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Tuolumne Meadows. Yosemite. By Cedric Wright
Tuolumne Meadows is situated in the midst of the broad Upper Tuolumne Basin, near the confluence of the Dana Fork and Lyell Fork of the Tuolumne River. During the glacial epoch two great ice streams, one coming from Mount Dana, the other from Mount Lyell, came together at the same spot. These two glaciers and a number of lesser ones that originated in the amphitheater-like hollows or “cirques” on the surrounding crests, filled the Upper Tuolumne Basin with ice to a depth of 2200 feet, as is clearly shown by the “ice lines” on Ragged Peak, to the north, and Johnson Peak, to the south. They created a “mer-de-glace” or ice sea 140 square miles in extent, the largest in the Sierra Nevada.
From this vast ice reservoir flowed the mighty Tuolumne Glacier, which was the longest and largest ice stream in the Sierra Nevada. It reached a maximum length of slightly over 60 miles and filled the Grand Canyon of the Tuolumne to the brim. At Pate Valley the Tuolumne Glacier attained the prodigious depth of 4500 feet, as is shown by the height of the moraines or debris ridges at the sides of the canyon.
In spite of its enormous size, however, the Tuolumne Glacier was unable to carry off the ice as fast as it accumulated in the Upper Tuolumne Basin. As a consequence overflows took place in different directions through gaps in the surrounding mountain crests. The largest volume escaped over the low, hummocky divide between Cathedral Peak and Tuolumne Peak and invaded the Tenaya Basin. It formed the bulk of the Tenaya Glacier, which was tributary to the Yosemite Glacier. Smaller outflows took place southwestward, over the Tuolumne Pass, southeastward over the Donohue Pass, eastward over the Mono Pass (into Bloody Canyon), and northeastward over the Tioga Pass.
As a result of its glacial history the Upper Tuolumne Basin is replete with features of unusual interest. On the rock floor, which is exposed to view in many places (notably along the lower course of the Dana Fork), grooves and striae produced by boulders and smaller rock fragments that were dragged by the ice, are abundant. Over large areas the granite still gleams with “glacier polish,” imparted to it by the scouring of the fine rock powder carried by the glaciers. Boulders and blocks, large and small, torn from the mountain sides and dropped by the ice, as it melted, are strewn about here and there; and moraines or ridges of rock debris that accumulated along the margins of the glaciers occur in parallel series at the edges of the basin.
Of peculiar interest are those rocky knobs that were overridden by the glaciers, worn smooth and rounded on their upstream sides, but left more or less hackly on their downstream sides, where the ice plucked more than it ground. These asymmetric rock forms are known by the Swiss name of roches moutonneés (sheep-like rocks). Lembert Dome, which is about 500 feet high, exhibits this characteristic glacial form on a large scale. It was overwhelmed by the ice to a depth of 1500 feet. The most remarkable and highest rock monument of this type is Fairview Dome, which stands at the lower end of the Tuolumne Meadows. It might seem incredible that this sugarloaf dome, 1000 feet in height, was overtopped by the ice, yet such is clearly attested by its roche moutonneé form, by the patches of glacier polish on its crown, and by the height of the “ice line” on Cathedral Peak, which is 700 feet above its summit.
Moraine ridges are most numerous on the north side of the basin, especially in Moraine Flat. Dog Lake occupies a hollow between moraines. In its vicinity strips of meadow land frequently occur between parallel moraines marking successive stages in the melting down of the last glacier that filled the Tuolumne Basin. Terminal Moraines, such as are formed at the fronts of glaciers, occur nowhere except immediately in front of the small glaciers that still remain on some of the higher peaks. The explanation is, doubtless, that the ancient glaciers melted back rather steadily when the Ice Age drew to a close, and did not pause long enough at any point to build up a strong ridge of debris at their front.
Tuolumne Meadows is an excellent central base from which to make trips to the “living” glaciers that still remain on the high peaks round about. There are within the Tuolumne Basin and its immediate vicinity seven of these living glaciers—a greater number than is to be found in any other area of equal extent in the Sierra Nevada. They are of small size, it is true, and hardly comparable to the famous glaciers on Mount Rainier, or to those in the Swiss Alps or in Alaska. The longest of them measure less than a mile in length, but they are nevertheless glaciers in the true sense of the term and not mere snow fields, for they are composed of hard, granular ice, they move slowly downhill with a slow flow-like motion, and they are broken by crevasses in consequence of their motion over irregular beds. Moreover, just as is the case with the large glaciers mentioned, so at the extreme head of each of these small glaciers there is between the ice and the rock of the mountain a gaping cleft (the bergschrund of Swiss mountaineers) that opens periodically as a result of the forward movement of the ice.
The largest ice body in the Tuolumne Basin lies on the north side of Mount Lyell. It is commonly known as the Lyell Glacier, but it consists in reality of two glaciers separated by a rocky spur. They might well be called the West Lyell and East Lyell glaciers. The ascent of Mount Lyell is usually made over the sloping surface of the West Lyell Glacier. The only obstacle that makes the climb difficult, especially in late summer, is the bergschrund at the head of the glacier.
A short distance farther west, on the north side of Mount Maclure, is the Maclure Glacier, a single, simple ice tongue, tapering downward to a blunt point, and enclosed by a massive moraine loop. Below the loop is a picturesque lakelet that reflects the glacier and the towering peak above.
Entirely different in character is the Dana Glacier, which occupies a deep cirque on the north side of Mount Dana. It is much broader than long, and, curiously, lies, not at the head of the cirque, which opens towards the northwest, but against its shady south wall, A moraine loop of great height encircles the ice front, showing that the glacier formerly was much larger and thicker than it is at present. The great volume of morainal material is accounted for by the fact that the ancient volcanic rocks of which Mount Dana is largely made break up rather readily under the repeated attacks of frost—more readily than the relatively massive granites that prevail throughout the High Sierra.
Two small glaciers lie tucked away under the north slopes of Kuna Peak and Koip Peak. They are readily reached from the trail that leads over the Parker Pass. Of much larger size is the Conness Glacier, which occupies a sheer-walled cirque on the northeast side of Mount Conness. Like the Dana, Kuna, and Koip glaciers, the Conness is much broader than long. It measures about three-fourths of a mile in breadth and a quarter of a mile in length. From the summit of Mount Conness one looks down upon the entire expanse of ice, but to reach the foot of the glacier one must go by way of the Tioga Pass and the Saddlebag Lakes.
Measurements by the National Park Service are being made annually to the fronts of all the glaciers described for the purpose of determining the extent to which they have advanced or melted back. This work is being done as a part of a general plan of glacier measurements throughout the western United States and Alaska that was put into operation a few years ago by the Committee on Glaciers of the Geophysical Union (Branch of the National Research Council in Washington). The principal object is to obtain systematic records of the advance or recession of the glaciers that will indicate the trend of climatic changes now in progress.
All of the glaciers in the Sierra Nevada have been melting back more or less constantly ever since the seventies of the last century. The little glacier which John Muir discovered in 1871 (on the Clark Range) has melted away entirely, and a host of small cirque glaciers of the same type doubtless have vanished from the range within the last fifty years.
The features of the Upper Tuolumne Basin are carved very largely from granite, a material of igneous origin that welled up in a molten state and crystallized into hard rock as it cooled. It was not, however, lava properly speaking, for it did not flow out upon the surface of the earth. It occupied vast subterranean chambers beneath the buckled and broken strata of an ancient mountain system that stood on the site of the present Sierra Nevada more than a hundred million years ago.
The reason why the granite is now exposed at the surface throughout the Upper Tuolumne Basin, and indeed throughout a large part of the Sierra Nevada, is that the ancient mountains that covered it have been completely worn down, the rocks as they weathered and disintegrated, being removed, fragment by fragment, grain by grain, by washing rains and the running water of brooks and rivers.
The granite peculiar to the Upper Tuolumne Basin is known as Cathedral Peak granite and is readily distinguished from the other types of granite in the Sierra Nevada (which represent different upflows of molten material) by the large, approximately rectangular crystals of whitish feldspar which it contains. In the ice-polished rock floors these crystals, which measure from one to two inches in length, resemble lumps of domino sugar disseminated through a buff or pinkish groundmass.
Of the older rocks that originally overlay the granite and made up the bulk of the ancient mountains just referred to, considerable masses remain on the peaks surrounding the Upper Tuolumne Basin, notably on Mount Dana, Mount Gibbs, Parker Peak, Koip Peak and Blacktop; likewise on Parsons Peak and Simmons Peak, and in a narrow belt extending along the northeast slopes of
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Cathedral Peak. Yosemite. By Philip Hyde
As a result of the intense pressure to which they were subjected when the ancient mountains were formed, the rocks were greatly altered in consistency, indurated and rendered crystalline—they were metamorphosed, as geologists say, and they are therefore properly referred to as metamorphic rocks. Among them were originally sandstones, shales, and limestones of marine origin. The sandstones have become quartzites; the shales, schists; and the limestone, marble.
There were, however, also large masses of lava and other volcanic rocks, and these have become metamorphosed into peculiar schistose rocks of various types. Such metamorphic lavas abound at the foot of Mount Lyell and on Mount Dana. They are readily recognized by their mottled appearance, the steam cavities or vesicles in the lavas having been filled with light colored minerals that contrast with the somber hue of the rocks themselves.
All the metamorphic rocks except the marble (of which there is but little in the High Sierra) are dark in general tone as compared with the granites. The mountains of which they are composed consequently have a dusky appearance in the landscape, alongside of the bright, granitic peaks—they seem overcast by perpetual cloud shadows.
One of several essays written by Dr. Matthes in the middle ’30’s at the request of the Yosemite Park and Curry Company in connection with the plan, initiated as early as 1923, to establish lodgings for the use of hikers from Yosemite Valley who wished to make overnight excursions into the high country. The history of these lodgings, known first as “Hikers’ Camps” and later as “High Sierra Camps,” has been told by Dr. Carl P. Russell (One Hundred Years in Yosemite: The Story of a Great Park and Its Friends, 1947 edition, pages 113-115). Though widely used in typewritten form, so far as known the essays were never printed.
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