This ecoregion is composed of rounded, folded and faulted sedimentary ridges intermittently surmounted by volcanoes. The mountains were heavily glaciated during the Pleistocene epoch. A marine climate prevails, and the region is generally free of permafrost. Many soils formed in deposits of volcanic ash and cinder over glacial deposits and are highly erodible. Vegetation cover commonly consists of dwarf scrub communities at higher elevations and on sites exposed to wind, and low scrub communities at lower elevations and in more protected sites.

The Aleutian Islands in southwestern Alaska is composed of a chain of sedimentary islands (eroded from older volcanic formations) that are crowned by steep volcanoes. Maritime climate prevails. The region is south of the winter sea ice pack and is generally free from permafrost. Vegetation cover mainly consists of dwarf scrub communities at higher elevations and on sites exposed to wind, and of graminoid herbaceous communities in more protected sites.

The Ahklun Mountains are located in the northeast section of the Togiak National Wildlife Refuge in southwest Alaska. They extend southwest from the Kanektok and Narogurum Rivers to Hagemeister Strait and Kuskokwim Bay and support the only existing glaciers in western Alaska. The Ahklun Mountains are the highest Alaskan mountain range west of the Alaska Range and north of the Alaska Peninsula: some summits in the range have many glaciers. To the west is the Kuskokwim River and to the east are the Bristol Bay lowlands.

The Ahklun Mountains have many lakes, some more than 1,300 feet (400 m) deep. The mountains cover approximately 80 percent of the Togiak National Wildlife Refuge. The refuge also contains tundra and coastal plains.