The Empire Mine State Historic Park is located outside Grass Valley, California & features an outdoor exhibit & trail system surrounding what was once one of the state's largest, oldest, longest, richest, & biggest gold-producing mine.  The Empire Mine was in operation from 1850 to 1956 & produced over eight-billion dollars worth of gold in today's standards.  The mine included over 367 miles of underground tunnels (or nearly the driving distance from San Francisco to Los Angeles, California) to an incline of 11,000 feet w/ a total depth of over a mile below the surface.  Today nearly all of the tunnels are flooded w/ underground water starting at 150 feet below the surface.  Seen here is an outdoor equipment exhibit as well as other buildings that were used during the mining operations.  This upper floor is part of the mine manager's office, the building restored after being built in 1898.  The offices themselves were under the ownership of William Bourn Jr. & the Newmont Mining Corporation.