The Aleutian Range consists of rounded east-trending ridges surmounted at intervals by rugged volcanoes. The mountains were heavily glaciated during the Pliestocene epoch. This Section is bordered to the north by the Bristol Bay Lowlands where the Aleutian Mountains become increasingly submerged southwestwardly, forming the Aleutian Islands. Lithology and Stratigraphy. The Aleutian Mountains consist of segments of the peninsular terrane, which includes mildly folded and faulted late Mesozoic sedimentary rocks, locally intruded by granitic rocks and surmounted at intervals by volcanic piles dating from the late Tertiary to the recent age.
Many volcanoes have calderas.
A major fault extends along the north side of the eastern part of the range, separating the sedimentary rocks from the granitic batholith on the north. Dominant soils are Typic Haplocryands and Typic Vitricryands. Most of the glacial deposits are mantled with volcanic ash and scoria and are very easily eroded. Soils are shallow on mountain peaks, rock escarpments, and colluvial slopes. Some depressions are filled with fibrous peat.