Thomomys clusius Coues, 1875 is a geomyid commonly called the Wyoming pocket gopher. Despite a varied taxonomic history, T. clusius is now recognized as a distinct species and as the smallest of 12 species in the genus Thomomys. The species is endemic to Wyoming, where it is restricted to about 1.97 million ha in the southern part of the state. T. clusius is often found in flat areas characterized by Gardner's saltbush (Atriplex gardneri) and fine-textured soils. Although the United States Fish and Wildlife Service concluded in 2010 that listing under the Endangered Species Act was not warranted, state and federal agencies continue to recognize T. clusius as a sensitive species due to its limited distribution and population size.