SCIENTIFIC BACKGROUND 159 



along and through the northeast side of the San Ber- 

 nardino Plateau, giving the scarped character to a part 

 of that side of the highland, and from thence south- 

 east through the Morongo (Little San Bernardino) 

 Mountains. The writer has observed this zone of par- 

 allel rifts near Old Woman Springs and Francis 

 Vaughan has described it and shown it upon his map.^ 

 From the results of one brief reconnoissance and from 

 map studies, it is probable that there are three parallel 

 faults in this general vicinity, one each of which runs 

 near Old Woman Springs, Rattlesnake Canyon and 

 Brush Canyon. The two last mentioned apparently ex- 

 tend southeast into the desert for an indefinite distance 

 along the north side of the elongated Little San Ber- 

 nardino Highland block. Volcanic effusions of basic 

 lava accompanied these lines of faulting in places 

 around the northeast and east ends of San Bernardino 

 Plateau. 



A VARIATION IN THE PLAN 



One encounters in the region of San Gorgonio Pass 

 a locality where there is a variation in the simple plan 

 of the fault pattern of this belt. Certain rifts of 

 easterly trend apparently branch off from the prevalent 

 northwest course of the San Andreas Rift. Of these 

 the Mill Creek, Raywood and Morongo Reservation 

 faults are conspicuous illustrations. 



Proceeding from the Old Woman Fault southwest- 

 wardly towards the coast there are several other mas- 

 ter faults of this northwesterly system, which occur 

 at intervals of from ten to twenty miles. These 

 have been reconnoitered, but as yet not sufficiently 

 sketched in detail. The most evident ones are the Mill 



'Geology of the San Bernardino Mountains. Univ. of Cal., Bull., Dec. 1922. 



