10 
GEOLOGICAL REPORT-THIRTY-FIFTH PARALLEL. 
surface of the Basin, which is, in fact, hut a combination of slopes flanking the ridges, producing 
by their intersection a series of basin-like depressions. The slope to the Mojave is perhaps 
unusually well defined and regular ; hut the same or a similar slope is found for the whole 
length of the southern end of the Basin, reaching from Bernardino mountain to the Sierra 
Nevada, and this last mentioned chain is flanked in a similar manner. The average inclination 
of these gradual descents is not over 50 feet to a mile. In passing either up or down the Mojave 
slope, the inclination of the surface is not very apparent, and becomes evident chiefly by the 
appearance of distant objects. When, however, the observer stands on a distant point and is 
able to view the surface at right angles to its direction of descent, the inclination is very appa¬ 
rent, and is so clearly defined and regular that it invites the use of the clinometer for its 
measurement. 1 
The surface of the Great Basin, unlike that of the great plain between the Sierra Madre and 
the San Francisco volcano, is not formed of horizontal strata, which leave table-like areas where 
cut by rivers or exposed to denudation. The materials composing the surface appear to he 
derived from the adjoining ridges and mountains, and are laid down around them with inclined 
surfaces, the coarser parts being nearest the elevations, while the finer materials are transported 
further out, and the sloping character of the surface is thus produced. 
Plain and valleys bordering the Pacific .—At the foot of the Cajon Pass, on the west, the country 
stretches out with a gradual descent to the Pacific. The distance from the Pass to the beach at 
the nearest point is about fifty miles, and by way of the trail to Los Angeles and San Pedro is 
over eighty. Although this region is traversed by many streams, and there are local depres¬ 
sions and elevations of slight extent, the whole, for convenience of description, may be consid¬ 
ered as a continuous and nearly unbroken slope, its upper margin being at an elevation of 
about 1,300 feet, its foot at the sea being on an average seventy miles distant. 
1 For further observations on the configuration of the Basin and the peculiarities of the slopes, see the author’s report on 
the geology of the route in California, surveyed by Lieutenant R. S. Williamson. 
