124 SOUTHERN CALIFORNIA GEOLOGY 



later northwesterly system, including the San Jacinto 

 and Elsinore rifts. It is likewise probably cut across 

 and terminated at its north end by the east-west fault 

 lines, which may continue eastward through San Gor- 

 gonio Pass into the Desert Side. 



Furthermore, it seems apparent that the belts of 

 parallel fault lines of one system, such as we have 

 described in this paper, have been cut across by belts 

 of another age and direction. On the Desert side it 

 may be plainly seen that the older belt of Basin Range 

 faults of north-south direction have been cut out by 

 the great Garlock fault of northeast direction ; that the 

 latter, in turn, was cut out at Tejon Pass by the faults 

 of northwest directions, which latter also cut out the 

 east-west belts of faults of the Cucamonga and Pinto 

 types at the Pacific and Desert sides. 



In addition, it will be found that the process of the 

 crossing of a belt of parallel, major faults of one par- 

 ticular epoch and direction by those of another belt 

 of later age and direction has taken place upon a still 

 gran,der scale throughout tropical and sub-tropical 

 America, all the way from California into the northern 

 edge of South America and to the eastern edge of the 

 Caribbean.^ 



THE FAULT BLOCK STRUCTURE 

 In instances where a belt of faults of one direction 

 is crossed by another of a different direction, the 

 crustal block between them may rise or sink, this 

 producing what is known as the fault block type of 

 physiography, as in the instances of the San Gabriel, 



'Taber, Stephen. "Great Fault Troughs of the Antilles," Journal of Ci€ol- 

 ogy, 1922. 



See also: Hill, Robert T. Fundamental Geographic Relations of the Three 

 Americas, National Geographic Magazine, 1896. 



