LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

CRETACEOUS EMBAYMENTS 15
bordering the embayments of Knoxville time need not be described here,
although latest among these basement rocks should be included all that
are properly embraced under the name Franciscan series. The recognition
of a late Jurassic (Portlandian and Tithonian) age for the Knoxville implies
that the closing epoch of Franciscan time was not later than mid-Portlandian
and, therefore, that it was possibly synchronous with some part
of the Mariposa-Mount Jura period. The next important dynamic event
in West Coast Mesozoic history came at the close of Knoxville time, when
distinct and widespread orogeny, whose regional or local effects are not
yet fully known, seems to have affected the entire Pacific Coast.
Its movements were not everywhere the same. In the area of the larger
California embayments, and in southwestern Oregon, their vertical components
were probably differential. In some of the mountain areas of
Klamathonia the land reliefs of Knoxville time were accentuated by
uplift, with a corresponding contraction of Hooded areas in the embayments.
In other places land surfaces were depressed, with sea encroachment
on their borders. The longitudinal extent of this orogeny >B not
yet known, but it appears to have reached Alaska on the north and
Mexico or farther on the south.
At the close of Knoxville time the sea-ways leading into the embayments
of Oregon and California seem to have been greatly narrowed and remained
so throughout Cretaceous time. During this period the mountains of
Klamathonia maintained their prominence, as with some modification
they continue to do. According to Diller (1894), the Klamath Mountains
of the present embrace most of the coastal region between the Umpqua
River in Oregon and the latitude of Red Bluff, California. This should
be regarded as a minimum estimate of their area. If the critical epoch
between the close of Knoxville and the opening of Cretaceous time is
chosen as the date for estimating the area of Klamathonia, its area would
embrace the peripheral zones of all known pre-Knoxville terrains, and
among them that of the Franciscan series, which in the outer Coast
Ranges extends northward beyond the Humboldt Bay. Metamorphic
rocks outcrop near Big Lagoon and at intervals along the coast as far
north as the Coquille River. At the close of Knoxville time the area of
Klamathonia may be estimated at 29,200 square miles, nearly 75 per cent
of which (22,000 square miles) lay within the present boundaries of California,
north of the 39th parallel. However, this estimate includes the
areas still extant as land and those now probably submerged along its
western borders.
There is no evidence that during any part of Knoxville or Cretaceous
time the sea had covered more than small, and essentially peripheral,
parts of Klamathonia, and these only in early Cretaceous time. Some
of the most remarkable aspects of this mountain block appear in its