LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

EMBAYMENTH OF THE TROUGH 35
The scattered areas of Lower Cretaceous sediments lying within the
Yolla Bolly basin, now detached from the body of the delta, and beyond
the present drainage divide contain much corroborative evidence as to
the source of these plant remains. The more westerly areas (Big Bar
and Forest Glen) contain not only similar plant remains but also the
marine, partly marine, and brackish water Mollusca already mentioned.
Diller, who has studied these areas more extensively than any other
writer, compares the deposits of Big Bar and Rattlesnake Creek (Forest
Glen) with those at Redding Creek, eastern Trinity County, and considers
them to be referable to the "top of the Knoxville or bottom of the Horsetown."
Both these horizons seem to come within the limits of the lower
Shasta series of the present paper. The Redding Creek area has yielded
many species of marine Mollusca that prove its lower Shasta, age and many
plant remainB, concerning which Knowlton remarks, in part (Diller, 1908,
p. 383):
''These species (with one exception) axe all reported by Ftmtaino from the Shasta
Sora of the localities along the west aide of tbo Sacramento Valley, and are therefore
regarded aa of Lower Cretaceous age."
It would appear, therefore, that the near relations of the detached areas
of Cretaceous sediment m the Yolla Bolly basin and those of the Sacramento
embayment are clearly shown in both their invertebrate fauna? and
in their Boras. However, the character and significance of fossil land
plants in marine deposits may well relate more correctly to the physiographic
or climatic condition in their source areas than to their position
in the stratigraphic column. If these plants have been derived from old
and geologically stable land areas, such aa that of Klamathonia, many
lineages and families may have survived there without interruption from
much earlier times than that represented in their burial, and they might
also survive many succeeding changes.
With regard to the Cretaceous deposits laid down in the Sacramento
embayment and in its delta area, one may expect the earliest sediments
would be laid down near their entrance point, or point of exit from the
basin. For the most part they would be spread unconformably upon the
older terrains existing there. This aspect of the succession has already
been discussed elsewhere (Anderson, 1933). As loading of this area
progressed it would induce further subsidence, and sediments would
spread fan-wise over the floor of the embayment.
Removal of materials from their source region would induce uplift in
compensation and would renew the vigor of the streams draining it. In
mid-Lower Cretaceous (Horsetown) time such a readjustment is recorded
in an uplift already mentioned, which points to an important epoch of the
period, at least OS affecting California and Oregon, and possibly the entire
West Coast, including Alaska.