Red Mountain, on the Diablo Range divide at the edge of San Antonio Valley, became notable for the white magnesite deposits visible on its slopes from miles away. Although the mineral was known earlier, mining did not begin until 1905 because the remote site lay far from the railroad. By 1908 the American Magnesite Company was the only active operator, and later major workings included the Red Mountain Mine and the Western Mine. The Red Mountain Mine developed into a small isolated camp housing about 30 people. Wartime demand during World War II briefly intensified production, but after the federal government canceled its contract in 1944, the camp was abandoned within a week and became a ghost town.