90 
WESTERN SLOPE OF CORDILLERAS—SAN EMILIO. 
Nevada. Further south, on the slope of the Colorado desert, gypseous and arenaceous beds of 
the Miocene group are found ; these beds probably overlie the unconformable sandstone of the 
Mojave valley. 
On the western slope the deposits appear to be all conformable ; but, as along the range 
extending from Temecula to San Diego the strata have been intruded upon by erupted trappean 
rocks, it is difficult to connect the slope of the sandstones with the granite. In San Diego 
county these strata are Miocene ; in Los Angeles and San Bernardino counties the sandstones 
which flank the granitic axis of Kikal Mungo are certainly conformable, and owe their elevation 
to the upheaval of that range ; the actual age of these strata was not determined in these coun¬ 
ties, but the continuity of the strata was traced to positions where the age was well known— 
thus, the Sierra Susanna is an offset from the Cordilleras, produced by a lateral upheave in a 
more westerly direction from-the main chain ; this upheave carries on its sides (and, indeed, is 
almost concealed by) the same sedimentary beds ; these are again uplifted in the Sierra Monica, 
are found at San Buenaventura, and finally at Santa Inez and Santa Barbara, where these sand¬ 
stones were perfectly examined, and the examinations of the fossils of which, (by Mr. Conrad,) 
show them to be Miocene strata. It is the lower beds of the Miocene group, the brown and red 
sandstones, which are displayed on the Pacific slope of the Cordilleras, the upper beds being 
much contorted, so as often to assume a vertical position, and so much abraded as to lie several 
hundred feet below the present level of the valley, the denuded trough being filled up by the 
deep deposits of blue clays and sand treated of when describing Los Angeles valley. 
The Cordilleras, therefore, have been upraised since the deposit of the Miocene beds of Cali¬ 
fornia, and are thus coeval with the Coast Ranges, with the sierras Santa Inez, San Rafael, and 
San Jose ; indeed, perhaps, the latter are the true continuation of the same chain toward the 
northwest. Both have the same direction, both have the same sedimentary beds flanking them, 
the nature of the axial rock similar, and the volcanic rocks erupted on its sides very similar; 
and, lastly, both are connected by an intervening mass of mountain, the San Emilio region; 
this district has been only alluded to heretofore by name, and deserves now a more enlarged 
notice. The name of San Emilio mountain has been applied to a lofty district which lies 
west of the Canada de las Uvas, between the termination of the Sierra Nevada and the southern 
extension of the Santa Lucia range. Viewed from a distance, as from the northern end of the 
Santa Maria valley, it appears a large well-defined mountain, which stretches east and west, 
and rises to an altitude between 7,000 and 8,000 feet; but on travelling up the Cuyama valley 
to the upper waters of the Santa Maria, and ascending to the sources of this stream, it becomes 
evident that what was apparent as a single mountain is an immense tract of elevated country, 
which is chiefly granitic and porphyritic on its eastern edge, where it is loftiest, and further 
west is made up of the yellow sandstones and overlying beds which, towards the north, con¬ 
stitute the slopes of Panza and San Jose; these constitute the divort between the Santa Maria 
and the Santa Clara waters, and form the most extensively elevated land of south California. 
Both volcanic dykes and veins of porphyritic granite are given off from each side, the former 
from Santa Lucia and the latter from San Emilio. The strata on the north side of this divort 
dip northeast into Cuyama valley, and the beds on the south into or toward the bed of the 
Santa Clara. The Peyrou, a tributary of that river, finds its sources here, and carves its way 
down through deep chasms in the granitoid rock, which lie between its sources and its debouche ; 
the same mode of segregation of the granitic mass observed at the Cajon and at Warner’s passes 
