LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

30 LOWER CRETACEOUS DEPOSITS INT CALIFORNIA AND OREGON
the name Yolla Bolly Rivet (and Basin) seems to be appropriate, and is
here used.
Post-Knoxville subsidence admitted marine waters into the basin from
the east, and early Cretaceous (Paskenta) deposits were laid down in it.
Materials were brought in by streams from the surrounding mountains,
then being denuded and peneplained. The outward drainage passed
eastward into the Sacramento embayment as it had done during Knoxville
time. Apparently this condition continued only during the earliest Cretaceous
epoch. At the beginning of the Horsetown epoch an uplift affecting
the Yolla Bolly basin expelled the marine waters from it, while active
erosion continued, by which a part of the earlier sediment was removed.
This uplift left the strandlines of the early Horsetown epoch in the position
where they are now found on the western border of the embayment,
as is shown later. Only remnants of the early Cretaceous sediment now
remain in the Yolla Bolly basin. The molluscon fossils found in these
deposits have been partly described by Stanton and partly by the writer
in the present paper.
These fossils clearly ally the Yolla Bolly sediments with the Paskenta
deposits in the Sacramento embayment. Incidentally they show also
that the marine currents from the embayment entered this now detached
basin, bringing with them the molluscan fauna.
The most westerly of these residual deposits contain many fossil land
plants and species of marine, partly marine and brackish-water Mollusea
(Aualla, Cyrena, Astarte, Corbnla, Gmiomya, and t/nto), some of which
are herein described.
From a study of the present environments of this basin and their geological
constitution, one may approximate tbe boundaries and extent of the
areas from which came the masses of the Knoxville and Shasta, sediment now
lodged in the area into which this drainage discharged. Much of this
basin lay between the massif of the great Trinity Range on the north
(maximum elevation 10,000 feet) and the almost equally impressive cluster
of the Yolla Bolly range on the south (elevation 8500 feet). These ranges,
with their cores of ancient crystalline rocks may be regarded as parts of
the north and south rims of the Yolla Bolly basin during late Mesozoic
times. Its western rim is less easily shown, but in part it seems to be
represented by the high, plateau-like mountain cluster dominated by
Lassie Peak, south and west of the upper branches of the Van Duzen
and Mad rivers. From this cluster, ribs of metamorphic and crystalline
rocks extend toward the north and northwest, appearing on the present
coast near Big Lagoon and along the West fork of the Trinity River.
In an earlier paper the writer (Anderson, 1902b) called attention to two
great systems of mountains within the Klamath complex, the older trending
northeast to southwest, and tbe younger at right angles to this direo-