Construction of the facility began in 1878, on the site of the Stony Bar mining camp along the American River. The prison officially opened in 1880 with a capacity of 1,800 inmates. They spent most of their time in the dark, behind solid boiler plate doors in stone cells measuring 4 by 8 ft (1. 2 by 2. 4 m) with 6-inch (15 cm) eye slots. Air holes were drilled into the cell doors in the 1940s, and the cell doors are still in use today.