257 



uplifted north of the San Andreas fault, but south of the fault 

 where the San Bernardino Valley is now, the surface was de- 

 pressed below sea level. 



Crumpled Clays and Sandstones Underlie 

 the Present Valley Alluviiim 



Somewhat later in Tertiary time, after the fracturing of the 

 earth along the San Andreas fault and the subsiding of the San 

 Bernardino Basin, a great area to the south was a lowland region 

 but little above sea level. The broad valleys were occupied by 

 lakes, of brackish or fresh waters. The great mountain ranges 

 that now surround the area had not been uplifted more than 

 slightly as compared to their present height. During a long 

 time sediments were carried from the adjacent higher lands 

 (which were later to be uplifted to become the present moun- 

 tains) and deposited to great thickness over the lowland. These 

 were the fine-grained sediments which are now the clays and 

 sandstones that form the crumpled, bent, and wrinkled beds 

 that lie buried beneath the "valley fill" which makes up the 

 present land surface south of the San Bernardino Valley, as 

 about Riverside. The sediments were made up of the rock 

 waste of the granitic rocks which form the cores of the present 

 mountain ranges, and wash from the hills and peaks which 

 dotted the ancient worn-down plain. Water occupied the 

 lowest valleys and spread widely over the land. Within it 

 islands of granitic and schistose rocks rose, as the Box Springs 

 and Lake View Mountains now rise above the Ferris and San 

 Jacinto plains, and as the Jurupa, Slover, Rubidoux and other 

 granitic and schistose mountains and hills farther north rise 

 above the surrounding plain. 



Fossil Remains of Extinct Animals found 



An interesting assemblage of animals roamed these plains in 

 Pliocene times, animals that have long since ceased and disap- 

 peared from the earth. Grazing over the open stretches were 



