CERBAT MOUNTAINS—YAMPAI VALLEY 51 
water. They are probably of Tertiary age, and the equivalents of the sandstones and conglom- 
erates of the opposite side of the valley, from which they differ only from the proximity of 
volcanic force during the period of deposition. Some of them are strikingly like the stratified 
tufas of the Des Chutes basin, Oregon, and are evidently the results of the same series of causes. 
The pass by which we crossed this range is simply a cafiada of erosion, through which the 
drainage of a portion of the plain bordering it on the east is carried down to the much lower 
oue on the west. 
——S—S—S—SS=S 
———— SS — = a 
Fig. 13.—caNapDA OF EROSION THROUGH WESTERN RANGE OF THE CERBAT MOUNTAINS. 
At our Camp 63, situated on the eastern base of the western range of the Cerbat mountains, 
the prevailing rock is a coarse gray, massive granite, which forms the highest summits in the 
vicinity, and here composes full half the mass of the chain; the remainder being compact and 
vesicular trap. The granite is in many places intersected by large veins of quartz, containing 
iron, and perhaps other metallic minerals, though no others were noticed. Many of the trap 
hills, composed of scoriaceous and decomposable material, have been extensively eroded, and 
their surfaces are covered with masses of chalcedony and crystallized quartz, formerly contained 
in the fissures and cavities of that portion of the rock which has been removed. The scanty 
supply of water which we obtained from this range, though apparently flowing from granitic 
rocks, is so highly impregnated with salt as to be scarcely drinkable. 
YAMPAI VALLEY. 
This valley seems to be topographically a basin, there being no outlet by which it is com- 
pletely drained. A large quantity of water poured into it would find exit by the cafiada 
through which we ascended to it; but the lower portion of its surface is probably annually 
covered by water, which is removed only by evaporation. Into this area Yampai creek flows 
