* 
1915] SMILEY—LAKE TAHOE REGION 267 
now commonly lie on the top of ridges overlying the schists and 
granites. On decay they produce a dark red soil, over which are 
scattered angular or roughly rounded gray or brown andesite 
boulders. 
The basalts, which locally may be present in considerable 
amount, lie above the andesite, which frequently shows a meta- 
morphosed condition due to the heat and pressure; on the summit 
of Mt. Tallac is such a contact. These basaltic irruptives are the 
Fic. 1.—Transition zone: pond vegetation with climax forest; Mount Tallac in 
the distance. 
most recent general feature of the geology, and the time inter- 
vening to the present has not been sufficient to materially modify 
the flows. 
The whole district, except the highest summits, has been sub- 
jected to severe glaciation. This occurred in the later part of the 
Pleistocene, and the interval since has been too short to obscure 
the evidences of ice action, particularly at the higher levels where 
the surface was swept bare. Today these barren areas lie exposed, 
practically destitute of soil, and constitute some of the most strik- 
ing evidences of glacial action to be found in the Sierra. At the 
time of maximum ice the higher levels were all filled with névé 
