[Mines and Mining; California; Nevada County; Grass Valley] Pennsylvania Mine, Grass Valley, California [title supplied]. Real photo post card (RPPC). N.p., n.d. View of the Pennsylvania Mine (later part of the Empire Mine) in Grass Valley, California, circa 1909. Postmarked Tuolumne & Stockton R. R., 16 August 1909. Addressed to Miss Bessie O'Day of San Francisco. 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. Very good, or better. (#165027).