DENUDATION OF MOUNTAINS—PAINTED CANON. 35 
Cottonwood valley is formed by the continuation of the Black mountains on the east and 
north; by the Dead mountain range on the south and southwest ; on the northwest by moun- 
tains extending into the desert, and which seem to connect the range which runs from Dead 
mountain with that part of the Black mountains lying west of the Colorado. The area enclosed 
by these mountain chains, though large, contains but little level or alluvial land ; none, indeed, 
except that embraced within the limits of Cottonwood valley ; a narrow space near its centre, 
where the conglomerate bluffs recede for a few miles, permitting a growth of vegetation, con- 
spicuous in which are many beautiful groups of cottonwoods. These trees, at the time of our 
visit, (February 25,) clothed in the vivid verdure of their spring dress, afforded a most agree- 
able contrast to the surrounding sterility, and suggested the name given to the valley. 
The alluvial bottom lands are bordered on every side by a broad inclined plain, which extends 
to the bases of the surrounding mountains, and gives a peculiar aspect to the scenery. There 
is, however, nothing in the structure of Cottonwood valley radically different from that of the 
other subordinate basins of the Colorado. 
The long slope which I have described as extending from the mountains to the river is only 
an exaggeration of the similar slope which borders the Mojave valley, and is visible on the 
sides and around the island-like mountains of the Colorado desert. 
As we ascend the river the basins through which it flows become smaller, and the slopes 
formed by the debris of the mountains bear a constantly increasing ratio to the level surfaces 
of the gravel mesas. On the Colorado desert the slopes of the mountains terminate below in 
level surfaces, which stretch away like the sea, till, perhaps, far beyond the limit of human 
vision, they meet similar slopes coming down from the opposite enclosing mountain wall. As 
the basins narrow, however, the bases of the slopes are brought nearer and nearer each other, 
until they meet ; when, if, as is usual, the basin is of elongated shape, a valley is formed whose 
sides slope from the bottom on either hand. In Cottonwood valley the bases of the slopes are 
separated only by the bottom lands of the river, and from this centre they rise, with an inclina- 
tion of 2° to 2° 30’, to the mountains, from five to ten miles distant. The amount of debris 
required to form these slopes proves that we now see only the stumps—if the expression is 
admissible—of the lofty mountains which once surrounded these areas. The relief of the moun- 
tains has also been greatly reduced by the partial filling of the dividing valleys by the materials 
removed from their sides and summits. : 
MOUNT DAVIS. 
Above Cottonwood valley is an interval of about twenty miles, extending to the entrance of 
Black caiion, which, though enclosed in the same great natural barriers with the area last 
described, is entirely without alluvial land, is set with several isolated mountains, and is 
traversed by many lines of upheaval, marked by protruded ridges or masses of volcanic rock. 
The first of these lines of disturbance crosses the Colorado, with a northwest trend, only four 
or five miles above the lodges of the Mojaves in Cottonwood valley. The river has cut through 
this ridge in a cafion of limited extent, whose walls are nowhere more than a hundred feet in 
height, having none of the grandeur of many of the cafions of the Colorado; yet the variety 
and intensity of the colors which the rocks forming it display, render it one of the most pic- 
turesque and interesting of the series, and well deserving of the name (Painted cafion) given it. 
The materials composing its walls are traps, trachytes, tufas, and porphyries; blue, white, 
brown, crimson, purple, &c., all the colors remarkably vivid, and the contrasts striking. 
The datwabeed mountains ssiewied to are usually composed of trap. They are nearly black in 
color, and, rising abruptly from the slopes which descend from the distant granitic chains, form 
peculiar features in the landscape. They suggested comparisons, in the minds of different 
members of the party, with colossal whales, raising their black and massive heads above the 
