In 1849, the Mount Diablo Coal Fields, also known as the Black Diamond Mine, was founded, shortly after Army Lieutenant William Tecumseh Sherman, whom later gained fame as a General during the U.S. Civil War, founded the town of Black Diamond.
The town of Somersville was one of five towns that were established within the Mount Diablo Coal Field, south of the town of Black Diamond.
The Black Diamond Mines had more coal output than any other set of mines within the state of California and continued to operate until 1900. Ultimately, the rising cost of mining coal, and the increase of the demand for oil due to the increase in automobile usage, lead the owner of the Black Diamond Mines to cease operations.
After the coals mines closed, the miners and their families, moved out of the five towns, leaving the various buildings abandoned for two decades.
In the 1920s mining operations for silica-rich sand, by the Hazel-Atlas Glass Company for the production of glass, began at the Black Diamond Mines. Sand mining continued until the 1940s, and the five mining towns became “ghost towns”.
Many of the miners who worked at the Black Diamond Mines are buried in the Rose Hill Cemetery.
Presently the former coal mine is under the ownership of the East Bay Park District as the Black Diamond Regional Preserve.
The entrance to the Black Diamond Regional Preserve hosts the Sidney Flat Vistor Center.
After the Black Diamond Coal Mines were abandoned the cemetery was vandalized frequently and grave markers were stolen. However, the grace makes for Walter E. Clare was returned when Black Diamond became a regional park.
The East Bay Regional Park staff give mine tours within one of the former Eureka mine.
Many of the trails on top of the former mines lead to various hills within the Mount Diablo Foothills.
Hamilton Historical Records 