At the southern end of the Mount Edziza volcanic complex, volcanism constructed the Spectrum Range three to 2.5 million years ago. Named for its extensive colouration, this nearly circular lava dome is up to thick and more than wide with a basaltic shield volcano forming its broad base. Since its formation, the Spectrum Range lava dome has been deeply cut by erosion, forming an extensive valley system. This valley system exposes large comendite and trachyte lava flows of the dome, including faults of a hidden wide caldera.