From Miller and others (1998): "Shishaldin Volcano, located near the center of Unimak Island, is a spectacular symmetrical cone about 16 km in diameter at the base. The mountain, which rises to a summit 2857 m above sea level, is the highest peak in the Aleutian Islands and has a small summit
crater from which a steady cloud of steam is emitted. The upper 2000 m is almost entirely covered by perennial snow and ice. It is flanked to the northwest by 24
monogenetic parasitic cones (Fournelle, 1988). The Shishaldin cone is less than 10,000 year old and is constructed on a glacially eroded remnant of an ancestral soma and shield (Fournelle, 1988), which in turn are underlain by
volcaniclastic rocks of probable late Tertiary age (McLean and others, 1978). Fournelle (1988) suggests that the basement may consist, at least in part, of plutonic rocks."