Landforms of British Columbia 1976 - Department of Geography

Johnston, W. A., and U&xv, W. L,, “Placer and Vein Gold Deposits of Barker-
ville,” Geol. Surv., Canada, Man. 149, 1926.1
[Photographs: B.C. 4661117; B.C. 516199; B.C. 517:Sl; B.C. 542~6, 33;
B.C. 566:81, 108; B.C. 567:64; B.C. 1409:20, 66.1
Thonqxon Plaieau
The Thompson Plateau (xv Plate XXVIIA) is the most southerly of the
plateau areas in the southern Interior, extending southward for about 1.50 miles
from its boundary with the Fraser Plateau at Clinton and having a width of 75 to
90 miles. It includes much of the familiar and well-travelled country in the vicinity
of Kamloops, Princeton, and Merritt, as well as the Okanagan and North Thompson
Valleys.
The plateau is bounded on the west and south by the Clear Range and the
Cascade Mountains. There is complete transition between the plateau and the
adjoinins mountains because the rise of the plateau surface toward the mountains
is gradual, with progressively higher summit levels and greater dissection of the
plateau surface. The boundary between them is an arbitrary line. On the southeast
and east the plateau is bounded by the Okanagan and Shuswap Highlands, and
there, too, the boundary is transitional. The boundary with the Okanagan Highland,
between @soyax and the Coldstream Valley, is north along the Okanagan Valley
to Penticton, thence northeastward along the northwest side of Little White Mountain
and the west side of the Buck Hills and down McAuley and Harris Creeks to
the Coldstream. From Vernon northwestward the boundary with the Shuswap
Highland is along the Louis Creek fault zc~ne to Barriere and thence northward
along the North Thompson River.
The Thompson Plateau has a gently rolling upland of low relief, for the most
part lying between 4,000 and 5,000 feet, but with prominences of more resistant
rock rising above it to 5.952 feet at Gnawed Mountains, 6,630 feet at Mount
Thynne, 6,684 feet at Cornwall Hills, 5,653 feet at Swakum Mountain, 6,220 feet
at Chuwhels Mountain, 6,218 feet at Lodestone Mountain, 6,545 feet at Pennask
Mount&s, 6,688 feet at Tahaetkun Mountain, 7,227 feet at Mount Brent, and
7,372 feet at Apex Mountain. This upland represents the late Tertiary erosion
surface that has been dissected by the Thompson River and its tributaries and by
the Similkameen and Okanagan Rivers tributary to the Columbia.
The plateau contains a great diversity of rocks; stocks of granitic rock intrude
sedimentary and volcanic formations of Palreozoic age. Flat-lying or gently dipping
early Tertiary (Eocene) laws obscure large areas of older rocks and their gentle
dips to a large extent are reflected by step-like slopes and large unbroken plateau
area.%
The area ws occupied by Pleistocene ice, and a thick mantle of drift covers
bedrock over a large part of it. Movement of the ice over the plateau produced
drumlin-like forms oriented southeasterly and southerly, From a divide just north
of Clinton, ice moved southeastward and southward along the length of the Thompson
River (see Fig. 10). The Pleistocene ended with a gradual stagnation and a
wasting of the ice in place. As a consequence, ice marginal meltwater channels
were quickly made, used temporarily, and then abandoned. On tnany slopes a
series of channels was formed at successively hxwx levels a.s ice surfaces wasted.
Such channels are to be seen cm the walls of the Okanagan Valley and in the Merritt
area. The irregular melting of stagnant ice lobes in the larger valleys created
nwnerous temporary glacial lakes into which silt-laden streams discharged, The
white silt banks seen in many parts of the southern interior, particularly in the
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