The Fraser Canyon is a stretch of the Fraser River where it descends rapidly through narrow rock gorges in the Coast Mountains en route from the Interior Plateau of British Columbia to the Fraser Valley. Colloquially, the term "Fraser Canyon" is often used to include the Thompson Canyon from Lytton to Ashcroft, since they form the same highway route which most people are familiar with, although it is actually reckoned to begin above Williams Lake, British Columbia at Soda Creek Canyon near the town of the same name.

Geology

The canyon was formed during the Miocene period (23.7-5.3 million years ago) by the river cutting into the uplifting Interior Plateau. From the northern Cariboo to Fountain, the river follows the line of the huge Fraser Fault, which runs on a north-south axis and meets the Yalakom Fault a few miles downstream from Lillooet. Exposures of lava flows are present in cliffs along the Fraser Canyon. They represent volcanic activity in the southern Chilcotin Group during the Pliocene period and the volcanic vents of their origins have not been discovered.

Geography

The canyon extends 270 kilometres (170 mi) north of Yale to the confluence of the Chilcotin River. Its southern stretch is a major transportation corridor to the Interior from "the Coast", with the Canadian National and Canadian Pacific Railways and the Trans-Canada Highway carved out of its rock faces, with many of the canyon's side-crevasses spanned by bridges and trestles. Prior to the double-tracking of those railways and major upgrades to Highway 1 (the Trans Canada Highway), travel through the canyon was even more precarious than it is now. During the frontier era it was a major obstacle between the Lower Mainland and the Interior Plateau, and the slender trails along its rocky walls - many of them little better than notches cut into granite, with a few handholds - were compared to goat-tracks.

North of Lytton, it is followed by BC Highway 12, then from Lillooet to Pavilion by BC Hwy 99 (the farther end of the Sea-to-Sky Highway, though not carrying that name in this area). The British Columbia Railway line follows the same stretch of canyon from Lillooet to just beyond Pavilion. Between there and the mouth of the Chilcotin River there are only rough ranching roads, and the terrain is a mix of canyon depths flanked by arid benchland and high plateau. Between Pavilion and Lillooet, the river's gorge is at its maximum depth, with the river throttled through a series of narrow gorges flanked by high cliffs, though still flanked above those cliffs by wide benchlands which stand on the foreshoulder of the mountain ranges flanking the gorge.

credited to wikipedia