Geological Survey Professional Paper 160 Geologic History of the Yosemite Valley

THE HIGH SIERRA

GENERAL CHARACTER

A glance, next, at the High Sierra, which lies immediately above the Yosemite region. It contains the sources of the Merced River, and from it in glacial time advanced the powerful ice streams that converged upon the Yosemite chasm. It therefore is and always has been the place of origin of the agencies that have played the leading parts in fashioning the chasm. (See p1. 11, A.)

PLATE 11.—A (top), THE HIGH SIERRA, FROM EL CAPITAN. Half Dome and the head of the Yosemite Valley appear in the center of the view. Freshly fallen snow whitens the distant peaks and gives them a wintry aspect representative in some measure of the conditions that prevailed during the ice ages, when large glaciers extended from the High Sierra down to the Yosemite region. B (bottom), LITTLE YOSEMITE AND CLARK RANGE, FROM HALF DOME. The Clark Range stands above the general level of the Yosemite upland, of which a long stretch, covered with forests, is visible beyond the Little Yosemite. At the left is Moraine Dome, from which the lateral moraines of the ancient Merced Glacier extend in serpentine curves. Photograph by F. C. Calkins.

In several respects the High Sierra differs markedly from the Yosemite region. Its sky line is formed not by the timbered swells of a rolling upland but by sharp-profiled mountain crests that rise, mostly bare, high above the timber line. The Yosemite upland, it is true, continues up into the High Sierra, but only in the form of shoulders along the sides of the main canyons. It is an inconspicuous feature beneath the majestic peaks.

The canyons in the High Sierra are less deeply cut than those in the Yosemite region. They range from less than 1,000 feet to a maximum of 2,000 feet in depth below the flanking shoulders; measured with reference to the higher peaks, however, they range from 3,000 to more than 4,000 feet in depth. Hanging valleys abound at the sides of the main canyons, but they differ from the hanging valleys of the Yosemite region in that they ascend steeply by successive stairlike steps, and they head in amphitheaters sculptured among the peaks. Lakelets of emerald and sapphire hues lie on the steps, contrasting vividly with the light buff tones of the surrounding granite. Snow banks and snow fields fleck the mountain sides; a few small glaciers gleam in the deeper hollows.

Besides being more rugged and having greater variety of scenery, the High Sierra is distinguished from the Yosemite region also by its vast expanses of bare rock. Not only are the peaks bare because of their great elevation, but the floors and sides of the canyons and hanging valleys are mostly bare, partly because the soil was scraped from them by the ancient glaciers, partly because the granite over large areas is sparsely fractured and affords but scant roothold for vegetation. The High Sierra as a whole, therefore, presents a singularly clean-swept appearance that would border on the desolate, were it not for groves of trees, bright-green meadows, northwestward, approximately at right angles to the directions which they pursue farther down the slope of the range.

The first mountain crest above the Yosemite region is the boldly sculptured Clark Range, which terminates in Mount Clark (11,506 feet), on the south side of the Merced. (See pl. 11, B.) It separates the Illilouette Basin and the upland south of the Little Yosemite from the Merced Basin. About 8 miles farther northeast, between the Merced Basin and the Tuolumne Basin, stands the still bolder Cathedral Range, which extends from Mount Lyell (13,090 feet), the highest summit in the central part of the Sierra Nevada, northwestward to Cathedral Peak (10,933 feet). (See pl. 12, A.) The northeast wall of the Tuolumne Basin is formed by the main crest of the Sierra Nevada, which is surmounted by Mount Dana (13,050 feet) and a long row of other peaks between 12,000 and 13,000 feet in altitude that overlook Mono Lake and the deserts at the east base of the range.

PLATE 12.—A (top), CATHEDRAL PEAK. The remarkable natural edifice that stands at the northwest end of the Cathedral Range. In the foreground is Cathedral Lake, which occupies a basin excavated in the granite by the ancient glaciers. B (bottom), MERCED LAKE. The lake lies in a Yosemite-like stretch of the upper Merced Canyon. Its basin, hollowed from the granite by the ancient Merced Glacier, is in process of being filled with river-borne sand and gravel and will in time be replaced by a level floor analogous to that of the Yosemite Valley. At the head of the lake is the forested delta of the river.

MERCED BASIN

The central feature of the Merced Basin is the upper Merced Canyon, a trench about 2,000 feet in depth and half a mile to a mile in width. Though narrower and less deep, some parts of this canyon resemble the Yosemite Valley in their style of modeling—indeed, the canyon may be said to contain a succession of minor yosemites separated from one another by more or less accentuated constrictions. Those stretches which contain Merced Lake (pl. 12, B) and Washburn Lake have especially pronounced Yosemite characteristics: they are broadly U-shaped, steep-sided troughs with smooth, parallel walls devoid of spurs.

The Merced Canyon rises headward by successive steps, like the canyons in the Yosemite region. Most of the steps, it is true, are low and ill defined, and as a consequence the river makes no leaping falls but only cascades, yet the essentially stairwise mode of ascent of the canyon is manifest from a longitudinal profile such as that in Figure 22. Like the Yosemite Valley the upper Merced Canyon has fairly definite brinks. Its walls rise sheer to the edges of shoulders that slope in general at moderate angles up to the bases of the surrounding mountain crests. These shoulders, which are the equivalent of the Yosemite upland, extend, interrupted by spurs and hanging valleys, to the very head of the Merced Basin.

The hanging valleys on the side of the Clark Range are the best developed. (See pl. 13, B.) Most of them terminate at heights of 500 to 700 feet above the floor of the main canyon, but one, Clark Canyon, terminates at a height of 2,500 feet. At the upper end of the basin several typical hanging valleys converge toward the cliff-encircled canyon head, their waters pouring down from all sides in falls and cascades. The stairwise-ascending rock floors of these hanging valleys are largely bare and in many places gleam with glacier polish. They are, indeed, the pathways of ancient glaciers and were shaped by those glaciers rather than by the present streams. The same is true of the broad rock floor of the main canyon, which for long stretches, especially below Merced Lake, is wholly bare and highly polished.

PLATE 13.—A (top), TUOLUMNE MEADOWS. These large meadows are the central feature of the upper Tuolumne Basin. In the background are, from left to right: Mount Dana, Mount Gibbs, and Kuna Crest. Photograph by G. K. Gilbert. B (bottom) HEAD OF UPPER MERCED BASIN, FROM SHOULDER NORTH OF WASHBURN LAKE. Below is the upper Merced Canyon, and beyond are some of the flanking rock benches and hanging valleys carved from prevailingly massive granite. At the right are the peaks of the Clark Range, and to the left of them is the sharp crest which connects with Mount Lyell.

The side valleys that head on the Cathedral Range are longer and deeper than those on the Clark Range and flanked by mountainous spurs. In spite of their ruggedness, however, some of these high-level valleys contain attractive stretches of meadowland. Two of them, the valleys of the Maclure Fork and Echo Creek, are so deeply cut at their mouths that they have lost the aspect of true hanging valleys. Nearly all head in amphitheaters deeply sculptured in the body of the range, but two head in broad gaps or passes that afford easy routes of communication across to the Tuolumne Basin. The valley of the Cathedral Fork of Echo Creek heads at the Cathedral Pass, and the valley of the twin streams Emeric Creek and Fletcher Creek heads at the Tuolumne Pass.

TENAYA BASIN

Forming part of the region tributary to the Merced River, yet a unit distinct from what has been called the Merced Basin, is the Tenaya Basin, which lies above Tenaya Canyon and contains the headwaters of Tenaya Creek. It is much smaller than the Merced Basin, being only 5 miles long and 4 miles broad, and it does not head at the main crest of the Sierra Nevada yet it is an area of peculiar interest because it was formerly the thoroughfare for large masses of glacier ice that were diverted into it from the adjoining Tuolumne Basin and went to fill Tenaya Canyon.

The Tenaya Basin lies wholly above 8,000 feet of altitude—4,000 feet higher than the Yosemite Valley. Tenaya Lake, which lies in its center, has an altitude of 8,141 feet. On the east the basin is walled in by the sheer cliffs of Sunrise Mountain and Tenaya Peak; on the west it is flanked by the less abrupt cliffs of Mount Hoffmann and Tuolumne Peak. At its head the basin is separated from the Tuolumne Basin by a relatively low, inconspicuous divide.

The basin as a whole is a land of bare, glistening granite. Only at the head of Tenaya Lake and for some distance below it are there stretches of verdant meadowland. All the low wavelike swells and ridges as well as the intermediate troughs in its floor are essentially devoid of soil and are made of smooth, sparsely fractured rock on which the trees grow far apart or are wanting altogether. What is more, the rock floor as well as the surrounding cliffs retain in many places the high polish that was imparted to them by the grinding glaciers. It was this fact that led the Indians to call Tenaya Creek Py-we-ack ("the stream of the glistening rocks").²⁴

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²⁴Bunnell, L. H., Discovery of the Yosemite and the Indian war of 1851, 4th ed., p. 207, 1911.

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TUOLUMNE BASIN

What is commonly termed the Tuolumne Basin is only a small part of the vast area of mountain country drained by the Tuolumne River; it is, strictly, the basin of the main branch of the river whose headwaters are on Mount Lyell and Mount Dana. Its natural lower limit is at Tuolumne Peak and the head of the Tuolumne Canyon. Its Central feature is the Tuolumne Meadows (pl. 13, A), the largest of the many subalpine gardens of the High Sierra, justly famed as one of the most attractive parts of the Yosemite National Park.

The basin, as thus defined, measures roughly 15 miles in length and 10 miles in greatest breadth and has an area comparable to that of the Merced Basin. It is, however, much less rugged, the broad meadows that stretch for many miles along the river and its two principal forks taking the place of a central rock-floored canyon. Because it is less deeply trenched, the Tuolumne Basin also is considerably higher than the Merced Basin. Its central meadows have an altitude of over 8,500 feet; they lie 1,500 feet above Merced Lake and 4,500 feet above the Yosemite Valley. Moreover, as the meadows extend with gentle slopes all the way to the Tioga Pass and Mono Pass on the crest of the Sierra Nevada, the Tuolumne Basin affords a particularly easy route of travel across the range. The Indians quickly perceived this fact and laid their trail from Mono Lake to the Yosemite region—the historic Mono Trail—through the length of the basin. The Tioga Road, which was built in 1882-83 to a mining camp near the main crest of the range, naturally was laid also through the Tuolumne Basin, and since this road has been acquired by the Government and improved for automobile traffic the Tuolumne Meadows have become the great thoroughfare for tourist travel between the Yosemite and Mono Lake.

Although the Tuolumne Basin differs so markedly in configuration from the Merced Basin, the two basins nevertheless have several features in common. The broad central valley of the Tuolumne, like the upper Merced Canyon, is flanked by elevated benches that are continuations of the Yosemite upland; and most of the valleys on these benches are of the hanging type, opening at heights of 500 to 1,200 feet above the grassy floor. Nor do the spurs between these hanging valleys project beyond the edges of the benches; they belong wholly to the upper story of the landscape, the broad valleys of the lower story being distinctly of the smooth-sided trough type.

The benches are best developed on the south side of the basin, where they attain a breadth of several miles. Especially is this true north and northeast of Tuolumne Pass, where they form a fairly continuous, undulating platform. This high-level surface rises gradually eastward, from 9,200 feet at the base of Cathedral Peak to 10,500 feet at the base of Mount Lyell, at the same time changing in aspect from a densely wooded to a desolate and barren country. (See pl. 41, A.)

PLATE 14.—MOUNT LYELL AND LYELL GLACIER. Mount Lyell stands at the head of the Merced and Tuolumne Rivers and is the culminating peak in the central part of the Sierra Nevada. The Lyell Glacier is the largest ice body in the Yosemite National Park.

Of peculiar interest to the sightseer as well as to the geologist are the small glaciers and ice fields that cling to the higher peaks about the Tuolumne Basin, for they are representative, on a diminutive scale, of the extensive ice masses that filled the basin during the glacial epoch. These small ice bodies lie in well-shaded amphitheaters or on slopes with northerly exposure. The Dana Glacier (pl. 28, B) is ensconced in a deep amphitheater north of the summit of Mount Dana. A somewhat broader ice mass clings to the slope north of Parker Pass. Largest and most prominent in the landscape are the glaciers on Mount Lyell and Mount Maclure. Each measures about half a mile in length, and the Lyell Glacier (pl. 14) is fully twice as broad. Situated close together, these dazzling ice bodies combine to give this group of peaks a truly alpine aspect, not excelled in beauty by any other part of the High Sierra.

The scientists of the Geological Survey of California, who first explored the range in the early sixties of the last century, paid little attention to these ice bodies and referred to them merely as snow fields. Nevertheless they are true glaciers, as was first pointed out by Muir. They are composed of old, granular snow ice and, though small, move slowly forward in the manner characteristic of large glaciers and are rent here and there by typical crevasses.