264 GUIDEBOOK OF THE WESTERN UNITED STATES 
fault probably passes under the settlement at Palm Springs, for it is 
well exposed a few miles south of that place, where the planes of 
movement are marked by wide bands of crushed and strongly weathered 
rock. There are springs along this broken zone, and also tufa deposits 
20 feet thick covering several acres, marking the position of ancient 
springs. Apparently this fault is now quiescent. There are several 
branch and cross faults in the Murray Hill district, on the east side of 
the valley about 5 miles southeast of Palm Springs. (Frazer.) 
Above Palm Springs Station the Coachella Valley becomes nar- 
rower as it rises into San Gorgonio Pass, which separates the San 
Jacinto Mountains on the south from the San Bernardino Mountains 
on the north. The principal narrowing takes place near the mouth 
of Whitewater Canyon, on the west side of a north-south fault on which 
a block of the old hard rocks is uplifted. Above this fault the side 
slopes become steeper, notably on the south side of the valley, where 
they rise 9,500 feet to San Jacinto Peak. On the north side there is 
a rise of about 6,000 feet to the crest of a high outlying ridge on the 
south slope of the San Bernardino Mountains. This gives a steep- 
sided profile, but the valley bottom appears nearly flat in cross section, 
and its center is occupied by wide, boulder-filled washes containing 
material moved by the occasional freshets. 
The streams flowing out of the mountains are building alluvial 
fans of large size, one of the most conspicuous of which is at the mouth 
of Snow Creek Canyon, south of Fingal siding, not far b= ond Palm 
Springs Station. 
San Gorgonio Pass is a dropped block of the earth’s surfa carrying 
an extensive body of recent sediments and lying between vo great 
ranges of crystalline rocks. It is from 2 to 3 miles wide, and. extends 
almost due east and west for about 18 miles in the ordinary ap ication 
of the name. To the east it merges into the Coachella Valley and to 
the west near Beaumont into the wide Beaumont Plain. Many of its 
relations have been discussed in detail by Russell, who regards the 
south wall as a fault scarp which has been moderately active in 
recent time, but the northern side is probably an old denuded thrust 
block face. The sediments at the margin of the pass were deposited 
under conditions somewhat similar to those now prevailing. 
In 1800 to 1850 many American explorers, mostly hunters, came 
into the lower Colorado River region. It is stated that in the gold 
rush of 1849-50, 10,000 people crossed the Colorado River at Yuma. 
The earliest trail ran from Yuma, passing south of the southeast end 
of the sand hills through Mexico, thence along the Alamo River, across 
the present Imperial Valley, up the valleys of Carrizo and San F elipe 
Creeks, and over Warners Pass behind the Santa Rosa and San Jacinto 
Mountains to the coast. It was along this route in 1848 that Lieut. 
W. H. Emory led a military reconnaissance, and in 1857 it was used 
