GOLD AND SILVER.

AURIFEROUS GRAVELS IN THE WEAVERVILLE QUAD­ RANGLE, .

By J. S. DILLEB.

INTRODUCTION. Few mining regions in California have attracted so much general attention and held it for so long a time as the of Siskiyou and Trinity counties, in the northwestern part of the State. The placers along Trinity and Klamath rivers were developed early in the gold rush and have been worked with varying energy to the present time. The La Grange mine, which is one of the largest hydraulic placers in the world, is now in the height of its activity. In order that an account of mining in the Weaverville quadrangle may have its proper setting it is necessary to consider the general relations of the mountain ranges in the adjacent portions of Cali­ fornia and Oregon. THE KLAMATH MOUNTAINS. GENERAL RELATIONS. The mountain belt of the Pacific coast in California and Oregon includes a number of distinct ranges whose distribution and compo­ sition are in part illustrated by the accompanying geologic map (fig. 1). On the north are the Cascade Range and the Coast Range of Oregon, separated by the Willamette or Sound Valley as far south as Eugene. On the south are the Sierrp Nevada and Coast Range of California, separated by the great valley of California. About the western part of the California-Oregon boundary, where all these ranges appear to meet, there is a distinct group of mountain ridges and peaks extending from a point north of the mouth of Rogue River in Oregon to Mad River in California. This group constitutes the Klamath Mountains. It embraces the South Fork, Trinity, and Salmon mountains of California and the Siskiyou and Rogue River mountains of Oregon. These ranges are distinguished largely from geologic data, as will be more readily understood by referring to ,the map (fig. 1). The symbols on the map indicate in general the geologic age of the sedi­ mentary rocks of the Klamath Mountains. To illustrate their areal 11 12 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1912, PART I. distribution more clearly, all details and small areas have been omitted and outlines have been broadly generalized to cover large areas of igneous rocks. The map shows at a glance that the forma-

Mddlemm Tertiary Earlier Cretaceous Jurassic;W#M PaleozoicV//A mmSchists LavasI&K-I of to Quaternary, Tertiary in California Cascade Range inclusive include 9 Trias sic FIGURE 1. Geologic map of the Klamath Mountains and adjacent ranges, California. Formations grouped and details generalized or omitted. ( tions outlined occur mainly in the northwestern part of. California, but they cover also a small area in Oregon. The Klamath Mountains and the Sierra Nevada are composed in the main of essentially the same formations, and in the southern part AURIFEROUS GRAVELS IN WEAVERVILLE QUADRANGLE, CAL. 13 of the Klamath Mountains the formations and lines of structure trend northwest and southeast, toward the Sierra Nevada, but in the northern portion they trend southwest and -northeast, toward the Blue Mountains of eastern Oregon. Besides this general align­ ment of the formations of the Sierra Nevada, Klamath, and Blue mountains, their mineral resources are similar, a feature in which they are strongly contrasted with the Cascade and Coast ranges in Oregon and California.

GEOLOGIC HISTORY. Little is known of the early geologic history of the Klamath Mountain region, yet it is evident that in pre-Devonian,1 possibly in Algonkian 2 or late Archean 3 time the region was beneath the ocean, receiving the sediments from which the mica schist and intercalated crystalline limestones of South Fork Mountain and the Salmon Mountains north of Weaverville were formed. The extensive development of Devonian and Carboniferous shales, sandstones, cherts, and limestones in the Klamath Mountain region shows that at least a part of the region continued beneath the sea through the whole or the greater part of the Paleozoic era, but the i