NEOCENE DEPOSITS OF CALIFORNIA 385 
subsidence of the same area, to enable the old channel deposits 
to accumulate to such great thickness in the wide cafions of the 
trunk streams. It is only in the Trinity valley deposit that a 
great thickness is seen, but there are no reasons for believing 
that similar accumulations were not made in the other valleys. 
The preservation of the deposit in Trinity valley has been espe- 
cially favored because the main stream abandoned the valley, 
which was not the case in the other valleys. It is probable that 
all the Neocene valleys were filled with alluvial deposits up to a 
certain baselevel plane and since largely reopened by erosion, a 
history which Lawson has shown to be duplicated in the Salinas 
valley in the southern Coast Ranges.* 
If we will take our stand on the summit of the low mountain 
range just west of the Trinity river at Bragdon, we will get a 
fair idea of the condition of the surface at the close of deposi- 
tion of the old channel deposit. We overlook the Neocene 
basin for miles to the northward and southward. We see that 
two limited areas apparently represent the original surface of the 
alluvial deposit. Some miles to the southward the summit of 
Buckeye Mountain appears, where it is composed of the river 
gravel, as a ridge with perfectly even crest-line, but sloping 
toward the east-southeast at a regular and low angle, estimated 
at about one hundred feet per mile. The altitude is 3,800 
feet: 
A little north of west from us, and distant only a few miles, 
another apparent remnant of the original surface forms a sort of 
plateau, only very slightly trenched by erosion, and known as 
the Greenhorn Flats. The elevation is about the same as Buck- 
eye Mountain, and there is a distinct slope toward the east- 
southeast at a regular rate of about the same degree as the other 
remnant. The conviction is forced on the observer that the 
entire deposit north of Weaverville has been tilted toward the 
east-southeast at the rate of about one hundred feet per mile, 
and the suspicion is raised that this tilting was so rapid that the 
Trinity River could not maintain its old course by down-cutting 
t Bulletin of the Department of Geology, University of California, Vol. 1, p. 154. 
