The Piñon Mouse is a large-eared, white-footed mouse with a tail as long as, or slightly longer than, the total length of its head and body. Its scanty fur is a cinnamon color.
The food habits of these mice are not well known. In California, specimens examined in midsummer had been eating primarily insects and spiders although by late summer their diet was predominantly acorn mast. In Colorado, the winter diet is primarily juniper berries.
Breeding habits are likewise poorly known. In southwest Colorado, breeding occurs from April through September and in Arizona, from February through November. Litter size ranges from three to six, with an average of four. At birth, the young are hairless and the eyes and ears are closed. Between 2 and 3 weeks of age the eyes and ears open. Their fur grows in by 2 weeks of age.
This species is restricted to rocky situations in cedar forests on the canyon slopes and floors in the Palo Duro Canyon region. Areas in the juniper-mesquite association that have large, massive boulders seem to support the highest populations. In Guadalupe Mountains National Park, the species is rarely found in the juniper and pinyon woodlands.
In Texas, known from the caprock at the eastern edge of the high plains in Armstrong, Briscoe, and Randall counties and in the Trans-Pecos from the Guadalupe Mountains in Culberson County.