TO 
The American Geologist. 
February, 1896 
from the base of the mountains into the very heart of the 
valleys, almost covering in many cases the clayey beds of the 
ancient lakes. These slopes are made up of gravels and 
boulders spread out from the mouths of the canons, partly 
perhaps at a time when the rainfall was greater but mostly 
by the cloudbursts of the present epoch. The climatic con¬ 
ditions now existing are particularly favorable for the for¬ 
mation of the detrital slopes, erosion being retarded but little 
by vegetation. The exceptionally sudden and severe precipi¬ 
tations of rain quickly gathering in torrential streams col¬ 
lect enormous amounts of material from the disintegrated 
surfaces and deposit it over miles of country. Thus is 
formed the detrital cone or fan which is sometimes 12 to 15 
miles long. When the canons are sufficiently near together 
the fans unite into one broad slope. In that part of the 
Mojave desert occupied by western San Bernardino county 
and eastern Kern, which seems to be underlaid chiefly by 
granite, erosion has reached an advanced stage with the pro¬ 
duction of excellent examples of base levelling. The rolling 
gravelly ridges with here and there knobs of granite, and the 
low granite ranges with gentle detrital slopes 6 to 8 miles 
long terminating in shallow alkali sinks, all point to the long- 
continued action upon the existing topography of the agencies 
of decomposition and erosion. One of the best examples of 
base levelling is the western portion of a granite ridge lying- 
south of the El Paso range and extending east and west for 
twenty miles. It is bordered by long gentle slopes of gravel 
and boulders, which extending upward into the shallow 
canons reach almost to the summit. Viewed from a distance 
of ten miles but little of the mountains appears to project 
above the plane of deposition. 
The elevated rugged mountains through central and north¬ 
ern Inyo county present the most striking contrast. The pre¬ 
cipitousness of their slopes and the deep narrow canons indi¬ 
cate that the forces of erosion are in their early prime. This 
is particularly well shown on the eastern slope of the Inyo 
range. The exceedingly abrupt scarp of the central portion 
of this range, fully comparable to that of the Sierra Nevadas, 
is indicative of a great elevation in recent geological times. 
The Salinas valley, which lies at the eastern base, has a com- 
