Uranium mining in Wyoming was formerly a much larger industry than it is today. Wyoming once had many operating uranium mines, and still has the largest known uranium ore reserves of any state in the U.S. At the end of 2008, the state had estimated reserves dependent on price: 539 million pounds of uranium oxide at $50 per pound, and 1,227 million pounds at $100 per pound. Wyoming has produced a total of 84,000 tonnes of uranium, and from 1995 until 2015, actually led the nation in production. Total reserves as of 2015 still amounts to 141,000 tonnes at 0.065 percent grade. However, since the early 1990s, this production has been by the in situ leach method. The Wyoming uranium mining industry was hard-hit in the 1980s by the drop in the price of uranium. When the uranium price dropped, the uranium-mining boom town of Jeffrey City lost 95% of its population in three years. Powder River Basin US Geological Survey geologist David Love discovered uranium in 1951 near Pumpkin Buttes, about 25 miles northeast of Midwest, Wyoming. Other deposits were found along a 60-mile northwest-southeast trend in the southwest part of the Powder River Basin, and production began in 1953. The deposits are roll fronts in fluvial sandstones of the Eocene Wasatch Formation and underlying Paleocene Fort Union Formation. The principal ore minerals are uraninite, coffinite, metatyuyamunite, and carnotite. Gangue minerals are calcite, gypsum, pyrite, iron oxide, and barite. Northern Black Hills Uranium was discovered in 1952 in Cretaceous sandstones of the Inyan Kara Group near its outcrop in Crook County, Wyoming, near the northeast edge of the Black Hills. Production began in 1953. Ore minerals are uraninite and coffinite in unoxidized sandstone, and carnotite and tyuyamunite in oxidized sandstone. Gangue minerals in unoxidized deposits are pyrite, marcasite, and calcite; in oxidized deposits calcite and iron oxide. No mining has taken place in the Northern Black Hills district in recent years, but recent high uranium prices have brought new exploration drilling to the area. Gas Hills The Gas Hills district, straddling the Natrona-Fremont county line in central Wyoming, was discovered on 9 Sept. 1953 by Neil McNeice, which led to the development of the Luck Mc Mine and others, with ore production beginning in 1955. The ore consisted of lenticular bodies of meta-autunite, uraninite, and coffinite in fluvial arkosic sandstones in the upper Wind River Formation of Eocene age.