Landforms of British Columbia 1976 - Department of Geography

Columbia. The mountains along the 49th parallel from Cultus Lake eastward to
the valley of the Similkameen River make up three ranges of the Cascade Moun-
tains. They extend northward to Lytton, a distance of 85 miles, and arc bordered
on their western side by the Fraser River and the Fraser Lowland.
The Cascade Mountains are separated by the Fraser River from the Pacific
Ranges of the Coast Mountains on the north (see Plate XIIIA). The Cascade
Mountains on the east are flanked by and merge in the Kamloops Plateau. Their
western boundary is clearly defined by the Fraser River, but their eastern margin is
a transition zone through which summit elevation progressively diminishes and
the degree of dissection decreases as the Kamloops Plateau is approached, The
boundary separating mountains and plateaus follows the Nicoamen River from its
mouth, thence more or less along the 5,000-foot contour west of Prospect Creek to
the head of Tulameen River and the head of Skagit River, thence down Copper
Creek and east from its mouth across to the Ashnola River, thence northeastward
past Crater Mountain to the valley of the Similkameen River.
The Cascade Mountains comprise the Skagit Range extending along the 49th
parallel between Cultus Lake and the Skagit River, the Hozameen Range between
Skagit River and Pasayten River, its extension northward from Coquihalla River to
Lytton, and the Okanagan Range between Pasayten River and Similkameen River.
The Cascade Mountains are composed of Paleozoic and Mesozoic sedimentary
and volcanic rocks, strongly folded and metamorphosed and intruded by granitic
batholiths. The summits of the peaks and ridges attain an approximately uniform
elevation, and it has been inferred that the mountains have resulted from the dissec-
tion of a late Tertiary erosion surface.*
In Oregon and Washington the highest peaks in the Cascade Mountains rise
above the general summit level. They are the peaks of Mount Baker (10,827 feet),
Glacier Peak (10,436 feet), Mount St. Helen, Mount Hood, etc., and all are vol-
canic cones built up by the accumulation of Pleistocene and Recent lava and ash
upon the Tertiary erosion surface.
In British Columbia the highest peaks are Mount Outram (8,000 feet),
Stoyoma Mountain (7,486 feet), Tulameen Mountain (7,499 feet), Grass Moun-
tain (7,580 feet), and Frosty Mountain (7,950 feet) in the Hozameen Range;
Silver Peak (6,808 feet), Mount Cheam (6,913 feet), and Welch Peak (7,733
feet) in the Skagit Range; and Crater Mountain (7,522 feet), Lakeview Mountain
(8,261 feet), Snow Mountain (8,507 feet), and Haystack Mountain (8,541 feet)
in the Okanagan Range. These peaks represent monadnocks on an elevated Ter-
tiary erosion surface of low relief.
The peaks and high ridges are serrate and show the effects of intense alpine
glaciation. Cirque basins are particularly noticeable on north and northeast slopes
of peaks and ridges. At lower elevations between 6,000 and 7,000 feet there are
rounded ridges and dome-shaped mountains which were overridden by ice at the
maximum of the Cordilleran ice-sheet. The valleys were occupied by glaciers, and
truncated spurs, hanging valleys, mountain tarns, and glaciated rock surfaces are
common.
Since the Pleistocene, ice has completely left the Okanagan and Hozameen
Ranges, and only a few small glaciers remain in the Skagit Range.
[References: Cairnes, C. E., “ Coquihalla Area,” Geol. &U-V,, Cunuda, Mem.
139, 1924; Rice, H. M. A., “Geology and Mineral Deposits of the Princeton Map-
area,” Geol. Surv., Canada, Mem. 243, 1947.1
[Photographs: B.C. 496:95; B.C. 498:25; B.C. 499:109; B.C. 653: 55;
B.C. 651: 4, 6.1
*Willis, Bailey, U.S.G.S., Prof. Paper 19.
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