Landforms of British Columbia 1976 - Department of Geography

[References: M&zKenzie, J. A., “ Geology of Graham Island,” GeoZ. ,%rv.,
Cunu&, Mem. 88, 1916; Sutherland Brown, A., “ Physiography of Queen Char-
lotte Islands,” Can. Geog. Jour., Vol. LXI, No. 1, 1960, pp. 30-37; Sutherland
Brown, A., and Nasmith, H., “ Glaciation of the Queen Charlotte Islands,” Gun.
Field Naturalist, Vol. 76, No. 4, 1962, pp. 209-219; Map No, 2F, “Queen
Charlotte Islands,” B.C. Dept. of Lands md Forests, 1954, 1 in. to 4 mi. Complete
coverage also available on N.T.S. sheets at lz50,OOO with lOO-foot contours.1
Vancouver Island Mountains
All of Vancouver Island except for a narrow strip of lowland along the
eastern and northern coast is included within the Vancouver Island Mountains of
the Insular Mountains. The lowland areas, the Nanaimo Lowland and Nahwitti
Lowland, are parts of the Coastal Trough and lie below 2,000 feet elevation, their
boundary with the mountains being drawn along the line of the 2,000-foot contour.
The Vancouver Island Mountains consist of the Vancouver Island Ranges
comprising the dominantly mountainous part of the Island; the Alberni Basin, a
low-lying area inland frnm the head of Alberni Canal; and the Estevan Coastal
Plain, a very narrow strip of coastal plain along the western and southwestern coast.
The highest peaks of the Vuncouver ZsZand Ranges are the Golden Hinde
(7,219 feet), Elkhorn Mountain (7,200 feet), Mount Victoria (7,095 feet), and
Mount Colonel Foster (7,000 feet), all in the central part of the Island. Summit
elevations diminish to northwest and southeast, with no peaks higher than 5,000
feet lying northwest of Nimpkish Lake or southeast of Cowichan Lake. Between
these two lakes lie the most rugged ranges on the Island.
The Vancouver Island Ranges (Lyee Plate JIIA) are composed of a hetero-
geneous group of pre-Cretaceous sedimentary and volcanic rocks folded about
northwesterly trending axes and intruded by numerous granitic batholiths. The
mountains arc the result of the mature dissection of a Tertiary erosion surface of
low relief (see p. 45). Extensive remnants of this surface are to be seen in the
vicinity of the Nanaimo Lakes in Strathcona Park, on San Juan Ridge, and at low
levels south of the San Juan River (see N.T.S. Sheets 92 F/l and F/11). Near
the Nanaimo Lakes the surface has an elevation of about 3,000 feet, with monad-
necks rising as much as 2,000 feet above it. Westward toward the centre of the
Island, dissectinn is more and more advanced and less of the Tertiary surface
remains. It was the erosion leading to formation of this Tertiary surface that
supplied the Oligocene and early Miocene sediments which were deposited on a
coastal plain along the west coast of the Island. Pre-Pleistocene uplift and dissection
of the surface produced an extremely rugged topography in the central and northern
parts of the Island, where uplift was greatest. This topography was modified by
glaciation during the Pleistocene, at which time high serrate peaks were sculptured
by alpine glaciers, upland surfaces below 4,000 feet* were modified by the
continental ice-sheet, and lower valleys were deepened and modified by the erosion
of valley glaciers.
Conspicuous features of southern Vancouver Island are fault-line scarps and
fault-controlled valleys such as those of Cowichan Lake, San Juan River, Loss
Creek, Bear Creek, and Leech River. In the Cowichan Lake area+ it has been
shown that structurally controlled valleys follow post-Upper Cretaceous fault zones.
[References: Hoadley, J. W,, “ Geology and Mineral Deposits of the Zeballos-
Nimpkish Area,” Geol. Surv., Canada, Mem. 272; Gunning, H. C., “ Buttle Lake
Map Area,” Geol. Surv., Canada, Sum. Rept., 1930, Pt. A, pp. 56-78; Gunning,
* Hoadley, J. W., Geol. Sure., Canada, Mem. 212, p. 1.
? Fyles, J. T., B.C. Dept. of Mims, Bull. No, 37, p. 9.
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