Glacial Phenomena in Nevada[20]
The monuments of the Ice Age in the Great Basin have been greatly obscured and broken, many of the more ancient of them having perished altogether, leaving scarce a mark, however faint, of their existence--a condition of things due not alone to the long-continued action of post-glacial agents, but also in great part to the perishable character of the rocks of which they were made. The bottoms of the main valleys, once grooved and planished like the glacier pavements of the Sierra, lie buried beneath sediments and detritus derived from the adjacent mountains, and now form the arid sage plains; characteristic U-shaped canyons have become V-shaped by the deepening of their bottoms and straightening of their sides, and decaying glacier headlands have been undermined and thrown down in loose taluses, while most of the moraines and striae and scratches have been blurred or weathered away. Nevertheless, enough remains of the more recent and the more enduring phenomena to cast a good light well back upon the conditions of the ancient ice sheet that covered this interesting region, and upon the system of distinct glaciers that loaded the tops of the mountains and filled the canyons long after the ice sheet had been broken up.
The first glacial traces that I noticed in the basin are on the Wassuck, Augusta, and Toyabe ranges, consisting of ridges and canyons, whose trends, contours, and general sculpture are in great part specifically glacial, though deeply blurred by subsequent denudation.
These discoveries were made during the summer of 1876-77. And again, on the 17th of last August, while making the ascent of Mount Jefferson, the dominating mountain of the Toquima range, I discovered an exceedingly interesting group of moraines, canyons with V-shaped cross sections, wide neve amphitheatres, moutoneed rocks, glacier meadows, and one glacier lake, all as fresh and telling as if the glaciers to which they belonged had scarcely vanished.
The best preserved and most regular of the moraines are two laterals about two hundred feet in height and two miles long, extending from the foot of a magnificent canyon valley on the north side of the mountain and trending first in a northerly direction, then curving around to the west, while a well-characterized terminal moraine, formed by the glacier towards the close of its existence, unites them near their lower extremities at a height of eighty-five hundred feet.
Another pair of older lateral moraines, belonging to a glacier of which the one just mentioned was a tributary, extend in a general northwesterly direction nearly to the level of Big Smoky Valley, about fifty-five hundred feet above sea level.
Four other canyons, extending down the eastern slopes of this grand old mountain into Monito Valley, are hardly less rich in glacial records, while the effects of the mountain shadows in controlling and directing the movements of the residual glaciers to which all these phenomena belonged are everywhere delightfully apparent in the trends of the canyons and ridges, and in the massive sculpture of the neve wombs at their heads. This is a very marked and imposing mountain, attracting the eye from a great distance. It presents a smooth and gently curved outline against the sky, as observed from the plains, and is whitened with patches of enduring snow. The summit is made up of irregular volcanic tables, the most extensive of which is about two and a half miles long, and like the smaller ones is broken abruptly down on the edges by the action of the ice. Its height is approximately eleven thousand three hundred feet above the sea.
A few days after making these interesting discoveries, I found other well-preserved glacial traces on Arc Dome, the culminating summit of the Toyabe Range. On its northeastern slopes there are two small glacier lakes, and the basins of two others which have recently been filled with down-washed detritus. One small residual glacier lingered until quite recently beneath the coolest shadows of the dome, the moraines and neve-fountains of which are still as fresh and unwasted as many of those lying at the same elevation on the Sierra--ten thousand feet--while older and more wasted specimens may be traced on all the adjacent mountains. The sculpture, too, of all the ridges and summits of this section of the range is recognized at once as glacial, some of the larger characters being still easily readable from the plains at a distance of fifteen or twenty miles.
The Hot Creek Mountains, lying to the east of the Toquima and Monito ranges, reach the culminating point on a deeply serrate ridge at a height of ten thousand feet above the sea. This ridge is found to be made up of a series of imposing towers and pinnacles which have been eroded from the solid mass of the mountain by a group of small residual glaciers that lingered in their shadows long after the larger ice rivers had vanished. On its western declivities are found a group of well-characterized moraines, canyons, and roches moutonnees, all of which are unmistakably fresh and telling. The moraines in particular could hardly fail to attract the eye of any observer. Some of the short laterals of the glaciers that drew their fountain snows from the jagged recesses of the summit are from one to two hundred feet in height, and scarce at all wasted as yet, notwithstanding the countless storms that have fallen upon them, while cool rills flow between them, watering charming gardens of arctic plants--saxifrages, larkspurs, dwarf birch, ribes, and parnassia, etc.--beautiful memories of the Ice Age, representing a once greatly extended flora.
