The northern foothills rise from an altitude of about 100 m at the Coastal Plain margin to 200 m at the Brooks Range foothills. The latter display local relief of 600 m or more, with buttes, knobs, mesas, and strike-oriented rivers. Diverse sedimentary rocks of Devonian to Cretaceous age underlie this terrain. Tight folding and overthrusting to the north produce the east-west grain in the topography. The folds are locally truncated by regional erosion surfaces.
Eolian silt overlies much of the foothill topography.
Much of the Colville River basin would be classified as polar desert. Mean annual precipitation is between 200 and 100 mm, predominantly as snow. Despite elevation of 2500 m in the Brooks Range, modern active glaciers are rare. Alaskan rivers that drain active glaciers have much larger sediment loads than those that do not. Thus, the Colville River delivers a load of only 5 to 10 million metric tons per year to the Arctic Ocean.