07 Eocene History of the Cascade Range

The Geology and Petrography of Crater Lake National Park, 1902




There can be no reasonable doubt that fossiliferous Cretaceous rocks of marine origin are widely distributed beneath the Cascade Range from Lassen Peak to the Columbia, and that during the Chico epoch the whole area was beneath the sea. At the close of the Cretaceous, important changes occurred in the distribution of land and sea. Northern California, as well as southern Oregon, was raised above the sea excepting the Coast Range region north of Rogue River, which remained beneath the sea during the early part of the Tertiary. The marine deposits of the Eocene period in the vicinity of Roseburg run under the Cascade Range, but have not yet been found on the eastern side. The conglomerates of the Eocene, like those of the Cretaceous, contain many pebbles of igneous rocks, but they are of types common to the Klamath Mountains and are rare or unknown among the lavas exposed in the Cascade Range. During the Eocene there was vigorous volcanic activitya in the Coast Range of Oregon, but the record of such activity has not yet been found in the Cascade Range. That volcanoes were active along the range during the Eocene is rendered more probable, although not yet beyond question, by Dr. J. C. Merriam’s discovery of Eocene volcanic deposits in the John Day region.b

aSeventeenth Ann. Rept. U. S. Geol. Survey, Part I, 1896, p. 456.
bBull. Dept. Geol. Univ. California, Vol. II, No. 9, p. 285.


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