NEOCENE DEPOSITS OF CALIFORNIA 379 
To what extent this valley may have been filled up by 
alluvial action we do not know, as, since its elevation, erosion 
has nearly reopened it, and the Neocene deposit within it 
appears merely as a small remnant. It seems to be continuous 
from end to end, and back of Hay Fork village forms a sort of 
terrace, occupying the north half of the valley and rising about 
sixty feet above the present stream level. It consists chiefly of 
layers of fine gravel and sand, indicating ordinary alluvial 
action. Near the upper end of the valley, interstratified with 
the gravel, I have found at least one bed of a white chalky 
material which seems to be rhyolite tuff, and Anderson reports 
this material from other parts of the formation. Near the lower 
end of the valley, where the deposit of gravel occurs in the bed 
of Hay Fork Creek, the stream exposes layers of lignite. It is 
the presence of this impure coal and the supposed tuff which 
postulate a pre-Pleistocene age for the deposit and the valley in 
which it occurs. 
Hay Fork valley is terminated at the western or down- 
stream end by a sudden narrowing of the valley of the Hay 
Fork Creek, which drains the old valley through a deep rocky 
gorge (said to be a veritable cafion), not to be explained by an 
increase in that direction in the resistant properties of the meta- 
morphic formations. 
Before discussing the Neocene deposit of the Trinity River, 
which is in many respects the most interesting and instructive 
of these old river channels, it will be necessary to direct atten- 
tion to one of the most salient points in the later history of this 
region. This is the abandonment by the Trinity River of its 
original course, between Trinity Center and Junction City, and 
the excavation by it of a new valley roughly parallel to the old, 
and distant from it on the average about five miles. The new 
course is southeast of the old, on the outer side of a curve and 
consequently considerably longer than the original course. The 
two valleys are separated by a rock ridge of no mean height. 
The.new valley is comparatively narrow and of the gulch type, 
although its floor in places has a width of one-fourth to one- 
half mile. 
