1915] SMILEY—LAKE TAHOE REGION 271 
tain valleys, a form very different from the V-shaped canons on the 
west side of the Divide, and also differing from the lower reaches of 
Truckee River into which the ice seems not to have entered. A 
typical example of such a U-shaped valley is the depression once 
filled by the Fallen Leaf Glacier and now having for its center the 
channel of Glen Alpine Creek. 
Climate 
In attempting a sketch of climatic conditions in the high Sierra, 
one is confronted with the fact that exact observations are too few 
Fic. 3.—Canadian and Hudsonian zones: Suzy Lake with Dick’s Peak at right 
to justify anything more than provisional statements. The data 
offered for the several stations have been gathered from the re- 
ports of the Weather Bureau; since detailed statement for the 
highest station has only been published since 1906, it has seemed 
best to make comparisons cover the same years even for stations 
Where data of a kind is obtainable through a longer period. 
The most constant feature of the alpine climate is the diminish- 
ing pressure with ascent. While there is little evidence to show that 
this factor is of itself important in the life of plants and animals, 
at least within the vertical range of the mountains of western North 
