FAULT FEATURES OF SALTON BASIN, CALIFORNIA 225 



nent mountain wall for 12 or 15 miles. Another fault passes 

 through Banner Canyon and Rodriguez Canyon, and extends along 

 the north side of Mason Valley and Vallecito Valley, the mountain 

 walls of these valleys probably representing considerably eroded 

 fault scarps. The last two faults unite in the vicinity of Agua 

 Caliente Springs, and are not known to continue farther, but may 

 extend along the north side of Carrizo Valley at the base of Valle- 

 cito Mountains and Fish Mountains. 



VALLEYS FORMED BY FAULTING 



Associated with the second system of faults are several peculiar 

 valleys for whose formation the faults have been responsible. The 

 largest of these valleys are Borego Valley, San Felipe Valley, Mason 

 Valley, and Vallecito Valley. Collins Valley, adjacent to Borego 

 Valley, and a little valley less than a mile in extent at Banner, were 

 formed in the same way. All of these valleys have for their north- 

 east boundary a high, steep mountain wall which originated as a 

 fault scarp along some one of the faults mentioned above. Thus 

 Borego Valley and Collins Valley lie southwest of the San Jacinto 

 fault. The general shape of each valley is triangular, and the 

 south and west sides are much more irregular in outline than the 

 northeast side, the mountainous borders on these sides being also 

 somewhat less abrupt than those on the northeast. Most of the 

 valleys are high at the southwest, and the drainage is to the north- 

 east. This has probably been the natural result of the tilting of 

 the faulted strips, which have all been dropped down on the north- 

 east and elevated on the southwest. 



Most of the faults have forced the drainage to follow northwest- 

 southeast directions, particularly in the various canyons such as 

 Coyote Canyon, Grapevine Canyon, and Banner Canyon, but some 

 streams, such as San Felipe Creek, northeast of San Felipe Valley, 

 and Baimer Creek at Banner, occupy deep gorges which cut directly 

 across the fault scarps at the northeast border of these valleys. It 

 is probable that these streams existed before the faulting, and that 

 . the faulting took place gradually, the streams cutting down as fast 

 as the rocks were Hfted across their beds. A further suggestion 

 that the earlier drainage lines may have had a northeast trend is 



