The Diamond Peak Wilderness is home to black-tailed deer, mule deer, and elk. In winter, the mule deer migrate eastward out of the wilderness to the sage desert, while black-tailed deer and elk drop down the west slope. Black bear and small mammals including marmots, snowshoe rabbits, squirrels, pine martens, foxes, and pikas inhabit the area all year long. The raven, Clark's nutcracker, Oregon jay, and water ouzel frequent the forest and streams year-round. Bufflehead and goldeneye ducks occasionally nest near the lakes.