Landforms of British Columbia 1976 - Department of Geography

The Interior Plateau is almost entirely drained by the Fraser River and its trib-
utaries; only minor drainage is to the Skeena, Peace, and Columbia Rivers.
The Interior Plateau consists of the following units: the Fraser Basin, the
Nechako Plateau, the Fraser Plateau, and the Thompson Plateau, and to the east of
these the Quesnel H’ghland, the Shuswap Highland, and the Okanagan Highland
which lie along the western side of the Colombia Mountains,
Fraser Basin
The Fraser Basin is an irregularly shaped area of low relief lying below the
surface of the Nechako Plateau. On the northeast the basin merges in the Rocky
Mountain Trench at an elevatioti of about 2,000 feet; elsewhere its boundary is
drawn along the generalized line of the 3,000.foot contour. The basin extends from
Williams Lake northward to McLeod Lake and from Fraser Lake eastward to Sinclair
Mills.
Its flat or gently rolling surface lies for the most part below 3,000 feet and is
covered with drift and has few exposures of bedrock. The surface is incised by the
Fraser River and its tributaries; the river at Prince George is at an elevation of l&50
feet. On much of the surface the drainage is poorly organized, and numerous lakes
and poorly drained depressions are preset,
The area was occupied by ice whose movement created drumlins and drumlinlike
forms in the glacial drift. The many hundreds of drumlins present indicate an
eastward and northeastward movement of ice in the area north of Prince George,
and a movement northward from Quesnel (see Fig, 10).
Eskers were formed by m&water during the waning stages of glaciation in the
Fraser Basin. The largest is the MacKinnon compound esker north of Carp Lake
about 35 miles long in a northeasterly direction. The Stuart River compound esker
is 25 miles long and I to 2% miles wide, and west of Prince George the Bednesti
compound esker about 15 miles long was formed by southeastward-flowing m&water
during a stage in the existence of glacial lakes.
As the ice melted, the pre-glacial drainage channels were blocked with drift
and wasting ice, and, in basins centred about Prince George, Fort St. James, and
Vaoderhoof, ice-dammed lakes formed at levels below 2,600 feet. Varved clays
were deposited in these glacial lakes, above the surface of which the tops of some
drumlins projected as islands. The glaciaI-lake clays have been shown by soil surveys
to underlie more than 750,000 acres. The area west and north of Prince George
occupied by the three glacial lakes has been called the iVechko P&z,*
The shape of the Fraser Basin and the slope of surfaces within it indicate that
the basin was eroded by a northward-flowing ancestral Fraser River+ which flowed
through the McLeod Lake gap and was a tributary of the Peace River. The ancient
Fraser River history is complex, as may be judged from the fact that early Tertiary
(Eocene and Oligocene) sediments were depositcd by southward-flowing streams$
and that later Tertiary (Miocene) sediments, at least from the mouth of the West
Road River north, were deposited by northward-flowing streams.8 The river development
was further complicated as late as the Pliocene by eruptions of lava, whose
effects are unknown.
Until a complete study of the Fraser River has been made, it will not be possible
to date the reversal of flow of the river between Prince George and Riske Creek and
to state definitely whether it was reversed by a rapidly eroding southward-flowing
* .4mstm”~, J. lx.. su.3 *iLwr, n. w., .4m. JOW. sci., “01. 246, w&3, p. 28%
+ I.W. rh”alS, B.C. “qlf. 0, M?“e.L &II. NO, 3, ,940, p, 3.
$ LW, PO”&a, B.C. r&St. Of Mm.5 B”U No. 11 p*rt “), 19.31, *p. 39, 40, a.
9 Lay, PO”~,slS, B.C. De@. 0, Mi”m, B”,L NO. I, @art “1, ,941, pp. 5% 53: mpr, n. UC, !3m,, SW”.,
Cmldrl, Map 4smo.
67