Landforms of British Columbia 1976 - Department of Geography
Landforms of British Columbia 1976 - Department of Geography
Landforms of British Columbia 1976 - Department of Geography
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The Alberta Plateau in <strong>British</strong> <strong>Columbia</strong> is drained and incised by the Liard<br />
and Peace Rivers and their tributaries. The elevation <strong>of</strong> the Liard River is less than<br />
1,000 f&at the mouth <strong>of</strong> the Fort Nelson River and <strong>of</strong> the Peace River about 1,475<br />
feet at the mouth <strong>of</strong> the Kiskatinaw, and incision has proceeded upstream on tributaries<br />
ayay from the two main rivers. The upland surface <strong>of</strong> the Alberta Plateau has<br />
been only partly dissected, and parts <strong>of</strong> it have been destroyed. Those parts (especially<br />
in the drainage basin <strong>of</strong> the Fort Nelson River) where the surface is reduced<br />
to below 2,000 feet elevation constitute the Fort Nelson Lowland, the boundary between<br />
the two being arbitrarily drawn at the 2,OOO-foot contour, Commonly this<br />
is along a scarp upheld by one <strong>of</strong> the Cretaceous sandstone members.<br />
The upland surface is flat or gently rolling, It lies for the most part between<br />
3,000 and 4,000 feet elevation, and rises to 5,000 feet between the Prophet and<br />
Muskwa Rivers, whereas in northwestern Alberta a large proportion is between<br />
2,000 and 3,000 feet.<br />
Dminage over part <strong>of</strong> the upland surface is poorly organized; there are large<br />
areas <strong>of</strong> mwkeg, and streams meander across the surface eventually to join one <strong>of</strong><br />
the trunk streams. North <strong>of</strong> the Peace River much <strong>of</strong> the drainage is controlled by<br />
the Halfway, Beatton, Sikanni Chief, Prophet, Muskwa, Fort Nelson, and Petitot<br />
Rivers. These have incised themselves below the upland surface into the s<strong>of</strong>t Fort<br />
St. John shale.<br />
Between the Prophet and Muskwa Rivers and north <strong>of</strong> the Sikanni Chief River<br />
there is an area <strong>of</strong> gentle folding in which the rivers are incised into shales that underlie<br />
a capping <strong>of</strong> Sikanni sandstone. As a consequence a distinctive cuesta topography<br />
has been developed. The gentle slopes <strong>of</strong> the cuestas generally face east and are<br />
structurally controlled by the gently east-dipping sandstbne. A steep scarp slope<br />
faces west and falls away into a lower area generally underlain by Fort St. John shale.<br />
The Alaska Highway from Beatton River north for 50 miles is located along the crest<br />
<strong>of</strong> a cuesta, west <strong>of</strong> which a low area about 10 miles wide lies between the cuesta<br />
scarp and the edge <strong>of</strong> the foothills.<br />
The @lateau for the most part is heavily wooded, but along the Peace River<br />
considerable areas, generally below 2,500 feet elevation, are flat or gently rolling and<br />
are only lightly wooded. Much <strong>of</strong> this riverside country has been cleared and is under<br />
cultivation (see Plate XXXIXB)<br />
The plateau was glaciated during the Pleistocene. Ice from the Keewatin centre<br />
<strong>of</strong> accumulation moved southwestward across the Alberta Plateau to the foothills and<br />
left a veneer <strong>of</strong> glacial till containing distinctive Keewatin boulders. After the maxinun<br />
expansion <strong>of</strong> Keewatin ice and its retreat, Piedmont and valley glaciers flowing<br />
eastward from the Rocky Mountains moved outward onto the plateau to leave<br />
moraines in a narrow belt along the eastern edge <strong>of</strong> the foothills. Ice movements can<br />
be interpreted from glacial fluting in the ground moraine and by the elongation <strong>of</strong><br />
drumlins. The minor relief on the plateau surface results from these features.<br />
As the ice waned, channels discharged glacial melhvater into valleys, some <strong>of</strong><br />
which were still blocked by ice. The Peace River valley was occupied by a proglacial<br />
lake which at one stage had its level at approximately 2,750 feet. This old<br />
lake, c&xl Lake Peace, had shorelines now traceable mainly by old beach lines<br />
and gravel occurrences. A lower and younger stage developed when the outlet was<br />
at 2,260 feet. Sediments were deposited in this lake basin to a thickness <strong>of</strong> about<br />
100 feet (see Plate XLIVB). Post-Pleistocene erosion has incised the trunk rivers<br />
to their present elevations.<br />
[References: Mathews, W. H., s Ground-water Possibilities <strong>of</strong> the Peace River<br />
Block,” B.C. Dept. <strong>of</strong> Mines, Ground-water Paper No. 3, 1955; Mathews, W. H.,<br />
“ Quaternary Stratigraphy and Geomorphology <strong>of</strong> the Fort St. John Area,~ B.C.<br />
95<br />
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