OCHRE Sey y. 
GEOLOGY OF THE COUNTRY BETWEEN THE MOJAVE VALLEY AND THE 
LITTLE COLORADO, 
QUATERNARY DEPOSITS OF MOJAVE VALLEY.— TERTIARY STRATA.—BLACK MOUNTAINS PPseioriomme os § PASS.—PLUTONIC } BOOKS WITH SILI- 
CIOUS MINERALS. np ere ROCKS OF EASTERN BASE 0 LONG VALLEY. AME ALLEY. 
EASTERN CHAIN OF CERBAT MOUNTAINS.—FIRST PLATEAU OF THE TABLE-LANDS.—CANON OF DIAMOND RIVER. dee te caNon 
OF THE COLORADO.—DETAILED SECTION OF ITS WALLS.—SILURIAN, DEVONIAN, AND CARBONIFEROUS ROCKS.—GRANITE PINNACLES OF 
ANCIENT SEA-BOTTOM.——HIGH MESA WEST OF LITTLE COLORADO.—SECTION OF MESA WALL AT CAMP 70.—MIDDLE AND UPPER CARBON- 
TA.—VALLEY OF LITTLE COLORADO, ITS GENERAL FEATURES AND MODE OF FORMATION.—CANON OF CASCADE RIVER.— 
DETAILED SECTIONS OF ITS CLIFFS.— ORIGIN OF GYPSUM.—COMPANIONSHIP OF SULPHATE OF LIME AND PEROXIDE OF IRON. 
Descending the Colorado to the first pass through the Black mountains, at the upper end of 
the Mojave valley, thence striking northeast to the mouth of Diamond river, and going thence 
eastward to Cascade river and to San Francisco mountain, we found the geology of our route to 
present the following features: 
MOJAVE VALLEY. 
Quaternary deposits.—From the immediate banks of the Colorado, the trail which we 
followed led some twelve miles up the gentle slope which I have described as bordering the 
river on either side in this valley, and extending to the bases of the mountains. 
This surface really deserves the name of desert throughout its extent; the narrow bottom- 
lands being immediately succeeded by bluffs of Quaternary gravel, of which the slopes and 
summits, though when we passed covered with a most brilliant array of spring flowers, usually 
sustain no vegetation, except here and there a dwarfed bush of Larrea or a clump of prickly 
Opuntia. After the ephemeral influence of the few spring showers has passed, the annual 
plants are soon burned up by the sun’s heat, and perfect sterility prevails throughout the 
remainder of the season. 
Tertiary strata. —The Quaternary gravels, transported by the river or brought down from 
the neighboring mountains, cover most of this slope, and compose the greater part of its mass 
near the river. As we approached the bases of the mountains, however, we found a series of 
Tertiary strata—tufaceous limestone, sand, gravel, &c.—exposed in all the ravines, and forming 
the first of the foot-hills. These strata closely resemble those occurring at Camp 49, above 
Pyramid cafion, but are composed of a larger proportion of volcanic materials, some of the 
beds being little else than stratified volcanic ashes. 
They are considerably disturbed, and bear testimony to violent volcanic action both during 
and subsequent to their deposition. I was not able to detect any traces of fossils in any of the 
beds examined. 
BLACK MOUNTAINS. 
Where we crossed them these mountains are composed entirely of erupted rocks—porphyries, 
amygdaloid, basalt, trachyte, &c.—similar to those so fully represented in my collections from 
the vicinity of Camp 49. The vivid colors of these rocks, and the picturesque pinnacles and 
castellated summits which they form, so characteristic of this range, are here quite as oe 
uous as in the localities where they have been heretofore described. 
L 
