THEORIES OF THE CAUSES OF FAULTINC] 201 



Piru Canyons. These are both shown on Kew's map of 

 that region. 



CAUSES OF THE FOLDING 



Aside from the larger questions concerning the 

 causes of earth movements in general, whether con- 

 tractional or isostatic, as briefly mentioned in the next 

 chapter, there are two theories as to the causes of the 

 elongated folds. One of these holds that they are 

 made by lateral compressions which resulted from 

 loadings of sediments along the margins of the sea. 

 The other holds that the folds are incidents of the 

 flotational and drifting movements which produced 

 the master faults. 



In the instance of the parallel ranges of the Ventura 

 Group, Kew holds that they were made by lateral 

 compression acting from the direction of the sea. 

 According to Willis, diagonal pressure on the fault 

 planes of the San Andreas Rift from the southwest 

 tends to move the block on the west to the northwest 

 and the blocks on the east to the southeast. He also 

 states that the pressure from the southwest is a "grow- 

 ing pressure." I have disproved this latter theory in 

 the introductory part of the work. 



There is some evidence on the side of those who 

 hold that these folds are the results of compressions 

 between the fault lines. The folds of the Badlands 

 Range of Pliocene strata are clearly the result of 

 compression within a fault block between the San 

 Jacinto and San Andreas Rifts. On the other hand, 

 cross-sections of the Downey (Los Angeles) Valley 

 Plain suggest that faulting followed or accompanied 

 the folding. A synclinal trough between the Domin- 



