The former Mexican Hat uranium mill site is located on Navajo Nation 1.5 miles southwest of Mexican Hat, San Juan County, Utah. The site is northeast of the town of Halchita, Utah, which began as the housing area for the mill's employees.

In 1956 through 1963, the Atomic Energy Commission [AEC] contracted with Texas-Zinc Minerals Corporation to produce uranium concentrate. The Mexican Hat mill was built and subsequently opened in November 1957. It produced an initial capacity of 775 tons of ore per day (TPD), increasing its capacity to 1,000 TPD in 1958. In June 1963, the mill and mill-site lease were acquired by the Atlas Corporation who continued to operate the Mexican Hat mill through February 1965. During its operating life, the mill processed nearly 2.2 million tons of ore averaging 0.28 percent U3O8. All in all, about 11.4 million pounds U3O8 was delivered to the AEC during this time. An on-site sulfuric acid plant continued to be operated until 1970 when the mill-site lease expired and control of the site, including its buildings and tailings piles, reverted to Navajo Nation.

At the time operations ceased, the mill site covered approximately 550 acres, including two on-site tailings piles covering about 70 acres and holding about 2.2 million tons of radioactive material. The site was not stabilized. By the early 1980s the contamination had migrated to contaminate an additional 250 acres adjacent to the mill site.

Subsequently, an on-site above ground disposal cell was constructed. The two tailing piles were consolidated, remaining mill structures were demolished, and radioactive debris and material from fifteen vicinity properties were placed in the cell, along with almost 1.3 million tons of tailings and contaminated structural debris transported from the Cane Valley UMTRA site in Arizona. Surface remediation at the Mexican Hat site was completed in 1995.

The final stabilized Mexican Hat Disposal Cell covers 72 acres and contains about 4.4 million tons of radioactive material resting on sandstone and shale. The cell is capped with a 3.5-foot thick engineered multilayered covering. A 2-foot thick radon/infiltration barrier of compacted sand and clay was placed directly on top of the contaminated material to reduce percolation of rainwater downward into the cell and the escape of radon gas to the atmosphere. A 6-inch thick layer of sand and gravel covers the radon barrier and provides drainage of rainwater away from the top of the cell. An erosion-protection layer comprising of eight inches of riprap was placed on top of the cell, and twelve inches of riprap is layered over the cell’s sloping sides. Nitrate, molybdenum, selenium, uranium, arsenic, chromium, radium, and net gross alpha radioactivity is present in about 0.55 million cubic yards of groundwater, though active remediation is not planned.

The U.S. Department of Energy is responsible for the long-term custody, monitoring and maintenance of the Mexican Hat Disposal Cell site. Because the land is located on the Navajo Nation, the Navajo Nation retains title to the land and tailings.