42 University of California Publications in Geology [Vol. 8 



Coyote Mountain rises from the west side of the Imperial Valley 

 and attains an altitude of about three thousand feet. It is connected 

 with the range of mountains to the west by a ridge which extends in 

 an east-west direction across an otherwise level expanse of desert. 

 Yuba Buttes 7 lie about six and a half miles to the southeast of Coyote 

 Mountain. 



The formations included in the sections at Carrizo Creek, Coyote 

 Mountain and Yuba Buttes, in order of sequence are : ( 1 ) the basal 

 complex of granites and metamorphics ; (2) andesite extrusive resting 

 upon the eroded surface of the basement rocks; (3) Tertiary sedi- 

 mentary beds of the Carrizo formation; and (4) Pleistocene lake beds 

 and gravels. 



The type section of the Carrizo formation is best exposed at Car- 

 rizo Creek, from which locality it has been named. These beds have 

 been known in previous descriptions as the Tertiary Beds at Carrizo 

 Creek. The formation appears as a broad syncline filling the Carrizo 

 Valley and flanking the slopes of Fish Creek Mountain, or Black 

 Mountain, on the north and Coyote Mountain and Coyote Ridge on the 

 south. None of the dips are over 35°, and toward the middle of the 

 valley the beds are almost horizontal. The thickness of the formation 

 is probably over twenty-five hundred feet. The beds consist of shale 

 and fine-grained muddy sandstone which at the base is markedly 

 coarser and conglomeratic. The formation extends to the north as far 

 as the southern end of the Santa Rosa Mountains, being exposed in 

 a limited area to the west and south of Salton Sea. At the north 

 end of the section the beds show about the same degree of deforma- 

 tion as at Carrizo Creek. 



Carrizo Creek Locality. — At the type locality the Carrizo forma- 

 tion may be divided into the Lower Division and the Upper Division. 

 The basis for this separation is both lithologic and biologic. The 

 lithologic change from the more or less coarse sandstone and con- 

 glomerate of the Lower Division to the fine-grained muddy sandstone 

 and shale of the Upper Division is extremely sharp. The change in 

 life is likewise distinct. In the Lower Division both the species and 

 individuals are numerous. In the Upper Division the paucity of species 

 is noticeable, although in occasional strata a single species may be very 



o Coyote Mountain is situated in sections 3, 4, 9, 10 of T 16 S, E 10 E, San 

 Bernardino Base Line and Meridian. 



? Yuha Buttes are located in sections 23 and 28 of T 16 S, R 11 E, San 

 Bernardino Base Line and Meridian. 



