1912] Kellogg: Pleistocene Rodents of California 153 



As to the age of the deposits, those of Potter Creek Cave, 

 containing the greater number of extinct species, are considered 

 older than those of Samwel Cave, and the asphalt beds might be 

 placed between the two, or are perhaps the oldest of the three. 

 It is a noteworthy fact in the case of all of the deposits that, 

 while among the carnivores and ungulates there are genera now 

 extinct, the rodents all belong to living genera, although some 

 are described as new species. The persistence of rodent forms is 

 quite remarkable, as they have changed but little through a long 

 period. 



Inasmuch as the rodents are considered especially good indi- 

 cators of environment and climate as shown in the life zones, 

 it was hoped that they might furnish some evidence as to changes 

 in climate during Pleistocene time ; but when we find in the caves 

 forms which belong to the present Canadian Zone mingled with 

 those of the Transition and even Upper Sonoran, and all found 

 at the various levels at which rodents occur in the deposits, it is 

 difficult to draw conclusions, and this wide range of forms would 

 not necessarily indicate that the climate differed greatly from 

 the present one of the regions in which the deposits occur. 



The rodent fauna of the caves is not one which accords with 

 the present topography of the region, a fact which is pointed 

 out very forcibly by Dr. Sinclair in reference to Potter Creek 

 Cave, when he says that "the present mountainous character of 

 the country is entirely out of harmony with the existence of 

 mastodons, elephants, and tapirs." The rodent forms Castor, 

 Aplodontia, and Microtias suggest that the cave regions of Shasta 

 County were more humid at the time of accumulation of these 

 deposits than they are at the present day. Two forms of ground 

 squirrel and three of the rabbit group would indicate a fairly 

 level country with grass and brush, while three forms of tree- 

 squirrels would show that the country included forest areas. 

 Presuming that the region was better watered and partly for- 

 ested, it is possible to account for the number of forms belonging 

 to the Canadian Zone. These two factors combined might permit 

 the presence of a fauna of a higher zone, although the climate 

 would not necessarily be much colder than it is to-day. 



The rodents of the Rancho La Brea deposits are close to the 



