Where did the mine companies operate according to the news item?

U.S. government health and safety officials are investigating the cause of the recent explosion at a West Virginia coal mine, which killed 12 miners. The accident was apparently an aberration in an industry which has prided itself on miner safety at a time of unprecedented expansion. [21]Mine companies operate in 27 states, from West Virginia in the east to Montana in the west, producing a total of about one billion tons a year, or more than a third of the world’s coal supply. The U.S. economy is dependent on coal production. [22]Coal-fired power plants generate about 50 percent of the nation’s electricity. More than half the nation’s coal is mined underground by thousands of men and women who daily risk injury and death. [23]But the occupation has become much safer since the late 1960s. when the U.S. Congress passed laws requiring federal mine inspections.