From 1860 to 1906 this area was the largest coal mining district in California. Five towns (Nortonville, Somersville, Stewartville, Judsonville, and West Hartley) grew up around twelve major mines. Today the towns are gone, the buildings having been moved to nearby communities after the mines closed. Mine openings, tailings, railroad beds, and a pioneer cemetery are being preserved by the East Bay Regional Park District .

California Registered Historical Landmark No. 932

Plaque placed by the State Department of Parks and Recreation in cooperation with the East Bay Regional Park District and Joaquin Murietta Chapter No. 13, E Clampus Vitus, September 27, 1980