326 University of California Publications in Zoology. ["Voi.. 7 



As the mountains were approached, a pronounced difference 

 in the fauna, especially as regards reptiles, was observed. The 

 number of species of the latter, as well as the number of indi- 

 viduals, increased markedly. Cnemidophorus tigris, Crotaphytus 

 collaris baileyi, and Uta stanshuriana were recorded for the first 

 time. Crotaphytus wislizenii, Sceloporus biseriatus, and Phry- 

 nosoma platyrhinos became abundant, whereas previously but 

 few specimens had been collected. Of the mammals, Neotoma 

 nevadensis, Lepus calif ornicus wallaivalla, and Perodipus microps 

 levipes were found in somewhat increased numbers. This locality 

 was the only one at which Onychomys brevicaudus was secured. 

 As regards birds, Say phoebes, western wood pewees, black- 

 throated sparrows, and western robins were more in evidence. 



These facts probably do not indicate difference in temperature 

 so much as they do that there is something present, whether a 

 more suitable dwelling-place or better food supply or something 

 else, which proves especially attractive or favorable to the species 

 in question. For example, the presence of rock piles in which 

 they may nest conveniently accounts, at least partly, for the 

 increase in numbers of wood rats. 



One factor which doubtless affects distribution is the nature 

 of the ground (see C. H. Merriam, 1892, p. 46). As Big Creek 

 Ranch is approached the flour-like, hard soil characteristic of 

 Quiun River Crossing is replaced by a more sandy, slightly 

 coarser material. The more favorable conditions in this respect 

 may account somewhat for the difference in number and abund- 

 ance of certain species of mammals and reptiles at the two 

 localities. 



Zonally Big Creek Ranch is inseparable from Quinn River 

 Crossing, except that it apparently possesses a facies representa- 

 tive of a higher division of Upper Sonoran. Nearly all of the 

 species taken at Big Creek Ranch occur elsewhere in Upper 

 Sonoran, and several are not found above that zone. 



Transitional elements were, however, noted at Big Creek 

 Ranch, which were lacking at Quinn River Crossing ; for example, 

 among plants, Populus tremuloides, Castilleia parvifolia, Alnus 

 tenuifolia, and Achillaea millefolium lanulosa; among mammals, 

 Erethizon epixanthum and Microtus mordax ; and among birds 



