Bulletin - United States Geological Survey Volume 545-549 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 Excerpt: ...cycles of erosion (p. 13) there are in southwest Oregon, as well as in northwest California, a number of important deposits of older gravels, now conglomerates, Cretaceous in age and of marine origin. These auriferous conglomerates in California were first described by R. L. Dunn and later by H. W. Turner,3 who recognized their marine origin. They are shore deposits about a Cretaceous island, the Siskiyou Island of Condon,3 whose approximate outline when the beach gravels, now conglomerate, were formed is shown in figure 9. During the Cretaceous period the island gradually subsided until it was almost if not completely covered by the sea. Among the later as well as the younger gravels of Trinity River above Weaverville are found pebbles of fossiliferous Cretaceous sediments which evidently came from the high mountains about the river's head, affording positive evidence of Cretaceous submergence. This Cretaceous cover, now almost completely washed away, was derived from the auriferous slate bedrock series of the Klamath Mountains and probably contained gold at many localities. By its disintegration and erosion the gold was liberated and concentrated in later gravels. This concentration appears particularly marked along the old coast line. The rich placers (indicated by X) along this old coast, line both southwest and northeast of Redding, Cal., as well as in the neighborhood of Yreka and in tbe Cottonwood mining district near the Oregon line, probably owe much of their richness to 'Dunn, R. L., California State Mineralogist Twelfth Rept., pp. 459-471,1894. Turner, H. W., Eng. and Mln. Jour., vol. 76, pp. 653-654,1903. Condon, Thomas, The two islands and what came ot them, 1902. Revised and enlarged by Ellen Condon McCornack In 1910 as "Oregon geology.&q...