Ranges from steep slopes, high peaks, and ridges at the higher elevations to gently sloping and benchy terrain in the lower elevations. The most prominent features are Chimney Peak, Donaca Lake and the Middle Santiam River. Native fish populations thrive in both river and lake.

Much of this wilderness is forested with mature stands of old-growth Douglas-fir, western redcedar and western hemlock at lower elevations and true firs near ridgelines.