Landforms of British Columbia 1976 - Department of Geography
Landforms of British Columbia 1976 - Department of Geography 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 71
Thompson and North Thompson River valleys, on lower Okanagan Lake, and else- where are remnants of silt beds deposited in extensive glacial lakes which occupied depressions along th5 front or sides of the wasting ice lobes as the ice-sheet melted and retreated northward, northeastward, and northwestward across the Thompson Plateau. [References: Rice, H. M. A,, “Geology and Mineral Deposits of the Princeton Map-area,” Geol. Surv., Canada, Mem, 243, 1947; Cockfield, W, E., “Geology and Mineral Deposits of Nicola Map-area,” Gtd. Surv., Canada, Mem. 249, 1948; Duffel], S., and McTaggart, K. C., “Ashcroft Map-area,= GeoL Surv., Canada, Mem. 262, 1952; Jones, A. G., “Vernon Map-area,” Geol. Surv., Canada, Mem. 296, 1959; F&on, R, J., “Merritt Area,” Gtd. SW-V., Camla, Map g-1962; Nasmith, H., “ Late Glacial History and Surficial Deposits of the Okanagan Valley, British Columbia,” B.C. Dept. of Mines, Bull. No. 46, 1962; Mathews, W. H., “Glacial Lakes and Ice Retreat in South Central British Columbia,” Roy. Sot., Cmada, Trans., Vol. XXXVHI, Sec. IV, 1944, pp. 39-57.1 [Photographs: B.C. 356:57; B.C. 498: 37; B.C. 651:20, 68, 83; B.C. 653: 71.1 Along its eastern margin, where the Interior Plateau borders the Columbia Mountains, the upland surface of the plateau is npwarped and rises from 5,000 feet elevation to more than 6,000 feet across a zone that is 30 to 50 miles wide. The deqe of dissection of the upland is greater where the upland surface is higher. There is thus a zone that is transitional between the Interior Plateau cm the west, where the dqree of dissection is low to moderate, and the Columbia Mountains con the east, where dissection and destruction of the elevated upland surface is complete. The transition acme is sufficiently large to deserve a separate designation and is called a “hi
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Thompson and North Thompson River valleys, on lower Okanagan Lake, and else-<br />
where are remnants <strong>of</strong> silt beds deposited in extensive glacial lakes which occupied<br />
depressions along th5 front or sides <strong>of</strong> the wasting ice lobes as the ice-sheet melted<br />
and retreated northward, northeastward, and northwestward across the Thompson<br />
Plateau.<br />
[References: Rice, H. M. A,, “Geology and Mineral Deposits <strong>of</strong> the Princeton<br />
Map-area,” Geol. Surv., Canada, Mem, 243, 1947; Cockfield, W, E., “Geology<br />
and Mineral Deposits <strong>of</strong> Nicola Map-area,” Gtd. Surv., Canada, Mem. 249, 1948;<br />
Duffel], S., and McTaggart, K. C., “Ashcr<strong>of</strong>t Map-area,= GeoL Surv., Canada,<br />
Mem. 262, 1952; Jones, A. G., “Vernon Map-area,” Geol. Surv., Canada, Mem.<br />
296, 1959; F&on, R, J., “Merritt Area,” Gtd. SW-V., Camla, Map g-1962;<br />
Nasmith, H., “ Late Glacial History and Surficial Deposits <strong>of</strong> the Okanagan Valley,<br />
<strong>British</strong> <strong>Columbia</strong>,” B.C. Dept. <strong>of</strong> Mines, Bull. No. 46, 1962; Mathews, W. H.,<br />
“Glacial Lakes and Ice Retreat in South Central <strong>British</strong> <strong>Columbia</strong>,” Roy. Sot.,<br />
Cmada, Trans., Vol. XXXVHI, Sec. IV, 1944, pp. 39-57.1<br />
[Photographs: B.C. 356:57; B.C. 498: 37; B.C. 651:20, 68, 83; B.C.<br />
653: 71.1<br />
Along its eastern margin, where the Interior Plateau borders the <strong>Columbia</strong><br />
Mountains, the upland surface <strong>of</strong> the plateau is npwarped and rises from 5,000<br />
feet elevation to more than 6,000 feet across a zone that is 30 to 50 miles wide.<br />
The deqe <strong>of</strong> dissection <strong>of</strong> the upland is greater where the upland surface is higher.<br />
There is thus a zone that is transitional between the Interior Plateau cm the west,<br />
where the dqree <strong>of</strong> dissection is low to moderate, and the <strong>Columbia</strong> Mountains con<br />
the east, where dissection and destruction <strong>of</strong> the elevated upland surface is complete.<br />
The transition acme is sufficiently large to deserve a separate designation and is<br />
called a “hi
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