388 
TURNER. 
Forming a set of terraces about 4,500 feet high about Mo¬ 
hawk Valley and well exposed along the Feather River 
where it enters the valley from the east, and by the public 
road just south of Wash Post Office, are beds of coarse 
gravel and sand containing some pebbles of late olivine 
basalt, a lava of much later age than the andesite. These 
beds appear to be the latest of the lake deposits. Lying 
usually somewhat below the 4,500 foot contour is the allu¬ 
vium, which will not be considered here as part of the lake 
beds. The alluvium is of very recent origin. 
Earlier Lake Beds. 
Underlying the coarser deposits, previously described, is 
an older series of beds not anywhere found, so far as I know, 
at a much greater elevation than 4,600 feet. These older 
beds are usually whitish in color and composed largely of 
sand and clay, with layers of carbonaceous shale. Since 
there is some doubt about the age of the beds, exposed at 
different points, some of them will be described separately. 
About one-fourth of a mile down-stream from Mohawk Post 
Office, on the west bank of the Feather River, and forming 
also the bed of the river, are beds, largely clay and sand, with 
a good deal of carbonaceous shale. Distinctly and uncon- 
formably overlying the fine material, which is horizontally 
stratified, is a later gravelly series, with some sand and clay. 
Vertically above the line of contact in the later material are 
some angular blocks of carbonaceous shale, only a few feet 
from the carbonaceous layer from which they came. There 
must have elapsed between the formation of the earlier fine 
and the later gravelly deposits sufficient time for some ero¬ 
sion and consolidation of the earlier beds to have taken place. 
It is also evident that the earlier deposition took place in 
comparatively still and deep water, while the later gravelly 
beds could only have been deposited in water moving with 
some rapidity. The entire exposure is about sixty feet high. 
The later beds are correlated with the gravels forming the 
4,500 foot terraces previously described. 
