Here is a look back at the timing of key events in the history of the Edgemont uranium mining industry:
1951: Uranium deposits are discovered in a canyon wall near Edgemont.
1952: The U.S. Atomic Energy Commission opens an ore sampling and buying station in Edgemont, one of many Western sites where the federal government buys uranium to fuel its growing stockpile of nuclear weapons.
1953: The Chicago North Shore and Milwaukee Railroad reorganizes and emerges as a subsidiary of a new holding company, Susquehanna Corporation, which will soon come to dominate Edgemont’s uranium industry.
1955: Mines Development Inc., a subsidiary of Susquehanna Corp., builds a uranium mill in Edgemont.
1960: Edgemont’s population hits 1,772, a 53 percent increase from 1950.
1971: The U.S. Atomic Energy Commission ends its uranium buying program.
1972: Operations cease at the Edgemont uranium mill.
1974: Susquehanna Corp. subsidiary Mines Development Inc. sells the Edgemont mill and associated mineral rights to the Tennessee Valley Authority for $6 million. The TVA hopes to mine uranium for a planned expansion of nuclear power generation but never reopens the Edgemont mines or mill.
1975: Susquehanna Western Inc., which had operated uranium mines near Edgemont, is sold by its parent company Susquehanna Corp. to Solution Engineering Inc. for $9.76 million.
1978: Congress passes and President Jimmy Carter signs the Uranium Mill Tailings Radiation Control Act, which tasks the U.S. Department of Energy with cleaning up mill waste, known as "tailings," and other contaminated material at uranium processing sites including the Edgemont mill.
1989: Decommissioning activities are completed at the Edgemont uranium mill. The work includes the hauling of 4 million tons of sand-like waste tailings to an excavated disposal cell a few miles south of the mill. The project, estimated to cost more than $40 million, is funded by the TVA, a federally owned corporation. Millions more are spent by the federal government to remove tailings that were used as fill around the foundation of Edgemont homes.
2000: Congress passes and President Bill Clinton signs amendments to the 1990 Radiation Exposure Compensation Act to make more people — including some in South Dakota — eligible for payments of up to $100,000 each for medical problems associated with uranium mining and milling.
2006: Powertech Uranium (later to become Azarga Uranium) purchases Denver Uranium and its mining rights in the Edgemont area. A mining project is soon proposed based on the “in situ” method, in which a solution is pumped underground to dissolve and lift uranium from rocks and pump it to the surface. The proposal is still pending regulatory approval.
2010: Edgemont’s population drops to 774, its lowest since the town’s population was first measured at 816 by the 1910 census.
2015: A team contracted by the Environmental Protection Agency conducts tests of water in the Cheyenne River and nearby streams northwest of Edgemont to determine if the waterways are being polluted by abandoned uranium mines. Results are pending.