Landforms of British Columbia 1976 - Department of Geography

The Horserunch Runge is a discrete unit within the Dease Plateau. It is a range
composed of sedimentary gneisses in a doubly plunging anticline whose western front
along the valley of the Dease River is a fault. The range stands well above the rest
of the Dease Plateau, with most peaks rising to more than 6,000 feet and the highest
to 7,300 feet. Steep-walled cirques which scallop the eastern side of the range are
occupied in several instances by tarn lakes.
[Reference: Gabrielse, H.!” McDame Map-area,” Geol. Surv., Cmmfu, Mem.
319, 1963.1
Stikine Ranges
The Stikine Ranges (see Plates XXIIIA and XXIIIB) extend northwestward
from their southern end at the Chukachida River for about 275 miles, their northern
end being in the Yukon 45 miles north of the border. Their greatest width is 85
miles, between the Three Sisters Range and Dal1 Lake.
They are bounded on the southwest by the Stikine Plateau along a sinuous line
which, at about 5,000 feet elevation, separates gently rolling plateau from maturely
dissected mountains. On the northeast the ranges are bounded by the Dease Plateau
and Kechika Ranges. The boundary with the latter is a prominent through valley,
a lineament which leaves the Trench at Sifton Pass and runs past the west end of
Denetiah Lake, past Dal1 Lake to Deadwood Lake.
The ranges have a core of granitic rocks which constitute the Cassiar batholith,
a composite batholith of Jurassic or Cretaceous age. The granitic rocks intrude
folded sedimentary and volcanic rocks of Paleozoic and Mesozoic age.
The ranges are drained by tributaries of the Finlay, Stikine, Kechika, Turn-
again, Dease, and Liard Rivers. Many of these valleys are wide, drift-filled, and
widely flaring, and the mountains are broken by them into irregularly shaped ranges.
The highest peaks in the ranges are in the granitic mountains between Thudaka
Creek and Turnagain River. The highest elevation (8,900 feet) is in the Thudaka
Range southwest of Obo Lake; others of 7,900 and 8,000 feet elevation lie between
it and Sharktooth Mountain (8,765 feet) just west of Dal1 Lake. Northward from
King Mountain (7,900 feet) at the head of Turnagain River are Glacial Mountain
(7,565 feet) in the Three Sisters Range and Quartz Mountain (7,548 feet) near
McDame. There is little diminution of summit height northward to Simpson Peak
(7,130 feet), which lies just south of the Alaska Highway at Swan Lake (2,760 feet).
The peaks and ridges above 6,000 feet are sharply scalloped by cirque glaciers.
The cirques are especially prominent on the north and northeast sides of ridges and
peaks whose southern slopes may be quite gentle and rounded (see Plate XXIIIA).
Below 6,000 feet the ridges and summits are rounded and the forms are softened
and less harsh. South of Sharktooth Mountain the mountain valleys are narrow
and have fairly steep glaciated walls, and it is evident that valley glaciation was
more intense in the ranges there. North of the Turnagain River the valleys become
progressively wider and more gently flaring. There the country is characterized by
rounded summits and wide drift-filled valleys. The elevation of the valley bottoms
is between 3,500 and 4,500 feet, so that although the peaks may be rugged the
relief is not excessive.
At the head of the Eagle River, some 8 to 15 miles westerly from Eaglehead
Lake, there is a group of five or more cinder cones of Pleistocene age. “The cones
are generally elliptical in plan and conical in section . . . their symmetrical shape
and long, black, talus slopes make them conspicuous landmarks in the region.“*
Although the country was covered by the Pleistocene ice-sheet, the obvious
glacial effects are largely those of late-stage cirque activity.
* Hanson, G., and McNaughton, D. A., Ge02. SWJ., Canada, Man. 194, 1936, p. 11.
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