Most California copper production came from the West Shasta district in northern California. Gold prospectors discovered the copper deposits of Shasta County in 1848, but no metal was produced until 1879, when some silver was produced from the Iron Mountain Mine. The copper was in massive sulfide deposits in the Devonian Balaklala Rhyolite. The principal mines were the Iron Mountain Mine, Mammoth Mine, and the Balaklala Mine. Copper production began in 1894, and continued off-and-on until 1976. Total production was 320 thousand tonnes of copper, 93 million pounds of zinc, 36 million troy ounces of silver, and 520,000 ounces of gold. The district also produced pyrite for sulfuric acid.