Most of the native shrubsteppe habitat in the northern Columbia Basin of eastern Washington has been invaded by cheatgrass (Bromus tectorum) or converted to agricultural lands. Therefore, ecological patterns and dynamics on native shrubsteppe and reestablished grasslands are of high conservation interest. Great Basin pocket mice (Perognathus parvus) from 48 study sites in this region to quantify seed by this species and to determine the influence of habitat type on cheek pouch seed contents. established Conservation Reserve Program (CRP) lands, older CRP lands, and shrubsteppe- B. tectorum constituted the majority of seeds collected from the cheek pouches. CRP habitats. On average, females collected a greater number of seed genera than males did, and pocket mice collected more seed generates as the autumn season progressed. Exotic B. tectorum has become the most frequently collected autumn food resource for pocket mice in the northern Columbia Basin.