88 SOUTHERN CALIFORNIA GEOLOGY 



Valley Plains. I cannot give further space to the 

 smaller valleys, but merely a few words concerning 

 some larger valley plains. 



THE FOOTHILL VALLEYS 

 The Foothill Valleys are the larger, fertile plains of 

 the Pacific side of Southern California, in which most 

 of the population lives and where agriculture is at its 

 best. They are the lowland parts of the Transverse 

 Belt and extend east and west along the south sides 

 of the Ventura Ranges and the San Gabriel Highlands, 

 and lie between them and the north end of the Penin- 

 sula Ranges. 



Commencing at the west, south of the Santa Bar- 

 bara Coast, lies the great submerged valley of the Santa 

 Barbara Channel; next, to the east, are the elon- 

 gated valleys between the flexured Ventura Ranges; 

 then the three great quadrangular Foothill Valleys, 

 San Fernando, San Gabriel and Ontario^ respectively. 

 These collectively extend eastward to the San Bernar- 

 dino Plateau. Next east is the valley of San Gorgonio 

 Pass, with its rich redlands of the Yucaipa and Beau- 

 mont Plains. Farther eastward still, out on the desert 

 side, are extensive valley plains and basins of the Dale, 

 Pinto and Amboy types. 



The Foothills Valleys are primarily structural 

 troughs. They are in parts and places synclinal, in 

 others combinations of synclinal and faulted struc- 

 ture, and, in still other instances downfallen or de- 

 pressed, trough-like blocks between faults. Some have 



'The term Ontario Valley is herein used for the large quadrangular valley 

 plain which lies between the north end of the Santa Ana Range on the 

 west and the San Bernardino Highlands on the east. It is sometimes called 

 the San Bernardino Valley, but the latter name is more appropriate for that 

 subdivision of the larger features which lie to the east of the west bank of 

 Lytle Creek. 



