384 University of California Publications in Zoology [Vol. 10 



species inhabiting them. Obviously the San Jacinto area of 

 Boreal is much smaller than that on the San Bernardino Moun- 

 tains. 



We proceeded to compare corresponding conditions elsewhere 

 in southern California, with the results shown in the accompany- 

 ing tables and diagram (see pp. 386, 387. and pi. 7). Examination 

 of a zone map of southern California shows the Boreal zone to be 

 represented in a series of isolated areas of varying limited 

 extent, these in most part marking the crest of the main divide 

 separating the desert and Pacific drainages. 



Prom the Mount Whitney region of the southern Sierra 

 Nevada this divide swings more and more to the westward until 

 the vicinity of Mount Pinos is reached. Here it bends abruptly 

 at almost right angles in a southeasterly trend, which is roughly 

 maintained at least to the Mexican line. The diagram (plate 7) 

 is constructed as though this backbone were in a straight line, and 

 serves to show the relative extent of the isolated areas of Boreal 

 included. 



The Boreal life zone on San Jacinto Peak is seen to be larger 

 in area than any others of the many mountain masses of 

 southern California, excepting the San Bernardino Mountains; 

 the number of Boreal types existing upon it exceeds those on any 

 others of the mountains coming into the problem, excepting, 

 again, the San Bernardinos. 



It might be suspected that degree of remoteness from the 

 very large Boreal area of the main Sierra Nevada would bear 

 direct relation to number of species represented upon these 

 detached mountains. According to this idea, the Sierras would 

 have provided the mother fauna, and the farther the emigration 

 of types along a possible line of dispersal, the fewer the survivors. 

 Thus Mount Pinos would share with the Sierra Nevada a larger 

 proportion of its species than any of the appropriate areas to 

 the south. But we find no such condition in fact. There are two 

 Boreal mammals and seventeen Boreal birds on Mount Pinos 

 as compared with seven and twenty-eight, respectively, on the 

 San Bernardinos, and five and twenty-two on the San Jacintos. 

 Rather, does it appear that the number of forms is associated 

 with the size of area concerned. 



