The Origin of the Desert Climax and Climate 131 



dence drawn from transads is confirmed by the occurrence of 

 juniper and cypress at La Brea and Carpinteria and of cypress 

 and nut pine at Ricardo. Quercus agri folia is found in all three 

 horizons, while 0. douglasi and chrysolepis, Pinus sabiniana, 

 Umbellularia, Arbutus, and Aesculus occur in the Pliocene else- 

 where in California, the last three extending at least as far back 

 as the Miocene of the John Day region. In the form of phylads, 

 all these except Pinus sabiniana occur across the desert today, and 

 it is probable that in the Pliocene and wet phases of the Pleisto- 

 cene the woodland was much the same as it now is about the 

 Grand Canyon, in southern Arizona, and in a few relict areas 

 in California. 



As might be expected, the problem of the extent and composi- 

 tion of former forest in the desert region presents more difficulty. 

 In the bordering ranges, especially, the frequent presence of 

 Pinus ponder osa, P. p. jeffieyi, and Pseud otsuga taxi folia indi- 

 cates that the montane forest was of wider occurrence before the 

 Recent period, but its movement must have been chiefly if not 

 entirely along mountain axes and not across the lowlands. The 

 most plausible assumption is that climax mixed prairie had come 

 into possession in the Lower Miocene and that this had been 

 preceded by a tall-grass community in the beginning subclimax 

 to hardwood forest, a condition visible today along the western 

 border of the oak-hickory association. This border receives ap- 

 proximately 40 inches of rainfall at the present time, but it 

 appears probable that more was needed in the Southwest to 

 compensate for the evaporation caused by higher temperature 

 and a longer season. In view of the fact that Chaney (1925:43) 

 estimates the rainfall of the Mascall at 30 inches during Middle 

 Miocene, a time when the oak-madrono forest was the chief 

 community, it seems certain that it must then have been drier 



