LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

CRETACEOUS SEDIMENTARY DIVISIONS 39
under tho name of "Shasta Group." The chronological span of the series
is from 'Neocomian to Gault, inclusive, except such part of the upper
Albian as belongs in the Chico series and is unconformable upon the
SKasta, On the west border of the Sacramento Valley the Shasta series
extends from north to south across the delta area, where it attains a
maximum thickness of nearly 27,000 feet, from the axial part of which
it diminishes in both directions. Toward the north the thickness drops
rapidly to nearly 11,000 feet on Roaring River, to less than 7000 feet on
the North fork of Cottonwood Creek, and to 4500 feet on Hulen Creek.
The thinning of the sections northward is due in part to transgressive
overlap along the north border of the Cretaceous area. Southward from
the axial area of the delta the thickness of the series drops to about 25,000
feet at Dry Creek, to 19,500 feet on the Cold fork of Cottonwood Creek,
to 16,275 feet on Redbank Creek, and to 13,000 feet on McCarthy Creek.
Farther south the thickness of the series is less easily determined, but,
notwithstanding the contributions by other streams from the west, the
thinning of the sequence continues. At Wilbur Springs, Cache Creek, and
in the Berryessa Valley, tho thickness is generally less than 14,000 feet,
but it is thicker south of Monticello. Farther to the south the series is
broken by faulting, and its sections are often incomplete or appear to
be missing in large part.
Near Mount Diablo the lowest part of the Shasta series baa been recognized
by its fauna (ammonoids, belemnoids, and Aucelia)} but the series
is much disturbed, and apparently only partial. In some places here it
rests unconform&bly upon Knoxville beds with coarse basal conglomerate,
as near Peachtree Springs. The same condition is found in the Berkeley
hills and in the Santa Clara Valley, where, west of Redwood City it contains
Aucclla. South of Los Gatoa, near "Wrights, CordeU Durrell found an
example of Neocraspediiea, well known in the lower Horsetown group of
the Cottonwood district, Shasta County,
In the Diablo Range, strata belonging to the Shasta series have been
recognized only at intervals, but their presence at such places indicates
that they extend along the Range to its southern terminus at Orchard
Peat, on the northern border of Kern County, although not now continuously.
The lowest beds (Paskenta) have been proved at Mount Diablo,
Quiiito Creek, Waltham Creek valley, and at Orchard Peak (Devils Den),
where they contain diagnostic ammonites and Aitcella. Most of the
published references to "Knoxville" beds in the Diablo Range refer
instead to lower Shasta (Paskenta) beds.
In the vicinity of Corral Hollow, and on Hospital Creek, farther south,
the upper part of the series has been proved by characteristic ammonites
{Cleoniccraa and Puzoitia).
Relations of the Shasta Series.—As found in its more complete sections