Mining was mostly by open pit, although there were also some underground mines. Strathmore Minerals Corp. of Kelowna, British Columbia is currently applying for permits to mine properties in the Gas Hills district. Little Mountain district In the Little Mountain mining district on the west side of the Bighorn Mountains, Big Horn County, Wyoming, uranium was produced from 1955 to 1970 from paleokarst breccias in the Madison Limestone of Mississippian age. The uranium occurs as carnotite and tyuyamunite. Shirley Basin Uranium was discovered in the Shirley Basin, Carbon County, in 1955. Production began in 1960 from underground and open-pit mines. Mining by in-situ leaching began in 1961, the first in-situ leach mining of uranium in the United States. The ore occurs as roll fronts in Eocene sandstone of the Wind River Formation, as uraninite with pyrite, marcasite, hematite, calcite, and organic matter. Crooks Gap district The Crooks Gap district of Fremont County contains uranium ore in fluvial sandstones of the Eocene Battle Spring Formation. Most uranium deposits are in the Wasatch, with ore zones containing uraninite and pyrite. Oxidized ores include uranophane, meta-autunite, and phosphuranylite. Current Activity By 2006, the only active uranium mine in Wyoming was the Smith Ranch-Highland in-situ leaching operation in the Powder River Basin, owned by Power Resources, Inc., a subsidiary of Cameco. The mine produced 907 tonnes of yellowcake (uranium oxide concentrate, U3O8) in 2006, making it the leading uranium producer in the United States. In October 2007, Energy Metals Corp. applied for a Nuclear Regulatory Commission (NRC) permit to start an in-situ leach mine at the Moore Ranch deposit in Campbell County in the Powder River Basin. Energy Metals is a subsidiary of Uranium One. The permit application is the first NRC application since 1988 for a new uranium recovery facility. The Moore Ranch deposit contains an estimated 5.8 million pounds (2600 tonnes) of uranium oxide. The uranium will be absorbed onto ion-exchange resin beads at the mine; the beads will be shipped to existing facilities of Power Resources Inc. (Cameco) in Wyoming and Nebraska for recovery of the uranium. In September 2014, Uranerz Energy shipped the first uranium concentrate from its Nichols Ranch mine in the Powder River Basin. Nichols Ranch is an in-situ leach mine, using oxygenated water and sodium bicarbonate to dissolve the uranium. The uranium is recovered at the surface onto resin beads by ion exchange. The resin beads are