Landforms of British Columbia 1976 - Department of Geography

locally, as a rule only on the northeastern sides of peaks above 5,000 feet ($ee Plate
XXXIXA) . By and large the foothills display landforms only slightly modified by
glaciation.
[References: Hage, C. O., “ Geology Adjacent to the Alaska Highway between
Fort St. John and Fort Nelson,” C&l. Surv., Cmzda, Paper 44-30; Pelletier, B. R.,
“Geology, Tetsa River,” Geoi. Sure., Canada, Map 29.1959; Pelletier, B. R.,
“ Triassic Stratigraphy, Rocky Mountain Foothills,” Geol. Surv., Canada, Paper
60-2; Stott, D. F., “ Cretaceous Rocks between Smoky and Pine Rivers,” Geol.
Surv., Canada, Paper 60.16; Pelletier, B. R,, and Stott, D, F., “ Trutch Map-area,”
Geol. Surv,, Canada, Paper 63-10; Mountjoy, E. W., “ Mount Robson (Southeast)
Map-area,” Gal. Surv,, Canada, Paper 6 l-3 1.1
[Photographs: B.C. 1204:52,58,69,73; B.C. 1950:74.1
B. Interior Plains
Somewhat more than 10 per cent of the area of British Colombia lies east of
the Rocky Mountain Foothills. This part of northeastern British Columbia, corn-
prising plateaus, plains, prairies, and lowlands, is essentially an area of low relief. It
is part of the Interior PI&m, which is an extensive region of central Canada extending
from the International Boundary to the Arctic Coast and from the eastern foothills
of the Rocky Mountains to the edge of the Canadian Shield.
In northeastern British Columbia the boundary between the Cordilleran Region
and the Interior Plains is easily defined between the higher longitudinal ridges of
the Rocky Mountain Foothills and the lower plateaus or westas of the plains. The
boundary follows a series of in echelon thrust faults which separate the more closely
folded and faulted rocks of the foothills from dominantly flat-lying or gentle east-
dipping rocks of the plains. The boundary crosses the Liard River west of the mouth
of Toad River and runs southeastward to cross the Alaska Highway at Mile 371,
thence southward on the west side of Prophet River past Klingzut Mountain and Bull-
head Mountain to cross the Peace River between Hudson Hope and Portage Moon-
tain. The boundary continues southeastward between Bulbnoose Mountain (6,627
feet) and Gwillim Lake to the junction of Belcourt Creek and Wapiti River.
The Interior Plains of northeastern British Columbia are underlain by sedimen-
tary rocks very largely of Cretaceous age. The rocks for the most part belong to the
Fort St. John Grciup, comprising a thick secluence of shales with several sandstone
members near the top, the Donvegan Formation, which is essentially a hard cliff-
forming sandstone, and the Smoky Group, comprising interbedded shales and sand-
stones. The rocks are flat lying or gently dipping, and as a consequence extensive
plateau areas and coestas develop on the more resistant sandstone members (xe
Plate XXXVIII). The interbedded shale is soft and more readily eroded, and one
finds Fort St. John (Buckinghorse) shale underlying most of the low areas. The
gentle warps and fold structures of the plains geology manifest themselves in
correspondingly gentle hills, domes, plateaus, cuestas, and other landforms.
The Interior Plains in northeastern British Columbia are represented by the
Alberta Plateau and its subdivision, the Fort Nelson Lowland.
ALBERTA PLATUU
A flat and gently rolling upland (see Plates XXXVIII, XXXIXB, and XLIVB)
lies east of the Rocky Mountain Foothills and in large part stands at elevations between
3,000 and 4,000 feet. It is a natural continuation into British Columbia of
the Alberta Plateau,* a physiographic unit which is also present in northern -4lberta.
. came,,, c,, S”d Malkdm, Wyatt, ad. SW~K cczumfcL bfem. 108, 191% Iv. X7-19.
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