AVERAGE ELEVATION OF THE SURFACE—METAMORPHIC ROCKS. 217 
: ELEVATION OF THE SLOPES OF THE BASIN. 
At Walker's Pass 3,243 
At Humpahyamup Pass 3,196 
At Taheechaypah Pass 3,668 
At Tejon Pass 3,987 
At Cañada de las Uvas 3,186 
At San Francisquito (Lake Elizabeth) 3,315 
At Williamson's Pass 2,962 
At Cajon Pass, at the summit, 4,676 ; two miles below, —the true margin of theslope.... 4,179 
This gives, as the mean elevation of the margin of the slope, 3,467 feet above the sea. Com- 
paring this with the elevation of the foot of the slopes, and disregarding the one great depres- 
sion of the sink of the Mojave, we have 2,923 feet as the mean elevation of the surface; but, 
considering the opposite elevations of the slopes around the Lost Mountains, it must be a little 
over 3,000 feet. This may be regarded as the mean elevation of the surface around and between 
the ridges and mountains. 
The basin-like structure is not confined to the interval between the Sierra Nevada and the 
bounding mountains on the east side, but is characteristic of these ranges also. According to 
the observations of Captain Whipple, the mountains between the Colorado and the Mojave, 
called the Pai-Ute Range, consist of many rugged ridges and peaks, with elevated valleys 
between them. A wide, local basin, with a dry lake at the bottom, is also found in the 
mountains east of the Mojave River, at the foot of the slope from the Cajon Pass. A similar 
structure is said to characterize the northern end of the Sierra Nevada. The Great Basin may, 
in fact, be considered as the flattened crest of a broad mountain chain. It is a succession of 
mountains and slopes, upon which the precipitation of water is so slight that the local basins 
are not overflowed so as to effect a drainage to the sea. 
The barren rocks and the peculiarly regular slopes, free from trees and grass, and looking 
like broad ocean beaches, give the whole region the appeafance of having been moulded to its 
present shape by the action of water. It seems almost as if it had but recently been covered 
by the sea, and that the waters had suddenly drained off. - 
GEOLOGICAL STRUCTURE OF THE LOST MOUNTAINS. 
The mountains alon g the Mojave River, especially those near the foot of the slope from the 
Cajon, are very much broken, and appear to extend to the base of San Bernardino mountain, on . 
the south, while on the north they form the flanks and outlying ridges of the Pai-Ute Range. 
All the ridges near the Mojave are barren and destitute of soil, and are very rugged and rocky. 
Their outlines are very irregular, and some of the subordinate ridges are entirely isolated from 
the main range, thus becoming Lost Mountains. When these are short and pointed they 
appear at a distance like a series of volcanic cones. The resemblance to cones and cratqrs was so 
great, that when I was descending the slope to the Mojave I confidently expected to examine 
volcanic phenomena, and was disappointed to find nothing but granitic and metamorphic 
rocks, 
The rocks on the right bank of the river consist of a belt of metamorphic slates, very com- 
pact, and so much changed as to resemble granite. They dip at an angle of 85 degrees, and 
are succeeded on the east by compact gray granite, which forms the mass of the ridge.’ It is 
much fissured and traversed by enormous veins of feldspar and quartz in coarse masses. This 
Sranite is very rough on its surface, and, in places, is covered by immense blocks of the same 
! See a small section, Chapter VI, page 64. 
28 F 
