386 
TURNER. 
as bed-rock to the miner, on which the late Cretaceous and 
Tertiary rocks rest unconformably everywhere in the Sierra 
Nevada. These rocks about Mohawk Valley are granite, 
diabase, porphyrites, and clastic rocks of Paleozoic or early 
Mesozoic age. 
Mohawk Valley is in Plumas county, California, on the 
eastern slope of the Sierra Nevada. Its general location 
may be seen in Figure 1. The geological map of Mohawk 
Valley and vicinity, Plate No. 4, covers the area included 
in the rectangle in Figure 1. 
Fig. i—O utline sketch of central California. 
That Mohawk Valley was once the bed of a lake is evident 
from the deposits of fine stratified material underlying it and 
from the terraces about it. The elevation of the lower parts 
of the valley, now occupied by farms, is about 4,500 feet and 
that of the highest terraces something more than 5,000 feet. 
There was thus at one time a depth of water of more than 
500 feet. We wfill first consider the certainly Pleistocene 
deposits. 
Pleistocene Lake Beds. 
The middle fork of the Feather River now flows through 
the valley, the former lake having been merely a widening 
