Six years after ARCO acquired rights to the "Richest Hill on Earth", Butte's mines were completely idle. ARCO founder, Robert Orville Anderson, stated "he hoped Anaconda's resources and expertise would help him launch a major shale-oil venture, but that the world oil glut and the declining price of petroleum made shale oil moot." At the time of the sale to ARCO, Anaconda had large working hard coal holdings in the Black Thunder mine at Thunder Basin, Wyoming. ARCO planned to diversify its energy business into coal. In June 1998, Arch Coal completed the acquisition of the coal assets of Atlantic Richfield.