. 
= 
1908] Grinnell—Biota of the San Bernardino Mountains. 5 
and elsewhere, and particularly by Dr. H. M. Hall in his ‘‘ Bo- 
tanical Survey of San Jacinto Mountain’’ (University of Cali- 
fornia Publications in Botany, Vol. I, 1902, pp. 1-140). It is 
therefore unnecessary for me to re-discuss a subject to which I 
feel I could add no new thoughts. One faetor, however. is es- 
pecially important with regard to the San Bernardino mountains ; 
and its results are conspicuous. And that is, the base level to 
the north is at an altitude of 4000 feet or more, while on the 
south it is much lower, 1500 to 2500 feet. This results in low 
zones being carried high up on north-facing slopes of the ranges 
next to the desert in spite of slope exposure. In fact, the Upper 
Sonoran (north of Sugarloaf, for imstance) goes to 7500 feet 
altitude, while in no place that I know of does it extend quite so 
high as that, on south-facing slopes on the Pacific side of the 
mountains. In-flowing desert air-currents from the north also 
seem to be an important factor, possibly explaining certain local 
extensions of zones. The extreme aridity of the desert side as 
compared with the moderate humidity of the Pacific side (greatest 
at the higher elevations) must also be considered as a factor in 
temperature modification. (See pl. 2.) 
In the following list I have included only plants of the most 
conspicuous kinds, for plants are the best indicators of zones. 
Throughout the lists of plants, birds, mammals, and reptiles, I 
have referred to the habitat of species by zones, wherever prac- 
ticable. I have often ignored the straggling occurrence of a plant 
or animal in one zone when its characteristic habitat is another 
zone. 
LOWER SONORAN. 
Yucca arborescensé Adenostoma fasciculatumy* 
Populus Fremontit Prosopis juliflorat 
Briogonum fasciculatum+* Covillea tridentata 
Grayia spinosat Lycium Anderson Wrightiit 
Platanus racemosat Ramona polystachyay 
~In another zone also. 
+ Pacific slope only or chiefly. 
+ Desert slope only or chiefly. 
