The Klamath Mountains region in northwestern California is the second-most gold-productive province in California. The principal gold districts are in Shasta, Siskiyou, and Trinity Counties. Although there are several important lode-gold districts, the placer deposits have been the largest sources of gold. The Klamath Mountains consist of a number of complex and rugged ranges that continue north into Oregon. The entire mountain mass is essentially an irregular and deeply dissected uplifted plateau. It is underlain by a series of complexly folded and faulted metamorphic rocks of Paleozoic and Mesozoic age that have been invaded by batholiths of Late Jurassic and possibly Early Cretaceous age. In some respects the Klamath Mountains resemble the Sierra Nevada, and sometimes the two mountain ranges are classified as a single metallogenetic province.
The major rock units of the Klamath Mountains include the Abrams Schist and Salmon Schist (pre-Silurian?); the Copley Greenstone, Balaklala Rhyolite and Kennett Shale (Devonian); slate of the Bragdon Formation (Mississippian), and the younger granitic rocks of the Shasta Bally batholith. On the west side of the province are extensive beds of sandstone, shale, and conglomerate of Jurassic age, and ultramafic rocks that are in part serpentinized. Between these two rock sequences lie beds of phyllite, chert, limestone and metavolcanic rocks of Paleozoic and Triassic age. The batholiths are composed chiefly of granodiorite or quartz diorite and are either round or elongated in a northerly direction. The largest ones are the Wooley Creek, Ironside Mountain, and Shasta Bally batholiths.
The most productive placer deposits in the Klamath Mountains have been those associated with the Klamath and Trinity Rivers and their tributaries. Gold is found not only in the gravels in the present stream channels, but also in older terrace and bench deposits adjacent to the channels. The terrace and bench deposits often were mined by hydraulicking.
Rising in southern Oregon, the Klamath River flows west across the Klamath Mountains and empties into the Pacific Ocean. The most important tributary streams of the Klamath River are the Shasta, Scott, and Salmon Rivers, and Cottonwood, Horse, Seiad, Thompson, Indian, Clear, Dillon, and Camp Creeks. Important centers of placer mining in the Klamath River system have been at Hornbrook, Yreka, Scott Bar, Hamburg, Somesbar, Orleans, Sawyers, Forks of Salmon, Callahan, and Cecilville.
The Trinity River, which flows into the Klamath River at Weitchpec, drains the southern portion of the Klamath Mountains. The most productive placer deposits of the Trinity River are those located along its main channel. These include the deposits at Carrville, Trinity Center, Minersville, Lewiston, Weaverville, Junction City, and Salyer. The principal tributaries of the Trinity River are Coffee Creek, Stewart's Fork, East Fork, New River, Indian Creek and Hayfork Creek. The La Grange mine, a few miles west of Weaverville, was one of the largest hydraulic mines in California. Other sources of placer gold in the Klamath Mountains have been the Smith River region in Del Norte County and the upper Sacramento River and its tributaries, which include Backbone, Clear, Cottonwood, and Beegum Creeks.
Lode-gold deposits are found throughout the Klamath Mountains. The most productive district has been the French Gulch-Deadwood district of Shasta and Trinity Counties, in the southern portion of the province. Other important sources of lode gold have been the Deadwood district of Siskiyou County (there are several Deadwood districts in California), Dillon Creek, Callahan, Oro Fino, Liberty, Sawyers Bar, Harrison Gulch, Whiskeytown, and Buckeye-Old Diggings districts. Considerable amounts of gold have been produced in the Shasta copper-zinc belt and lesser amounts in other copper deposits, such as the Copper Bluff mine at Hoopa.
The gold nearly always occurs in native form in quartz veins, usually associated with pyrite and smaller amounts of other sulfides. The veins occur in all metamorphic rocks of Jurassic and older ages, the Bragdon Formation (Mississippian) containing the most numerous and productive veins. A few lode-gold deposits are found in granitic rocks. Undoubtedly the mtroduction of the veins is related to the granitic intrusions. Often the gold-quarrz veins and the ore shoots in the veins are associated with fine- to mediurngrained diorite, quarrz diorite, and aplite dikes. In several districts these dikes are known locally as "birdseye porphry" dikes.