The Origin of the Desert Climax and Climate 117 



Thousand Creek 



Rodents — 



Lcpus vetus 



Citellus sp. 



Peromyscus antiquus 



Peromyscus sp. 



Arctomys (Marmota) nevadensis 



Arctomys (Marmota) minor 



Aplodonda alexandrae 



MAMMALS 



{Continued) 



Diprionomys parvus 

 Diprionomys magnus 

 Entoptychus minimus 

 Mylagaulus monodon 

 Eucastor lecontei 

 Dipoides sp. 



Ungulates — 

 Pliohippus spectans 

 Hipparion sinclairi 

 Hipparion occidentals 

 Hipparion leptode ? 

 Hipparion anthonyi 



Proboscideans: remains — 



Rodents — 

 Otospermophilus gidleyi 



BIRDS 



Branta sp. 



Rattlesnake 



MAMMALS 



Pliauchenia ? or Alticamelus 



Sphenophalos sp. 



Ilingoccros or Sphenophalos } sp. 



Teleoceras ? near fossiger 



Prosthennops ? sp. 



? Platygonus rex 



Lepus (Hypolagus) vetus 



The three PHocene formations considered comprise a wide 

 extent of territory in the lee of the rising mountains, from the 

 Mohave Desert at the south to northwestern Nevada and eastern 

 Oregon. In spite of a difference of several degrees of latitude, the 

 ungulate faunas have much in common, the significant fact 

 being the predominance of advanced types. Merriam has char- 

 acterized the Ricardo region as follows (1919:526) : 

 The Ricardo fauna suggests climatic conditions permitting the de- 

 velopment of vegetation suitable for grazing animals. This indicates 

 a somewhat heavier growth of grass than is found in this region at 

 the present time. There is nothing in the constitution of the fauna 

 to suggest conditions radically different from those obtaining today, 

 but the presumption is in favor of less extreme aridity than is now 

 known on the western border of the Mohave Desert. The conditions 



