LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

EMBAYMENTS OF THE THOUGH 21
west, those adjacent to the Joaquin embayment seem relatively small and
unimportant,
SACRAMENTO EMBAYMENT
In early Cretaceous time the northern embayment of the Great Valley
trough extended from its major outlet near San Francisco Bay toward
the north, or northwest, not only to the present extremity of the Great
Valley, but far beyond it toward the west, and penetrated the interior of
Klamathonia, More definitely, it seems to have reached a considerable
part of the basin area of the modem Trinity River and to have received
waters from far beyond it, to the west and north. Cogent evidences of
these conditions are to be seen in the residual outliers of Cretaceous sediment,
marine, partly marine, or of brackish character, still extant, detached
from the main embayment, and scattered about the areas of this basin.
This arm of the SacT&menbo embayment existed under marine, or partly
marine, conditions only in early Cretaceous time (pre-Horsetown). During
part of the Horsetown and subsequent epochs marine waters were
withdrawn from it, presumably as a result of uplift in restricted mountain
areas surrounding its area.
CUETACEOD3 DEPOSITS
General Statement.—The Cretaceous deposits of the Sacramento embayment
have been more extensively studied than have those of the
Joaquin embayment, but they are still only imperfectly known. Within
the limits of the Great Valley, the oldest Cretaceous deposits appear to
rest in some places in sequential contact upon those of the latest Jurassic
(Knoxville) epoch, whereas in other areas this is clearly not the case. In
the intermontane extension of the trough, the oldest Cretaceous beds rest
directly upon pre-Knoxville basement rocks, in the manner of an overlap,
with no Knoxville sediment intervening, and this condition is also found
in other areas farther south.
In this more restricted embayment the Cretaceous deposits outcrop in
two marginal zones on opposite sides of its general valley, but they are of
quite unequal stratigraphical thickness and are&l extent and ore for the
most part of different ages.
In the northern end of the Great Valley trough, north of the latitude
of the 39th parallel, the Cretaceous deposits outcrop in two marginal
zones on opposito sides of the valley, in which they are of quite unequal
thickness; for the most part they belong to different epochs of Cretaceous
time. The eastern zone is of relatively small stratigraphical importance,
as well as in its exposed areas. Its deposits belong to only Upper Cretaceous
horizons, as do most of those in the Joaquin embayment, in which
beds older than Cenomanian are not found. For the most part these are
buried under volcanic agglomerates, which permit their exposures only at