The Spectrum Range, named for its extensive colorful solfataric alteration, is one of four large composite volcanoes that make up the Mount Edziza-Spectrum Range volcanic complex, in which a predominately rhyolitic lava dome complex overlies a basal basaltic shield volcano. The Pliocene center contains Pleistocene subglacial and subaerial cones on the SW flank and Holocene pyroclastic cones and lava flows on the NW and SW sides. The Mess Lake Lava Field on the NW flank consists of young lava flows and tephra from three pyroclastic cones, including The Ash Pit, which may be the youngest volcanic feature of this complex.