The long-tailed pocket mouse, Chaetodipus formosus, occurs in part of the southwestern United States, as well as in Baja California, Mexico. In Utah, the species occurs in the western portion of the state, where it is common in rocky desert areas with gravelly soils. Long-tailed pocket mice are nocturnal and dormant during the winter, retreating to underground burrows during periods of inactivity.
Females typically give birth to an average of five young during late spring, although no young may be produced during years of low precipitation. The long-tailed pocket mouse primarily eats seeds, but other plant materials and insects are consumed as well. Similar to other pocket mouse species, the long-tailed pocket mouse has external fur-lined cheek pouches used for temporary food storage. Long-term seed storage occurs in underground burrows.