Black Thunder Coal Mine, Wyoming

For years Black Thunder was the "world's largest single coal-mining complex," until it was recently surpassed by the nearby North Antelope Rochelle mine. It is now the second largest coal mine in the nation. Either way, the mine produces nearly 10 percent of the U.S. coal supply annually. In total, more than 2.2 billion tons of coal have been mined since 1977. It is operated by Arch Coal, which bought out ARCO's Thunder Basin Coal Company in 1998. Black Thunder is one of several major mining operations extracting coal from a 50-mile-long seam in the Powder River Basin area, one of the largest coal deposits in the world.