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The Spectrum Range is a mountain range in Cassiar Land District of northwestern British Columbia, Canada.

Names and etymology
The Spectrum Range was labelled as the Rainbow Mountains on a BC Lands map published in 1929 which was followed by renaming of the mountain range to the Spectrum Mountains in 1945. In 1954, the form of name was changed to the Spectrum Range in accordance to the Geological Survey of Canada memoir 247 published in 1948. These names for the mountain range refer to its multicoloured rocks; pale green, light grey and white rocks weather to bright hues of orange, yellow and red.

Location
The Spectrum Range lies east of the Boundary Ranges of the Coast Mountains and west of the Skeena Mountains at the southern end of the Tahltan Highland in Cassiar Land District. To the southwest, the Spectrum Range is surrounded by the Arctic Lake Plateau which includes adjacent volcanic features such as Outcast Hill, Wetalth Ridge, Exile Hill, Nahta Cone and Tadekho Hill. The Kitsu Plateau surrounds the Spectrum Range to the northwest and includes the Mess Lake Lava Field which comprises geologically recent lava flows and tephra from three pyroclastic cones. To the northeast, the Spectrum Range is surrounded by the Obsidian and Artifact ridges, which extend east from the Spectrum Range and Kitsu Plateau, respectively.

The Spectrum Range lies at the southern end of the Mount Edziza volcanic complex which includes the adjacent Arctic Lake and Kitsu plateaus, as well as Mount Edziza and the Big Raven Plateau to the north. This volcanic complex consists of a group of overlapping shield volcanoes, stratovolcanoes, lava domes and cinder cones that have formed over the last 7.5 million years. It contains an intermontane plateau that is overlain by four central volcanoes along its north–south trending axis; the Spectrum Range is the southernmost and third oldest central volcano.

Structure
Extending outward from the central portion of this nearly circular group of pyramidal peaks and long, narrow-creasted ridges is a crudely radial drainage system characterized by deeply incised valleys. Talus and felsenmeer deposits cover large portions of the valley slopes which rise to broad, rounded crests of the interfluvial ridges. These ridges are the eroded remains of a once continuous lava dome whose original surface is only preserved as a few small remnants on the summits of the higher peaks. The ridges and peaks decrease in elevation away from the central portion of the mountain range.

The current, approximately 19 km dome comprising the Spectrum Range originally had a width of more than 25 km as indicated by the existence of erosional remnants around its northern and southwestern edges. It was also originally higher than its current elevation of 2430 m as evidenced by the thick, gently dipping lava flows comprising the summit of Kitsu Peak, the highest point of the Spectrum Range. The original volume of the Spectrum Dome is estimated to have been about 101 km3 based on restoration calculations of the original surface.

Glaciation
The Mount Edziza volcanic complex was covered by a regional ice sheet during the Pleistocene which receded and advanced periodically until about 11,000 years ago when deglaciation was essentially complete in a steadily warming climate. This warming trend ceased about 2,600 years ago, causing glaciers to advance from the Spectrum Range and elsewhere along the volcanic complex as a part of the neoglaciation. The present trend towards a more moderate climate put an end to the neoglacial period in the 19th century which has resulted in rapid glacial recession throughout the Mount Edziza volcanic complex. This rapid glacial recession is apparent from the lack of vegetation on the barren, rocky ground between the glaciers and their trim lines which are up to 2 km apart.

Unlike Mount Edziza which has an approximately 70 km2 ice cap, the Spectrum Range is covered with relatively small separate glaciers that occupy cirques on most peaks greater than 2130 m in elevation. The largest glacier is Nagha Glacier which initiates just northwest of Yeda Peak and terminates at the head of the valley between Yagi Ridge and the Kitsu Plateau. Yeda Glacier, an informally named glacier at the head of Ball Creek, existed south of Yeda Peak in 1988.

Drainage
As a part of the Mount Edziza volcanic complex, the Spectrum Range is drained on all sides by streams within the Stikine River watershed. Kitsu Creek is a northwest-flowing stream originating from the northern side of Kitsu Peak. It contains one named tributary, Nagha Creek, which also flows northwest from the Spectrum Range. Tadekho Creek originates from between Kuno and Yeda peaks and flows to the northwest. Kitsu and Tadekho creeks both flow into Mess Creek which is a northwest-flowing tributary of the Stikine River.

The Little Iskut River originates from Little Ball Lake just south of Kounugu Mountain and flows to the northeast where it collects Stewbomb Creek flowing east from the Spectrum Range. Stewbomb Creek contains one named tributary, Artifact Creek, which originates adjacent to Kitsu Peak and flows through a valley between Artifact and Obsidian ridges. Ball and More creeks both flow south from the southern end of the Spectrum Range near Yeda Peak, the former of which contains an east-flowing tributary called Chachani Creek. The Little Iskut River and Ball and More creeks are tributaries of the Iskut River which flows south and then west into the Stikine River.

Background
The Spectrum Range is part of the Northern Cordilleran Volcanic Province, a broad area of shield volcanoes, lava domes, cinder cones and stratovolcanoes extending from northwestern British Columbia northwards through Yukon into easternmost Alaska. The dominant rocks comprising these volcanoes are alkali basalts and hawaiites, but nephelinite, basanite and peralkaline phonolite, trachyte and comendite are locally abundant. These rocks were deposited by volcanic eruptions from 20 million years ago to as recently as a few hundred years ago. The cause of volcanic activity in the Northern Cordilleran Volcanic Province is thought to be due to rifting of the North American Cordillera driven by changes in relative plate motion between the North American and Pacific plates.

Basement
Underlying nearly all of the Spectrum Range is the Kounugu Member of the Nido Formation, one of many stratigraphic units comprising the Mount Edziza volcanic complex. Basaltic lava flows of this Pliocene geological member are exposed around the perimeter of the Spectrum Range and are limited only to the area south of the broad east–west valley of Raspberry Pass. They issued from at least four separate eruptive centres that have been either deeply eroded or have been completely destroyed by erosion.

Also underlying the Spectrum Range are flat-lying basalt flows of the Raspberry Formation, the oldest unit of the Mount Edziza volcanic complex. This geological formation is of late Miocene age and originated as a composite shield volcano that erupted lava from at least three locations near Raspberry Pass. The Nido and Raspberry formations are underlain by the Stikinia terrane, a Paleozoic and Mesozoic suite of volcanic and sedimentary rocks that accreted to the continental margin of North America during the Jurassic.

Composition
The Spectrum Range consists mainly of trachyte, comendite and pantelleritic trachyte and rhyolite of the Spectrum Formation, the fifth oldest stratigraphic unit of the Mount Edziza volcanic complex. More than 90% of these volcanic rocks were erupted as lava while less than 10% of them were erupted as pumice and pyroclastic flows; the lava is in the form of flows that individually reach thicknesses of up to 200 m.

Caldera
In the middle of the Spectrum Range at the base of the volcanic pile is a buried depression that may be a caldera or an irregular collapse structure. It occurs within a roughly circular area about 9.6 km in diameter and likely formed by collapse of a shallow magma chamber during eruption of the Spectrum Formation lavas. At least 1 km of vertical caldera collapse may have resulted if the magma chamber was similar in diameter to this circular area, but poor exposure of the depression and of the bounding vertical faults has given fragmentary evidence. The southwestern side of a northwesterly-trending, nearly vertical fault adjacent to Stewbomb Creek has dropped at least 90 m and is cut by parallel rhyolite dikes.

Eruptive history
The rocks comprising the Spectrum Range were deposited by volcanic eruptions during the second magmatic cycle of the Mount Edziza volcanic complex 3.1 million years ago.

Provincial park
The Spectrum Range lies at the southern end of Mount Edziza Provincial Park, a protected area founded in 1972 to showcase the volcanic landscape.