Landforms of British Columbia 1976 - Department of Geography

ones, and widening and deepening the valleys, the essential topographic framework
was nevertheless present before the coming of the ice. Great volumes of glacial
materials were deposited in the form of an almost universal mantle of drift on valley
sides and bottoms, as outwash plains of glacial sands and gravels, and as ice marginal
deposits in the waning stages of glaciation.
The land stood at a high level before the onset of the Pleistocene. The great
load of glacial ice, with a thickness of as much as 8,000 feet in some areas, depressed
the land with respect to its earlier level. With the melting of the ice and the
consequent lightening of the load, the land has risen in Recent time, essentially to
its former position. The rise has been unequal, ranging from a few tens of feet
to a few hundred. Streams have been rejuvenated because of the rise, with the
result that box canyons have been cut in the lower courses of many of them.
[References: “ Guidebook for Geological Field Trips,” prepared by GeoZog&
CUZ D&z&oti CZub, Vancouver, March, 1960; Kerr, F. A. “ Lower Stikine and
Western Iskut River Areas,” Geol. surv., Cuflu&.r, Mem. 246, 1948; Kerr, F. A..
“ Taku River Map-area,” GeoZ. Surv., Cum& Mem. 248, 1948.1
II. INTERIOR SYSTEM
The interior of British Columbia, between the Coast Mountains and the
Rocky Mountains, contains a great diversity of landforms. These include low-
lying plains and basins, plateaus in varying stages of dissection, highlands, and
mountains of many sorts, all parts of the Interior System. Despite divergencies in
physical appearance, common denominators of geology and of physiographic
development bring coherence to the group as a whole, and distinguish it from the
flanking systems to the west and east,
On the west the Interior System is flanked by continuous mountains from
the 49th parallel to the Yukon Border. These are the Cascade Mountains and the
Coast Mountains of the Western System. Separation of the two systems is readily
made along a sinuous boundary running southeastward from the south end of Atlin
Lake to Ningunsaw Pass, thence to Aiyansh and Terrace, and southward along
the eastern side of the Coast Mountains to Charlotte Lake, the north end of Taseko
Lakes, Lillooet, Lytton, and Keremeos.
On the east the Interior System is flanked by the Liard Plateau north of
Liard River and by the Rocky Mountains south of Liard River. The boundary
separating the two systems extends between the Liard Plain and the Liard Plateau,
skirts the northern Rocky Mountains, and runs southeastward along the eastern
side of the Rocky Mountain Trench to the 49th parallel.
The Interior System takes in a very large part of British Columbia and the
Yukon, and for convenience of description three major subdivisions of that part
west of the Rocky Mountain Trench have been made. The Northern Plateau and
Mountain Area is very largely in the Yukon, but part of it extends into northern
British Columbia as the Yukon Plateau and Liard Plain. The Central Plateau
and Mountain Area largely lies north of latitude 55 degrees north. Its southern
boundary, between Whitesail Lake and the mouth of the Nation River, is along the
northern edge of the Nechako Plateau. The Southern Plateau and Mountain Area
includes large areas of plateau in central and southern British Columbia and the
highlands and mountains in the southeastern part of the Province.
NORTHERN PLATEAU AND MOUNTAIN AREA
The Northern Plateau and Mountain Area extends into northern British
Columbia as the southern part of the Yukon Plateau, comprising parts of the Tagish
Highland, of the Teslin and Nisutlin Plateaus, and of the Liard Plain.
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