Landforms of British Columbia 1976 - Department of Geography

YUKON PLATEAU
Tagish Highland
Extending between the Coast Mountains and the Yukon and Stikine Plateaus,
from the Taku River northward into the Yukon, is a mountainous area, intermediate
in elevation and relief between the plateaus on the east and the mountains on the
west. It is a belt of transition between plateau and mountains, in which there are
numerous seas of gently sloping upland. In this belt the late Tertiary erosion sur-
face, which forms the upland surface of the plateaus, is warped upward to the west,
and becomes progressively more dissected westward, so that in the Coast Mountains
few, if any, undissected upland surfaces remain.* Where the belt is sufficiently
wide, it is designated the Tagish Highland? (see Plates XIIIB and XVB for an
example of the gradation of plateau through highland into mountains, by increasing
dissection of the upland surface). The highland has a maximum width of 25 miles
measured northwest from Fantail Lake and a minimum width of about 5 miles
at Taku River.
The Tagish Highland is underlain very largely by Paleozoic and Mesozoic
sedimentary and volcanic rocks, folded about northwesterly trending axes and
lying east of the eastern margin of the Coast Intrusions. The Tagish Highland
is characterized by areas of relatively smooth, gently rolling upland surface lying,
for the most part, between 5,000 and 6,500 feet, with local peaks rising above.
The high points within the highland are largely domed mountains standing between
6,000 and 7,000 feet elevation, the highest being Paradise Peak (7,215 feet) east
of Sloko Lake. The area is incised to an elevation of about 2,200 feet by rivers
tributary to Atlin and Tagish Lakes, and to elevations of less than 500 feet by
Taku River and its tributaries. The valleys are wide and U-shaped, and many to
the west of Atlin are occupied by lakes, The relief in the Tagish Highland is
variable, depending on whether it is measured in relation to the drainage of tl&
Taku River or of the Yukon River. It ranges from about 3,500 feet to as much
as 5,000 feet.
The area was covered by ice during the Pleistocene, and at its maximum
extent the Cordilleran ice-sheet reached an elevation between 6,000 and 6,500
feet. In the area west of Atlin Lake the direction of ice movement was northerly
and northwesterly.
During deglaciation, cirque basins were eroded largely on the northern and
eastern sides of the peaks and ridges, generally at elevations above 5,500 feet.
[References: Wheeler, J. O., “ Whitehorse Map-area,” Geol. Surv., Canada,
Mem. 312, 1961; Aitken, J. D., “Atlin Map-area,” Geol. Surv., Canada, Mem. 307,
1959; Kerr, F. A., “ Taku River Map-area,” Geol. Surv., Canada, Mem. 248,
1948, pp. 16, 40-41.1
[Photographs: B.C. 687:12; B.C. 899:53, 79, 92, 102, 107.1
Teslin Plateau
The Teslin Plateau extends southward from the Yukon into British Columbia.
On the wgst the plateau is bordered by the Tagish Highland along a line running
southeast from Talaha Bay on Tagish Lake to Atlin Lake and thence to the south
end of Atlin Lake. From there the Teslin Plateau is separated from the Taku
Plateau on the south by the valley of O’Donnel River, Silver Salmon River, and
Taysen Creek to Nakina. From Nakina the boundary runs northeastward to the
* Kerr, F. A., GeoZ. Swv., Canada, Man. 248, 1948, p. 113.
t The word “highland ” was suggested by its use in Washington for a physiographic unit which extends
northward into British Columbia. See discussion on page 72.
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