Among the oldest rocks in Oregon, some of the formations in these terranes date to the Triassic, nearly 250 million years ago.[25] Between 165 and 170 million years ago, in the Jurassic, faulting consolidated the Klamath terranes offshore during what geologists call the Siskiyou orogeny. This three- to five-million-year episode of intense tectonic activity pushed sedimentary rocks deep enough into the mantle to melt them and then forced them to the surface as granitic plutons. Belts of plutons, which contain gold and other precious metals, run through the Klamaths and include the Ashland pluton, the Grayback batholith east of Oregon Caves National Monument, the Grants Pass pluton, the Gold Hill pluton, the Jacksonville pluton, and others.[24] Miners have worked rich deposits of gold, silver, copper, nickel, and other metals in several districts of the Klamaths. Placer mining in the mid-19th century soon led to lode mining for gold. Aside from a mine in eastern Oregon, the Greenback Mine along Grave Creek, a Rogue tributary, was the most productive gold mine in Oregon
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