RIVER VALLEYS—THE GREAT BASIN, 9 
by the survey is at the base of the volcano, where the valley of the Colorado Chiquito was left. 
The highest point on the level of the upper edge of the slope, a few miles west of the pass, is 
7,400 feet. The mean altitude of the plateau may be considered as 6,000 feet, which is about 
that of the slope, or plain, between the Sierra Madre and the ranges on the east of the Rio 
Grande. 
Val del China.—When compared with the vast region which has just been considered, this 
valley is of little importance. It is a narrow depression west of the volcanoes of San Francisco 
and Bill Williams’ mountain, and serves to separate them and the Black Forest mountains from 
the Aztec range. The direction of the valley is nearly northwest and southeast, being parallel 
with the range on the west. The stream called Partridge creek, upon the map, flows through 
it towards the south, and unites with a tributary of the Gila river. The barometrical observa- 
tions were commenced at the sources of this creek, and continued along its course until it was 
left to commence the ascent of the Aztec range. The lowest point reached was 4,867 feet, and 
the width of the depression is about eighty miles. 
Valley of Hawil-hamook, or Bill Williams’ fork of the Colorado.—The valleys west of San Fran- 
cisco volcano are entirely different from the broad table-lands found between the ranges on the 
eastern side. They become more narrow and trough-like, the slopes on each side becoming 
more abrupt and decided. This valley is entered from Cactus Pass of the Aquarius mountains 
by a sharp and abrupt descent. The barometric profile presents the elevations along the 
course of the stream southward, but the profile presented as the basis of the geological section 
crosses the head-waters of the river, and thus the full depth of the valley reached by the survey 
is not represented. Itis bounded on the west by the Cerbat range, with which it is parallel. 
Valley between the Cerbat range and the Colorado river.—This depression was seen from the 
trail, but, as we have already explained, no observations for profile were made. The elevation 
of the region is approximately represented on the geological section, and its breadth is probably 
fifty miles. It probably corresponds in its general characters of surface to the slopes of the 
Great Basin presently to be described. 
Valley of the Colorado river.—This is the deepest and most rugged valley crossed by the survey, 
and is the lowest point reached west of the valley of the Mississippi, and east of the Pacific 
slope. It is bounded on both sides by rugged and barren mountains rising in places directly 
from the stream, and in others leaving a narrow belt of low land or slopes at their bases. The 
elevation of the river where it was crossed is about 350 feet, and the valley of course increases 
in altitude towards the nort 
The Great Basin.—On nen the western side of the Pai-Ute range west of the Colorado, 
the southern end of that vast region known as the Great Basin is reached. That this portion 
really belonged to the Basin, was determined by Lieutenant Williamson’s explorations of the 
Mojave river, showing that it was not a tributary of the Colorado, as had been supposed, but 
that it became lost in the deep soil and sand of the lower partof the Basin. The general 
characteristics of the topography of the Basin may be enumerated in a few words. Itcon- 
sists of a combination of short ridges and ranges, isolated, but rising so closely together in 
places, that a series of small local basins is produced between their sides andends. The general 
trend of these ranges is from north to south, so that they are ranged in parallel lines, or overlap 
one beyond another. It has generally been considered that the surface of the Great Basin was 
of nearly uniform elevation, and that it was like a plain or table-land. The point, however, 
Teached by the survey, or the bed of the Soda lake, which is probably the end of the Mojave 
river, is very low, being only 1,116 feet above the sea, and very much lower than the average 
elevation of the purines. of the bak It is indeed the lowest point of the Great Basin now 
known. From the Soda lake the valley or dry bed of the Mojave river furnished a gradual 
ascent until within twenty miles of the crest of the Bernardino Sierra, when the road leaves | 
the river and commences the ascent of a gently rising slope, which terminates at the summit of 
the Cajon Pass. This slope may be regarded as a fair type of those which make up the wide ` 
25 
