154 University of California Publications in Geology [Vol.7 



forms living in this region at the present time, and are definitely 

 of the Upper Sonoran Zone, and of a plains country. It is there- 

 fore difficult for us to believe that any marked changes in climate 

 or topography have occurred in this region since the period of 

 accumulation of the remains representing the Raneho La Brea 

 fauna. 



List of Rodents Arranged According to Existing Life-zones 



POTTER CREEK CAVE 



UPPER SONORAN 



Citellus b. douglasi 

 Lepus ealifornicus 

 Sylvilagus auduboni 



UPPER SONORAN 



Citellus b. douglasi 

 Peromyscus m. gambeli 

 Sylvilagus auduboni 



UPPER SONORAN 



Citellus b. captus, n. subsp. 

 Peromyscus m. gambeli 

 Microtus ealifornicus 

 Thomomys b. pallescens 

 Perodipus agilis 

 Sylvilagus auduboni 

 Sylvilagus b. cinerascens 



TRANSITION 

 Citellus b. douglasi 

 Eutamias, sp. 

 Microtus ealifornicus 

 Thomomys mierodon 

 Thomomys leucodon 



SAMWEL CAVE 



TRANSITION 



Sciurus g. fossilis, n. subsp. 

 Castor subauratus 

 Peromyscus m. gambeli 

 Microtus ealifornicus 

 Thomomys mierodon 

 T h om o my s leucodon 



RANCHO LA BREA 



BOREAL 



Arctomys flaviventer 

 ( 'allospermophilus chrysodeirus 

 Sciurus albolimbatus 

 Sciuropterus a. klamathensis 

 Aplodontia m, fossilis 

 Neotoma e. occidentalis 

 Lepus a. klamathensis 



BOREAL 



Callospermoplrilus chrysodeirus 

 Sciurus d. albolimbatus 

 Sciuropterus a. klamathensis 

 Aplodontia m. fossilis 

 Neotoma c. occidentalis 

 Erethizon epixanthum 

 Lepus a. klamathensis 



Species in Cave Faunas 



ARCTOMYS FLAVIVENTER Aud. and Bach? 



An incisor and the anterior portions of two lower mandibles 

 from Potter Creek Cave represent this species. Arctomys is now 

 not to be found in the Shasta region. One incisor is larger and 

 has a more marked orange color than those of specimens from the 

 Sierra. In the first character it approaches the Alaska form, but 

 the color seems to be a variable character. The material is tenta- 

 tively referred to A. flaviventer. 



