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From the 1860s to the turn of the 20th century, the Mount Diablo Coal Field was the largest coal-producing region in California and once boasted five thriving communities. With the decline of coal mining some residents turned to ranching. Later rich deposits of sand were mined for glass and foundry use. In 1973, the East Bay Regional Park District acquired the land. Today visitors to Black Diamond Mines Regional Preserve, located 45 miles east of San Francisco, can explore miles of trails, tour the Hazel-Atlas silica sand mine, and visit historic Rose Hill Cemetery.