The Spectrum Range is one of four large stratovolcanoes that make up the Mount Edziza volcanic complex. A predominantly lava dome overlies a basal shield volcano.
The range is Pliocene in age and on its southwestern flank contains Pleistocene subglacial and subaerial cones and its northwest and southwest sides contain Holocene pyroclastic cones and lava flows. The youngest feature in the volcanic complex could be The Ash Pit.