Abert's squirrels (Sciurus aberti) are reported to be dependent on ponderosa pine (Pinus ponderosa) forests for food, cover, and nest sites. Introduced Abert's squirrels in the Pinaleño Mountains of Arizona, however, occupy forests that contain little to no ponderosa pine. We documented diet and tree use of Abert's squirrels in mixed-conifer forests of the Pinaleño Mountains using observations of marked animals. Individuals ate similar food items as Abert's squirrels in ponderosa pine forests, including seeds, inner bark, buds, and fungi, but 5 conifer species were used as food sources. Douglas-fir (Pseudotsuga menziesii) and southwestern white pine (Pinus strobiformis) were the most frequently eaten conifer species. Abert's squirrels also were observed in all tree species. Our results suggest that the dependence of Abert's squirrels on ponderosa pine is not as strong as previously reported.