365 



zone of crushing, crumpling, and folding of the rocks of the 

 San Andreas fault, not merely a break in the rocks of the earth's 

 crust. The rift zone, as has been stated, extends for hundreds 

 of miles north and south of this region. A fracture may be 

 represented by an open fissure at the surface, which by erosion 

 may become partially filled with detritus. Sag ponds are a 

 common feature along fault zones, in which the run-off from 

 rains or waters from springs collect to form ponds. 



Antelope Valley and Playas 



Several playas or dry lakes occur in the Antelope Valley, 

 the largest of which is Rosamond Dry Lake. Antelope Valley 

 is separated by low mountains north of Rosamond and south of 

 Mojave. Fremont Valley extends to the El Paso Range and 

 east to Randsburg and Johannesburg. Ten or 12 miles north 

 of Lancaster, approaching Mojave, is Soledad Mountain (eleva- 

 tion 4,183 feet), an interesting gold mining district. Eleven 

 miles west of Mojave is the Tehachapi Pass (elevation 3,793 

 feet) through which a highway leads to Bakersfield and the 

 San Joaquin Valley. 



Antelope Valley is underlain by a large amount of rock 

 debris, which has been washed down from the surrounding 

 mountains. The rocks weather into fragments that range in 

 size from minute particles to boulders several feet in diameter. 

 If the mountain streams furnish enough water ponds or lakes 

 may be formed in the lower parts of closed basins. The rain- 

 fall is so slight, however, and the evaporation is so great a lake 

 is not formed except after heavy rains in the mountains. Such 

 a lake usually contains only a few inches of water, which soon 

 evaporates, leaving a bare smooth flat of clay or silt, locally 

 known as a "dry lake" but by geologists called a playa. 



Artesian Wells at Lancaster 



The notable water-bearing formation in Antelope Valley is 

 the alluvium that underlies the valley. It is composed of 

 gravel, sand and clay washed down from the surrounding 



