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BOUNDARIES OF THE GREAT BASIN——ASPECT OF THE SURFACE. 213 
like character of that region 1s established, and there is little reason to doubt that the original 
statement, and the representation of the southern boundary of the Great Basin, was correct. 
The boundaries of this region, as at present known, may, then, be stated as follows: On the 
north by the elevated ridges in which the tributaries of the left bank of Snake River take their 
rise, extending east and west near the parallel of 42? ; on the east by the dividing ridge 
between the waters of the sources of the Colorado River and the Salt Lake, (the Wahsatch or 
Timpanogos Mountains,) and by the range between the Colorado and the Mojave, (Pai Ute 
range;) on the south by the Bernardino Sierra, from San Bernardino Mountain to the 
Sierra Nevada ; and on the west by the Sierra Nevada. 
The region thus bounded is a nearly triangular area, with its apex at the south in the Peak 
of San Bernardino, latitude 34° 30’, and its base nearly along the parallel of 42?—the dividing 
line between the Territories of Utah and Oregon ; it also extends beyond and includes some of 
the elevated lakes of the crest of the Sierra Nevada. Its northeastern angle also extends into 
Oregon, including Bear River, the principal tributary of the Salt Lake. Its greatest length, 
measured from San Bernardino to its northwestern extremity; is nearly 700 miles; or, measured 
from Bernardino Mountain northwards along the meridian, is about 500 miles. "The width, on 
the parallel of 42°, is over 500 miles ; but south of the parallel of 36°, it is less than 180 miles. 
This narrow portion of the Basin, its southern extremity, reaches to within fifty miles of the 
Pacific Ocean ; and although it is narrow, and of small extent when compared with the wide 
area between the Sierra Nevada and the Great Salt Lake, it is believed that the great charac- 
teristic features of arid barrenness, described by Frémont and others, are so strikingly displayed 
that a good conception of the whole area can be obtained from it. "The geology, also, of the 
portion examined is so simple and well defined, and the structure of the region is such, that its 
geology may be regarded as an index to the geological structure of a wide area towards the 
north. 
The first view of the surface of the southern part of the Basin was obtained from the Tejon 
Pass, at an elevation of about 6,000 feet. Istood on the crest of the Sierra Nevada, among 
oak groves, and near the margin of a forest of pines, but in the east a vast wilderness lay 
stretched out before me. It was not a wilderness of unbroken forest, but a desolate, barren 
region, parched and desert-like, its color that of dry gravel and sand. Here and there over the 
broad area were isolated ridges of barren rocks, rising in some places in conical peaks, flanked 
by long slopes, and in others extending for miles in a continuous series, one behind the other, 
until their outlines were blended with the distant horizon. "Those persons whose eyes have only 
been familiar with green fields and wooded hills can scarcely form an adequate conception of the 
appearance of these bare mountains and the desert-like character of this inland region. Its 
surface is diversified only by these bald, barren, and rocky ridges, which rise at intervals, and 
present a strong contrast with the fertile, soil-covered ridges of the Sierra Nevada, watered by 
brooks and covered with verdure. 
This strong contrast, or vividly marked change in the aspect of the country, is a grand 
demonstration of the climatal influence of the Sierra Nevada. This lofty chain of snowy peaks 
rises like a wall between the Pacific and the interior, and acts the part of dessicator to the 
moist winds that pour in from the ocean, abstracting the vapor that they hold, and condensing 
it upon the summits in fields of snow. 
The moisture being thus abstracted from the winds, they pass inland over the surface of the 
Basin, and, instead of bearing clouds of vapor to be there condensed, they are in a condition to 
