1908] (frinnell—Biota of the San Bernardino Mountains. 3 
and returned through Bear valley to Bluff lake, where we re- 
mained until September 4th, leaving the mountains on that date 
by the way of the Santa Ana canon. 
In 1906, the region was entered June 9th by the Mill creek 
route to Skinner’s, thence over the Mountain Home trail to Seven 
Oaks. Base camp was made on the upper Santa Ana at the 
mouth of the South Fork, and from here, Dollar lake, Dry lake, 
San Gorgonio peak and Sugar-loaf were visited at different times. 
On August 6th, my field work for that year ended. 
In 1907, I arrived in the region June 13, and again camped on 
the upper Santa Ana, at the mouth of the South Fork, until 
July 12, then three miles further down towards Seven Oaks, 
near the Cedar cabin. Dry lake and San Gorgonio peak were 
again visited, and I left the mountains for good on August 22. 
During this season a large share of the time was spent in com- 
piling the present report. 
LIFE ZONES OF THE REGION. 
The Lower Sonoran zone, the Upper Sonoran zone, the Tran- 
sition zone and at least the two lower divisions of the Boreal zone 
are represented in the San Bernardino mountain region. 
The Lower Sonoran occupies the Mojave desert plateau, which 
bounds the region on the north, and parts of the much lower San 
Bernardino valley and San Gorgonio pass which lie to the south. 
Tongues of this zone extend into the foothills on either slope, and 
islands of it occupy hot pockets at somewhat higher elevations. 
The Upper Sonoran covers the largest area of any of the zones, 
embracing as it does the vast chaparral belt of the Pacific slope 
as well as the pinon belt of the desert slope. It interdigitates 
below with the Lower Sonoran and above with the Transition, 
while islands of it exist in both. 
The Transition is next in point of extent, comprising the 
major part of the considerable forested area. It predominates 
above the 6500-foot contour, though tongues and islands of Upper 
Sonoran invade far above this level on both the Pacific and desert 
slopes. (See pls. 1, 2.) 
The Boreal zone occupies the highest parts of the region 
