226 JOHN S. BROWN 



afforded by the granite ridges which divide some of the valleys. 

 San FeHpe Valley, for instance, is cut nearly in two by a low spur of 

 granitic rock projecting from the southwest, while Mason Valley 

 and Vallecito Valley are entirely separated by such a ridge, except 

 for a very narrow, rock-cut canyon. These ridges may very likely 

 represent drainage divides which existed before the faulting. 



TYPE OF FAULTING 



Most of the faulting observed is of the normal type. The Indio 

 fault is associated with much folding, and it is possible that it may 

 be in part due to thrust movements. 



AGE OF FAULTING 



The age of the various faults is very difficult to establish, since 

 the age of the rocks displaced is so indefinitely known. The original 

 settling of the Salton Basin must be pre-late Tertiary in age, 

 because in the resulting basin great thicknesses of late Tertiary 

 sediments were deposited. Considerable faulting has occurred 

 since the deposition of these beds, such as that along the Indio fault, 

 and the San Jacinto fault where Tertiary beds are displaced. The 

 fact that movement has occurred along the recognized fault lines 

 during recent notable earthquakes in California indicates that some 

 of those faults are still active; and the excellent state of preserva- 

 tion of many of the scarps suggests that much of the displacement 

 along some of them has occurred in Quaternary time. 



REFERENCES 



Arnold, Ralph, " Tertiary and Quaternary Pectens of California," U.S. Geol. 



Surv. Prof. Paper 47 (1906). 

 Blake, William P., "Geological Report of California," H. Balliere, New 



York (1858). Enlarged from Pacific Ry. Reports, Vol. V. 

 Fairbanks, H. W., "Geology of San Diego County, California," Cal. State 



Mining Bureau, XI Ann. Rept. (1892), pp. 76-120. 

 Kew, W. S. W., "Tertiary Echinoids of the Carrizo Creek Region in the 



Colorado Desert," Univ. of Cal. Bull. Dept. of Geol. Vol. VIII, No. 5 (1914)- 

 Mendenhall, W. C, "Notes on the Geology of Carrizo Mountain and 



Vicinity," Jotir. Geol., Vol. XVIII (1910), pp. 336-55. See also, "Ground 



Waters of the Indio Region, Cal.," U.S. Geol. Surv. Water-Supply Paper 



225 (1909). 

 Vaughan, T. W., "The Reef Coral Fauna of Carrizo Creek, Imperial County, 

 Cal., and Its Significance," U.S. Geol. Surv. Prof. Paper g8 (1917), pp. 

 355-86. 



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