198 SOUTHERN CALIFORNIA GEOLOGY 



the Grand Canyon of the Colorado. Most of the mas- 

 ter rifts of Southern Cahfornia which were all made 

 in the Pleistocene or preceding epochs, show some evi- 

 dences of recent movement. 



Some of the master rift-lines of the Pleistocene may 

 have been inherited from older and earlier fault lines. 

 In fact, there is some suggestion that the path of the 

 transverse structures described represented a renewal 

 of movement along the lines of an old east-west embay- 

 ment which existed in Paleozoic times, as shown by 

 Schuchert in his paleogeographic maps. 



CAUSES OF THE DIRECTION OF TRENDS 

 A most striking feature of the faulted structures 

 is their occurrence in parallel and belted groups of 

 various directions. The inquiry naturally arises as to 

 how these conditions have been brought about. 



Inasmuch as the load-relieving quantities of sed- 

 iments derived from the continents are laid down as 

 loads in the margins of the sea, the sinking of the 

 margin and the corresponding risings of the adjacent 

 land are usually parallel to sea coasts. From these 

 facts it may be deduced that the directions of most 

 of the master displacements of faulting or folding 

 which accompanied such stresses likewise paralleled 

 to the shore at the time of their creation. But all 

 of the various belts of master faults in Southern 

 California do not now trend in directions parallel to 

 the present-day directions of the coast. Neither are 

 they parallel to the normal north-southerly or longi- 

 tudinal direction of the earth's axis which direction 

 the coast tends to follow. Certain factors to be later 

 discussed are responsible for this notable deviation in 



