Landforms of British Columbia 1976 - Department of Geography

Derangement of drainage occurred during the Pleistocene, when, in the waning
stages of ice occupation, ice-tongues blocked valleys, pro-glacial lakes were formed,
and valleys were filled with outwash materials to depths of hundreds of feet.
MACKENZIE RIVER DRAINAGE BASIN
The Liard and Peace Rivers and their tributaries, parts of the Mackenzie River
system, drain some 108,000 square miles in northern and northeastern British
Columbia. The greater part of the Omineca and Cassiar Mountains, the Liard
Plain and Plateau in British Columbia, the Rocky Mountains north of Monkman
Pass, the Rocky Mountain Foothills in British Columbia, and the Alberta Plateau
and Fort Nelson Plain lies within the drainage basin of the Mackenzie River.
only a small part of the Liard River lies within British Columbia-a length
of about 250 miles, from a point a few miles above Lower Post at the confluence of
the Dease River to a point 25 miles below the junction of the Fort Nelson River.
The elevation of the Liard River at Lower Post is 1,965 feet, at Whirlpool Canyon
just below the mouth of Coal River it is 1,500 feet, at the junction of Toad River 15
miles below Hells Gate it is 1,000 feet, and it is about 750 feet where the Liard
crosses the border into the Territories.
Downstream from Lower Post, along its course across the Liard Plain, the Liard
River flows on an easy gradient, incised 50 to 75 feet below gravel terraces on either
side (see Plate XVA). Downstream from the Alaska Highway Crossing at Mile
496 the Liard enters a canyon, skirts around the northern end of.the Rocky Moun-
tains, and runs through a succession of rapids before resuming a more placid flow
downstream from Hells Gate.
In its course through British Columbia the Liard River is joined from the
south by the following major tributaries: the Dease River rising at Dease Lake
(elevation 2,425 feet) and flowing 115 miles northeastward, the Kechika River
flowing northwestward for 145 miles from Sifton Pass (elevation 3,273 feet), the
Toad River flowing 105 miles from an elevation of 5,000 feet at its head, and the
Fort Nelson River rising in the northern Rocky Mountains at an elevation of 4,500
feet near Mount McCusker and flowing 3 10 miles northward into the Liard.
The headwaters of the Liard River, upstream from the confluence of the
Kechika, are on the western side of the Rocky Mountains and the Liard Plateau.
The course of the river was established before the uplift of the mountains. Its
position was maintained during mountain-building in the Paleocene and again
during the re-elevation of the region in the Pliocene.
The Peace River is formed by the junction at Finlay Forks (elevation almost
2,000 feet) of the Finlay and Parsnip Rivers, both of which rise on the western side
of the Rocky Mountains, the Finlay at Thutade Lake (elevation 3,264 feet) at the
southern end of the Spatsizi Plateau on the western side of the Omineca Mountains,
and the Parsnip (elevation 4,000 feet) southwest of Mount Vreeland. Downstream
from Finlay Forks the Peace River cuts through the Rocky Mountains (see Plate
XLIVA) and Rocky Mountain Foothills without serious interruption by rapids,
except in the Ill-mile length of the Peace River Canyon at Hudson Hope, where
the river cuts across the eastern margin of the foothills. The present canyon is the
result of Pleistocene diversion of the river from its earlier course, which was through
the Rocky Mountain Portage north of the canyon.
East of the mountain front the river receives the Halfway and Beatton Rivers
as major tributaries on the north side and the Pine and Kiskatinaw Rivers on the
south. In the stretch downstream from Hudson Hope the river is flowing just
below 1,500 feet elevation, incised some 700 feet or more below the adjacent plateau
surfaces (see Plate XLIVB) .
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