Rocky Mountain elk (Cervus elaphus nelsoni), Rocky Mountain mule deer (Odocoileus hemionus hemionus), and cattle frequently co-occur on landscapes in the northwestern United States. We hypothesized that niche overlap would be greatest between introduced cattle with either of the 2 native herbivores because coevolution between native elk and mule deer should have resulted in strong patterns of resource partitioning. We observed strong differences among species in use of space, especially elevation, steepness of slope, and use of logged forests. We used 2 temporal windows to examine both immediate (6 h) and long-term (7 days) effects of competition. We noted strong avoidance over a 6-h period among the 3 ungulates. That effect was weaker for the previous 7 days. Cattle were generalists with respect to habitat selection; the 2 native herbivores avoided areas used by cattle. Mule deer and elk avoided one another during the short temporal window (6 h), although spatial differences in habitat use often were not maintained over 7 days. Elk used lower elevations when cattle were absent and moved to higher elevations when cattle were present, indicating shifts in niche breadth and competitive displacement of elk by cattle. We demonstrated strong partitioning of resources among these 3 species, and presented evidence that competition likely has resulted in spatial displacement.