Losses from the Chilean takeover however, had seriously weakened the company's financial position. Later in 1971, Anaconda's Mexican copper mine Compañía Minera de Cananea, S.A. was nationalized by president Luis Echeverría Álvarez's government. An unwise investment in the unsuccessful Twin Buttes mine in southern Arizona further weakened the company. In 1977 Anaconda was sold to Atlantic Richfield Company (ARCO) for $700 million. However, the purchase turned out to be a regrettable decision for ARCO. Lack of experience with hard-rock mining, and a sudden drop in the price of copper to sixty-odd cents a pound, the lowest in years, caused ARCO to suspend all underground mining operations in Butte in 1980. ARCO closed the Berkeley Pit and shut off the deep pumps in 1982, allowing the pit and mines to fill with water. The Continental Pit, the last active Anaconda mining property in Butte, was closed in 1982.