SCIENTIFIC BACKGROUND 115 



These are in places conspicuous along the courses 

 of the San Andreas, San Gabriel and San Jacinto faults. 

 Zones of this character may be seen along the south 

 sides of the Verdugo and San Gabriel ranges. 



A narrow, trough-like zone of faulting accompanies 

 the San Andreas Rift along most of the north side of 

 the San Gabriel Range, through the Cajon Pass 

 and along the southwest base of the San Bernardino 

 Highland.^ San Francisco is situated on a narrow 

 fault zone of this character which there accompanies 

 the San Andreas rift (See Plate III). Its members 

 are plainly reflected in the physiography of the 

 city and surroundings. For the purposes of this paper 

 the narrow zones may be considered an individual fault 

 line. When a collection of parallel fault lines or zones 

 occur at widely separated intervals throughout a broad 

 area of country, they constitute a belt of faults which 

 may be termed a belted group. There are several of 

 these belts in Southern California. These will later be 

 described. 



EXTRA TERRITORIAL EXTENT OF THE 

 MASTER FAULTS 

 The great master fault lines and structures which 

 are manifested in Southern California are not confined 

 to its territory but extend beyond its borders to the 

 east and southward. The San Jacinto, Elsinore and 

 other master fault lines can be traced into Mexico to 

 the southeast just as can be some of the great master 

 faults of Trans-Pecos Texas and New Mexico. Because 



'The details of this portion of the rift along the north side of the San 

 Gabriel Range have recently been published by Noble in the Carnegie Year 

 Book No. 25, Washington, 1925-26, pp. 416-423. Much of the data of value 

 concerning the Cajon Pass in an appendix to the U. S. Geological Survey 

 Guide Book of the Santa Fe Railway Route, was placed under my name by 

 the editor, who should have accredited it to Dr. Noble. 



