Landforms of British Columbia 1976 - Department of Geography

Dept. of Mines and Petroleum Remmx?s, 1963; Camsell, C., and Malcolm, Wyatt,
“Mackenzie River Basin,” Geol. Swv., Canada, Mem. 108, 1919; McLeam, F. H.,
and Kindle, E. D., “Geology of Northeastern British Columbia,” Geol. Surv.,
Canada, Mem. 259, 1951.1
[Photographs:~ B.C. 1090:60;’ B.C. 1197:96, 111;’ B.C. ‘1204:58; B.C.
1206:78; B.C. 1207:13,32; R.C.A.F.T25R:l92.]
Fort Nelson Lowland
The dissection of the Alberta Plateau by the Liard and Peace Rivers and their
tributaries has produced lowland areas, below 2,000 feet elevation, that are designated
the Fort Nelson Lowland and the Peace River Lowland. The Peace River
Lowland extends into British Columbia as a small digitate area along the main
river and its tributaries, It occupies a large area in northern Alberta.
The Fort Nelson Lowland (see Plate XLA) is an area of extremely low relief,
in places flat and in places very gently rolling, that lies below an elevation of 2,000
feet. The boundary with the Alberta Plateau is the lh~e of the ‘Z,mO-foot contour,
which in many places is along a sandstone scarp formed by one of the several Cre
taceous sandstone members underlying the plateau. The lowland lies within the
drainage basins of the Fort Nelson, Hay, and P&tot Rivers, but over large areas
drainage is not well established and lakes and muskegs abound (zee Plate XLB) .
The Fort Nelson and Petitot Rivers are incised as much as 500 feet below the general
level of the lowland, which is at about 1,5w feet elevation. Elsewhere streams
meander across a surface which has remained unmodified since its emergence from
the covering of Pleistqcene ice.
Between the Fort Nelson and P&tot Rivers and extendiig northwestward from
Kotcho Lake is an area of somewhat higher ground 100 miles long and 30 miles wide
that reaches an elevation of 2,465 feet on the Etsho Escarpment. It could be coo.sidered
as an outlier of the Alberta Plateau.
A topographic feature which extends southwestward from Petitot River at the
123rd meridian to the Fort Nelson River is an alignment of cuesta ridges reaching a
height of 2,376 feet at their highest. The ridges have an eastward-facing scarp slope
and a gentle west-dipping dip slope. This line of cuestas is the topographic expression
of Mississippian limestone and Permian chert members brought to the surface
by the Bovie fault, which extends southward into British Columbia from the Northwest
Territories,* where it has been geologically mapped for 25 miles north of the
border.
The lowland is for the most part underlain by flat or gently dipping Cretaceous
shales and sandstones, but exposures of bedrock are rare. The topography for the
most part reflects the gentle stmchwes in the underlying rocks. However, geologic
mapping in the Yukon indicates that between the eastern edge of the Liard Plateau
and the Bovie fault there is an area of some structural complexity in which the flat
structures of the plains give way to northeasterly trending folds and faults which are
not fully expressed topographically. It is apparent that the eastern limit of mountain
&uctures does not coincide precisely with the physiographic boundary of the plains.
Any further subdivision of the plains in this area should be made on the basis of
gdogy.
During the Pleistocene the Fort Nelson Plain was covered by a continental icesheet
(the Keewatin) whose centre of accumulation lay west of Hudson Bay. Ice
moved westward and southwestward across the lowland, transporting boulders and
drift from Precambrian areas far to the east. The lowland is veneered with glacial
drift upon which is impressed a well-developed lineation parallel to the direction of
l “O”&S, R, ,. w., and rami% D, K.. Gd. SW”., ca”mi*, B.per 594.
96