164 SOUTHERN CALIFO'RNIA GEOLOGY 



ous faults and phenomena of the northwest trend. The 

 first of these is the San Jacinto Rift, which is one of 

 the largest and best defined of all the master faults 

 of Southern California. 



Its course, with the exception of a short stretch 

 across the Ontario Valley and the Badlands Range, 

 constitutes the strongly emphasized scarp lines and 

 topographic borders of the southwest margins of the 

 Badlands and San Jacinto Ranges. It branches off 

 from the main San Andreas Fault zone in the north 

 side of the east end of the San Gabriel Highland and 

 follows the course of Lytle Creek Canyon through the 

 mountains into the San Bernardino (Ontario) Valley 

 Plain. Its presence across the last mentioned feature 

 is also indicated by the southeast course of Lytle Creek. 

 The fault diagonally crosses the San Timoteo (Bad- 

 lands) Range east of Reche Canyon to a point north 

 of Moreno, from whence it follows and corresponds 

 with the south border scarp of the combined Bad- 

 lands and San Jacinto Ranges as far as Saboba Hot 

 Springs, near San Jacinto. Along the portion of its 

 course between the Jack Rabbit Trail and Saboba 

 there are many hot springs. There are also several 

 parallel rift-lines and step-down benches along this 

 portion of its course. These suggest a series of upward 

 movements to the northeast. The zone divides into 

 two well-defined, adjacent and parallel lines from San 

 Jacinto River southeast. The main and westernmost 

 of these is traceable on southeastward, via Hemet, 

 across the spurs of the Peninsula Highland into the 

 desert near Calexico and Mexicali, and on indefinitely 

 into Mexico, where its course is marked by near-by 



