CHAPTER XVII. 
THE COLORADO DESERT. 
Extent and boundaries op the desert.—Desert beyond the Colorado.—Surface op the desert.—Hard clay.—Slopes.— 
Undulating hills op sand.—Level and higher plain covered with pebbles.—Silicified fossils.—Polished surfaces of the 
pebbles.—Polished and blackened rocks.—Abrasion and polishing produced by driving sand.—Elevation of the surface 
of the desert.—Depression of a portion below the sea-level.—Terraces.—New river.—Geological formations.—Meta- 
morphic rocks.—Alluvium, its extent and lithological characters.—Fossils.—Tertiary strata—Fossils. —Ancient lake.— 
Former extension of the gulf to san Bernardino mountain.—Origin and formation of the lake.—Elevation of the former 
shore.—Calcareous depositions from the water of the lake.—Analysis of the travertin of pilot knob.—Sand-hills.— 
Position of the sand-hills determined by the terrace.—Outline of the sand hills.—The sand not an obstacle to the con¬ 
struction of a railroad.—Sources of water on the desert.—New river.—Cook’s well.—Alamo well.—Soda springs.—Salt 
lagoon.—Distances between localities of water —Necessity for wells.—Artesian wells.—Agricultural capabilities of 
THE DESERT.—BOTTOM LAND OF THE COLORADO AND GILA.—CoHUILLA VILLAGES.—NECESSITY FOR IRRIGATION.—IRRIGATION BY NEW 
r river.—Climate and winds.—Clearness of the air.—Colors of distant mountains.—Mirage.—Effect of the climate on the 
VEGETATION. 
The region of country known as the Colorado Desert is a long plain or valley west of the 
Colorado River, near its mouth. It extends from the base of Mount San Bernardino to the head 
of the Gulf of California, and is separated from the coast-slope by the Peninsula Mountains. 
The limits of the plain on the north and northeast are determined by the ranges of mountains 
which extend from San Bernardino Mountain to the mouth oi the Gila and beyond into Sonora. 
On the south and east, the Desert is bounded by the Colorado River and the Gulf. The area 
thus bounded is a long and nearly level plain, extending in a northwest and southeast direction, 
from latitude 34° on the north to the parallel of 32° on the south. Its greatest length in this 
direction, from the base of San Bernardino Pass to the Gulf, is one hundred and eighty miles, 
or, measuring from the base of the Pass to the mouth of the Gila, it is one hundred and forty 
miles. Its greatest width is about seventy-five miles, measured in a north and south direction 
along the Colorado River, between the head of the Gulf and the mountains north of Fort Yuma. 
The plain narrows as it extends back from the Colorado River, and opposite Carrizo Creek its 
width is reduced to between sixty and seventy miles, and still further westward, near to its 
extremity at the San Bernardino Pass, it will not average over twenty-five miles. These 
measurements are approximate, and give for the whole area, west of the Colorado, about 8,250 
square miles, or, including a portion of the plain beyond the river, about 9,000 square miles. 
A similar Desert borders the Colorado River on the east side, and appears to extend for a long 
distance up the Gila, and to reach to the foot of a range of mountains in Sonora, but, as the 
exploration did not extend so far as to ascertain the boundaries, it is not included in the descrip¬ 
tion. The coloring on the map is, however, extended so as to indicate the geological character 
of that part of the region near the river. 
The exact parallelism of the valley of the Desert with the coast, and with an intermediate 
line, formed by a succession of the narrow valleys of Yallecito, San Felipe, Warner’s, and the 
San Luis River, and also with the Bernardino Pass, is worthy of notice. It is strikingly 
exhibited by the distribution of the colors of the map. They clearly mark out the direction and 
