Landforms of British Columbia 1976 - Department of Geography

“ Striae, roches moutonn&s, and like phenomena indicate that this ice sheet
moved in a generally southerly direction, but with a tendency to follow the main
topographical features such as the Purcell and Rocky Mountain Trenches. Thus
the ice on the east flank of the Purcell Range moved southeast and that on the west
flank southwest. It seems probable that the land surface overlain by the ice was one
of high relief, with the principal ridges and valleys in much the same positions as
those of today. Over these mountains and ridges and over the ice filled transverse
valleys the ice sheet, although thick, apparently moved as a unit. As it thinned down,
the underlying topography assumed control and a stage of valley and alpine glaciation
ensued. During this stage the ice sheet broke up into lobes which flowed down
the principal
“
valleys.
the ice sheet in the floor of the Rocky Mountain Trench disappeared
by a process of stagnation, breaking up into units and melting away in situ. The
results of this process are apparent in the huge kettles, kames, etc., that line much
of the floor of the trench.“*
[References: Schofield, S, J., “ Geology of Cr?nbrook Map-area,” Geol. Swv.,
Conada, Man. 16, 1915; Walker, J. F., “Geology and Mineral Deposits of
Windermere Map-area,” Geol. Surv., Camda, Man, 148, 1926; Walker, J. F.,
“Kootenay Lake District,” Geol. Surv., Cmmda, Sum. Rept., 1928, Pt. A, pp.
119-13.5: Evans, C. S., “ Brisco-Dogtooth Map-area,” Gevl. Surv., Cmmdo, Sum.
Rept., 1932 Pt. AH, pp. 106-176; Rice, H. v, A., “Nelson Map-area (East
Half),” Geol. Surv., Canada, Man. 228, 1941; Reesor, J. E., “ Lardeau Area,”
Gd Surv., Canada, Map 12.1957; Reesor, .I. E,, “ Dewar Creek Map-area with
Special Emphasis on the White Creek Batholith,” Gal. Swv., Cmudu, Man. 292,
1958; Leech, G. B., “St. Mary Lake Area,” Gal. Swv., Canada, Map 15-1957;
Rice, H. M. A., “ Cranbrook Map-area,” Geol. Swv., Canada, Mem. 207, 1937.1
[Photographs: B.C. 898:80, 82; B.C. 899:3, 18.1
III. EASTERN SYSTEM
The East& System is the easternmost of the three primary subdivisions of the
Canadian Cordillera in British Columbia and flanks the Interior System along its
eastern side. The boundary between the two lies along the Rocky Mountain Trench
and alpng the eastern side of the Liard Plain. On its eastern side the Eastern System
in turn is flanked by the Interior Plains of Central Canada. The northeastern part
of the Province extends across the full wiflth of the Eastern System and into the
Interior Plains, but southeast of the Narraway River the eastern margin of the
Eastern System Iies in Alberta, and for a length of 450 miles only the western part
of the System is in British Columbia.
The Eastern System is a mountainous belt extending northwestward along the
entire length of the Province from the 49th parallel for 900 miles to the 60th parallel.
It has a width of 50 miles at its narrowest section at the head of the Murray River
and a width of 90 miles between Sifton Pass and the Tetsa River.
The Eastern System consists of the Arctic Mountain Area, the Mackenzie
Mountain Area, and the Rocky Mountain Area, The Mackenzie Mountain Area
lies largely in the Yukon and District of Mackenzie, and only a small part of one
of its subdivisions, the Liard Plateau, extends southward into British Columbia as
far as the Liard River, The northern limit of the Rocky Mountain Area is the Liard
River, from which it extends southeastward for 850 miles to the 49th parallel. The
Rocky Mountain Area is divided into the Rocky Mountains and the Rocky Moun-
l Ri.2, H. hf. A, Gd S”,“., can~d‘7, Man. 228, 19.41, p. 3.
82