242 Adventures in Scenery 



The most conspicuous bench of the San Jacinto Mountains 

 is found on the southwestern slope. It extends the entire length 

 of the mountain face, and lies about a mile below the high- 

 peaks level. It is thought that this bench has resulted from 

 the relative uplift of the San Jacinto Mountains in relation to 

 the San Jacinto Valley block to the southwest, and that it was 

 originally cut by stream erosion or planation at an elevation 

 near that of the alluvial plain of the San Jacinto Valley below; 

 in other words that the two surfaces were originally at about 

 the same level. 



Near the top of the great mountain pyramid there is a plain 

 surface at an elevation of about 10,500 feet. Tahquitz Valley 

 is a gently sloping plain which has an average elevation of about 

 7,500 feet. It is known that the great mountain pyramid is 

 bounded on three sides by faults. The most logical explanation 

 of these benches therefore seems to be successive uplifts of the 

 mountain block and that each of these benches represents a 

 period of erosion. 



The Core of the Range an Intnided 

 Batholith of Granite 



Thus the San Jacinto Mountains are seen to constitute an 

 immense uplifted block, cut off on three sides by great fault 

 zones, the core of the range being an intruded batholith of 

 granite, a vast series of ancient sedimentary rocks originally 

 forming a roof over the intruded granite and now largely 

 removed by erosion during the long lapse of time since the 

 original uplift, probably in Jurassic time. The slopes of the 

 mountains are exceedingly steep and rugged, particularly the 

 northern and eastern sides, carved by torrential streams which 

 tear with great force down the slopes during times of precipi- 

 tation in winter and spring. The towering heights of San 

 Jacinto Peak and San Gorgonio Peak, monarchs of their re- 

 spective ranges, stand as sentinels on either side of the great 

 San Gorgonio Pass, the first discovered pass across the moun- 



