Black Diamond Mines Regional Preserve

 park, NRHP - National Register of Historic Places, historic landmark

The coal mines were in operation from the 1860s through 1910. These mines contained four-fifths of the largest coal mining area in California. In the peak production years of 1867 to 1882, the local coalfield supplied over 25% of all coal received at San Francisco
and, for several years, captured in excess of 40% of the market share. In the mines was mined four-fifths of all the lignite ever mined in California. These mines were the most important source of high silica sand used in California's steel foundries during the formative period of this industry, during the 1920s to the 1940s.

Sand has been mined in California for three main purposes: with gravel, as a contributor to road aggregate; for glass making; and for use in the iron and steel industry. The high silica content of the Mt. Diablo area sands make them particularly suitable for casting iron, steel, and other metals. by the early 1900s the demand for cast steel for use in the construction, shipbuilding, and other industries was strong
enough to encourage the serious exploration of sand deposits throughout the state.

Both the above-and below-ground coal mining features of the Black Diamond Mines district are the most extensive in California. d Mines district are by far the most extensive in California. The mines contain numerous examples of Welsh-derived, hard-mining technology and engineering including at least 1260 acres of mined-out rooms connected by over 200 miles of gangways and other passages.

The Black Diamond Mines district contains three of the five settlements that grew up around the coal mines: Nortonville, Somersville, and Stewartville.

The Hazel-Atlas sand mine, which can be toured, operated from 1920-1949. It is estimated that a minimum of 200 miles of underground accessways (adits, gangways, etc.) leading onto at least 1260 acres of mined-out rooms were excavated in the district.

This was California's largest coal mining operation: nearly four million tons of coal ("black diamonds") were removed here. Rose Hill cemetery has graves of Welsh miners. Throughout the park is evidence of earthquake faults and shifting.

National Register of Historic Places #91001425

www.ebparks.org/parks/black_diamond
www.ebparks.org/files/EBRPD_files/brochure/b_diamond_ma...
www.baynature.com/v08n02/v08n02_blackdiamond.html