GEOLOGY OF CARRIZO MOUNTAIN, CALIFORNIA 349 



Farther to the east and south, as in the vicinity of the Yuha Oil 

 Well, at horizons which are presumably higher than those in the Car- 

 rizo Valley, although the conditions governing our brief reconnais- 

 sance were such that it was not possible to determine the relations 

 with any certainty, the sandstone beds are more abundant. Many of 

 them here weather in curious nodular forms of great variety. Such 

 forms have been well described by Professor Blake. ^ 



Fig. 7. — Erosion in tlie Miocene shales of the Carrizo Valley. 



The Carrizo Valley is synclinal, the shales rising gently northward 

 and southward from the axis of the valley toward the bases of Black 

 and Carrizo mountains. Near the borders dips of 5° to 20° were 

 measured, while in the center of the valley the beds are nearly hori- 

 zontal or exhibit irregular attitudes. Faults of small displacement 

 were noticed near the head of Garnet Canyon, others north of Car- 

 rizo Creek have been described and figured by Blake, and Fairbanks 

 beheves that the abrupt eastern face of Black Mountain overlooking 

 the desert is a fault scarp. 



In the vicinity of Yuha Oil Well more pronounced structures 



I "Explorations and Surveys for a Railroad Route from the Mississippi River 

 to the Pacific Ocean" (War Dept., 1857), Geological Report by Wm. P. Blake, p. 102. 



