Landforms of British Columbia 1976 - Department of Geography

upper Fraser River is the result of river piracy on a grand scale at a time that is not
precisely known, but that possibly was post-Miocene.*
The Pleistocene and Recent history of the river is not fully documented. During
the Pleistocene the entire area was completely covered with ice which, as it melted,
gave rise to streams that occupied temporary meltwater channels at various heights
above the present river and its tributaries. South of the ice divide in the vicinity of
Dog Creek (seep. 102), at a time when the valley of the Fraser River was blocked
with ice to a level of about 3,500 feet, meltwater escaped by way of Canoe Creek
and the falls at the head of The Chasm, across the head of Bonaparte River into
Deadman River, and built a huge delta into glacial Lake Kamloops, ultimately escap-
ing southward through the Okanagan Lake valley.
Main valleys were blocked during the waning of the ice, and pro-glacial lakes
were formed along the sides or against the front of the wasting ice. The levels of
these lakes fell as the ice melted and their outlets were lowered. The lakes dimin-
ished in size and eventually disappeared as the ice melted completely and drainage
was re-established.
In the vicinity of Quesnel, Prince George, Vanderhoof, and Fort St. James,
extensive areas were occupied by pro-glacial lakes, whose surface levels ranged from
2,600 down to 2,450 feet. The Thompson River valley from Spences Bridge up-
stream as far as Shuswap Lake was occupied by glacial Lake Kamloops, whose ele-
vation ranged from 1,800 to 1,600 feet. Three stages in the development of glacial
lakes in the Nicola River valley in the vicinity of Merritt are delineated by deltas
and wave-cut benches. The lakes, named Lake Quilchena at 3,450 feet, Lake Ham-
ilton at 3,150 feet, and Lake Merritt at 2,450 feet, drained northward into the Salmon
and Thompson Rivers and southward into the Tulamecn and Similkameen Rivers,
because the Fraser River valley was still occupied by ice. The lakes disappeared
with the disappearance of valley ice, and as the Fraser River re-incised its valley in
a deep fill of glacial materials which had been deposited during the Pleistocene.
When the complex history of development of the Fraser River system is fully
known, the interplay of river piracy, late Tertiary and Pleistocene vulcanism, and
glacial diversion will make a most interesting story.
COLUMBIA RIVER DRAINAGE BASIN
The Columbia River drainage basin has a total area of 259,000 square miles,
of which 39,550 square miles arc in British Columbia. The river has a total length
of about 1,210 miles, of which the upper 459 miles lie within the Province.
The Columbia River has its source in Columbia Lake (elevation 2,664 feet)
in the Rocky Mountain Trench. It flows northwestward for 195 miles through the
wide but gradually narrowing valley of the Trench before making its great bend
around the northern end of the Selkirk Mountains. From there it flows southward
between high ranges of the Selkirk and Monashee Mountains to enter Upper Arrow
Lake (elevation about 1,400 feet) at Arrowhead. Downstream from the outlet of
Lower Arrow Lake the Columbia is joined by its chief tributary, the Kootenay, at
Castlegar and flows southward past Trail to cross the International Boundary into
Washington.
The Kootenay River rises in the Rocky Mountains and enters the Rocky Moun-
tain Trench at Canal Flats. It flows southeast through the Trench into Montana
and around a loop past Libby and Banners Ferry, to reenter British Columbia south
of Creston and flow into the south end of Kootenay Lake at 1,740 feet elevation.