Page:Popular Science Monthly Volume 52.djvu/629

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THE GREAT SIERRA NEVADA FAULT SCARP.

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THE GREAT SIERRA NEVADA FAULT SCARP.
By HAROLD W. FAIRBANKS, Ph. D.

THAT portion of California lying east of the crest of the Sierra Nevada Mountains has had a remarkable geological history. There are many phenomena to be witnessed in that region which possess much interest aside from their purely scientific aspect, and deserve to be better known than they are at present. The enormous scale on which faulting has taken place, resulting in the precipitous eastern wall of the Sierra Nevadas, and the variety and extent of the comparatively recent volcanic outbursts along the lines of fracture, bring the magnitude of geological processes vividly before our eyes. There are probably no better examples of topographic features due to the elevation and depression of great blocks of the earth's crust, through the formation of faults, to be found in any other portion of the world. From a scenic standpoint, also, the region is unique. The lofty, jagged crest of the Sierras rises over fourteen thousand feet, culminating in Mount Whitney, the highest peak in the United States south of Alaska, while in marked contrast to the ice and snow of these mountain heights are the hot and scorching wastes of Death Valley, which lies but a short distance to the east, depressed over three hundred feet below the level of the sea. Snow-clad mountain and desert sand, mighty earth blocks, volcanic craters, lava flows, and alkaline lakes—where can be found greater attractions for the student of Nature?

The Sierra Nevada Mountains, having a length of over three hundred miles and a width of seventy-five miles, consist essentially throughout much of their extent of one great block of the earth's crust, having been elevated along a north-and-south line through a series of movements which have been frequently repeated during a long period of geological time. The block as a whole was not elevated, but tilted from the east, so that on that side there is an abrupt wall many thousands of feet in height, while on the west the slope is long and gradual. Owing to this fact it is only when seen from some point at its eastern base that the magnitude of this range of mountains is appreciated. Although the valleys at the eastern foot of the mountains vary from three thousand to six thousand feet in altitude, the wall of rock forming the scarp rises so abruptly and with such colossal proportions that it is absolutely overpowering in its grandeur. To the east and running parallel with the Sierra Nevadas are other giant ranges formed in much the same manner, being only slightly lower but separated from each other by desert valleys.