Spectrum Range

The Spectrum Range, formerly gazetted as the Spectrum Mountains and the Rainbow Mountains, is a small mountain range in Cassiar Land District of northwestern British Columbia, Canada. Located at the southern end of the Tahltan Highland, it borders the Skeena Mountains in the east and the Boundary Ranges of the Coast Mountains in the west. The Spectrum Range is surrounded by the Arctic Lake Plateau in the southwest and the Kitsu Plateau in the northwest, both of which contain volcanic features such as cinder cones. It lies at the southern end of the Mount Edziza volcanic complex which includes the two neighbouring plateaus, as well as Mount Edziza and the Big Raven Plateau to the north. The mountain range is drained on all sides by streams within the Stikine River watershed and, unlike Mount Edziza to the north, contains relatively small separate glaciers. Mount Edziza Provincial Park is the main protected area surrounding the Spectrum Range.

The Spectrum Range is the eroded remains of a large lava dome whose original surface is only preserved as a few small remnants on the summits of the higher peaks. This dome formed between 3.5 and 2.5 million years ago during the second magmatic cycle of the Mount Edziza volcanic complex and was originally more than 25 kilometres (16 miles) wide. Much of the dome consists of massive rhyolite and trachyte lava flows, but relatively minor basalt lava flows erupted later during the dome's formation. These lava flows form the nearly circular group of pyramidal peaks and long, narrow-crested ridges comprising the Spectrum Range; the basalt flows mainly cap the higher peaks. Volcanism in the last 2.5 million years has mainly occurred on the northwestern and southwestern sides of the Spectrum Range, but the precise age of the latest eruption is unknown.