TERTIARY STRATA OF THE GREAT BASIN. 185 
into fantastic forms. Indications of horizontal argillaceous strata are also found around the 
bases of several of the ** Lost Mountains." 
High, rounded hills, evidently sedimentary, were visible several miles north of the entrance 
to the Tejon Pass from the Great Basin, and strata of different colored clays were exposed by a 
land-slide, or deep erosion, produced by a sudden fall of rain. These strata attain a great thick- 
ness, and may be of the age of those seen near the summit of the Cañada de las Uvas. It is 
also probable that they produce the beds of salt which are resorted to by the Indians from the 
Tejon. 
These brief descriptions of the chief exposures of the sedimentary formations of the southern 
part of the Basin are sufficient to show the great diversity in their lithological characters, and 
the diffieulty of grouping them correctly without further explorations, and the collection of 
fossils. We may, however, separate them, lithologically, into four groups, or divisions: 
1st. The soft, unconsolidated strata of variously colored clay and sand, or clay and sand mingled 
together, forming rounded hills, with the strata generally horizontal; 2d. The compact sand- 
stone and semi-consolidated argillaceous strata; 3d. The sandstones and thick beds of breccia 
of volcanic rocks, upheaved so far as seen; 4th. The coarse-grained granitic sandstone of the 
Cajon and Cottonwood Creek. 
I would include in the first group the soft strata on the east base of the Sierra Nevada, near 
Taheechaypah Pass ; the strata in the Cañada de las Uvas, just beyond the summit; those near 
the entrance to Williamson's Pass, and in its vicinity ; and the strata bordering the Mojave, 
along the lower parts of its course. In the second group we may include the compact sand- 
stones of the valley of Lake Elizabeth, supposed to be horizontal, and the upraised strata in the 
eastern part of the Canada de las Uvas, containing the fossil stems. It is possible, also, that 
the nearly horizontal strata underlying the superficial accumulations of the slope of the Basin, 
at the entrance to the Tejon Pass, have similar lithological characters. I include in the third 
group the outcrops of breccia and conglomerate on the margin of the Basin, north of Lake 
Elizabeth, and at the entrance to Williamson's Pass. It is probable that strata similar to these 
will be found at other points. These divisions are, of course, merely temporary and for conve- 
nience of description. 
It is most probable that the strata of the first group will be found to be of the age of the 
Pliocene or recent Tertiary. They are more recent than the other groups, the age of which can- 
not be closely determined, although probably Miocene, or Eocene, or both. 
The outcrops along the northern base of the Bernardino Sierra, including those of the Cafiada 
de las Uvas, have an average elevation of 3,500 feet above the sea ; that near Taheechaypah 
Pass must be nearly 4,000, and those along the Mojave from 1,100 to 2,600 feet. 
We may conclude that the greater part of the surface of the southern part of the Basin is 
underlaid by the extension of these strata under the more recent accumulations which form the 
slopes. This is indicated not only by the outerops along the Bernardino Sierra, but by those of 
the Mojave River, and around the detached ridges between the Mojave and the Sierra Nevada. 
It is probable that the strata of the Cajon Pass and its vicinity (those of the fourth group) are 
in a great measure local and do not extend far from the mountains. The materials do not 
àppear to have been transported from a distance, or to have been long agitated together under 
water. The rock probably accumulated in the vicinity of, or around, a coast of granitic rock, 
Which was abraded with great rapidity. 
24 F 
