22). 

EXPLANATION 

Shading used for three-dimensional effect 

Volcanic deposit from eruption of 

Johnson Granite Porphyry 

Johnson Granite Porphyry. 

Pattern indicates solidified rock 

Cathedral Peak Granodiorite 

Pre-existing rock intruded by 

Cathedral Peak Granodiorite 

by erosion during 

last 85 million years 

FINAL STAGES 

IN THE EVOLUTION OF THE 

TUOLUMNE INTRUSIVE SUITE. 

The Johnson Granite Porphyry intrudes the Cathedral Peak Granodiorite 

and erupts through a volcanic caldera, spewing 

volcanic ash and debris 

onto the Earth's surface. 

The volcanic deposit and 

much of the underlying 

rock are subsequently 

removed by erosion to 

create today's land surface . (Fig. 22) 

21 
METAMORPHIC ROCKS-ANCIENT 

SEDIMENT AND LAVAS 

Metamorphic rocks are derived from preextstmg 

rocks by mineralogic and structural changes in response 

to increases in temperature, pressure, and shearing 

stress at depth within the Earth's crust. In the Sierra 

Nevada, some of this heat and pressure was supplied by 

the intruding granitic rocks, but much of it was 

imposed simply by depressing sedimentary and volcanic 

rocks once exposed at the Earth's surface downward to 

depths where higher temperature and pressure are the 

normal environment. The metamorphic rocks in the 

Yosemite area were derived from a great variety of 

sedimentary and volcanic rocks and thus exhibit a great 

variety in themselves. Some rocks have been only 

mildly metamorphosed and still retain original structures, such as sedimentary layering, that help to identify the nature of the original rock. Others have been 

so strongly deformed and recrystallized that original 

textures and structures have been destroyed, and determination of the original rock type is difficult. 

Metamorphosed sedimentary rocks in the Yosemite 

area include rocks that were originally sandstone and 

siltstone, conglomerate, limestone, shale, and chert. 

Metamorphosed volcanic rocks in the Yosemite area 

include those derived from lava flows and various types 

of pyroclastic rocks- those formed from violently 

erupted volcanic debris. 

The rocks into which the Sierra Nevada batholith 

was emplaced are weakly to strongly metamorphosed, 

mildly to complexly deformed strata of probable Paleozoic and Mesozoic age. In the Yosemite area these 

metamorphic rocks occur in two northwest-trending 

belts situated largely east and west of the park proper 

and in small isolated bodies scattered throughout the 

park. Fossils are scarce, and the radiometric ages of 

most of these rocks are poorly known. 

Rocks of the western metamorphic belt underlie 

much of the foothills of the western Sierra between the 

San Joaquin and Feather Rivers, and form the western 

wallrocks of the Sierra Nevada batholith. In the canyon of the Merced River approaching Yosemite on 

Route 140, strikingly banded chert is exposed in the 

vicinity of the "geological exhibit" and eastward for 

several miles (fig. 23). This banded chert was formed 

from the skeletons of very tiny, silica-secreting marine 

animals called radiolarians; upon the death of such 

animals, their skeletons settle to the ocean bottom, 

where they collect in enormous numbers. Although the 

chert beds are moderately to strongly deformed, the 

22 

CONTORTED CHERf BEDS along the Merced River west 

of El Portal are ancient marine sediment that has been metamorphosed. (Fig. 23) 

rock is easily recognizable as of sedimentary origin. In 

contrast, metamorphic rocks just west of El Portal and 

just west of Crane Flat along the Big Oak Flat Road 

(Route 120) have a metamorphic layering that largely 

destroys original bedding, and the origin of these rocks 

as sediment is less obvious. Fossils in a limestone bed 

just west of the "geological exhibit" on Route 140 

indicate a Triassic age for at least some of the rocks 

exposed along this part of the Merced River canyon. 

The eastern belt of metamorphic rocks extends for 

about 50 mi from south of Mammoth Lakes to north of 

Twin Lakes (pl. 1). Furthermore, rather than bounding 

the batholith, this belt is a giant septum of metamorphic rocks separating plutonic rocks on either side. 

This eastern belt includes rocks of both sedimentary 

and volcanic origin, which range in age from early 

Paleozoic to late Mesozoic. The Paleozoic rocks are 

metasedimentary and include such varieties as 

quartzite, metaconglomerate, and marble. The commonest rock, however, is hornfels- a catchall term for 

a fine-grained metamorphic rock composed of a mosaic 

of equidimensional grains formed by recrystallization of 

sedimentary and volcanic rocks of various compositions. These Paleozoic rocks are well exposed along 

Route 120 near Ellery Lake east of Tioga Pass. 

The Mesozoic rocks of the eastern metamorphic belt 

are chiefly of volcanic origin-tuff and other 

explosively ejected fragmental volcanic rock-with 

lesser amounts of sedimentary rock. These Mesozoic 

rocks, which lie generally west of the Paleozoic rocks in 

the eastern metamorphic belt, make up the Ritter 

Range and the southeastern margin of the park, and 
much of the Sierran Crest northward through Kuna 

Peak, Mount Dana, Gaylor Peak, and continuing north 

of the park beyond Twin Lakes (pl. 1). Relict sedimentary bedding is commonly preserved-steeply dipping, 

as west of Saddlebag Lake, or highly contorted, as near 

Spotted Lakes at the south end of the park (fig. 24). 

Of particular interest are the little-deformed metamorphic rocks of Cretaceous age. Metamorphosed volcanic rocks near the summit of Mount Dana have a 

radiometric age of about 118 million years, and those 

from the Ritter Range of about 100 million years, 

which means that their eruption from volcanoes 

occurred at the same time that some of the smaller 

plutonic-rock suites were emplaced at depth. In the 

Ritter Range, a thick deposit of volcanic breccia has 

been interpreted as resulting from collapse of an 

ancient volcanic caldera. 

A 

B 

LATE CENOZOIC VoLCANIC RocKsBoRN oF FIRE 

Volcanic rocks, like their plutonic counterparts, are 

also classified on the basis of composition. Because 

volcanic rocks erupted onto the Earth's surface cool and 

solidify more quickly than plutonic rocks, they tend to 

be finer grained or even glassy, with few minerals 

identifiable to the eye. Those few visible minerals, 

however, are guides to the rock's composition. Late 

Cenozoic volcanic rocks in Yosemite have a very limited range in composition; they generally contain little 

or no quartz and range from basalt and andesite (containing little or no potassium feldspar) to latite (containing both potassium and plagioclase feldspar). A 

volcanic rock containing quartz-rhyolite- does occur 

just east of Yosemite at the Mono Craters. 

Late Cenozoic volcanic rocks of the Yosemite area 

formed both by the eruption of vast volumes of lava 

and by much smaller eruptions. The products of great 

eruptions extend into the northern part of the park but 

are much more extensive in the northern Sierra; they 

include lava flows, tuff, and volcanic mudflows. Details 

of the nature and distribution of all these volcanic 

rocks are deferred to the section dealing with the late 

Cenozoic. 

METAMORPHIC ROCKS with relict sedimentary bedding. 

A, Steeply dipping, as northwest of Saddlebag Lake. B, Highly 

contorted, as near Spotted Lakes. Photograph by john P. Lockwood. (Fig. 24) 

23 
24 

The Earth is generally depicted as consisting of a 

series of concentric shells-a relatively thin outer 

crust, an intermediate mantle, and an interior core 

(fig. 25). The Earth's crust and uppermost part of the 

upper mantle together form the rigid outer part of the 

Earth-the lithosphere-which is broken into plates 

that ride over a less rigid, viscous layer within the 

upper mantle that yields plastically. There are seven 

very large plates, and a dozen or so small ones (not 

all of which are shown in fig. 26.) The large plates 

consist of both oceanic and continental portions; the 

present North American plate, for example, includes 

not only the North American Continent but Greenland and the west half of the North Atlantic Ocean 

as well. The crust beneath continents is typically 20 

to 34 mi thick and is less dense than the crust 

beneath oceans, which typically is only 4 to 5 mi 

thick. The plates generally are internally rigid, and 

most dynamic geologic activity is concentrated 

along the plate boundaries; these boundaries are 

marked by long, narrow belts of earthquake and 

volcanic activity. 

Each of the plates is moving relative to all the 

others. In the simplest mode, two plates slide past 

each other along a strike-slip fault (fig. 27A). The San 

Andreas fault, running much the length of California 

and forming part of the present boundary between 

the North American and Pacific plates, is an example. Where plates move away from each other, primarily along the system of great submarine ridges 

in the world's oceans, hot material wells up from 

below to fill the gap (fig. 27 B). As this hot material 

cools to form basalt, it becomes attached to the 

plates on either side of the spreading zone, and new 

crust is created. Where plates converge, one tips 

downward and slides beneath the other- a process 

called subduction (fig. 27C). Generally, a plate with 

dense oceanic crust slides beneath one with more 

bouyant continental crust. Thus, new oceanic crust 

created at spreading centers is recycled back into 

the Earth's interior through subduction, and and the 

total surface area of the Earth remains unchanged. 

PLATE TECTONICSA DYNAMIC GLOBE 

INTERIOR OF THE EARTH, showing relation of crust and 

mantle to the rigid lithosphere-the stuff of which the mobile 

plates are made. (Fig. 25) 
180° 

60° 

40° 

oo 

40° 

60° 

MAJOR LITHOSPHERE PLATES OF THE 

WORLD, showing boundaries that are presently active. Double 

line, zone of spreading, from which plates are moving apart; 

barbed line, zone of underthrusting (subduction), where one plate 

is sliding beneath another- barbs on overriding plate; single line, 

strike-slip fault, along which plates are sliding past one another. 

See figure 27 for examples of plate motions. (Fig. 26) 

.. ., 

PACIFIC 

PLAT E 

120° 60° 0' 60° 120° 180° 

EURASIAN PLATE 

~ 

ANT ARCTIC PLATE 

THREE PRINCIPLE KINDS OF PLATE MOTION. 

A, The plates slide past each other along a strike-slip fault. B, 

The plates move away from each other at a divergent boundary. C, 

The plates move toward each other at a convergent boundary; the 

process of subduction consumes crust at convergent plate boundaries. (Fig. 27) 

25 
GENESIS OF 

YOSEMITE'S ROCKS 

The geologic story of Yosemite as presented up to 

this point has been largely a description of the rocks as 

we see them now. But how did they get this way? And 

when? The search for answers to these questions 

involves interpretation of geologic observations made in 

Yosemite and elsewhere in the Sierra Nevada, together 

with numerous inferences based on accumulated geologic knowledge and on theoretical concepts. Some 

parts of the geologic history can be deciphered with 

confidence and in considerable detail, but other parts 

are less complete because the geologic data are very 

spotty. 

A SINGLE QuiET PLATETHE PALEOZOIC 

The framework within which most geologists today 

view geologic processes, such as the creation of 

batholiths and the building of mountains, is that of the 

theory of plate tectonics (see section above entitled 

"Plate Tectonics - • • • "). Tectonics is the study of 

the deformation of earth materials and the structures 

resulting from that deformation. The "tectonics" in 

plate tectonics refers to deformation and structure on 

a global scale. 

The oldest rocks in the Yosemite area were derived 

from sediment deposited during early Paleozoic time, 

beginning about 500 million years ago. During the 

Paleozoic, the area that was to become Yosemite was 

near the west edge of the growing North American 

Continent. The setting, for the most part, was a 

relatively passive one. Paleozoic sediment derived by 

erosion of still older rocks to the east was delivered 

by ancient streams flowing westward to a sea along 

the continental margin. Deposition of such sediment 

throughout most of the Paleozoic, though not necessarily continuous, resulted in the accumulation of 

thousands of feet of mud and sand, which eventually 

consolidated into shale and sandstone. Plant and 

animal life in the sea contributed their part by 

depositing calcium carbonate and silica, later to 

become beds of limestone and chert. 

During the Paleozoic, the continent and its adjacent sea appear to have been traveling together on a 

single plate. All was not totally passive, however, 

because there is evidence for folding and deformation 

26 

of some early Paleozoic strata during the late Paleozoic. It is not possible to relate such deformation 

to specific plate-margin tectonics because of severe 

overprinting by later tectonic events. By the end of 

the Paleozoic the geometry at the west edge of the 

North American plate had changed, and an oceanic 

plate was now underriding, or being subducted 

beneath, the North American plate. 

A TIME OF FIRE AND UPHEAVALTHE MESOZOIC 

The presence of a subduction zone along the west 

margin of the North American plate had profound 

effects on that plate. As the cool oceanic plate was 

subducted, the overriding continental plate was 

deformed. But more important to the Yosemite story 

were the igneous effects of subduction. Wherever convergent plate margins and subduction zones are present 

today, magma is generated at depth, and linear belts of 

volcanoes form atop the overriding plate, parallel to the 

subduction zone. Mount St. Helens, for example, and 

other volcanoes of the Cascade Range lie parallel to an 

active subduction zone that extends from northern 

California to Canada, and we infer that ancient subduction zones produced similar belts of igneous activity. 

We can only speculate as to the nature of the 

physical and chemical processes that take place within 

a subduction zone. A prevalent theory is based on 

experiments indicating that the presence of water 

lowers the melting temperature of rock materials. This 

theory holds that water entrapped in the descending 

slab of oceanic crust is driven out as the slab reaches 

higher temperatures and leaks upward into the overriding lithosphere, where partial melting results (fig. 28). 

Magma generated in the mantle part of the lithosphere 

has the composition of basalt or andesite, but as the 

magma rises into the continental crust, a more silicic 

magma may be generated-one with the composition 

of rhyolite or granite. After rising toward the Earth's 

surface, this silicic magma may erupt as rhyolite volcanoes, or cool and come to rest as great bodies of 

granitic rock within the upper crust. Most geologists 

now believe that this is the mechanism-greatly simplified here- through which the Sierra Nevada 

batholith was generated and emplaced. 

By early Mesozoic time, more than 200 million years 

ago, magma reached the Earth's surface in a belt of 

volcanoes and spewed forth to form great volumes of 

volcanic rock, metamorphosed remnants of which are 

now exposed in the area of the Sierran crest (pl. 1). By 
this time, silicic magma had also formed, some of 

which cooled and solidified below the Earth's surface to 

form bodies of granitic rock; one such body is now 

exposed in Lee Vining Canyon (intrusive suite of 

Scheelite, pl. 1 ). Subduction along the margin of the 

North American plate was not continuous during the 

Mesozoic, and subsequent movement of granitic magma 

into the upper crust was somewhat episodic; the greatest volumes were emplaced during the middle Jurassic 

and Late Cretaceous. By the beginning of the 

Cenozoic, the magmatic system in the Sierran region 

shut off, leaving behind the mass of granitic rock we 

now call the Sierra Nevada batholith. 

Emplacement of plutonic rocks within the upper 

crust was probably accompanied by many contemporaneous volcanic eruptions at the Earth's surface. Evidence in the Yosemite area for such eruptions includes 

the texture of the Johnson Granite Porphyry (fig. 21) 

and similar porphyries in other intrusive suites, and the 

100- to 118-million-year ages of the volcanic rocks near 

Mount Dana and in the Ritter Range. In addition, 

volcanic eruptions associated with emplacement of the 

Sierra Nevada batholith and other contemporaneous 

batholithic complexes now exposed along the western 

margin of the North American Continent provide the 

only apparent source for the extremely voluminous 

deposits of Cretaceous volcanic ash to the east in the 

continental interior. 

Not all of the oceanic plate was being subducted 

during that time, however. Parts of that plate, particularly the upper layer of marine sedimentary rocks on 

the oceanic crust, were added, or accreted, to the 

leading margin of the overriding continental crust. The 

banded chert in the Merced River canyon west of El 

Portal, once part of an ocean floor, was added to the 

North American plate by such a process. 

The end result of the intrusion of the batholith, the 

construction of volcanoes, and the deformation of the 

metamorphic rocks was a linear mountain range parallel to and inboard of the continental margin. This 

range has been referred to as the ancestral Sierra 

Nevada. Mountains are born, only to be worn down by 

erosion; and erosive forces begin to act even as the 

mountains are being upraised. Nevertheless, the 

ancestral Sierra probably reached elevations above 

13,000 ft, similar to those in the Cascade Range in 

western Washington and Oregon, a range being constructed over an active subduction zone today. 

What caused magmatism in the Sierra to cease 

during the late Mesozoic? Many geologists speculate 

that the subducting oceanic slab speeded up and flattened out, so that the zone of magma generation 

shifted eastward. Although there are no giant 

batholiths in Nevada, many bodies of granitic and 

volcanic rock occur there that are chiefly of Cenozoic 

age, younger than the Sierra Nevada batholith. 

Once the magmatic construction of the ancestral 

Sierra Nevada ceased, erosion became the dominant 

force in shaping the range, mostly by removing it. 

Before the end of the Mesozoic, some 63 million years 

ago, the volcanoes had largely been removed, and the 

batholith itself was exposed and being eroded. Sediment derived from this erosion was transported by 

streams coursing down the slope of the range to the 

Central Valley, where it now forms deposits as much as 

tens of thousands of feet thick. By middle Cenozoic 

time, so much of the range had been removed that it 

had a relief of only a few thousand feet or so. 

THE SIERRA GROWS AGAINTHE LATE CENOZOIC 

During early Cenozoic time the Sierra Nevada 

region was relatively stable, and the range continued to 

be worn down faster than it was rising. But during the 

late Cenozoic, from about 25 to 15 million years ago, a 

dramatic change in plate motion along the edge of the 

North American plate occurred, with far-reaching 

effects. The oceanic plate that was being subducted 

beneath the Sierra Nevada was totally consumed into 

SUBDUCTION OF AN OCEANIC PLATE 

during convergence with a continental plate. 

Magma, formed by partial melting of overriding 

continental plate, rises into continental plate to form 

volcanoes and plutons along a mountain chain. (Fig. 

28) 

27 
the subduction zone, and the plate that replaced it was 

moving in a different direction-northwesterly. The 

boundary between the North American plate and this· 

northwesterly-moving plate, called the Pacific plate, 

became a strike-slip fault along this segment of California-the San Andreas fault (fig. 26). 

This change in plate-boundary motion, from convergence to lateral motion, caused a change in the 

pattern of stresses imposed on the Sierran region. The 

continental crust east of the Sierra began to expand in 

an east-west direction, and the thick, light-weight 

Sierran crust began to rise.again. The exact mechanism 

of this uplift is not understood, but the results are there 

to see. In the Yosemite area, the Sierra is clearly an 

uptilted block of the Earth's crust, with a long slope 

westward to the Central Valley and a steep escarpment 

separating it from the country to the east (fig. 29). 

Total uplift in the vicinity of Mount Dana during late 

Cenozoic time to the present is estimated at about 

11,000 ft. 

The uplift began slowly and accelerated over time. 

The range certainly is still rising-and the rate may 

still be accelerating. The estimated current rate of uplift 

at Mount Dana, less than 1 Yz inches per 100 years, may 

appear small, but it is greater than the overall rate of 

smoothing off and lowering of the range by erosion. 

Thus, there is a net increase in elevation. Estimates of 

uplift amount and rate are based on studies of lava flows 

and stream deposits thought to be nearly horizontal 

when formed, but which are now tilted westward 

toward the Central Valley. Progressive tilt is indicated 

by older deposits with greater inclinations than younger 

ones. 

Fran<;ois Matthes inferred from his studies that the 

late Cenozoic uplift occurred in a series of three pulses, 

interrupted by pauses in uplift. In his view, each pulse 

initiated a new cycle of erosion and thus produced a 

stage of landscape incision characterized by successively 

greater relief: Matthes' broad-valley, mountain-valley, 

and canyon stages. More recent studies show that 

28 

UPLIFT AND TILT of the Sierran block, with east 

escarpment formed along fault. Arrows show direction of 

movement on fault. (Fig. 29) 

fortuitous correlation and the commonly local control 

of erosion weaken Matthes' case for three distinct pulses 

of uplift. This does not mean that the uplift was 

entirely uniform-few things in geology are-but 

rather that uplift, once initiated, was more nearly 

continuous than he envisioned. 

At the same time that the Sierra was undergoing 

uplift and erosion and incision by streams, volcanoes 

again became active in parts of the range, particularly 

north of Yosemite. During the interval from about 20 

million years ago to about 5 million years ago, vast 

volumes of volcanic material were erupted from a belt 

of volcanoes extending along what is now the Sierran 

crest north of Yosemite. These volcanoes were the 

southward extension of the Cascade Range of volcanoes 

still active in northern California, Oregon, and Washington. With the advent of the San Andreas strike-slip 

fault, the subduction complex associated with Cascade 

volcanism migrated northward, and the Sierran volcanoes turned off. Lassen Peak in northern California is 

the southernmost volcano of this chain that is still 

active. 

During this late Cenozoic volcanism, the Sierra 

Nevada north of Yosemite was virtually buried by lava 

flows, volcanic tuff, and volcanic mudflows. The volcanic material traveled great distances. Much of it 

reached the margin of the Central Valley, and some of 

it traveled as far south as the northern part of Yosemite. 

Three separate units of this volcanic extravaganza-a 

mudflow, a lava flow, and a volcanic tuff-successively 

flowed down the valley of a south-flowing tributary of 

the ancestral Tuolumne River and into the main channel in the vicinity of Rancheria Mountain northeast of 

Hetch Hetchy (figs. 30, 31). Erosional remnants of the 

volcanic mudflow indicate that it flowed almost as far 

west as Groveland, some 20 mi west of the park. Other 

erosional remnants of this mudflow indicate that it was 

so thick that it actually flowed upstream along the 

ancestral Tuolumne River at least 5 mi above the 

junction of the south-flowing tributary. 

Other volcanic rocks in Yosemite represent local 

eruptive events. One such event is recorded by a basalt 

plug-a solidified remnant of lava in a volcanic conduit -locally known as "Little Devils Postpile" and 

located on the south side of the Tuolumne River several 

miles west of Tuolumne Meadows. The outcrop, easily 

reached by the Glen Aulin trail, exhibits crudely 

developed columnar joints (fig. 32). This basalt is about 

9 million years old. 

One small lava flow of basalt, about 3 Yz million years 

old, was erupted just south of Merced Pass, and a few 
ANCIENT CHANNEL OF THE TUOLUMNE 

RIVER on Rancheria Mountain northeast of Hetch 

Hetchy. The river flowed westward away from the viewer 

into the V-shaped notch cut into granite in the center of the 

photograph. About 10 million years ago, the channel and 

about 50 ft of river gravel were buried beneath a volcanic 

mud flow, the material seen on the slope above the "V". Its 

cross section now exposed by erosion, this ancient channel 

was first described as such by Henry W. Turner, who took 

this photograph about 1900. (Fig. 30) 

scattered flows of similar age lie just south and southeast 

of the park. These flows record the most recent igneous 

activity in Yosemite. 

Things have not remained quiet east of Yosemite, 

however. A cataclysmic eruption about 700,000 years 

ago created 10- by 20-mi-wide Long Valley caldera, 

within which now sits the town of Mammoth Lakes. 

This eruption spewed forth 2,500 times as much ash as 

the 1980 Mount St. Helens eruption; layers of the ash 

from Long Valley caldera have been found as far east as 

Nebraska. Volcanic rocks of Mammoth Mountain and 

the basalt at the Devils Postpile were erupted subsequently. The Mono Craters and lnyo domes between 

Mono Lake and Mammoth Lakes have been erupting 

episodically during the past few thousand years, and the 

most recent domes were formed only about 600 years 

ago. Such activity is almost certainly not yet finished. 

VOLCANIC MUDFLOW DEPOSIT on 

Rancheria Mountain. Brown, smooth-appearing 

slope to the right, at middle distance, is underlain by 

a volcanic mudflow deposit filling an ancient stream 

channel. This photograph, which is another view of 

the channel in figure 30, shows its position on the 

slope above Piute Creek, which drains away from the 

viewer to the present canyon of the Tuolumne River 

in the background. The former Tuolumne River 

flowed from left to right into the base of the brown 

area, concealed by trees in the center of the photograph, and at this point was more than 1 ,500 ft 

above the present canyon of the Tuolumne. This 

difference in elevation indicates the amount of stream 

incision by the Tuolumne River since its former channel was filled and abandoned and the river was 

forced to cut a new one. Photograph by Clyde 

Wahrhaftig. (Fig. 31) 

COLUMNAR JOINTS in a basalt plug-a remnant of a 

volcanic conduit- at "Little Devils Postpile," adjacent to the 

Tuolumne River west of Tuolumne Meadows. (Fig. 32) 

29 
0 1 KILOMETER 

REGIONAL JOINTS 

emphasized by vegetation, as 

seen on an aerial photograph- Yosemite Creek 

basin north of Yosemite Valley. Northeast-trending joint 

set is more closely spaced 

than northwest-trending set. 

Sparser, east-west-trending 

set is also present. Accompanying sketch map shows 

orientation of major joints 

and illustrates the significant 

control of stream courses by 

joints. (Fig. 33) 

30 

FINAL EVOLUTION 

OF THE LANDSCAPE 

THE RoLE oF JoiNTS 

The bedrock structures having the greatest effects on 

Yosemite's landform development are joints. Joints are 

more or less planar cracks commonly found as sets of 

parallel fractures in the rock. Regional-scale joints 

commonly determine the orientation of major features of the landscape, whereas outcrop-scale joints 

determine the ease with which rock erodes. Joints 

are of overwhelming influence on landform development in granitic terrane because they form greatly 

contrasting zones of weakness in otherwise homogeneous, erosion-resistant rock and are avenues of 
access of water and air for weathering. In metamorphic rocks, such planar structures as bedding or 

aligned minerals commonly determine the orientation of fractures. 

A regional system of widely spaced master joints is 

conspicuous throughout the granitic terrane, particularly in the High Sierra where rock exposures are 

extensive. These joints generally are nearly vertical 

and are not to be confused with the gently dipping 

sheet joints that are subparallel to topographic surfaces. Linear depressions commonly follow the master 

joints, and even in highly dissected regions, straight 

segments of streams are joint controlled. Generally, 

two principle sets of joints can be identified nearly at 

right angles, one set commonly trending northeast 

and the other northwest (fig. 33). The orientation 

changes from place to place, but most joints are 

straight or only gently curved. Some individual joints 

can be traced for many miles. The continuity of joint 

sets across the boundaries between individual granitic 

plutons indicates that the joints formed after consolidation of the entire batholith and thus are not 

cooling fractures of the individual bodies. The 

regional joint system evidently resulted from stresses 

imposed on the batholith during later tectonic 

events, such as tilting of the Sierra region. 

Some movement other than simple opening along 

the joint planes has probably taken place along most of 

the master joints. Such lateral, or fault, movement, 

even though slight, would crush or break rock along 

the joint. Deep weathering and erosion along these 

zones of broken rock form long, linear depressions, 

many of them now channels for streams. Areas of 

granite within blocks bounded by master joints are 

themselves jointed to a lesser degree but remain more 

INCLINED JOINTS determine westward slope of upper surfaces of the Three Brothers. Photograph from National Park 

Service collection. (Fig. 34) 

STAIRCASE FALLS. Stairtreads follow joints inclined eastward. Photograph by Tau Rho Alpha. (Fig. 35) 

cohesive and form the bolder areas between master 

joints. 

On a more local scale, vertical joint sets are responsible for the orientation of major features, such as the 

planar face of Half Dome and the series of parallel cliffs 

at Cathedral Rocks. An individual cliff face itself may 

not be the original controlling joint surface, because 

material is continually spalling off, but its orientation is 

controlled by a preexisting joint. 

Although vertical master joints prevail, inclined 

joint sets have added to the diversity of Yosemite's 

landforms. The west faces of the Three Brothers in 

Yosemite Valley were largely determined by a set of 

master joints that slope about 45° westward (fig. 34 ). 

The slope between Cathedral Rocks and Bridalveil 

Creek also follows a set of westward-inclined joints. 

The stairtreads of Staircase Falls follow east-dippiJ;lg 

joints (fig. 35). 

At outcrop scale, two nearly vertical joint sets, 

perpendicular to each other, combine with nearly hori31 
zontal joints to create approximately rectangular blocks 

(fig. 36). Generally, the more siliceous, or quartz-rich, 

rocks (granite and granodiorite) have more widely 

spaced joints than the less siliceous rocks (tonalite and 

diorite). Also, the finer grained rocks generally have 

more closely spaced joints than the coarser grained 

ones. Thus, both composition and texture influence 

the spacing of joints in a given rock mass. 

The least siliceous of the plutonic rocks in Yosemite 

Valley, for example, is the diorite that occurs at the 

Rockslides; this rock is also generally finer grained than 

most of the granitic rocks. The diorite is the most 

closely jointed rock in the valley, and enormous piles of 

joint-derived blocks of diorite have accumulated 

throughout the area of the Rockslides (fig. 37). 

RECTANGULAR BLOCKS formed in El Capitan Granite 

by intersecting joints. (Fig. 36) 

In a particularly striking contrast to the jumbled 

piles of debris at the Rockslides is the largely unbroken 

face of El Capitan, a short distance to the east- one of 

the sheerest cliffs in the world. It consists chiefly of El 

Capitan and Taft Granites, two of the most siliceous 

plutonic rocks in this area. The composition of these 

rocks determines the characteristics of El Capitan 

itself-massiveness and resistance. Because El Capitan 

is largely unjointed, the talus pile at its foot is small. 

Cathedral Rocks and the Leaning Tower are composed 

of El Capitan Granite, complexly intruded by Bridal veil 

32 

THE ROCKSLIDES ANDEL CAPITAN. The Rockslides (left) is a jumbled collection of talus 

blocks of diorite, the most closely jointed rock in Yosemite Valley. In contrast, El Capitan (right) is largely 

unjointed granite, and the pile of debris at its foot, though concealed in this photograph, is comparatively 

small. (Fig. 37) 
Granodiorite; these pinnacles stand out as they do 

because of their siliceous composition. 

The apron or lower part of the cliff east of Glacier 

Point consists of unjointed Half Dome Granodiorite 

capped by well-jointed tonalite; from a viewpoint in 

Stoneman Meadow, an observer, by noting this difference in structure, can trace the contact between the 

two rock types quite closely (fig. 38). 

So mammoth a feature as Half Dome could only 

have been carved from a sparsely jointed rock. In spite 

of James Hutchings' eloquent statement accompanying 

the frontispiece to this volume, Half Dome is nearly as 

whole as it ever was. The impression from the valley 

floor that this is a round dome which has lost its 

northwest half is an illusion. From Glacier Point or, 

even better, from Washburn Point, we can see that it is 

actually a thin ridge of rock oriented northeast-southwest, with its southeast side almost as steep as its 

northwest side except for the very top. Although the 

trend of this ridge, as well as that of Tenaya Canyon, is 

probably controlled by master joints, 80 percent of the 

northwest "half" of the original dome may well still be 

there. What probably happened is that frost splitting of 

the rock at the back of a tiny glacier against Half Dome 

above Mirror Lake gradually quarried back the steep 

northwest face. As the base of the cliff was hewn away, 

Half Dome 

Granodiorite 

ultimately parts of the sheets parallel to the original 

upper surface of Half Dome were left projecting outward at the crest of the vertical cliff. Sharp angular 

bends in the gross form of Yosemite Valley suggest that 

the entire valley, as well as Tenaya Valley, may have 

been eroded along a complex joint system now concealed by stream deposits on the valley floor. 

The type of jointing that has most influenced the 

form of Yosemite's landmarks, however, is the broad, 

shell-like unloading joints or sheeting, also commonly 

referred to as exfoliation. Granitic rocks crystallize at 

considerable depth within the Earth while under 

great pressure from miles of overlying rock. As the 

still-buried plutonic rocks are uplifted into mountains and the overlying rock is eroded, the unloading, or release of the previously confining pressure, 

causes the rock to expand toward the Earth's surface. 

In jointed rocks, such expansion is taken up by 

adjustments along the numerous partings; but in a 

massive monolith, the stresses accumulate until they 

exceed the tensile strength of the rock, and the outer 

and more rapidly expanding layer bursts loose. Over 

time, the process is repeated, and the monolith 

becomes covered with several layers of shells. The 

outermost layer, exposed to the weather, gradually 

disintegrates, and the pieces fall off. The process of 

BOLD EXPOSURE of unjointed Half Dome Granodiorite (in sun) capped by 

mostly well-jointed tonalite (in shade) making up Glacier Point. The contact between 

the two rock types angles upward to left. (Fig. 38) 

33 
PROGRESSIVE ROUNDING OF MASSIVE GRANITE as successive sheets (dashed lines) are formed and spalled off 

in response to unloading, or release of the confining pressure under 

which the granite crystallized deep within the Earth. This is a form 

of exfoliation. (Fig. 39) 

sheeting eliminates projecting corners and angles and 

replaces them with curves (fig. 39). As succeeding 

shells drop off, these curves become more and more 

gentle, and thus a smoothly rounded surface evolves. 

Because the expansion that forms sheet joints 

takes place perpendicular to the Earth's surface, the 

shape of sheets generally reflects the topography, 

although their formation subtly modifies the topography at the same time. If the ground surface is level, 

the sheets will be horizontal (fig. 40A). If the granite 

underlies a hill, the sheets will curve accordingly, 

convex upward (fig. 40B); and if beneath a valley, 

concave upward (fig. 40C). Sheeting also tends to 

parallel the walls of canyons. If the canyon wall 

slopes toward the river, the sheets do also. If the 

walls are vertical, the sheets are also vertical (fig. 

400); thus, the vertical cliffs of Yosemite that appear 

td be unbroken monoliths may have hidden vertical 

fractures behind and parallel to the cliff face. The 

undulating surface of the wall below Clouds Rest is 

an outstanding example of sheeting that parallels the 

topographic surface; the sheets are concave in the 

bowl-shaped basins high on the cliff face and convex 

on the intervening spurs (fig. 41 ). 

The Royal Arches is a gigantic expression of sheet 

jointing, with sheets as much as 200 ft thick (fig. 

42). Too far below the surface to form the tops of 

domes, the arches reveal a cross- sectional view of 

sheet jointing in Half Dome Granodiorite that has 

been truncated by the north wall of Yosemite Valley. 

Similar features can also be seen on the walls behind 

Upper Yosemite Fall and at the head of Ribbon Fall 

alcove. . 

34 

A 

B 

SHEET JOINTS FOLLOW TOPOGRAPHIC SURF ACES. A, Horizontal sheeting exposed on quarry face, cut into 

broad, level surface. B, Convex sheeting on granite dome. C, 

Concave sheeting on valley floor. D, Near-vertical sheeting on 

Matthes Crest. Unloading has taken place from both sides of a 

steep linear ridge. Photograph from National Park Service collection. (Fig. 40) 
UNDULATING SURFACE below 

Clouds Rest. The sheet joints are concave in 

the bowl-shaped basins high on the cliff face, 

and convex on the intervening spurs. (Fig. 41) 

ROYAL ARCHES, in left center of photograph and topped by North Dome, is a gigantic expression of sheet joints, with 

sheets truncated by north wall of Yosemite Valley. Photograph by Eadweard Muybridge, about 1872. (Fig. 42) 

35 
Three surfaces 

weathering, 

corners rounded 

((-=;;;~ ~~f1·- ' . II .i"f•' fi" )1 

l • I 

.,;r'l . '" :1 Two surfaces weathering, 

t J' ..,., ._, edges rounded 

One surface 

weathering 

WEATHERING OF JOINT BLOCKS and stages in the 

formation of corestones. Corners and edges of granite blocks are 

attacked more readily by weathering along joints, and rounded 

corestones result. (Fig. 43) 

SPHEROIDAL WEATHERING around corestones. Rectangular pattern of sheets reflects horizontal and vertical orientation of joints originally bounding the disintegrating blocks. 

Roadcut at Big Meadow overlook, Big Oak Flat Road. 

(Fig. 44) 

36 

WEATHERING AND EROSION 

INFLUENCE OF THE ROCKS 

ON WEATHERING 

Unfractured granite is impermeable, and because 

weathering processes depend on the presence of 

moisture, exposed granite surfaces weather slowly. 

However, where buried by soil and in contact with a 

chemically reactive mixture of water, atmospheric 

gases, and organic decay products, granite weathers 

much more readily. Joints in the granite that provide 

avenues for deep circulation of ground water permit 

weathering to proceed well below the buried bedrock 

surface. As weathering penetrates the rock from joint 

surfaces, the edges and comers of the joint blocks are 

affected more rapidly than the sides, because they are 

attacked from two or three directions at once (fig. 43). 

The unweathered remnant of granite in the center of 

the joint block becomes a rounded boulder, called a 

corestone, and the process of its formation is a form of 

exfoliation called spheroidal weathering (fig. 44 ). 

Where water collects in small natural depressions 

on granitic-rock surfaces, the weathering process 

commonly enlarges the depressions to form weather 

pits, or pans (fig. 45). The pans are typically flat 

bottomed, a fact that has not yet been completely 

explained. A possible explanation is based on the 

proposition that the most active environment for 

weathering is the zone of alternate wetting and drying along the margins of the pools that collect in the 

pans. The margins tend to deepen and enlarge until 

all points of the bottom of the pan are equally wet or 

dry at the same time. Thereafter, they weather downward at a rate that is constant over all of the pan 

surface. This explanation also accounts for the overhanging rims, which are very common, and for 

coalescing pans, which also are common. The flat 

floors of the pans are horizontal even where the pans 

occur on the sides of boulders. The weathered material in the pans is removed by wind, although in 

deeper ones a granite sand remains. The process is a 

slow one-such pans normally are not found on 

surfaces scraped smooth during the last major glaciation, which ended some 10,000 years ago. 

The weathering and disintegration of rock, making it susceptible to erosion, depend on both rock 

composition and rock texture. The darker varieties of 

medium-grained granitic rocks, particularly those 

rich in biotite, weather more readily than the lighter 

colored varieties. Expansion of the biotite by absorption of water helps free the crystal from surrounding 
WEATHER PANS formed 

on summit of North Dome, high 

above Yosemite Valley. Neighboring pans coalesce as a result 

of progressive expansion at the 

expense of intermediate partitions. Photograph from 

National Park Service collection. (Fig. 45) 

mineral grains and thus leads to disaggregation of the 

rock. The resulting granular product, a granitic sand 

called grus, is easily eroded (fig. 46). For this reason, 

many topographic basins in granitic terrane are in 

areas underlain by biotite granodiorite, and ridges are 

held up by granites that contain less biotite. Finer 

grained plutonic rocks (both light and dark colored) 

are generally more resistant to formation of grus than 

coarser grained ones. Because the fine-grained rocks 

occur mostly as dikes and other small bodies, they 

have less effect on major landforms, although they 

sometimes create rather spectacular features (figs. 4 7, 

48). 

The composition and texture of metamorphic rocks 

also affect their weathering and erosion. Again, the 

presence of mica facilitates breakup of the rock during 

weathering. The most resistant metamorphic rocks are 

those containing abundant quartz, such as metamorphosed sandstone, and those made dense and hard 

from baking by magma. Many metamorphic rocks are 

more resistant than plutonic rocks; metamorphic rocks 

hold up much of the Sierran crest along the east edge 

of the park, as well as the Ritter Range southeast of the 

park. 

RESISTANT POTASSIUM FELDSPAR PHENOCRYSTS protrude from weathered surface of Cathedral Peak 

Granodiorite. Matrix minerals formerly enclosing the phenocrysts 

have been weathered to grus (granite sand) and washed away. 

(Fig. 46) 

37 
AGENTS OF EROSION 

Erosion, simply stated, is the removal of earth materials from high areas to low areas. Erosion thus tends to 

level a high area. 

Two agents of erosion are chiefly responsible for 

sculpting the present Yosemite landscape-flowing 

water and glacial ice. Flowing water had the major role, 

and glaciers added the final touches. The major drainages, the intervening divides, and the general landforms were all established before glaciation. Some of 

the glacial modifications were profound: the creation of 

alpine topography full of cirques and aretes along the 

higher divides, the rounding of many valleys from Vshaped to U-shaped and their straightening in the 

process, and the creation of hundreds of lakes and 

ponds where formerly there were none. 

Still another agent of erosion is simply gravity. The 

downslope movement of rock materials without the aid 

of a transport medium produces landslides and rockfalls. Although generally of local extent, such movement is important, particularly in mountainous terrain. 

In the winter of 1982, a rockfall dropped huge blocks of 

granite on Route 140 near the junction of the Old 

38 

KNOBS of resistant fine -

grained diorite protrude from 

weathered outcrop surface of 

El Capitan Granite. (Fig. 47) 

NATURAL BRIDGE formed where weather-resistant aplite 

bridges an opening eroded in underlying, less resistant Half Dome 

Granodiorite. (Fig. 48) 

Coulterville Road, about 2 mi east of the Arch Rock 

Entrance Station (fig. 49). The highway remained 

closed until a way could be blasted through the debris, 

and the little-used Old Coulterville Road on the slope 

above was blocked severely enough to be abandoned. 

ROCKFALL of blocks the size of small houses temporarily 

closed the El Portal Road east of Arch Rock Entrance Station in 

1982 until a way could be blasted through the debris. (Fig. 49) 
THE ROLE OF FLOWING WATER 

The work of flowing water can be seen at all scales, 

from that of tiny rivulets cascading down a slope after a 

rain and transporting soil-size particles, to raging flood 

torrents with streams using stones as hammers to break 

up material in their beds. But flowing water can transport cobbles and boulders only during the high-energy, 

turbulent flow of floods. Thus, the effectiveness of 

erosion by flowing water depends largely on processes of 

weathering, the breakdown of parent rock into molecules and rock or mineral fragments that the streams 

can transport easily. 

With the onset of late Cenozoic uplift of the range, 

the major streams were rejuvenated and made more 

vigorous by their increased gradients. In a mountain 

range that is rising faster than upland material can be 

removed, the tendency is for major streams to cut deep 

canyons, with both the local topographic relief and the 

maximum elevation of the range increasing. This canyon cutting requires that river-channel incision be faster 

than hillslope erosion. If river-channel incision can 

keep up with uplift but hillside erosion cannot, then 

stream channels become progressively deepened relative 

to areas between streams. In particular, for rocks resistant to weathering, channel incision will be relatively 

much faster than hillslope erosion, and a canyon is 

formed. Yosemite has superb examples in the canyons 

of the Tuolumne River, the Merced River (fig. 50), and 

the South Fork of the Merced River. The upper basins 

of these rivers ~ere later modified by glacial erosion, 

but the fact that the rivers flow in deep canyons beyond 

the western reach of past glaciers shows that canyon 

cutting was accomplished solely by the action of 

streams. 

The general courses of the major streams in 

Yosemite, with few exceptions, were probably inherited 

from the preuplift drainage pattern and depend mainly 

on the westerly slope of the range. The courses of the 

tributaries to the trunk streams and the shapes of their 

drainage basins depend more on granite composition 

and joints, as discussed in previous sections. 

The results of stream incision are depicted in a series 

of sketches that interpret landscape development from a 

region of gently rolling hills with meandering streams 

to one of canyonlands cut into the upland surface (fig. 

51). These scenes should be viewed as snapshots in a 

continuing process, rather than as distinct stages in 

landscape evolution. Note that granite domes form as 

the relief increases. The final scene is one conception 

of what Yosemite looked like about 2 or 3 million years 

ago, before the onset of glaciation. 

DEEPLY INCISED, UNGLACIATEDCANYON of the 

Merced River about 7 mi west of El Portal. Photograph by 

Dallas L. Peck. (Fig. 50) 

UPLIFT AND STREAM INCISION. A, About 15 million years ago, the Yosemite area was a rolling surface of 

rounded hills and broad valleys with meandering streams. B, By 10 million years ago, uplift of the range was sufficient to 

steepen stream gradients, and the valleys deepened. C, Before the onset of glaciation possibly some 2 million years ago, 

streams had incised deep canyons into the west flank of the range. (Fig. 51) 

39 
THE ROLE OF GLACIERS 

The Yosemite landscape as we see it today strongly 

reflects the dynamic influence of moving ice that long 

ago covered much of it several times. We are still 

uncertain as to how many times ice mantled Yosemite, 

but at least three major glaciations have been well 

documented in the Sierra Nevada, and other evidence 

suggests additional glacial episodes. 

Formation of glaciers requires that some of the snow 

that falls each winter persist through the following 

summer into the next winter's accumulation season. 

40 

VALLEY GLACIER sectioned 

to show relation between accumulation and wastage areas. Annual 

snowline, or firn limit, is the boundary where accumulation from seasonal snowfall equals loss from 

melting and evaporation. (Fig. 53) 

Thus, heavy winter snowfall or cool summer temperatures, or both, favor the growth of glaciers. If these 

conditions persist for a few centuries, possibly less, the 

layers of accumulating snow form a deposit thick 

enough for the snow in the lower part of the deposit to 

be compacted into ice (fig. 52). At a thickness of about 

100 ft, ice begins to flow outward under its own weight, 

and on slopes will begin to flow downhill at lesser 

thicknesses; when it flows, a glacier is born. 

As the glacier flows downhill, it enters regions of 

warmer climate, where the snow does not persist from 

year to year. The boundary where loss from melting and 

evaporation equals accumulation from snowfall is called 

the annual snowline or firn limit- "fim" being the 

term for partially compacted snow carried over from 

previous seasons (fig. 53). The firn limit fluctuates 

from year to year in response to changes in precipitation and temperature. The firn limit can be as much 

as 1, 000 ft lower in elevation on the shaded north 

sides of mountain peaks than on their sunny south 

sides. For this reason, nearly all of the small presentday glaciers in the Sierra are on north-facing slopes. 

The section of the glacier through which the 

maximum amount of ice flows coincides with the firn 

MACLURE GLACIER, showing annual layers of ice 

accumulation exposed after melting of seasonal snow. Note people 

for scale in lower right. The layers slant upward into the glacier; 

the youngest layers are highest up the slope. Photograph from 

National Park Service collection. (Fig. 52) 
limit, because as the glacier flows toward the firn 

limit, it is continually augmented by new net snowfall; and downvalley from the firn limit, more ice is 

lost by melting and evaporation- together called 

ablation- each year than is added by snowfall. As the 

glacier flows downvalley from the firn limit, more and 

more of the ice ablates, and the glacier grows thinner 

or narrower, or both. Ultimately a point is reached 

where the ice front can advance no farther because 

the ice melts there as rapidly as it is provided by 

inflow from upglacier. If the yearly rates of accumulation and ablation were constant, this point would be 

fixed. However, they vary, and for that reason alone 

the terminus of the glacier is not likely to be fixed in 

position. As the climate turns warmer or drier, a 

glacier will gradually waste away, rather than melting 

catastrophically. 

Glacial erosion 

The velocity at which a glacier slips over its bed is 

only about half the ice velocity measured at its surface; 

the difference is taken up by deformation within the 

moving ice. But it is the slippage over the bed that is 

responsible for glacial erosion. Wherever basal flow is 

especially strong, or the rock easily removed, bedrock 

basins are carved, which eventually hold lakes. The 

glaciers widen and deepen valley bottoms to give a 

characteristic U-shaped profile. On the leesides of bedrock projections into the ice are regions of low pressure 

where meltwater refreezes in cracks in the rock, prying 

loose blocks of bedrock that are then incorporated into 

the glacial ice and quarried away. Asymmetric rock 

knobs with smoothly abraded stoss, or upstream, sides 

and jagged and quarried leesides are called roches 

moutonnees and record the direction of glacier flow 

(fig. 54). Commonly translated as "sheep," moutonnee is actually a French adjective meaning "fleecy"; 

the term was introduced into geology in 1786 to 

describe rounded Alpine hills whose repeated curves, 

taken as a whole and as seen from a distance, 

resemble a thick fleece. As rock fragments embedded 

in the basal ice are dragged across the bedrock 

surface, they impart scratches, grooves, crescentic 

gouges, and a shining polish (fig. 55). 

Another feature of glacial erosion is the bowlshaped, theaterlike valley head called a cirque (fig. 

56). During the summer season, when no new snow 

is accumulating and the ice pulls away from the rock 

face at the head of the glacier, a great crevice, called 

a bergschrund, opens. This opening exposes the rock 

at the head of the cirque to freezing and thawing, 

ROCHE MOUTONNEE, sectioned to show the influence of 

jointing on its development. The ice moves upward over unjointed 

rock, smoothing it off, and plucks up and carries away blocks of 

jointed rock. (Fig. 54) 

A 

B 

IMPRINTS ON THE ROCK left by passing debris-laden 

ice. A, Glacial polish and striations {lower right). Crescentic 

gouges, or percussion marks, are visible in center; horns of the 

crescents point upglacier. Chatter marks (not illustrated) consist of 

a group of crescent-shaped cracks pointing downglacier, but 

generally they do not form gouges. Photograph by john P. Lockwood. B, Glacial polish and striations. Polished surface layer 

flakes off, and this evidence of glaciation gradually disappears. 

This excellent and accessible exposure is at the foot of Polly Dome 

along the Tioga Road on the north side ofTenaya Lake. (Fig. 55) 

41 
MOUNTAIN CREST, showing valley glacier and glacial 

sculpture. (Fig. 56) 

which wedges blocks of rock free from the base of the 

cliff. The freed blocks, frozen · into the main mass of 

ice during the winter season, are then transported 

out of the cirque by the glacier; retreat of the 

headwall thus enlarges the cirque. 

The cliffs behind the cirques and above the glacier 

surface elsewhere are also sculpted by the freezing of 

water in cracks in the rock. Expansion of water when 

it freezes to ice breaks and wedges out blocks, which 

then avalanche onto the glacier's surface below. The 

falling blocks knock loose any projecting rock in 

their paths, and chip away fragments as they bounce 

down the cliff face. The hollows created by the 

detachment of these blocks and by the erosion they 

cause on their fall collect and hold more moisture 

than do the projecting ribs between them; they thus 

retreat more rapidly by frost wedging than do the 

ribs, so that even if initially smooth, a cliff face, 

given enough time, can become intricately sculptured. 

As the cliffs on opposite sides of a ridge are 

quarried back by frost action above the active cirque 

glaciers, they eventually intersect to form a sharp, 

jagged rock crest called an arete, with sharp peaks, 

called horns, where the ridges branch (fig. 56). The 

sharp change in character of the walls of glaciated 

valleys- from intricate and jagged sculpturing above, 

to smooth sculpturing below-marks the edge, or 

trimline, of the former glacier and makes it possible to 

reconstruct the former margin of the mountain icefield (fig. 57). 

Glaciated valleys are nearly straight and have Ushaped crossprofiles, in contrast to the sinuous Vshaped valleys of normal stream erosion (figs. 50, 58). 

At the high velocities of running water, inertia throws 

the fastest current against the outside of a bend. At the 

much slower velocities of glacial ice, the fastest flow is 

on the insides of bends, where the distance is shorter 

and the ice surface is steepest. Thus, whereas a stream 

erodes the outsides of bends preferentially and makes its 

course more sinuous, glacial erosion is concentrated on 

the insides of bends, removing the overlapping spurs of 

This V-shaped valley .... modified by water . then modified by ice . 

42 
the original stream-eroded valley and leaving a wide, 

straight valley floor in place of the sinuous one. A 

major factor leading to the U-shaped crossprofile of 

glacial valleys is the ability of a glacier to erode far up 

the valley walls. The entire glaciated valley was once 

occupied by the former glacier that carved it, whereas a 

stream occupies only the very bottom of its valley. 

In addition to truncated spurs, hanging tributary 

valleys are formed on the sides of glaciated valleys. In a 

landscape developed by stream erosion, tributary 

streams normally join the main-trunk river at the same 

level. During glaciation, the upper surfaces of the 

glaciers occupying the tributary valleys join at the level 

of the surface of the ice filling the main channel; but 

beneath the ice the trunk glacier, with its greater 

thickness and erosive power, carves much more deeply 

into the bedrock than the tributary glaciers can. When 

the glacier wastes away and the ice is all gone, the 

tributary valleys are left hanging high up on the sides of 

the trunk valley, and their streams cascade or fall to 

join the main river below (fig. 58). During the time 

since the pre-Tahoe glaciation, when Yosemite Valley 

acquired nearly its present form, spray from the waterfalls freezing in cracks in the rock at the base of the cliff 

promoted spalling of rock slabs there and formed the 

recessed alcoves into which the falls now leap. Most of 

the waterfalls in Yosemite Valley formed in this manner 

and, indeed, are the finest examples anywhere (fig. 59). 

Thus, throughout the world the name "Yosemite" has 

come to spell "waterfalls." 

VALLEY MODIFICATION by glacial erosion, showing 

stages in the conversion of a meandering V-shaped valley into a 

straightened U-shaped valley. (Fig. 58) 

results in this U -shaped valley 

JAGGED UNGLACIATED SPIRES of Unicorn Peak rising above smooth shoulders of glacially scoured granite. Boundary 

between jagged sculpture above and smooth below, called the trimline, marks upper limit of a former glacier along the valley wall. 

(Fig. 57) 

BRIDALVEIL FALL, an outstanding example of a waterfall 

issuing from a hanging valley far above Yosemite Valley floor. 

Photograph by julia A. Thomas. (Fig. 59) 

43 
Glacial deposition 

Glacially carved landforms are the most striking 

evidence of the passage of long-gone ice masses. But 

glaciers must eventually deposit the materials they are 

transporting, and in the process they also build up 

characteristic landforms. The material deposited by 

glaciers is an unsorted mixture of boulders, sand, and 

day called till (fig. 60). Till may be deposited by the 

glacier on its bed as it is actively flowing, or the till 

may be left behind as the ice melts away, generally 

beginning as an accumulation of rock debris on the 

ice surface. Other depositional evidence of ice 

includes glacial erratics, boulders left behind as the 

ice melted (fig. 61). Direction of glacial transport is 

commonly indicated by boulders of rock types different from the bedrock on which they rest, but that 

can be traced back upglacier to a source area. 

Whereas till is the unsorted material deposited by a 

glacier, the deposit itself is known as moraine, and 

such moraine takes different topographic forms, 

depending on how the till was deposited. 

The most distinctive morainal features in the Sierra 

Nevada are lateral moraines, linear ridges of till that 

rest on the sides of the glaciated valley and extend 

parallel to the valley axis (fig. 62). These ridges 

generally define the maximum height and width of 

the glacier that deposited them. Commonly, lateral 

moraines curve around at their lower ends to form 

terminal moraines, ridges of till deposited at the terminus of a glacier. When a glacial cycle ends, glaciers 

do not always melt back uniformly; instead, they 

commonly pause periodically in their retreat, constructing a series of recessional moraines. Excellent 

examples of all these varieties of moraines can be 

seen in Lee Vining Canyon just east of the park (fig. 

63). 

Most of the terminal and recessional moraines on 

the west side of the Sierra Nevada have been 

breached or removed by swift meltwater streams, and 

it is doubtful whether they were even deposited in 

the steep narrow canyons of most of the west-flowing 

streams, such as the Merced River west of Yosemite 

Valley. The glaciers that debouched onto the 

lowlands along the east base of the Sierra Nevada, 

however, left distinct terminal moraines, some of 

which presently enclose lakes. 

Where two glaciers join to form a single trunk 

glacier, the lateral moraines being formed on their 

adjoining sides will continue as a linear train of 

debris outward onto the surface of the trunk glacier. 

44 

GLACIAL TILL, an unsorted mixture of boulders, sand, and 

clay, exposed along the Tioga Road at Siesta Lake. (Fig. 60) 

GLACIAL ERRATIC transported by a glacier and left precariously balanced near Olmsted Point as the ice melted. (Fig. 61) 

This train is called a medial moraine, and when the 

glacier melts, the debris will form a linear ridge 

parallel to the axis of the glacial valley. Such a 

medial moraine can be seen where the Merced and 

Tenaya Glaciers once joined at the east end of 

Yosemite Valley. 

The total amount of till left as moraine in 

Yosemite and elsewhere on the west slope of the 

Sierra Nevada is small, however, in comparison with 

the amount of glacially derived debris that was 

flushed out of the mountains by streams swollen with 

glacial meltwater. Most of that debris was then 

deposited as alluvial fans and valley fill in the Central Valley, and some of the finer material traveled 

even farther, finally coming to rest in the San Francisco Bay and the Pacific Ocean. 
I 

MORAINES formed by a valley glacier. 

Lateral moraine formed along side margin 

of glacier; terminal moraine formed at point 

of farthest glacial advance; and recessional 

moraine formed during pause in retreat of 

glacier. Ground moraine is a rather shapeless, hummocky till deposited beneath a 

glacier or simply left behind as the glacier 

retreats or wastes away. (Fig. 62) 

MORAINES IN LEE VINING CANYON east of Tioga 

Pass, looking westward toward crest of the Sierra. Paired lateral 

moraines on both sides of the canyon extend toward the viewer; the 

outer pair (0) represent the Tahoe glaciation, and the inner pair 

(I) the Tioga glaciation. The inner pair of moraines coalesce to 

form a terminal moraine (T) at lower left. A recessional moraine 

(R) crosses the valley as a low, tree-lined ridge. Photograph by 

Clyde Wahrhaftig. (Fig. 63) 

THE RECORD OF 

PLEISTOCENE GLACIATIONS 

The record of glaciation in Yosemite National Park is 

very incomplete. Only for the last two major glaciations 

can the extent of the ice be reconstructed with any 

confidence. Older glacial deposits, if preserved at all, 

are so fragmentary that it is generally impossible to 

distinguish the separate ice advances that may have 

deposited them. The glaciers grew and melted . away in 

response to climatic changes of long duration that were 

probably worldwide, and so a record of all the glaciations that might have affected Yosemite must be sought 

elsewhere. 

During worldwide glacial cycles, large volumes of 

water evaporated from the oceans are stored on land as 

ice; this storage causes a decrease in the volume of 

water remaining in the oceans. During evaporation of 

seawater, the light isotope of oxygen- oxygen-16- is 

more easily lost to atmospheric vapor than is the heavy 

isotope-oxygen-18. When this vapor precipitates on 

land and is stored as ice, rather than returning to the 

oceans, the ratio of these two isotopes of oxygen 

remaining in the ocean will change. Organisms living 

in the oceans at any given time secrete calcareous shells 

whose ratio of oxygen isotopes is comparable to that of 

the water in which the organisms lived. Measurements 

of fluctuations in this ratio provide indirect measurements of ice volume, with times of large ice volume 

interpreted as glacial episodes. Isotopic measurements 

on such shells extracted from deep-sea sediment samples indicate about 10 major glacial episodes during the 

past 1 million years. Normally, evidence for only a 

small fraction of these glaciations can be found in a 

45 
given area on land, because the more extensive glaciers 

destroy the moraines of earlier, less extensive ones. 

Only if older glaciers extended beyond the limits of 

younger glaciers will the older deposits remain to document the earlier glacier's existence, and so the glaciations now recognized in Yosemite may be only a 

fraction of those that actually occurred. 

Fran~ois Matthes presented evidence for three major 

glaciations in Yosemite, which he called, from youngest 

to oldest, Wisconsin, El Portal, and Glacier Point. 

Working on the east side of the Sierra about the same 

time, Eliot Blackwelder recognized four major glaciations: Tioga, Tahoe, Sherwin, and McGee; these latter 

terms have become firmly established and have largely 

replaced those of Matthes. His Wisconsin is now 

thought to include equivalents of both the Tioga and 

Tahoe glaciations, and his El Portal is probably equivTIOGA MORAINE in Harden Lake area, showing sharp 

crest and abundant boulders exposed on surface. (Fig. 64) 

TAHOE MORAINE in Harden Lake area, showing subdued 

crest and only scattered boulders exposed on surface. (Fig. 65) 

46 

alent to the Sherwin. The evidence for Matthes' separate Glacier Point glaciation is unconvincing, and there 

may not be an equivalent of the McGee in Yosemite. 

Many additional glacial episodes have been proposed to 

account for the diverse deposits of till, outwash, and 

glacial-lake sediment on the east side of the Sierra 

Nevada. There is disagreement, however, as to whether 

each of these deposits represents separate glaciations or 

pulses within major glaciations, and they have not been 

recognized in Yosemite. 

In Yosemite, deposits of three separate glacial episodes are now distinguished on the following basis: 

1. Tioga (youngest): Unweathered till consisting of 

fresh granitic boulders and loose, porous gravel and 

sand, making sharp-crested moraines that have 

closely spaced boulders on their upper surfaces (fig. 

64). 

2. Tahoe (intermediate): Subdued moraines whose buried granodiorite boulders have commonly disintegrated at least partly to grus. The summits of these 

moraines tend to be rounded, and exposed boulders 

along their crests are generally sparse (fig. 65). 

3. Pre-Tahoe (oldest): Outside the ice limits defined by 

the intermediate moraines, a few glacial erratics, 

commonly perched (fig. 66), and patches of formless 

glacial till give evidence of at least one earlier ice 

advance more extensive than the glaciers that 

deposited the intermediate moraines. 

By recognizing these distinctions, we can at least 

partly reconstruct the glacial geology of Yosemite. 

THE GLACIAL GEOLOGY OF YOSEMITE 

The glacially related features of today's landscape, 

both erosional and depositional, largely reflect the 

latest major glaciation, the Tioga. The effects of multiple glaciations are cumulative, however, and the effects 

of earlier glaciations must have been substantial, 

although we can only gauge them by inference. We 

shall examine the end results of these episodic glaciations culminating with the Tioga, and then examine 

the evidence for the work of earlier glaciations. 

The Tioga glaciation began about 30,000 to 60,000 

years ago, when a cooling climate permitted small 

glaciers to develop in high cirques originally formed and 

then abandoned by earlier glaciers. With continued 

cooling, these glaciers grew and moved outward and 

downward to coalesce into a mountain icefield, with 

only the higher peaks and divides projecting through as 

an~tes and horns. With further growth, the icefield fed 

fingers of ice into the major drainages on the west slope 
PERCHED ERRATIC deposited on ridge west of Upper 

Yosemite Fall during a pre-Tahoe glaciation. Pedestal height of 5 

ft indicates amount of rock weathered away since boulder was 

dropped by the ice. Photograph from National Park Service 

collection. (Fig. 66) 

of the Sierra, until the ice reached its maximum extent 

about 15,000 to 20,000 years ago (fig. 67). 

The icefield in the upper Tuolumne River basin, and 

in the tributary basins to the north, fed the glacier that 

moved down the canyon of the Tuolumne River 

through Hetch Hetchy Valley. Some of the ice filling 

the basin of the Lyell Fork of the Tuolumne spilled over 

low passes to augment ice in the Merced River basin 

that flowed down through Little Yosemite Valley. 

Tuolumne ice also flowed over a pass into the Tenaya 

Lake basin and down Tenaya Canyon to join the main 

Merced Glacier in Yosemite Valley. During the Tioga 

glaciation, the glacier in Yosemite Valley reached only 

as far as Bridalveil Meadow. 

Tioga ice also flowed eastward from the summit 

region to cascade down canyons cut into the east 

TIOGA ICEFIELD AND VALLEY GLACIERS, showing maximum extent during the Tioga glaciation, the last major 

glaciation in the Sierra Nevada, which peaked about 20,000 to 

15,000 years ago. (Fig. 67) 

Contours m feet; 

blue arrows indicate 

direction of flow 

of Ice. 

47 
U-SHAPED GLACIATED VALLEY, the Lyell Fork of the Tuolumne River, looking southward. Photograph by Robert W. 

Cameron. © Cameron and Company; used with permission. (Fig. 68) 

escarpment of the Sierra. Southeast of the park, ice 

from the Mount Lyell area flowed eastward onto the 

Mono lowland and southeastward and southward down 

the Middle and North Forks of the San Joaquin River. 

In the southern part of the park, ice in the South Fork 

of the Merced River reached nearly to the present site 

of Wawona. 

In addition to the major icefields in the headwaters 

of the Tuolumne and Merced Rivers and the major 

valley glaciers they fed, smaller, isolated glaciers formed 

in favorable localities, as on Buena Vista Crest, Horse 

Ridge, and above Siesta Lake near the Tioga Road. 

Each played a part in creating today's landscape. 

At the time of the Tioga glacial maximum, glacial 

Lake Russell was much larger than the present-day 

Mono Lake (fig. 67 ). The surface elevation of Lake 

Russell at that time was about 6,800 ft, 425 ft higher 

than the 1980 elevation of Mono Lake of about 6,375 

48 

ft. The increased volume of Lake Russell was probably 

due to a much lower rate of evaporation of water from 

the lake during Tioga time, partly because of the 

prevailing cooler climate and partly because the lake 

probably was covered by ice much of the time. 

The Tuolumne Meadows area is one of the most 

accessible, as well as one of the best, places to see how 

glaciers modified the landscape by both erosion and 

deposition. The Lyell Fork of the Tuolumne River flows 

to the meadows through one of the park's finest examples of a U-shaped valley (fig. 68). The frost-riven 

spires of Unicorn and Cathedral Peaks standing above 

smoothly rounded granite shoulders graphically indicate 

the height to which Tioga ice reached (fig. 57). Glacial 

polish high on Fairview Dome indicates that it was 

overtopped by ice (fig. 69). Lembert Dome, on the 

northeast side of the meadows, is a roche moutonnee 

that records stoss-side smoothing and leeside plucking 
on a grand scale, as does the smaller but easily 

ascended Pothole Dome at the meadow's west end (fig. 

70). Glacial polish and striations can be seen on many 

outcrops, and erratic boulders abound. 

A series of potholes angles diagonally from level 

ground up the south side of Pothole Dome (fig. 71). 

The rock polish near these potholes can easily be 

mistaken for glacial polish, but it has a different origin. 

Unlike glacially polished surfaces, which are generally 

planar, these surfaces are fluted (fig. 72), like those 

forming on bedrock today by flowing water of the 

Tuolumne River. Both the polish on this part of Pothole Dome, and the potholes themselves, were created 

by water in a subglacial stream that flowed upward over 

the dome in a tunnel beneath ice of the Tioga glacier. 

Glacial polish can, indeed, be seen on the gentle eastfacing slope of the dome, the stoss side of this roche 

moutonnee. 

POTHOLE DOME, a large 

roche moutonnee on the west side 

of Tuolumne Meadows, was 

shaped by glacial smoothing and 

plucking. Ice moved from right 

(stoss side) to left (leeside). 

Fluted surface was shaped by 

subglacial water scour (see fig. 

72). (Fig. 70) 

POTHOLES angling up side of Pothole Dome, west side of 

Tuolumne Meadows. Bowl-shaped potholes are carved into the 

rock by the grinding action of stones whirled around and kept in 

motion by the force of a stream in a given spot. Here, the stream 

flowed in a tunnel beneath the ice that covered this area during the 

Tioga glaciation. (Fig. 71) 

GLACIAL POLISH high on east shoulder of Fairview Dome. 

It and similar polish and erratics on the summit indicate that the 

dome was once overtopped by ice. (Fig. 69) 

SUBGLACIAL WATER POLISH on Pothole Dome, 

formed by water flowing beneath the glacier. Surface is fluted 

rather than flat, as with glacial polish (compare with fig. 55). 

Polished surface layer is flaking off, similar to the glacial polish 

shown in figure 558. (Fig. 72) 

49 
Most of the till in the Tuolumne Meadows area was 

deposited as hummocky ground moraine beneath the 

glacier, or left behind as the glacier wasted away. The 

small lakes in ground moraine southeast of the 

entrance station at Tioga Pass appear to be kettles, 

depressions left by the final melting of blocks of ice 

buried in till (fig. 73 ). Elongate ridges of moraine 

flank the roadway between Tioga Pass and Tuolumne 

Meadows, and a cross section through such till is 

exposed in a roadcut about 1 Yz mi east of the 

Toulumne River bridge. Lateral and recessional moraines are inconspicuous and may be absent in the 

Tuolumne Meadows area, but magnificent examples 

of both are in lower Lee Vining Canyon along the 

Tioga Road east of the park (fig. 63). 

Yosemite Valley, in spite of its profound glacial 

modification, is not a good place to see much direct 

evidence of glaciation. The Tioga glacier only 

reached as far as Bridalveil Meadow, where its terminal moraine, although well exposed in a roadcut (fig. 

74 ), is relatively inconspicuous, and lateral moraines 

are absent. Glacial polish and striations are scarce, 

but they can be seen on a low, flat shelf of rock near 

the base of the north valley wall opposite the west 

end of the Yosemite Lodge, and along the base of the 

cliffs on the north side of the Tenaya Lake Trail, 

about 500 to 1,000 ft east of Mirror Lake. Glacial 

polish also occurs in such places as on the slope of 

the Glacier Point apron, but these localities are 

50 

KETTLES (small lakes) near 

Tioga Pass, filling depressions 

left by the final melting of blocks 

of glacial ice. View eastward 

across Dana Meadows toward 

Mount Dana. (fig. 73) 

accessible only to the experienced climber. This 

paucity of direct evidence is probably the basis for 

Josiah Whitney's stand against the glacial origin of 

Yosemite Valley, noting as he did the glaciation of 

Hetch Hetchy Valley, where he described glacial 

polish at least 800 ft and a glacial moraine 1, 200 ft 

above the valley floor. 

The Tahoe glaciation was almost everywhere somewhat more extensive than the Tioga, and so its moraines lie outboard of Tioga moraines. Recent studies 

suggest that Yosemite Valley was an exception: a Tahoeage glacier reached Yosemite Valley but was smaller and 

thinner, and did not extend as far into the valley as 

Tioga ice did. If both the Tioga and Tahoe glaciers had 

limited erosive power in Yosemite Valley because they 

both were relatively thin, then the valley must have 

attained nearly its present shape during one or more 

pre-Tahoe glaciations. 

Direct evidence for pre-Tahoe glaciation in Yosemite 

Valley is also elusive. It consists mostly of scattered, 

commonly perched erratics on upland areas adjacent to 

the valley (fig. 66). These perched erratics rest on 

pillars of rock protected from weathering and erosion by 

the erratic itself. The surrounding area commonly has 

been lowered several feet or more by erosion since the 

erratics were left as the ice melted. This amount of 

erosion, which is not seen in areas overridden and 

scoured by Tahoe ice, is the main argument for 

attributing these erratics to a much earlier glaciation. 
Readily accessible examples of pre-Tahoe erratics, 

though not perched, occur near the radio-relay tower 

on Turtleback Dome above the Wawona Road. A small 

patch of old, deeply weathered till is exposed in a 

roadcut on the Big Oak Flat Road just east of the 

bridge crossing Cascade Creek. This till, about 1,000 ft 

above the valley floor, would hardly be recognized as 

such without the artificial cut. These erratics and till 

are assigned to one or more pre-Tahoe glaciers that 

filled Yosemite Valley (fig. 75). No terminal moraine for 

this glaciation remains in the Merced River canyon, 

but the glacier could not have extended more than a 

short distance below the town of El Portal, where the 

canyon abruptly starts to meander and has a V shape 

(fig. 76). 

Evidence for three separate glaciations in Yosemite is 

most readily seen at Harden Lake, about 3 mi down the 

Old Tioga Road from White Wol£ Harden Lake sits on 

the edge of the upland bordering the Grand Canyon of 

the Tuolumne River, which was completely filled with 

ice during each of the three recognized glaciations. 

Harden Lake is sandwiched between fresh, bouldery 

lateral moraines reflecting pulses of Tioga ice (fig. 64). 

Outside of these moraines, farther from the canyon, are 

Tahoe moraines, still-linear but subdued ridges, with 

extensive soil cover and only scattered boulders on the 

surface (fig. 65). Farthest from the canyon, outside of 

the Tahoe moraines, are pre-Tahoe erratics and highly 

dissected till whose original morainal form has been 

destroyed by erosion. 

GLACIAL MORAINES IN YOSEMITE VALLEY. 

A, Tioga-age terminal moraine exposed in roadcut just east of 

Bridalveil Meadow. This moraine contains large boulders of 

Cathedral Peak Granodiorite, clear evidence of glacial transport from Tuolumne Meadows via Tenaya Canyon or from the 

upper Merced River basin via Little Yosemite Valley. B, Tiogaage recessional moraine exposed in roadcut below Cathedral 

Rock. Large boulder in center is of Cathedral Peak Granodiorite. (Fig. 74) 

A 

B 

GLACIERS COME AND GO. Sketches of Yosemite Valley area, showing extent of pre-Tahoe glacier (A), extent of Tioga glacier 

(8~ and glacial Lake Yosemite after retreat of Tioga ice {C). (Fig. 75) 

-: ~ , 

~~::-· 

A 

51 
EXPLANATION 

Maximum extent of 

Tioga ice 

D 37' 

45' 

Maximum extent of 

Pre -Tahoe ice 

A El Portal 

B Arch Rock 

C Elephant Rock 

D Bridalveil Fall 

E Ribbon Fall 

F El Capitan 

G Yosemite Falls 

H Sentinel Rock 

I Sentinel Dome 

J North Dome 

K Mirror Lake 

L Half Dome 

M Glacier Point 

N Nevada Fall 

0 lllilouette Fall 

P Mt. Starr King 

PRE-TAHOE GLACIATION-its extent in the Yosemite Valley area in comparison with that of the Tioga glaciation. (Fig. 76) 

WHAT THE GLACIERS MISSED 

Among the aretes and cols of the Sierran crest and 

adjacent spurs are anomalous areas with gently rolling 

surfaces that escaped glacial sculpting; the Dana Plateau 

is an outstanding example (fig. 77). These areas apparently never accumulated enough snow to generate 

glaciers on their upland surfaces. Not only is the 

Sierran crest swept by strong winds, but it also receives 

less snowfall than areas farther west because most of the 

moisture is wrung out of the upwelling stormclouds 

before they reach the crest. Glaciers did form in cirques 

on the lower protected slopes of these plateaus, particularly on northerly slopes, where sufficient snow 

could accumulate by wind drift from the plateaus to the 

windward and remain through the summer. But these 

glaciers never succeeded in cutting cirques far enough 

back into the plateaus to entirely destroy them. 

These upland surfaces did not totally escape the 

effects of glacial climate. Cycles of freezing and thawing 

broke the bedrock along fractures and heaved it into a 

mass of jumbled blocks. Such rubble-covered surfaces 

are scattered along the Sierran crest, as at Dana Plateau 

(fig. 78), and include the summit of Mount Whitney 

50 mi to the south. The south-facing slope of Mount 

Hoffmann, our original vantage point in the park, is a 

somewhat similar upland surface, although slow disintegration and spalling of granite sheets has created an 

52 

DANA PLATEAU, unglaciated remnant of an ancient land 

surface sharply truncated by glacial cirques. Ellery Lake and the 

Tioga Road lie 2,000 ft below. At upper right is Mount Dana, 

with an unglaciated surface sloping downward to right. These two 

remnant surfaces are parts of a once-continuous surface breached 

by a glacial cirque excavated by past glaciers and now containing 

the present-day Dana Glacier, seen as the gray, oval-shaped spot 

on the snow below Mount Dana (see fig. 82). Photograph by 

Robert W Cameron. ©Cameron and Co.; used with permission. 

(Fig. 77) 
BOULDER-STREWN UPLAND SURFACE on the 

Dana Plateau. Frost-heaved joint blocks have been rounded by 

sand-blasting action of wind-driven grit. Snow chute on Mount 

Dana near right margin leads down to the Dana Glacier across 

Glacier Canyon from the plateau. View southeastward. Width of 

view in middle distance is about Yz mi; southeast edge of plateau is 

about I Y:z mi away. (Fig. 78) 

53 
irregular, flaggy surface. This unglaciated surface is 

abruptly truncated by a glacial cirque cut deeply into 

the north face of Hof&nann- a striking contrast in 

erosional processes (fig. 79). 

These upland surfaces have a significance far beyond 

being unglaciated, because they are very ancient. They 

are remnants of the gently rolling terrain that existed 

here before the late Cenozoic uplift and incision of the 

Sierra that began about 25 million years ago. As the 

range was uplifted and tilted, the major westwardflowing streams incised deeper and deeper canyons, 

cutting headward into the range. The upland areas 

near the stream headwaters were the last to be 

affected-some remnants still remain undissected. 

WEST SHOULDER OF MOUNT HOFFMANN. 

Smooth, unglaciated south-facing slope (to left) is abruptly truncated by a north-facing glacial cirque-a striking contrast in 

erosional processes. (fig. 79) 

MODERN GLACIERS 

Although Tioga glaciers were the last to cap large 

parts of the Sierra Nevada, the modem Sierran glaciers 

are not remnants of Tioga ice. Instead, they formed 

during one or more post-Pleistocene cool cycles that 

Fran<;ois Matthes collectively called the "Little Ice 

Age." Because of ambiguity in its definition and wide 

variation in its application, students of glacial geology 

have generally abandoned the term, and postPleistocene glaciations are referred to as Neoglacial 

events. The latest of these Neoglacial events in the 

Sierra Nevada, to which the present-day glaciers 

belong, has been called the Matthes glaciation in 

honor of his pioneering studies. 

After the end of the Pleistocene (10,000 years ago), 

temperatures in many parts of the world rose, reaching 

54 

a maximum about 5,000 years ago. By that time, 

probably no glaciers survived in the Sierra Nevada. 

Temperatures then dropped, first slowly, then more 

rapidly; and small glaciers began to form in the Sierra 

once again by about 2,500 years ago. 

World climate has continued to fluctuate through 

warming and cooling cycles up to the present. Historical records in the Alps indicate a major glacial 

advance about A.D. 1600, when glaciers descended 

into valleys and overwhelmed pastureland and villages. 

The most recent major advance there occurred about 

1850. If Sierran glaciation was synchronous, Yosemite's 

modem glaciers would have been near their most recent 

maximum about the same time that John Muir was 

making his studies. We do know that Sierran glaciers 

have been receding rather rapidly since Muir's day: The 

first "living glacier" discovered by Muir in 1871, on 

Merced Peak, no longer exists. 

As of 1980, there were nearly 500 glaciers remaining 

in the Sierra Nevada, most of them so small as to 

barely show evidence of iceflow, such as a bergschrund. 

The largest glacier left in the Sierra, the Palisade 

Glacier in the John Muir Wilderness, covers little more 

than Yz mi2; and the largest in Yosemite, the Lyell 

Glacier, less than Y4 mi2 (figs. 80, 81). 

Few of the modem glaciers extended very far from 

their cirques, but many left rather impressive arcuate 

piles of moraine, considering their small size. Dana 

Glacier and its moraines are the most readily accessible 

of those remaining in the park (fig. 82); it is about a 3-

hour hike upcanyon from the south shore of Tioga 

Lake east of Tioga Pass, but does require scrambling 

over large boulder piles. The glacier is now but a mere 

shadow of its former self as shown in a photograph 

taken early in the 20th century (fig. 83). This 1908 

photograph shows Dana Glacier nestled up against its 

terminal moraine, and so it had not receded much, if 

any, from its latest advance. In the 67 years between 

the two photographs, the glacier lost about threefourths of its area and a much larger fraction of its 

volume. 

LYELL AND MACLURE GLACIERS. Lyell Glacier (on 

left) is divided into two parts by an intervening ridge. Lobate 

terminal moraine below indicates that at the maximum extent of the 

glacier, the two parts joined at the base of that ridge. Gray areas 

are ice exposed after melting of seasonal snow. Crevasses are 

especially well displayed in the ice exposed on the Maclure Glacier 

(on right). View southward. Photograph by Austin Post, August 

1972. (Fig. 80) 
LYELL AND MACLURE 

GLACIERS, as they were mapped in 

1883 by Willard D. Johnson of the U.S. 

Geological Survey. Comparison with the 

present-day glaciers in figure 80 indicates 

their much greater extent at that earlier 

date. Mount Maclure, named by Josiah 

Whitney for an early American geologist, 

is here mistakenly labeled "McClure." 

This error may be the source of occasional 

confusion in associating the mountain with 

Lt. N. F. McClure, who, however, was 

not on the scene as a guardian of Yosemite 

National Park until after 1890. (Fig. 81) 

55 
DANA GLACIER, 1975. Crevassed ice of the Dana Glacier 

is exposed in left center of photograph, and the glacier's 

bergschrund is barely visible in shadowed area above. Since the 

early part of the 20th century, the glacier has retreated headward 

from its terminal moraine, visible in lower right (compare fig. 83). 

View southwestward. Photograph by Malcolm M. Clark, September 1975. (Fig. 82) 

DANA GLACIER, 1908. When this photograph was taken 

early in the 20th century, ice of the Dana Glacier abutted the 

terminal moraine, visible in center. Note bergschrund near glacier 

head below cirque headwall. View southeastward. Photograph 

by G. K. Gilbert, August 1908. (Fig. 83) 

56 

AFTER THE GLACIERS 

The cold cycle that brought about the Tioga glaciation ended about 10,000 years ago. Because glaciers 

during Neoglacial episodes were so small, running 

water, along with gravity, has dominated further shaping of the Yosemite landscape since Tioga time. The 

principal changes in landscape have been the filling of 

lakes with rehandled Tioga till; meadows have formed 

as a result. 

One lake to be converted to meadows was ancient 

Lake Yosemite, which occupied Yosemite Valley 

upstream from a moraine dam near the foot of Cathedral Rocks (fig. 75). This was only the last of many 

"Lake Yosemites" that probably followed each glaciation. The deep excavation created by earlier glaciers, as 

much as 2,000 ft into bedrock beneath Yosemite Valley, 

was aleady filled with glacial till and sediment long 

before Tioga time, and the Tioga ice had insufficient 

erosive power to reexcavate the valley to any appreciable depth. Lake Yosemite eventually filled in with silt, 

leaving today's level valley floor. 

Gravity, commonly aided by water and ice, acting 

on slopes oversteepened by glacial undercutting, modifies the landscape most visibly. Canyon walls are constantly shedding rock fragments, and tremendous cones 

of debris accumulate in winter below avalanche chutes 

(fig. 84). 

Rockfalls, the largest probably triggered by earthquakes, can catastrophically move large volumes of 

material (fig. 85). One rockfall, graphically described 

by John Muir, occurred in Yosemite Valley during the 

great Owens Valley earthquake of 1872: "The Eagle 

Rock on the south wall, about a half mile up the 

Valley, gave way and I saw it falling in thousands of the 

great boulders I had so long been studying, pouring to 

the Valley floor in a free curve luminous from friction, 

making a terribly sublime spectacle-an arc of glowing, 

passionate fire, fifteen hundred feet span, as true in 

form and as serene in beauty as a rainbow in the midst 

of the stupendous, roaring rock-storm." In May 1980, 

two people were critically injured on the Sierra Point 

Trail east of Happy Isles by rocks dislodged during a 

much smaller earthquake whose epicenter was near 

Mammoth Lakes, over 35 mi to the east. Ironically, 

this trail had been officially closed some years earlier, 

owing to the danger of loose rock. Another rockfall 

that killed three hikers on the Yosemite Falls Trail 6 

months later may have been a delayed result of rock 

loosened during that same earthquake. A rockfall created the dam that formed Mirror Lake, which, in tum, 
is being filled by sediment carried by Tenaya Creek. 

Dynamic change is indeed taking place, though slowly. 

One lifetime is not enough to see dramatic changes. 

No sooner had the glaciers departed than weathering 

processes began to attack the freshly scoured rock 

surfaces left behind. Surface spalling leaves only remnants of once-extensive glacial polish. When the polish 

and glacial striations are all gone, some of the most 

striking evidence for past glaciation will be lost. 

The landscape is slowly but continually being modified. The Sierra Nevada continues to rise-and continues to be eroded. Lakes are being filled with sediment. When erosion outpaces uplift, as it eventually 

will, the range will be reduced to rolling upland, much 

as it was tens of millions of years ago. In the meantime, 

Yosemite remains a delight to the visitor, especially to 

those who learn to read the story its rocks and landscape have to tell. 

AVALANCHE CHUTES AND TALUS CONES in Lee 

Vining Canyon east of Tioga Pass. (Fig. 84) 

THE SLIDE on Slide Mountain west of Matterhorn Peak, near north boundary of the park. This giant rockslide, more than liz mi long 

and lj4 mi wide, roared down with such energy that it climbed almost 200 vertical feet up the opposite side of the canyon. Photograph by 

Robert W. Cameron. © Cameron and Co.; used with permission. (Fig. 85) 

57 
DEFINITION OF TERMS 

I have tried to minimize the usc of technical terms in 

this volume, but some jargon is inevitable in any 

discussion of technical matters. Most of the strictly 

geologic terms that are apt to be stumbling blocks are 

defined where they first appear in the text; for ease of 

reference, some of them are summarized here in this 

short glossary. Geologic time terms are not included 

(see fig. 7). 

ALLUVIAL FAN. A sloping, fan-shaped mass of loose 

rock material deposited by a stream where it emerges 

from a canyon onto a broad valley or plain. 

ALLUVIUM. A general term for clay, silt, sand, and 

gravel deposited by running water, such as a stream. 

ANDESITE. A volcanic rock of intermediate composition, with a silica (Si02) content generally of from 

50 to 60 percent. 

ARETE. A narrow, serrate mountain ridge (fig. 56). 

BASALT. The most common type of volcanic rock, 

generally fine grained, dark, and heavy, with a silica 

(Si02) content of no more than about 50 percent. 

BATHOLITH. A very large body of plutonic rock. The 

Sierra Nevada batholith is a composite of numerous 

smaller bodies (plutons) that represent repeated 

intrusions of granitic magma. 

BEDDING. The arrangement of sedimentary rock in 

beds or layers, reflecting the fact that water or wind 

spread sediment they deposit in thin sheets. The 

beds of sedimentary rock are these successively accumulated sheets. 

BERGSCHRUND. A deep crevice near the head of an 

alpine glacier that separates moving ice from the 

headwall of the cirque. It may be covered by or filled 

with snow during the winter, but visible and 

reopened in the summer (fig. 56). 

BRECCIA. A consolidated rock composed of angular 

rock fragments. 

CIRQUE. A bowl-shaped, theaterlike basin at the head 

of a glacial valley (fig. 56). 

CLEAVAGE. The tendency of a mineral to break along 

definite planes controlled by its molecular structure 

and producing smooth surfaces. 

CoLUMNAR JOINTING. Joints that bound parallel prismatic columns, polygonal in cross section, formed by 

contraction during cooling in some lava flows, dikes, 

and volcanic plugs (a plug consists of solidified lava 

in an old volcanic conduit) (fig. 32). 

CoNGLOMERATE. A rock, the consolidated equivalent 

of gravel. 

58 

CRUST (OF THE EARTH). The outermost of the concentric shells that make up the Earth. The crust is 4 

to 5 mi thick beneath oceans and 20 to 35 mi thick 

beneath continents (fig. 25). 

DIKE. A sheetlike body of igneous rock that was 

intruded while molten into cracks in older rocks 

(figs. 13, 17). 

DIORITE. A plutonic rock composed primarily of plagioclase and dark minerals; generally fine grained 

(figs. 9, 12). 

ERRATIC (GLACIAL). A rock fragment, generally large, 

that has been transported from a distant source by 

the action of glacial ice (fig. 61). 

ExFOLIATION. Any process by which concentric 

scales, plates, or shells of rock are successively 

spalled or stripped from the surface of a rock mass. It 

produces such diverse results as the spalling off of 

glacial polish a fraction of an inch thick and the 

formation of sheet joints many feet thick (figs. 39, 

55). 

FAULT. A fracture in the Earth's crust along which 

there has been movement parallel to the fracture 

plane. 

GRADIENT. As applied to streams, the inclination of 

the bed. 

GRANITIC ROCKS. Includes granite (in the technical 

sense), granodiorite, and tonalite {see fig. 9 for 

classification of plutonic rocks). 

GRUS. The fragmental products of granular disintegration of granitic rocks in place; granitic sand (fig. 45). 

HIGH SIERRA. A term coined by J.D. Whitney (1868) 

to describe the higher region of the Sierra Nevada, 

much of it above timberline. 

IGNEOUS ROCK. A rock formed by solidification of hot 

molten material, either at depth in the Earth's crust 

(plutonic) or erupted at the Earth's surface (volcanic). 

INTRUDE, INTRUDED, INTRUSION. Process by which 

magma invades or is injected into preexisting rock 

bodies. 

INTRUSIVE SUITE. A grouping of individual plutons or 

plutonic rock units having significant features in 

common and thought to have formed from the same 

parent magma. 

IsoTOPE. Any of two or more forms of an element 

with the same or very closely related properties and 

the same atomic number but different atomic 

weights. Some isotopes are radioactive and change 

to different isotopes at a constant rate (fig. 7). 

]OINT. A fracture along which there has been little or 

no movement parallel to the fracture plane. 
LITHOSPHERE. The rigid outer portion of the Earth 

comprising the Earth's crust and the uppermost part 

of the upper mantle (fig. 25). 

MAGMA. Naturally occuring molten rock generated 

within the Earth. Magma may intrude to form 

plutonic rock or be extruded to form volcanic rock. 

MANTLE (OF THE EARTH). The intermediate of the 

concentric shells that make up the Earth; it lies 

beneath the crust. (fig. 25). 

METAMORPHIC ROCK. Rock changed materially in 

composition or appearance by heat, pressure, or 

infiltrations at depth in the Earth's crust. 

MINERAL A naturally occurring, inanimate substance 

of definite chemical composition and distinctive 

physical and molecular properties. Minerals make up 

rocks. 

MoRAINE. An accumulation of glacial till with an 

initial topographic expression of its own, commonly 

a ridge. Several varieties are described in the text 

{fig. 62). 

PEGMATITE. An exceedingly coarsely crystalline plutonic rock, commonly in dikes or pods a few feet 

across. Individual crystals are several inches to a foot 

or more across. 

PHENOCRYST. A large crystal in an igneous rock, 

embedded in a finer grained matrix. 

PLATE {TECTONIC). A segment of the Earth's crust in 

constant motion relative to other segments (fig. 26). 

PLuTON. A general term applied to any body of intrusive igneous rock of deep-seated origin, regardless of 

shape or size. 

PLUTONIC ROCK. Igneous rock formed by solidification 

of magma deep within the Earth's crust. 

PoRPHYRITIC. Said of an igneous-rock texture with 

larger crystals scattered through a finer grained 

matrix. 

PoRPHYRY. A porphyritic rock with conspicuous phenocrysts in a very fine grained matrix {fig. 21). 

PRE-TAHOE GLACIATION. Composite of the one or 

more major glaciations in Yosemite that preceded the 

Tahoe glaciation. Supersedes the El Portal and 

Glacier Point glaciations of Matthes' usage in 

Yosemite. 

PYRocLASTIC ROCK. Rock formed of ash or other 

fragmental material explosively ejected from a volcano. 

QUARTZ MONZONITE. A granitelike plutonic rock 

containing about equal proportions of potassium 

feldspar and plagioclase and less than 20 percent 

quartz under the classification system now in use. 

Rocks in the Yosemite area containing more than 20 

percent quartz that were previously called quartz 

monzonite are now classified as granite {fig. 9). 

RHYOLITE. A light-colored volcanic rock with a high 

silica {Si02) content of at least 70 percent. 

ROCHE MOUTONNEE. A protruding knob of bedrock 

glacially eroded to have a gently inclined, striated 

upstream slope and a steep, rough, and hackly downstream side. Commonly translated as "sheep," 

moutonnee is actually a French adjective meaning 

"fleecy"; the term was introduced into geology in 

1786 in describing rounded Alpine hills whose 

repeated curves, taken as a whole and as seen from a 

distance, resemble a thick fleece {figs. 54, 70). 

ScHIST. A crystalline metamorphic rock composed 

chiefly of platy mineral grains, such as mica, oriented so that the rock tends to split into layers or 

slabs. 

ScHLIEREN. Streaky concentrations of dark minerals 

in a granitic rock, caused by movement within the 

partially solidified magma (fig. 16). 

SEDIMENTARY ROCK. Rock formed by consolidation of 

sediment {gravel, sand, mud) deposited at the surface of the Earth. 

SILICA {Si02). Occurs as the natural mineral quartz, 

including various fine-grained varieties, such as 

chert. The element silicon (Si) also occurs in most 

rock-forming minerals {silicates), such as feldspars. 

SuBDUCTION. The process wherein an oceanic plate 

converging with a continental plate is deflected 

downward and consumed into the mantle beneath 

the continental plate {fig. 28). 

TAHOE GLACIATION. The intermediate of the three 

major glaciations recognized in Yosemite. Approximately equivalent to the earlier part of the Wisconsin glaciation of Matthes. 

TALUS. An accumulation of coarse, angular rock fragments derived from and resting at the base of a cliff 

or very steep slope. 

TILL Glacially transported material deposited directly 

by ice, without transportation or sorting by water 

{fig. 60). 

TIOGA GLACIATION. The latest of the three major 

glaciations recognized in Yosemite. Approximately 

equivalent to the younger part of the Wisconsin 

glaciation of Matthes. 

TRIMLINE. A sharp boundary line marking the maximum upper level of the margins of a glacier. It 

commonly separates jagged cliffs above from glacially 

smoothed rock surfaces below {figs. 56, 57). 

TuFF. Rock formed from consolidation of volcanic ash. 

59 
REFERENCES AND 

ADDITIONAL READING 

History 

Brewer, W.H. (Farquhar, F.P., ed.), 1930, Up and down 

California in 1860-1864; the journal of William H. 

Brewer, Professor of Agriculture in the Sheffield Scientific School from 1864 to 1903: New Haven, 

Conn., Yale University Press, 601 p. 

Fascinating account of Brewer's excursions with the California Geological Survey, including its first excursion to 

Yosemite in 1863. 

Bunnell, L.H., 1980, Discovery of the Yosemite in 1851: 

Golden, Colo., Outbooks, 184 p. 

Reprinted from "Discovery of the Yosemite and the Indian 

war of 1851 which led to that event, " first published in 

1880. First-hand account of the first entry into Yosemite 

Valley by white people. 

Farquhar, F.P., 1969, History of the Sierra Nevada: 

Berkeley, University of California Press, 262 p. 

Chapters on numerous subjects bearing on Yosemite, 

including the discovery of Yosemite Valley and the Big 

Trees by the Walker party. 

Hubbard, Douglass, 1958, Ghost mines of Yosemite: P.O. 

Box 881, Fredericksburg, Tex., Awani Press, 32 p. 

History of the Great Sierra Mine north of Tioga Pass and 

other prospects along the east edge of the park. "Mine" is 

somewhat of a misnomer because no production was ever 

achieved, although construction of 'the Great Sierra 

Wagon Road, forerunner of the Tioga Road, was an epic 

of western roadbuilding in 1883. 

Hutchings, J.M., 1872, Scenes of wonder and curiosity in 

California; a tourist's guide to the Yosemite Valley (2d 

ed.): New York, A. Roman and Co., 292 p. 

Hutchings, a pioneer innkeeper in Yosemite Valley, grandiloquently promoted tourism with such descriptions as 

that accompanying the frontispiece to this volume. 

Muir, John, 1912, The Yosemite: New York, Century Co. 

[reprinted 1962 by Doubleday & Co., New York, 

Natural History Library N26, 225 p.] 

Includes his graphic description of a rockfall in Yosemite 

Valley, triggered by the 1872 Owens Valley earthquake. 

Reid, R.L., ed., 1983, A treasury of the Sierra Nevada: 

Berkeley, Cali£, Wilderness Press, 363 p. 

An excellent collection of tidbits, including Muir's description of the discovery of his first "living glacier" and the 

text of the Yosemite Grant to the State of California. 

Russell, C.P., 1957, One hundred years in Yosemite; the 

story of a great park and its friends: Yosemite 

National Park, Calif., Yosemite Natural History Association, 195 p. 

History of Yosemite from its discovery through 1956, with 

60 

a detailed chronology appended. Later editions have an 

expanded chronology. 

Whitney, J.D., 1865, Geology, volume I, Report of progress and synopsis of the field work, from 1860 to 

1864: Geological Survey of California, 498 p. 

Includes a description of the California Survey's first 

excursion to Yosemite in 1863. 

Whitney, J.D., 1870, The Yosemite guide-book: 

Cambridge, Mass., Harvard University Press, 186 p. 

Popular reprint of "The Yosemite Book" that appeared in 

a very limited edition in 1868 because of the inclusion of 

original photographic prints by Carleton E. Watkins and 

W. Harris. This book was the first of its kind, with the 

object "to call the attention of the public to the scenery of 

California, and to furnish a reliable guide to some of its 

most interesting features, namely, the Yosemite Valley, the 

High Sierra in its immediate vicinity, and the so-called 

'Big Trees.' " That it did! 

GEOLOGY 

Much of the geologic history in the cited publications is 

outdated, except in the most recent technical ones, especially 

with respect to the timing of geologic events, including the uplift 

of the Sierra Nevada. Nevertheless, they contain much descriptive information of value and are cited in that regard. 

Alpha, T.R., in press, Sketches of Yosemite National Park 

from Glacier Point, Sentinel Dome, and Mount 

Hoffmann: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-1888 (black-and-white ed. ). 

Views of Yosemite physiography from three popular vantage points. Multicolored edition is published by the 

Yosemite Institute. 

Balogh, Richard, 1977, Where water flowed "uphill" on 

Pothole Dome: Yosemite National Park, Calif., 

Yosemite Natural History Association, Yosemite 

Nature Notes, v. 46, no. 2, p. 34-39. 

Description of the effects of subglacial stream action on 

Pothole Dome. 

Bateman, P.C., 1983, A summary of critical relations in 

the central part of the Sierra Nevada batholith, 

California, U.S.A., in Roddick, J.A., ed., CircumPacific plutonic terranes: Geological Society of America Memoir 159, p .. 241-254. 

The most comprehensive technical summary of the 

geology of the Sierra Nevada batholith to date. 

Bateman, P. C. , in press a, Constitution and genesis of the 

central part of the Sierra Nevada batholith: U.S. 

Geological Survey Professional Paper. 

A technical report that summarizes the rationale for 

separating and naming individual plutonic-rock units and 

intrusive suites in the central Sierra Nevada, including the 

Yosemite area. This report supersedes that by Bateman 

(1983). 

Bateman, P.C., and Chappell, B.W., 1979, Crystalliza-
tion, fractionation, and solidification of the 

Tuolumne Intrusive Series, Yosemite National Park, 

California: Geological Society America of Bulletin, 

pt. 1, v. 90, p. 465-482. 

Technical analysis of the geology of the Tuolumne Intrusive Suite (formerly called the "Tuolumne Intrusive 

Series"). 

Bateman, P.C., and Wahrhaftig, Clyde, 1966, Geology of 

the Sierra Nevada, in Bailey, E.H., ed., Geology of 

northern California: California Division of Mines and 

Geology Bulletin 190, p. 107-172. 

Though written before the advent of the concept of plate 

tectonics, this article remains the best general descriptive 

summary of the geology of the Sierra Nevada. 

Cameron, Robert, 1983, Above Yosemite, with a text by 

Harold Gilliam: San Francisco, Cameron and Co., 

144 p. 

Superb collection of color photographs of Yosemite as seen 

from the air, many illustrating geologic features as well as 

beautiful scenery. 

Fryxell, Fritiof, ed., 1962, Fran<_;ois Matthes an:d the marks 

of time; Yosemite and the High Sierra: San Francisco, Sierra Club, 189 p. 

Collection of geological essays by Fran~ois Matthes, written for a lay audience. 

Hill, Mary, 1975, Geology of the Sierra Nevada: Berkeley, 

University of California Press, 232 p. 

Geologic introduction to the Sierra Nevada in nontechnical language. 

Hill, Mary, 1984, California landscape, origin and 

development: Berkeley, University of California 

Press, 262 p. 

Describes in nontechnical language the geologic processes 

that contribute to landscape development, with many 

examples selected from the Sierra Nevada. 

Huber, N.K., 1981, Amount and timing of late Cenozoic 

uplift and tilt of the central Sierra Nevada-evidence 

from the upper San Joaquin River basin: U.S. Geological Survey Professional Paper 1197, 28 p. 

Concludes that the late Cenozoic uplift was relatively 

continuous rather than episodic and that the current uplift 

rate at Deadman Pass west of Mammoth Lakes is about 

1 Y2 inches per 1 00 years, a figure that in this volume has 

been extrapolated to Mount Dana. 

Jones, W.R., 1976, Domes, cliffs, and waterfalls; a brief 

geology of Yosemite Valley: Yosemite National Park, 

Calif., Yosemite Natural History Association, 21 p. 

Nicely illustrated booklet, with brief geologic summary. 

Jones, W.R., 1981, Ten trail trips in Yosemite National 

Park: Golden, Colo., Outbooks, 78 p. 

Includes a description of a hike up Mount Hoffmann, 

with comments on the geology along the way. 

Jones, W. R., 1981, Yosemite, the story behind the scenery 

(revised ed. ): Las Vegas, Nev., KC Publications, 48 

p. 

Beautifully illustrated book on geologic and other naturalhistory subjects. 

Matthes, F.E., 1930, Geologic history of the Yosemite 

Valley, with an appendix on The granitic rocks of the 

Yosemite region, by F.C. Calkins: U.S. Geological 

Survey Professional Paper 160, 137 p. 

A classic study in glacial geology. Some of its conclusions 

have been challenged, but it remains the best source of 

descriptive material on the glaciation of Yosemite. 

Matthes, F. E. (Fryxell, Fritiof, ed. ), 1950, The incomparable valley; a geologic interpretation of the Yosemite: 

Berkeley, University of California Press, 160 p. 

An eloquent version of Matthes' classic study, expressly 

written for the lay reader. 

Osborne, Michael, 1983, Granite, water and light; waterfalls of Yosemite Valley: Yosemite National Park, 

Calif., Yosemite Natural History Association, 48 p. 

Outstanding photographs, focusing on the waterfalls. Brief 

geology. 

Russell, I. C., 1889, Quaternary history of Mono Valley, 

California: U.S. Geological Survey Annual Report 8, 

p. 261-394 [reprinted 1984 by Artemisia Press, P.O. 

Box 119, Lee Vining, CA 93541]. 

Russell blends science with prose so vivid that this report is 

essential reading for anyone with an interest in the Mono 

Basin, Mono Craters, and the glaciers of the adjacent 

High Sierra, both present and past. Illustrated with 

etchings and the superb cartography of Willard D. 

Johnson (see fig. 81 of this volume). Glacial Lake Russell, 

which occupied the Mono Basin during the Tioga Glaciation, was so named in recognition of this pioneering work. 

Schaffer, J.P., 1983, Yosemite National Park-a naturalhistory guide to Yosemite and its trails (2d ed.): 

Berkeley, Calif., Wilderness Press, 274 p. 

An excellent trailguide, with brief commentaries on the 

geologic features along many routes. 

Sharp, R.P., 1960, Glaciers: Eugene, Oregon System of 

Higher Education, Condon Lecture Publications, 78 p. 

An illuminating discussion of glaciers for the nonspecialist. 

GEOLOGIC MAPs 

These maps show details of geology not possible to include in 

this volume, and together with yet unpublished maps they form 

the foundation upon which I have constructed the geologic 

story. 

Alpha, T.R., Huber, N.K., and Wahrhaftig, Clyde, 1986, 

Oblique map of Yosemite National Park, California: 

U.S. Geological Survey Miscellaneous Investigations 

Series Map 1-1776. 

This map depicts Yosemite's landforms as viewed looking 

down toward the northeast at an angle of 30°. It is an 

enlarged and more detailed version of figure 6 in this 

volume. 

61 
Alpha, T.R., Wahrhaftig, Clyde, and Huber, N.K., in 

press, Oblique map showing the maximum extent of 

20,000-year-old (Tioga) glaciers, Yosemite National 

Park, California: U.S. Geological Survey Miscellaneous Investigations Series Map I-1885. 

This 7TU1P depicts the Tioga icefield and associated valley 

glaciers as viewed looking down toward the northeast at 

an angle of 30°. It is an enlarged and more detailed 

version of figure 67 in this volume. 

Bateman, P. C., in press b, Pre-Tertiary bedrock geology of 

the Mariposa 1° X 2° quadrangle, central Sierra 

Nevada, California: U.S. Geological Survey Miscellaneous Investigations Series Map. 

This geologic 77U1P shows the bedrock geology with 

Cenozoic volcanic rocks and surficial deposits stripped off 

so as to concentrate on the plutonic rocks of the Sierra 

Nevada batholith and associated metamorphic rocks. All 

but the north one-fourth of Yosemite National Park lies 

within the limits of this 7TU1p. 

Bateman, P.C., in press c, Geologic map of the Bass Lake 

quadrangle, west-central Sierra Nevada, California: 

U.S. Geological Survey Geologic Quadrangle Map. 

Bateman, P.C., Kistler, R.W., Peck, D.L., and Busacca, 

A.J., 1983, Geologic map of the Tuolomne Meadows 

quadrangle, Yosemite National Park, California: U.S. 

Geological Survey Geologic Quadrangle Map 

GQ-1570, scale 1:62,500. 

Bateman, P. C., and Krauskopf, K. B., in press, Geologic 

map of the El Portal quadrangle, west-central Sierra 

Nevada, California: U.S. Geological Survey Geologic 

Quadrangle Map. 

Calkins, F. C., 1985, Bedrock geologic map of Yosemite 

Valley, Yosemite National Park, California, with 

accompanying pamphlet by N.K. Huber and J.A. 

Roller: U.S. Geological Survey Miscellaneous Investigations Series Map 1-1639, scale 1:24,000. 

Chesterman, C. W., 197 5, Geology of the Matterhorn 

Peak 15-minute quadrangle, Mono and Tuolumne 

Counties, California: California Division of Mines 

and Geology Map Sheet 22, scale 1:48,000. 

Chesterman, C.W., and Gray, C.H., Jr., 1975, Geology 

62 

of the Bodie IS-minute quadrangle, Mono County, 

California: California Division of Mines and Geology 

Map Sheet 21, scale 1:48,000. 

Huber, N.K., 1983, Preliminary geologic map of the 

Pinecrest quadrangle, central Sierra Nevada, California: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-1437, scale 1:62,500. 

Huber, N.K., Bateman, P.C., and Wahrhaftig, Clyde, 

compilers, in press, Geologic map of Yosemite 

National Park and vicinity, Calilfomia: U.S. Geological Survey Miscellaneous Investigations Series 

Map 1-1874, scale 1:125,000. 

Huber, N.K., and Rinehart, C. D., 1965, Geologic map of 

the Devils Postpile quadrangle, Sierra Nevada, California: U.S. Geological Survey Geologic Quadrangle 

Map GQ-437, scale 1:62,500. 

Keith, W.J., and Seitz, J.F., 1981, Geologic map of the 

Hoover Wilderness and adjacent study area, Mono 

and Tuolumne Counties, California: U.S. Geological 

Survey Miscellaneous Field Studies Map 

MF-1101-A, scale 1:62,500. 

Kistler, R. W., 1966, Geologic map of the Mono Craters 

quadrangle, Mono and Tuolumne Counties, California: U.S. Geological Survey Geologic Quadrangle 

Map GQ-462, scale 1:62,500. 

Kistler, R. W., 1973, Geologic map of the Hetch Hetchy 

Reservoir quadrangle, Yosemite National Park, California: U.S. Geological Survey Geologic Quadrangle 

Map GQ-1112, scale 1:62,500. 

Peck, D.L., 1980, Geologic map of the Merced Peak 

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

Geological Survey Geologic Quadrangle Map 

GQ-1531, scale 1:62,500. 

Wahrhaftig, Clyde, in press, Glacial map of Yosemite 

National Park and vicinity, California: U.S. Geological Survey Miscellaneous Investigations Series 

Map. 

Map showing the 7TU1ximum extent of Tioga-age glaciers 

and the distribution of glacial moraines of various ages. It 

provides the technical background for figure 67 in this 

volume (Tioga icefield and valley glaciers). 
A WORD OF THANKS 

Geologist Alfred C. Lane once wrote, "The progress 

of knowledge is like the growth of a coral reef; each 

generation builds upon that which has been left behind 

by those who have gone before." So it is with this 

volume. I have drawn upon so many sources of information in presenting this geologic story of Yosemite that it 

is impossible to acknowledge the individual contributions of each. This is especially true of the historical 

material and of the numerous works that have delineated the regional geologic framework within which I 

have placed Yosemite. For those who wish to delve 

further into various aspects of Yosemite history and 

geology, several pertinent references, briefly annotated, 

are listed in the bibliography; these, in tum, will lead 

to additional source materials. 

I must, however, specifically acknowledge the modem geologic mapping and detailed studies by my U.S. 

Geological Survey colleagues that made possible the 

present volume, as well as the new geologic map of 

Yosemite National Park published separately (Huber 

and others, in press). For that foundation and for their 

continuing support and contributions, I thank Paul 

Bateman, Lew Calk, Frank Dodge, Bill Keith, Ron 

Kistler, Dallas Peck, Dean Rinehart, Jim Seitz, and 

Clyde Wahrhaftig. Clyde Wahrhaftig also developed 

the explanation for the formation of weather pans, 

described on page 36. 

Julie Roller assisted me in the field and in the early 

stages of writing this volume and compiling the geologic map. Thoughtful manuscript reviews were 

provided by many of my colleagues, as well as by 

Genny Smith of Palo Alto and Mammoth Lakes, 

Calif., and Jim Sano of the National Park Service. 

Finally, during excursions to Yosemite, the hospitality 

and enthusiastic support of every member of the Park 

Service staff there contributed significantly to the success of the project. Jan van Wagtendonk was particularly helpful in assisting with logistic support. 

Thanks are also due to the individuals and organizations permitting use of their photographs; those not by 

myself are credited in the:; captions, except for the 

frontispiece, which was contributed by Dallas Peck. 

Throughout the process of illustrating this volume, I 

have had the distinct pleasure of drawing upon and 

working with the artistic talents of cartographer Tau 

Rho Alpha and illustrator Susan Mayfield. In particular, Tau created the oblique views of Yosemite's 

physiography (fig. 6) and the Tioga glaciation (fig. 67), 

and the panorama from Mount Hoffman (fig. 5). The 

oblique views (figs. 6, 67) have been published in 

much-enlarged, more detailed versions as U.S. Geological Survey Miscellaneous Investigations Series Maps 

I-1776 and I-1885, respectively. 

63 
INDEX 

A,B 

Arch Rock, 18, 38 

Big Oak Flat, 17 

Big Oak Flat Road, 22, 51 

Blackwelder, Eliot, 46 

Bridal veil Canyon, 4 7 

Bridalveil Creek, 31 

Bridalveil Fall, 19 

Bridal veil Meadow, 4 7, 50 

Brewer, William, 3, 5 

Buena Vista Crest, 6, 48 

Bunnell, Lafayette, 2 

c 

Calaveras Grove, 3 

Calkins, Frank C., 3 

Cascade Creek, 51 

Cascade Range, 26 

Cathedral Peak, 48 

Cathedral Rocks, 18, 31, 56 

Central Valley, 3, 5, 11, 27, 44 

Church Bowl, 19 

Clark Range, 6 

Clouds Rest, 6, 34 

Crane Flat, 22 

D-F 

Dana Plateau, 52 

Devils Postpile, 29 

Dewey Point, 18 

El Capitan 18, 32 

Ellery Lake, 22 

El Portal, 18, 22, 27, 51 

Fairview Dome, 48 

fireplace Bluffs, 18 

Fissures, The, 18 

G 

Gardiner, James, 3 

Gaylor Lakes, 20 

Gaylor Peak, 23 

Glacier Point, 15, 19, 33, 50 

Glen Aulin Trail, 28 

Groveland, 28 

B 

Half Dome, 6, 31, 33 

Harden Lake, 51 

Hetch Hetchy Valley, 10, 28, 4 7, 50 

High Sierra, 3 

Hoffmann, Charles, 3 

Horse Ridge, 48 

Hutchings, James, 33 

64 

1-K 

Illilouette Ridge, 19 

John Muir Wilderness, 54 

Johnson Peak, 21 

King, Clarence, 3 

Kuna Peak, 23 

L 

Leaning Tower, 18, 32 

Lee Vining Canyon, 17, 27, 44, 50 

Lembert Dome, 21, 48 

Leonard, Zenas, 2 

"Little Devils Postpile", 28 

Little Yosemite Valley, 4 7 

Long Valley Caldera, 29 

Lundy Canyon, 17 

Lyell Fork of the Tuolumne River, 47 

M 

Mammoth Lakes, 22, 29, 56 

Mammoth Mountain, 29 

Mariposa Grove, I 

Matthes, Fran~ois C., 3, 38, 46, 54 

May Lake, 5 

Merced Gorge, 18 

Merced Grove, 2 

Merced Pass, 29 

Merced Peak, 54 

Merced River, 2, 22, 27, 39, 44, 48, 51 

Mirror Lake, 19, 33, 50, 56 

Mono Craters, 23, 29 

Mono Lake, 29, 48 

Monut Dana, 23, 27 

Mount Hoffmann, 3, 5, 10, 52 

Mount Lyell, 48 

Mount St. Helens, 26, 29 

Mount Whitney, 52 

Muir, John, 1, 3, 6, 54, 56 

N-P 

Nevada Fall, 19 

Old Coulterville Road, 38 

Old Tioga Road, 51 

Olmstead Point, 20 

Pohono Trail, 15 

Pothole Dome, 21, 49 

R 

Rancheria Mountain, 28 

Ribbon Fall, 34 

Ritter Range, 22, 27, 37 

Rockslides, 18, 32 

Royal Arches, 19, 34 

s 

Saddlebag Lake, 23 

San Andreas Fault, 24, 28 

San Joaquin River, 22, 48 

Savage, Maj. James, 2 

Sentinel Dome, 19 

Siesta Lake, 48 

Soda Springs, 21 

Spotted Lakes, 23 

Staircase Falls, 31 

Stoneman Meadow, 33 

T 

Taft Point, 15, 18 

Tenaya Canyon, 33, 47 

Tenaya Lake, 5, 20, 47 

Tenaya Lake Trail, 50 

Three Brothers, 18, 31 

Tioga Lake, 54 

Tioga Pass, 20, 22, 50, 54 

Tioga Road, 2, 19, 48, 50 

Tuolumne Grove, 2 

Tuolumne Meadows, 6, 17, 20, 28, 48 

Tuolumne River, 2, 11, 21, 28, 39, 47, 49 

Turtleback Dome, 18, 51 

Twin Lakes, 22 

U,V 

Unicorn Peak, 48 

Union Point, 19 

Upper Yosemite Fall, 34 

Vernal Fall, 19 

w 

Walker, Joseph, 2 

Washburn Point, 19, 33 

Wawona, 48 

Wawona Road, 51 

White Wolf, 51 

Whitney, Josiah, 3, 5, 50 

y 

Yosemite Creek, 5, 19 

Yosemite Falls, 15, 19 

Yosemite Falls Trail, 56 
7kG~S~-~ 

YOSEMITE 

NATIONAL PARK 
0 2 MILES 

0 2 KILOMETERS 

CONTOUR INTERVAL 80 FEET 

GEOLOGIC MAP OF THE 

YOSEMITE VALLEY AREA 

PLATE 2 

TUOLUMNE 

INTRUSIVE SUITE 

EXPLANATION 

Surficial deposits 

Alluvium, talus, and glacial deposits 

D 

Aplite 

D 

Half Dome Granodiorite 

Granodiorite 

-

of Kuna Crest 

D 

Sentinel Granodiorite 

CRETACEOUS 
.. 

Quartz diorite of El Capitan 

INTRUSIVE SUITE OF 

BUENA VISTA CREST 

INTRUSIVE YOSEMITE SUITE VALLEY OF l 

Bridalveil Granodiorite 

Granodiorite of 

lllilouette Creek 

D 

Taft Granite 

El Capitan Granite 

CRETACEOUS 

FINE GOLD 1 Granodiorite of Arch Rock 

INTRUSIVE SUITE l

[2TI 

Tonalite of the Gateway 

Diorite 

~ 

~ 

and gabbro 

Metamorphic rocks 

CRETACEOUS 

} 

PRECRETACEOUS 

Geology generalized from detailed mapping 

by F.C. Calkins (1985), RW. Kistler (1973), 

and D.L Peck (written commun, 1983) 

1 Bateman (in press a) 

120°00' 119°30' 119°00' 38°15'r--------------.--------------~-------------.-.------------, 

,---------- 1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

L __ _______ _ 

I 0 

~ 

- --- ----l I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

'- . 0 • 

-:r · =>: 

37°15 ~------------~--~----------~------------~--------------~------ ----~ 

INDEX MAP for topographic and geologic maps of the 

Yosemite area. In addition to geologic maps of Yosemite Valley 

and Yosemite National Park and vicinity, geologic maps of the ISminute quadrangles with underlined names are available.