The Rainbow Range is an eight-million-year-old (Miocene) massive peralkaline shield volcano in the Anahim Volcanic Belt which includes the lower but similar Itcha and Ilgachuz Ranges. The shield has a diameter of is now heavily eroded by glaciers carving into the volcanic rock and sands over millions of years. The volcanism that created the shield is not well studied and is poorly understood. It is thought to be the result of the North American Plate passing over a hotspot, similar to the one feeding the Hawaiian Islands, known as the Anahim hotspot. The only real separate volcanic peak associated with the Rainbow Range is Anahim Peak which sits on its northeast flank. Other peaks in the range are other high eroded remnants of the shield, including Beef Peak, TaiaTaeszi Peak, Mount MacKenzie and Tsitsutl Peak , which is the highest summit of the Rainbow Range.