Black Diamond Mines

Black Diamond Mines is a 2,078-acre district in central Contra Costa County, California, where coal was prospected in the mid-1850s. Five towns grew around the pitheads, including Nortonville and Somersville, and the coal boom lasted into the early 1900s, when the last mines closed and the towns were abandoned. High-silica sand was mined here from about 1925 to 1951. Recorded remains number 272 features, including building platforms, cellar holes, a cemetery, large coal tailings piles, brick hoisting footings, sealed adits and vents. Underground workings are estimated at 200 miles of passages and over 1,200 acres of mined-out rooms. The district is significant for its link to California's most important coal mining, for the best array of coal mining features and the state's only surviving room-and-pillar sand mine, and for its potential to inform on Welsh immigrants. It is now a regional preserve used for recreation.