Mountains of the South 241 



the uplifting of the San Jacinto mountain block. It has been 

 stated that the San Jacinto Mountain range is a great triangular 

 uplifted block, bounded on three sides by faults. Just when 

 faulting and the uplifting of the block began is not definitely 

 known but is thought to have been probably in early Tertiary 

 time. The uplifting of the great block was not by a sudden 

 convulsion. Indeed there is reason to think that the uplifting 

 of the mountain mass may be still in progress, evidence of which 

 is seen in earthquakes of recent occurrence, which are known 

 to have been caused by earth movements along the San Jacinto 

 fault. At any rate it is known from indisputable geologic 

 evidence that the disturbance by which the mountains were 

 uplifted to their present height was in very recent geologic 

 time. The earthquake which affected San Jacinto and Hemet 

 was apparently caused by earth movement along the San Jacinto 

 fault. Displacement of the earth by faulting has caused the 

 San Jacinto Valley to stand at a lower level than the very recent 

 Pleistocene beds in the Badlands near by. During late Tertiary 

 and Quaternary time vertical movement amounting to thou- 

 sands of feet displacement have taken place along the San 

 Andreas and San Jacinto fault zones. 



Stages of Uplift Marked by Benches 

 of Erosion 



A series of benches has been cut at various levels in this great 

 block of granitic and metamorphic material. These it is 

 thought may be related to successive stages of uplift of the 

 mountain mass. Their correspondence in time has not been 

 definitely established, but since other mountains, as San Gabriel, 

 San Bernardino, and Santa Ana are known to have been uplifted 

 at successive intervals since late Tertiary time down to their 

 final uplifting to their present heights in very recent geologic 

 time, probably Pleistocene (Quaternary) , it seems not unreason- 

 able to think that these benches are due to successive uplifts of 

 the mountain block, each uplift being preceded by the develop- 

 ment of an erosion level. 



