Landforms of British Columbia 1976 - Department of Geography

The Parsnip and Finlay Rivers were involved in the erosion of the Rocky
Mountain Trench, in which late Cretaceous or Paleocene rocks (Sifton Formation)
occur. It is concluded that their regional courses as well as that of the Peace River
were established very early in the Tertiary, and that all three are antecedent to the
late Tertiary (Pliocene) uplift of the Rocky Mountains. Also the upper Finlay
River, above Ware, is antecedent to the latest uplift of the Omineca Mountains in
the late Tertiary.
At an early stage in the development of the Peace River system, it is thought
that the Nechako Plateau, Fraser Basin, and upper Fraser River above Dome Creek
drained northward through the Crooked River depression into the head of the Peace
River. The history of the capture of this drainage by the southward-flowing Fraser
River is not known, but it was an important event in the evolution of both the Peace
and Fraser River systems.
YUKON RIVER DRAINAGE BASIN
A small part of northern British Columbia, some 10,000 square miles compris-
ing parts of the Tagish Highland, Tesljn Plateau, Nisutlin Plateau, Kawdy Plateau,
and Cassiar Mountains, lies within the drainage basin of the Yukon River.
The drainage area is dominated by Tutshi Lake (2,320 feet), Tagish Lake
(2,152 feet), Atlin Lake (2,192 feet), Gladys Lake (2,915 feet), and Teslin Lake
(2,239 feet), into which most of the drainage flows and from which, on the Yukon
side of the border, the Lewes and Teslin Rivers flow northward into the Yukon River.
These lakes provide a stable base level of erosion, and the headward erosion of drain-
age tributary to them is at a low rate. In contrast, the rapid headward erosion of the
Taku River and its tributary the Nakina has led to the capture of streams formerly
draining northward either into Atlin, Gladys, or Teslin Lakes, It is expected that
these Pacific rivers will continue to expand their drainage basins at the expense of the
Yukon River system, and that further captures of northerly flowing tributary streams
will be effected.
Most of the Yukon River drainage basin in British Columbia is drained by small
streams, of which the Jennings River is the largest. It rises at Jennings Lakes (3,800
feet) in the Cassiar Mountains and flows westward for the most part across the
Kawdy Plateau for 70 miles into the south end of Teslin Lake.
FRASER RIVER DRAINAGE BASIN
The Fraser River rises at Moose Lake in the Park (Main) Ranges of the Rocky
Mountains, flows northwestward to the Rocky Mountain Trench at Jackman and
along the Trench to Sinclair Mills (see Plate XXII). Thence it swings around the
north end of the Cariboo Mountains and flows southward through the Fraser Basin
and Fraser Plateau, being flanked at various heights above the river by gravel and
silt terraces. Southward from Quesnel the river becomes more and more constricted
as the river becomes more deeply incised below the surface of the plateau which rises
to the south. At Soda Creek, the downstream limit of early navigation on the upper
Fraser, the river flows at 1,390 feet elevation, with the valley walls rising steeply to
the floor of the Fraser Basin at about 3,000 feet. Downstream from this point the
river is constrained by a gorge 1,000 feet or more deep incised in the bottom of the
main valley. Below Big Bar the river leaves the Fraser Plateau and begins to flow
through more mountainous country, with the Camelsfoot Range on the west and
the Marble Range on the east (see Plate XLIIIA). Farther south the river has the
Pacific Ranges on the west and the Hozameen and Skagit Ranges on the east and
south (see Plate XIIIA) . Its total length from headwaters to the sea is 850 miles.
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