Spend all the time you can spare or steal on the tracks of this grand old glacier, charmed and enchanted by its magnificent cañon, lakes and cascades and resplendent glacier pavements.
The Nevada Glacier was longer and more symmetrical than the last, and the only one of the Merced system whose sources extended directly back to the main summits on the axis of the Range. Its numerous fountains were ranged side by side in three series, at an elevation of from 10,000 to 12,000 feet above the sea. The first, on the right side of the basin, extended from the Matterhorn to Cathedral Peak; that on the left through the Merced group, and these two parallel series were united by a third that extended around the head of the basin in a direction at right angles to the others.
The three ranges of high peaks and ridges that supplied the snow for these fountains, together with the Clouds’ Rest Ridge, nearly inclose a rectangular basin, that was filled with a massive sea of ice, leaving an outlet toward the west through which flowed the main trunk glacier, three-fourths of a mile to a mile and a half wide, fifteen miles long, and from 1000 to 1500 feet deep, and entered Yosemite between the Half Dome and Mount Starr King.
Could we have visited Yosemite Valley at this period of its history, we should have found its ice cascades vastly more glorious than their tiny water representatives of the present day. One of the grandest of these was formed by that portion of the Nevada Glacier that poured over the shoulder of the Half Dome.
This glacier, as a whole, resembled an oak, with a gnarled swelling base and wide-spreading branches. Picturesque rocks of every conceivable form adorned its banks, among which glided the numerous tributaries, mottled with black and red and gray boulders, from the fountain peaks, while ever and anon, as the deliberate centuries passed away, dome after dome raised its burnished crown above the ice-flood to enrich the slowly opening landscapes.
The principal moraines occur in short irregular sections along the sides of the cañons, their fragmentary condition being due to interruptions caused by portions of the sides of the cañon walls being too steep for moraine matter to lie on, and to down-sweeping torrents and avalanches. The left lateral of the trunk may be traced about five miles from the mouth of the first main tributary to the Illilouette Cañon. The corresponding section of the right lateral, extending from Cathedral tributary to the Half Dome, is more complete because of the more favorable character of the north side of the cañon. A short side-glacier came in against it from the slopes of Clouds’ Rest; but being fully exposed to the sun, it was melted long before the main trunk, allowing the latter to deposit this portion of its moraine undisturbed. Some conception of the size and appearance of this fine moraine may be gained by following the Clouds’ Rest trail from Yosemite, which crosses it obliquely and conducts past several sections made by streams. Slate boulders may be seen that must have come from the Lyell group, twelve miles distant. But the bulk of the moraine is composed of porphyritic granite derived from Feldspar and Cathedral Valleys.
On the sides of the moraines we find a series of terraces, indicating fluctuations in the level of the glacier, caused by variations of snow-fall, temperature, etc., showing that the climate of the glacial period was diversified by cycles of milder or stormier seasons similar to those of post-glacial time.
After the depth of the main trunk diminished to about five hundred feet, the greater portion became torpid, as is shown by the moraines, and lay dying in its crooked channel like a wounded snake, maintaining for a time a feeble squirming motion in places of exceptional depth, or where the bottom of the cañon was more steeply inclined. The numerous fountain-wombs, however, continued fruitful long after the trunk had vanished, giving rise to an imposing array of short residual glaciers, extending around the rim of the general basin a distance of nearly twenty-four miles. Most of these have but recently succumbed to the new climate, dying in turn as determined by elevation, size, and exposure, leaving only a few feeble survivors beneath the coolest shadows, which are now slowly completing the sculpture of one of the noblest of the Yosemite basins.
The comparatively shallow glacier that at this time filled the Illilouette Basin, though once far from shallow, more resembled a lake than a river of ice, being nearly half as wide as it was long. Its greatest length was about ten miles, and its depth perhaps nowhere much exceeded 1000 feet. Its chief fountains, ranged along the west side of the Merced group, at an elevation of about 10,000 feet, gave birth to fine tributaries that flowed in a westerly direction, and united in the center of the basin. The broad trunk at first poured northwestward, then curved to the northward, deflected by the lofty wall forming its western bank, and finally united with the grand Yosemite trunk, opposite Glacier Point.
All the phenomena relating to glacial action in this basin are remarkably simple and orderly, on account of the sheltered positions occupied by its ice-fountains, with reference to the disturbing effects of larger glaciers from the axis of the main Range earlier in the period. From the eastern base of the Starr King cone you may obtain a fine view of the principal moraines sweeping grandly out into the middle of the basin from the shoulders of the peaks, between which the ice-fountains lay. The right lateral of the tributary, which took its rise between Red and Merced Mountains, measures two hundred and fifty feet in height at its upper extremity, and displays three well-defined terraces, similar to those of the south Lyell Glacier. The comparative smoothness of the upper-most terrace shows that it is considerably more ancient than the others, many of the boulders of which it is composed having crumbled. A few miles to the westward, this moraine has an average slope of twenty-seven degrees, and an elevation above the bottom of the channel of six hundred and sixty feet. Near the middle of the main basin, just where the regularly formed medial and lateral moraines flatten out and disappear, there is a remarkably smooth field of gravel, planted with arctostaphylos, that looks at the distance of a mile like a delightful meadow. Stream sections show the gravel deposit to be composed of the same material as the moraines, but finer, and more water-worn from the action of converging torrents issuing from the tributary glaciers after the trunk was melted. The southern boundary of the basin is a strikingly perfect wall, gray on the top, and white down the sides and at the base with snow, in which many a crystal brook takes rise. The northern boundary is made up of smooth undulating masses of gray granite, that lift here and there into beautiful domes of which the Starr King cluster is the finest, while on the east tower of the majestic fountain-peaks with wide cañons and neve amphitheaters between them, whose variegated rocks show out gloriously against the sky.