Empire Mine State Historic Park
Empire Mine State Historic Park is a state-protected mine and park in the Sierra Nevada mountains in Grass Valley, California, U.S. The Empire Mine is on the National Register of Historic Places, a federal Historic District, and a California Historical Landmark. Since 1975 California State Parks has administered and maintained the mine as a historic site. The Empire Mine is "one of the oldest, largest, deepest, longest and richest gold mines in California". Between 1850 and its closure in 1956, the Empire Mine produced 5.8 million ounces of gold, extracted from 367 miles (591 km) of underground passages.
Source: Wikipedia
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