 In September 2004, Arch again added to its Powder River Basin reserves when it was the winning bidder on Little Thunder, a 719-million-ton federal reserve tract adjacent to the Black Thunder Coal Mine.In December 2005, Arch Coal sold select eastern assets to Magnum Coal Company to unlock the value of some of its Central Appalachian holdings, sharpened its focus in that region, and strengthened its balance sheet in preparation for future growth.In August 2006, Arch acquired a one-third interest in Knight Hawk Coal, a growing coal producer in the Illinois Basin.