This feature is part of the Savonoski River Cluster of volcanoes, as defined by Hildreth and others (2004) 
. From Hildreth and others (2004) 
: "Rainbow River Cone (Peak 3980) is a small basaltic volcano (51.8-53% SiO2) perched on a basement ridge east of Rainbow River, 15 km NW of Mount Denison. The glacially sculpted cone, 1 km wide with 330 m relief, consists of radially dipping stacks of thin lavas and breccia sheets intercalated with scoria falls, well exposed on bounding cliffs, cut by numerous dikes, and gutted by a northerly cirque. Lavas and ejecta contain phenocrysts of plagioclase, orthopyroxene, clinopyroxene, olivine, and Fe-Ti oxides. An ice-scoured lava plateau (390 +/- 39 ka) extends 1 km SE from the cone."