Aboveground mounds and underground burrows are multifunctional and influence behavior and habitat of Gunnison's prairie dogs (Cynomys gunnisoni). Four colonies were studied June–September 2004 to examine function of mounds with respect to vigilance for predators, and to estimate magnitude of soil mixed by these prairie dogs. Frequency of vigilance atop mounds increased in taller vegetation and individuals at perimeters of colonies oriented toward the outside more frequently than to the interior of colonies. Mounds accounted for an average of 10,374 kg of soil/ha that was excavated from the burrow. This mass of subsoil moved to the surface and the 7–17 m³ of air in the burrow make the geomorphic effect of prairie dogs potentially significant.