 In June 1998, Arch Coal expanded into the western United States with the acquisition of the coal assets of Atlantic Richfield.Included in this transaction were the Black Thunder Coal Mine and Coal Creek mines in the Powder River Basin of Wyoming; the West Elk longwall mine in Gunnison County, Colorado; and a 65% interest in Canyon Fuel Company, which operates three longwall mines in Utah.In October 1998, Arch added to its Powder River Basin reserves when it was the winning bidder on Thundercloud, a 412-million-ton federal reserve tract adjacent to the Black Thunder mine.