84 University of California Publications in Geology [VOL. 10 



GEOLOGIC SIGNIFICANCE OF THE FAUNAS 



The faunas, consisting as they do in large part of horses, camels, 

 and antelope-like forms, point to a plains or open valley environment 

 in this region in middle Miocene time. 



The deposits in which the faunas occur are of types which suggest 

 that they were laid down under subaerial conditions as waste slope and 

 playa lake deposits ; the evidence for this view is corroborated by the 

 occurrence of the mammalian remains, which are usually scattered and 

 frequently much gnawed by rodents. The angularity of the coarser 

 terrestrial deposits precludes their fluviatile origin, and the lack of 

 classification and bedding in the fine materials militates against their 

 being in any large measure of truly lacustrine origin. The faunas 

 and the formations in which they occur thus indicate that the climate 

 was one of semi-aridity or aridity. Fossil wood and palm leaves at 

 one or more horizons probably do not negative this view. 



The age of the faunas being established as approximately middle 

 and upper Miocene respectively, stratigraphic relations indicate that 

 important crustal movements occurred in this region between Jurassic 

 and middle Miocene time and in post-middle-Miocene time. 



The movements subsequent to the Jurassic and antecedent to the 

 middle Miocene are indicated by the relation of the mamma] -bearing 

 group to a succession of sediments which lie with marked unconformity 

 below these strata and rest unconformably on the plutonic rocks of 

 presumable Jurassic age. This lower sedimentary series, which is well 

 exposed along lower Oil Canon, has been deformed to the extent that 

 the strata attain a vertical position over much of the area in which 

 they are exposed. It is not improbable that deformative movements 

 affected the territory immediately previously to the deposition of the 

 mammal-bearing group, inasmuch as the topography on w 7 hich these 

 beds were laid down was one of some relief and indicates active erosion 

 immediately preceding their deposition. 



The crustal movements subsequent to middle Miocene time in the 

 Tehachapi Pass region are evidenced by the folding which the mammal- 

 bearing group has suffered since its deposition ; dips of twenty to thirty 

 degrees are common in the strata. Following this folding, erosion 

 cut away no small part of the total mass of the accumulated sediments 

 and probably produced on the region a land surface of gentle relief. 

 The latest diastrophic event was the faulting along the southeastern 

 base of the present range, by which the mountain area was displaced 



