The Western United States: A Geographical Reader. Harold W. Fairbanks
to work making new beds. They cut down through the lava and the buried gravel until they finally reached the solid rock underneath. Into this rock, which we call "bed-rock," they have now worn cañons two thousand feet deep. The beds of gravel that lay under the old streams frequently form the tops of the hills between these deep cañons. Here they are easily accessible to the miners, who by tunnels or surface workings have taken out many millions of dollars' worth of gold.
The important cañons of the northern Sierras, where the gold is found, have been made by the American and Feather rivers. Farther south are the deeper and more rugged cañons of the Tuolumne, Merced, King's, and Kern rivers, which open to us inviting pathways into the mountains.
It might be supposed that the mantle of snow and ice which at that time covered most of the surface of the earth would have protected it from further erosion, but this was not the case. In the basin at the head of each stream the snow accumulated year after year until it was more than a thousand feet deep. Under the influence of the warm days and cold nights the snow slowly turned to ice, and moved by its own weight, crept down into the cañons. The solid rock walls were ground and polished, and even now, so long a time after the glaciers have melted, some of these polished surfaces still glisten in the sunlight. The glaciers deepened and enlarged the cañons, but running water was the most important agent in their making.
Upon the disappearance of the glaciers, the streams went to work again deepening their cañons. From their starting-points, under the lofty crags, they first ran through broad upland valleys, then tumbled into the cañons; but until they had reached the lower mountain slopes, to which the glaciers had not extended, they passed through a dreary and desolate region devoid of almost every sign of life. The glaciers had swept away all the loose rock and soil, and it was many long years before the surface again crumbled so that forest trees could spread over it once more.
The grandeur and attractiveness of the Yosemite is partly due to the precipitous cliffs enclosing the valley, some of which are nearly four thousand feet in height, partly to the high waterfalls, and partly to the green meadows and forest groves through which the Merced River winds.
although the glaciers had little to do with the making of the Yosemite Valley, yet they added to its attractiveness. The valley is situated where a number of smaller streams join the Merced River. Erosion was more rapid here because the granite was soft, while the vertical seams in the rock gave the growing valley precipitous walls. When the glacier came it pushed out the loose rocks and boulders, and dropping a portion of them at the lower end, made a dam across the Merced River. At first a shallow lake filled the valley, but after a time the silt and gravel which the streams were continually bringing in filled the lake, and formed marshy flats. Finally, grasses and trees spread over these flats and gave the valley the appearance which it has to-day.
Besides the meadows, the glaciers gave us two of the waterfalls. Yosemite Creek, which comes down over the walls twenty-seven hundred feet in three successive falls, was turned into its present channel by a dam which a glacier had left across its old course. A glacier also turned the Merced River at its entrance to the main valley so as to form the Nevada Fall.
After the valley had been made and clothed in vegetation, it was discovered by a small tribe of Indians who came here to make their home, secure from all their enemies. There were fish in the streams and animals in the woods. The oaks supplied acorns, and in early summer the meadows were covered with strawberries. Legends were associated with many of the cliffs and waterfalls, for the Indians, like ourselves, are impressed by the wonders of Nature.
Hetch-Hetchy Valley, twenty-five miles north of the Yosemite, has been formed upon much the same plan, but a portion of its floor is marshy and there are few waterfalls. King's River Cañon has no green meadows and no high waterfalls, while its great granite walls are not so precipitous as those of the Yosemite. Next to the Yosemite, in the wildness of its scenery, is Tehipite Cañon. This cañon is situated upon the middle fork of King's River, about a hundred miles south. For many miles its walls and domes present ever changing views.
A continual struggle is going on between the forces within the earth and the sculptor working upon its surface. First one, then the other, gains the advantage. Where the mountains are steep and high, often the forces within have recently been active. Where they are low and the slopes are gentle, the sculptor has long held sway. She begins by making the surface as rough and picturesque as possible, but after a time she destroys her own handiwork.
AN OREGON GLACIER
There are records all about us of events which took place upon the earth long before there were any human inhabitants. These records have been preserved in the rocks, in the geographic features of the land and water, and in the distribution of the animals and plants. On every hand appear evidences of changes in the surface of the earth and in the climate.
Through all the central and northern United States, if we except some of the mountains of the West, the winter snows entirely disappear long before the coming of summer. But the climate of this region has not always been so pleasant and mild. Lands now densely peopled were once buried under a thick mantle of ice which lasted through many thousands of years.
Scattered over the surface of the northern United States are vast numbers of boulders and rock fragments which are not at all like the solid rocks beneath the soil. The history of these materials takes us back to the Glacial period, which can be best understood from a study of some one of the glaciers now existing upon the mountains of the northwestern part of our country.
Among the lofty mountain ranges of the Cordilleran region there are many peaks upon which perpetual snow-banks nestle, defying the long summer days. Where the winters are long and cold and the storms are severe, immense drifts of snow collect in the hollows and cañons of the mountain slopes. Each summer all or a part of this snow melts. Upon the northern slopes the melting process is slower, and if there happens to be a large basin upon that side, an extensive field of snow remains until the winter storms come again. Each winter new snow is added to the surface, while the older snow, becoming hard and firm through repeated freezing and thawing, at last turns to ice.
This mass of snow and ice does not remain stationary, as might be expected from its apparent solidity. Under the influence of its own weight and of alternations of heat and cold, it flows down the incline like a very thick liquid. During the winter the ice melts but little, and the movement is slow, but in the summer, under the influence of the warm days and cool nights, both the melting and the rate of flow of the ice are increased. A moving body of snow and ice of this sort is called a "glacier." It creeps down the mountain slope and into some cañon, until, in the warmer air of the lower mountains, the rate of advance is exactly balanced by the rate of melting at the lower end of the mass. The glaciers in the United States are at present comparatively small, but once these icy masses stretched over the mountains and lowlands of a large portion of the continent.
In the southern Sierra Nevada mountains no permanent snow exists below an elevation of about eleven thousand feet, but as we go north snow-fields are found lower and lower, until in the fiords of Alaska enormous glaciers reach down to the sea.
A glacier worthy of our study may be found upon the Three Sisters, a group of lofty and picturesque volcanic mountains rising from the summit of the Cascade Range in central Oregon. There is a deep depression between two of the peaks, which slopes down to the north and is thus particularly well adapted to catch and retain the drifting snows. Consequently the glacier to which it gives rise is of exceptional size, being nearly three miles long and half a mile wide.
Showing snow-fields and glacier. Fields of recent lava appear in the foreground
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