[3][4] Covered in dense temperate rainforest on its western exposures, the range rises to heavily glaciated peaks, including the largest temperate-latitude ice fields in the world.

The Pacific Ranges are the southernmost subdivision of the Coast Mountains, extending from the lower stretches of the Fraser River to Bella Coola.

Further north the northwesterly structural trend of the Coast Mountains lies partly in a large continental rift responsible for the creation of several volcanoes.

The first event began 130 million years ago when a group of active volcanic islands approached a pre-existing continental margin and coastline of North America.

[6] As the North American Plate drifted west and the Insular Plate drifted east to the old continental margin of western North America, the Bridge River Ocean eventually closed by ongoing subduction under the Bridge River Ocean.

[6] Named after the Coast Mountains, the basement of this arc was likely Early Cretaceous and Late Jurassic intrusions from the Insular Islands.

[8] This started a period of mountain building that affected much of western North America called the Laramide orogeny.

[9] In particular a large area of dextral transpression and southwest-directed thrust faulting was active from 75 to 66 million years ago.

[8] Much of the record of this deformation has been overridden by Tertiary age structures and the zone of Cretaceous dextral thrust faulting appears to have been widespread.

[6] This molten granite burned the old oceanic sediments into a glittering medium-grade metamorphic rock called schist.

[6] Volcanism began to decline along the length of the arc about 60 million years ago during the Albian and Aptian faunal stages of the Cretaceous period.

[7] This resulted from the changing geometry of the Kula Plate, which progressively developed a more northerly movement along the Pacific Northwest.

[6] Volcanism along the entire length of the Coast Range Arc shut down about 50 million years ago and many of the volcanoes have disappeared from erosion.