The coal was carried to the San Joaquin River by three railroads: the Empire, Pittsburg, and Black Diamond, for shipment by barge to markets in San Francisco, Sacramento, Stockton and other communities. Coal mining activity ended as better-quality imported coal became affordable and as petroleum emerged as an energy source. After the coal mines closed, the towns were abandoned and the area was used mainly for cattle grazing. In 1974 the Southport Land and Commercial Company (former Black Diamond Coal Mining Company) donated 160 acres of its land holdings to help It become Black Diamond Mines Regional Park.