The most conspicuous topographic features of the better known portion of the Great Basin are long, narrow, and frequently sharp-crested ridges, with a gentle slope on one side and a steep escarpment on the other. The steeper side in a large number of instances is known to be the upraised side of a fault. Each of these basin ranges, as they are termed, may be considered as the upturned edge of a block of the earth's crust, in general from 60 to 100 or more miles long, and 10 to perhaps 20 miles wide. The crest-lines of the tilted blocks are frequently serrate, on account of differences in the hardness and texture of the rocks and the effects of weathering. There is frequently, however, an older structure revealed in them, showing that the region was folded and otherwise disturbed previous to the later movements which produced the leading features in the present topography. It is probable that this older structure in some instances has had an important bearing on the forms of some of the ranges, but our knowledge in this direction is too limited to warrant presentation in a popular treatise.
Many of the basin ranges are imposing on account of their height and ruggedness, when seen from the adjacent, deeply filled valleys, although scarcely more than half of their actual elevation above the sea is revealed from such points of view. Exceptions to this general statement occur, however, in southeastern California, where, in Death Valley, the land is 480 feet below sea-level. This is the only region in North America which, like the basin of the Dead Sea, is below the level of the ocean's surface. On the border of Death Valley the mountain ranges rise from 6,000 to 10,000 feet, and the highest summit, known as Telescope
Peak, is reported to have an elevation of nearly 11,000 feet above the sea. In the central and northern portions of the Great Basin the valley floors have a general elevation of from 5,000 to 6,000 feet. The mountains rise from these valleys to a height of from a few hundred to 4,000 or 5,000 feet. Among the highest, if not actually the culminating peaks well within the Great Basin are White Mountain, on the California-Nevada boundary, about 30 miles southeast of Mono Lake, which has a summit elevation of 13,000 feet, and Jeff Davis Peak, in eastern Nevada, which rises 13,100 feet above the sea and 8,000 feet above the adjacent valleys.
The numerous sharp-crested ranges of the region under review are frequently remarkable for the richness of the colours of the naked rocks. The mountain slopes and towering angular summits when outlined against the morning or evening sky are frequently as brilliantly dyed as are the New England hills when clothed in the harlequin foliage of autumn. Before sunrise and after sunset each serrate crest-line is the sharply cut border of a silhouette of the deepest and richest purple. The diversity of scenery in the Great Basin is increased by mountains of volcanic origin, including several modern craters, some of which hold lakes, and by lava-flows of recent date, and by great alluvial fans or detritus cones which stream out into the valleys from the mouths of gorges in the bordering mountains.
The Great Basin proper, with its rugged topography and arid climate, is not an agricultural region. Small portions of it, however, when water can be had for irrigation, have been transformed into fruitful farms and gardens which yield bountiful returns. But even a century hence, when all has been accomplished in the way of reclaiming the arid valleys that can be done by utilizing the available water for irrigation, only a small per cent of the whole will be under cultivation.
SIERRA NEVADA AND CASCADE MOUNTAINS
To the west of the Great Basin, and extending from southern California northward to beyond the United States-Canadian boundary, there is a lofty and extremely rugged belt of mountains consisting of two ranges—the Sierra Nevada at the south and the Cascade Mountains at the north. Topographically, these two ranges form a single elevated belt of country, but custom, and as is now generally understood the geological structure and history, draws a dividing line between them in northern California. The Sierra Nevada-Cascade range extends far into Canada, and is there known as the Coast Range. No adjustment of the nomenclature in use on the two sides of the international boundary has been made, and in order to conform with current usage, it is necessary to consider separately the two portions of the range on opposite sides of the forty-ninth parallel.
The Sierra Nevada has its southern terminus at Tejon Pass, in southern California, and extending from there northward to Lassen Peak, in the northern part of the same State. With the exception of a small area to the east and north of Lake Tahoe, the entire range is included within the boundaries of California. This is geographically one of the best defined of the larger mountain ranges in the United States. Its eastern border especially is easy to trace, as for the most part it is determined by a great escarpment, corresponding to the fault scarp which borders one side of so many of the basin ranges. The Sierra Nevada, in fact, may be considered as one of the basin ranges of great size and forming the western wall of the region of interior drainage lying to the eastward. This abrupt eastward-facing mountain slope is in reality a great fault scarp, formed mainly by the upheaval of the west side of an intersecting system of fractures. It is not known, however, how much of the escarpment is due to the upheaval of the west side of the belt of fracture, or how much to the sinking of the eastern side. There have no doubt been many up and down movements along this belt, of which
the present mountain wall is the algebraic sum. The escarpment rises in general from 5,000 to 6,000 feet above the desert valleys to the eastward, and reaches a maximum of about 14,000 feet in the vicinity of Death Valley. It is exceedingly precipitous and rises to an irregular serrate crest-line, from which the general slope westward to the Great Valley of California is gentle.