Empire Mine State Historic Park is the site of one of the oldest, deepest, and most productive gold mines in California. The park is in Grass Valley at 10791 East Empire Street. In operation for more than 100 years, the mine extracted 5.8 million ounces of gold before it closed in 1956. The park contains many of the mine’s buildings, the owner’s home and restored gardens, as well as the entrance to 367 miles of abandoned and flooded mine shafts. The park has 856 acres of forested backcountry and fourteen miles of trails - including easy hikes for hiking, mountain biking, and horseback riding.

The "Secret Room"
To keep track of the mine's 367 underground workings, a place called "The Secret Room" (named for its blacked-out windows) was built. In it, the entire room was filled with a scale model of the mine's below the surface workings. Few people knew the room existed while the mine was in operation. Today, visitors to the park can see it in the Visitor Center. The model represents five square miles of underground workings. When the visitors go down the actual shaft in the park, they have journeyed only "one inch" on the model. Anything past "two inches" on the model is underwater in the actual mine.