In 1955, the United States Atomic Energy Commission built a uranium ore processing plant on the 2,000 remaining acres. Weldon Spring Uranium Feed Mill Plant produced yellow cake uranium ore. In 1966, the plant closed and remained abandoned for 20 years. The site was contaminated with over 1.5 million cubic yards of asbestos, radioactive uranium and contaminated rubble. The U.S. Department of Energy began a decontamination of the site in the late 1980s and completed it in 2001, with a 45-acre rubble mountain over the site.