Vol. 6] Mcrriam : Virgin Valley and Thousand Creek 



219 



Creek Beds so far as known suggest that the topography of the 

 region in this epoch resembled an advanced stage in the evolu- 

 tion of the topography begun in Virgin Valley time. Consider- 

 ably elevated regions still existed, but around these the deposits 

 had been built up till many of the minor irregularities had been 

 completely buried, and a much wider expanse of level country 

 was presented. According to any interpretation which may be 

 put upon the depositional history of this region we must con- 

 sider that the extent of plains territory here during Thousand 

 Creek time was approximately as great as that of the wide 

 stretches of level land in the great valleys of the Basin region 

 at the present time. 



In the mammalian fauna, the ungulates of the Thousand 

 Creek Beds represent in general types somewhat better adapted 

 to a plains region than was the fauna of the Virgin Valley 

 epoch. The only horses present are Pliohippus, and possibly 

 Equus, with well-developed prismatic crowns of the molar teeth, 

 while the only booid artiodactyls are antelopes with long-crowned 

 molars. 



That the fauna of the region was not limited entirely to open 

 and semi-arid plains is suggested by the presence of a goose 

 (Branta), a mole (Scapanus) . and a possible representative of 

 Ursus. Among the rodents the sewell (Aplodontia) was presum- 

 ably a dweller in a moist region with abundant vegetation. 

 Arctomys is not a characteristic plains form, but might have 

 lived on the borders of open country. 



The mammalian fauna as a whole suggests plains with 

 occasional lakes or meadows bordering rugged or elevated areas. 

 The degree of humidity may have been somewhat greater, and 

 vegetation more abundant than at the present time. The pres- 

 ence of Arctomys may suggest a slight cooling of the climate, 

 either due to general climatic changes, or to elevation of this 

 region. 



