For thousands of years, Indians lived in the greater Bay Area, and Black Diamond lay in the backcountry between the Chupcan of Concord, the Volvon of Clayton, and the Ompin of Pittsburg, all Bay Miwok speakers. After 1772, the arrival of Spanish, Mexican, and American settlers rapidly transformed Bay Miwok life, though many California Indians continued to practice ancestral traditions. From the 1850s to the early 1900s, Black Diamond became California’s largest coal mining operation, with the towns of Nortonville, Somersville, Stewartville, West Hartley, and Judsonville thriving as nearly four million tons of coal were mined. People came from around the world, and as many as 900 miners, including some as young as eight, worked long hours in hundreds of miles of underground workings; at its peak, the coalfield was reported to be the population center of Contra Costa County, and its mines significantly affected California’s economy as the state shifted from a rural to an industrial base. In the 1920s, underground sand mining began near deserted Nortonville and Somersville, supplying sand for glass production in Oakland and foundry sand in Pittsburg, until foreign competition and the closing of the steel foundry ended mining by the late 1940s after more than 1.8 million tons had been removed. Cattle ranching was the area’s major industry before coal was discovered, and after the mines closed some miners turned to ranching, reusing abandoned mining materials in their new work; descendants of the original mining families still graze cattle there. In the early 1970s, the East Bay Regional Park District began acquiring land for a regional preserve that now includes most of the mining district within nearly 6,096 acres. Its trails cross grassland, foothill woodland, mixed evergreen forests, chaparral, stream vegetation, and exotic plantings, including tree species introduced by coal miners, while the area also contains notable native plants, Mount Diablo endemics, spring wildflower displays, and a wide range of wildlife, from raccoons and deer to mountain lions, birds of prey, and several rare species. Although little remains of the mining communities, Rose Hill Cemetery preserves the memory of former residents, including children lost to epidemics, women who died in childbirth, and men killed in mining disasters; though more than 10 nationalities lived in the mining area, it served as a Protestant burial ground for many Welsh residents.