The Hanna Basin Mining District site (Site) includes historic mine features within several watersheds south of Leo, Wyoming where Tronox once operated. The Site consists of the following three sites: Hanna Basin (coal), North Hanna Basin (uranium), and North Hanna (phosphate). The Site is located in Carbon County, Wyoming, and is about 35 miles long by 20 miles wide in the south-central portion of the state. This basin, a structural and sedimentary basin, is sandwiched between the Granite, Seminoe, and Shirley Mountains to the north, the Medicine Bow Mountains to the south, the Rawlins uplift to the west, and Carbon Basin to the east.
Hanna Basin contains thick coal beds. The north boundary of the Hanna Basin coalfield is Medicine Bow River, six miles north of the town of Hanna while the North Platte River formed the approximate western boundary of the coalfield about 15 miles west of Hanna. The Hanna coalfield is approximately 750 square miles. A 2001 study by the U.S. Geological Survey also found conditions of this basin were favorable to support natural gas accumulation. Trace elements also found in Hanna coal include uranium, arsenic, mercury, and selenium. As for phosphate in the area, a 2003 Bureau of Land Management publication describing mineral resources in a geographic area that includes Hanna Basin states that limited phosphate resources were available in the general area, but no known commercial production of phosphate ore had occurred. Rather, a number of phosphate mining and processing operations were situated near the Wyoming-Idaho state line, Lincoln County specifically.
The town of Hanna is located in the southeastern portion of Hanna Basin. This town was established in 1889 by Union Pacific Railroad when it began to conduct coal mining operations. Coal mining in the basin has been relatively non-stop since about 1889 either through underground mining, stripping mining, or exploratory drilling.
