SCIENTIFIC BACKGROUND 111 



FAULTING 



The presence of faulting is indicated by the bold 

 escarpments of mountain borders, trough-like valleys, 

 and by benches, foothills, "kern buts," "kerncols," 

 (gun-sight gaps) faceted spurs, (salients) ^ springs, 

 ponds, "green spots" and other phenomena, as more 

 fully set forth in the writings of Fairbanks, the Cali- 

 fornia Earthquake Commission, Noble, Lawson and 

 others. Master rifts may also be present beneath the 

 areas of valley plains and yet unobservable at the 

 surface, where they are usually concealed by the over- 

 lay of more recent formations. This latter fact is one 

 which has an important bearing upon matters to be 

 discussed later. 



CLASSIFICATION OF THE FAULTS 



Extensive dissertations on the kinds of faults — nor- 

 mal, reverse, horizontal, rotational — may be found in 

 any text-book on geology. For the purposes of this 

 paper the faults of Southern California, which are 

 mostly normal with some conspicuous exceptions, may 

 be first classified into two general categories according 

 to their relative size, occurrence and geographic con- 

 spicuity. These may be termed the master and in- 

 terior faults respectively, after the manner proposed 

 by Professor Chester Longwell in discussing the faults 

 of Southern Nevada. 



^Truncated salients (or "spurs" as they are called by Davis), which denote 

 fault lines, attend the south border of the Verdugo Range west of Burbank 

 and in the north part of Glendale, also the northeast side of the San Rafael 

 Range, west of Devil's Gate, and many places along the south front of the 

 San Gabriel and San Bernardino Highlands. They are superbly shown along 

 the courses of the great rifts through San Gorgonio and Cajon Passes, 

 especially along the north scarp of the San Jacinto Range near El Cabezon. 

 The <'aces of the triangular facets of the truncated salients have themselves 

 often been considerably modified by the later development of drainage grooves 

 in them so that they now present the outline of an inverted Y. Conspicuous 

 examples of these are seen northeast of Pasadena and near Eaton Wash, 

 along the south side of Verdugo Hills and elsewhere. The relative antiquity 

 of the fault lines may be predicted from the degree of erosion of their facets. 



