Much of the area exhibits glacial features, but in the north only the higher peaks were once covered by glaciers. Deep, narrow valleys are prevalent.
Winters are milder and summers cooler than in the interior.
The growing season is 4 months. Many hills and ridges, however, support only a tundra vegetation consisting of sedges and shrubs. There are forests of white spruce and paper birch on the hills overlooking the Yukon and Kuskokwim Rivers. Alpine meadow vegetation is predominant at higher elevations. There are low to moderate populations of brown bears.