[3] Three Bay Miwok tribes, the Chupcan, Ompin, and Volvon, lived in the areas surrounding the Black Diamond Mines Regional Preserve.

[5] The rich coal deposits and sandstone hills of Black Diamond Mines Regional Preserve were formed by geological activity in the Tertiary period.

During this era, the Pacific Ocean stretched over much of the California central valley with the coastline reaching the lower regions of the Sierra Nevada mountains.

[7] Tectonic activity between the North American and Pacific plate, along with sea level changes, brought about four series of marine sediment deposition.

At the beginning of this third cycle, tectonic activity caused an uplift of the continental shelf seafloor, resulting in the creation of shallow marshes.

[7] These sediments, along with the favorable hot and humid climate, fueled the growth of coastal marsh flora that eventually formed into coal.

The Mount Diablo Mountain Range of today was created at the beginning of the fourth depositional cycle when the continental shelf began to rise up once again.

[7] In 1859 William C. Israel discovered a coal deposit while clearing out a spring on his land at Horse Haven Valley, six miles south of Antioch.

The mines were the Empire, Central, Star, Corcoran, Pittsburg, Manhattan, Eureka, Independent, Union, Black Diamond, Mt.

The coal produced was of a low grade (sub-bituminous or lignite), but for a time in the 19th century, was the only readily accessible and economic source in California.

[15] A few whose earthly remains were laid to rest here include: In the 1920s, a mine producing high-quality silica sandstone was started by owner Marvin Greathouse on a hillside above the Somersville townsite.

[19] EBRPD originally repurposed the Hazel-Atlas mine as a museum in the 1970s, but storm damage in 2007 forced closure of this attraction for extensive repairs.

[20] The trails offer views of Mount Diablo, the Sacramento-San Joaquin River Delta, and on clear days, the Sierra Nevada.

The property had been deeded to the holding company by Gordon Grevelle, president of Suncrest Homes, who had originally planned to build a gated residential community there when he had bought the tract in 1987.

After going through an extensive permitting process and a decline in the California housing market, Grevelle decided that the project he had envisioned would be unlikely to meet his financial goals.