274 GUIDEBOOK OF THE WESTERN UNITED STATES 
between the faults, bordered on each side by the old schists. In 
general in this vicinity the faults are bordered on the north by sand- 
stone of Tertiary age lying on gneiss or schist, and on the south 
side is schist more or less heavily covered by young gravel. (Noble.) 
Although the San Gabriel and San Bernardino Mountains contain 
similar rocks, are separated only by Cajon Pass, present identical 
relations to the valley of southern California and to the Mohave 
Desert, and are both uplifted fault blocks, they are very dissimilar 
in configuration. The San Gabriel Mountains are deeply cut by 
canyons containing graded streams and are made up of separate 
sharp peaks and knifelike ridges of various heights; no level areas 
remain, either about the summits or in the valley bottoms. The 
higher part of the San Bernardino Mountains has a very different 
character, for its west end, at least, presents a strikingly level sky 
line, mostly at elevations from 5,000 to 6,000 feet, and the range 
contains many broad valleys, some with meadows and lakes, sepa- 
rated by rolling ridges, a topography of an old and well-reduced 
type. According to recent observations by Noble this condition is 
due largely to the relatively recent removal of Tertiary deposits 
from the plain on which they were laid down. Remnants of these 
strata remain in places. To the east, where the elevation increases, 
San Bernardino Mountain and San Gorgonio Mountain rise con- 
siderably above the general level. Along the lower margins of the 
range the forms are strikingly new, and several of the streams are not 
reduced to grade but after meandering through the broad uplands 
plunge over falls into steep canyons in the front of the range. These 
differences in the configuration of the two ranges are not related to 
rock texture, drainage pattern, or difference in precipitation; it is 
suggested that the San Bernardino fault block was uplifted much 
later than the block constituting the San Gabriel Range, which has 
preserved none of these old forms. (Mendenhall.) 
Bloomington, a small place 4 miles west of Colton, is in the midst 
of a thriving irrigation district with many groves of oranges and 
Bloomington. Olives. To the north is a fine view of the San Gabriel 
Elevation 1,000 feet, Mountains, with their imposing high peaks and 
New Orleans 1,948 deeply incised canyons. Along the foot of the range 
_ is the main fault, but it is everywhere buried under 
valley fill. Just south of Bloomington are the Jurupa Mountains, 
rising about 1,000 feet above the plain; they consist of quartzite, 
% The San Gabriel Mountains con- | rocks, mainly schists, some of which 
sist of granite rocks of several kinds were origmally’ ig hales and sandstones 
and a variety of other crystalline | (me' 
