Landforms of British Columbia 1976 - Department of Geography

The western boundary of the Eastern System lies along the Rocky Mountain
Trench, a remarkable structural and topographic feature which extends from the
49th parallel northwestward for 900 miles, ahnost to the Liard River (see Plate
XXII and Fig. 12). The eastern boundary of the Western System is not so clearly
defined, but is a line drawn to separate the various ranges of the Coast Mountains
from a succession of flanking mountains, highlands, and plateaus on the east.
Although in some instances there is a gradual transition between Western and Inte-
rior Systems, elsewhere the transition is abrupt, and a clear-cut separation may be
made, using a boundary drawn along the eastern side of the Coast Mountains in the
approximate position of the 5,000-foot contour (see Plate XIB).
I. WESTERN SYSTEM
The Western System in British Columbia includes all that part of the Province
lying west of a rather sinuous boundary-line running northward from Keremeos
through Lytton to Smithers and thence to Telegraph Creek and Atlin. It consists
essentially of the mountainous mainland coast, but included within the System are
a number of low-lying areas along the coast, as well as the mountains of Vancouver
Island and of the Queen Charlotte Islands.
There are three major subdivisions of the Western System. These are, from
west to east, the Outer Mountain Area, the Coastal Trough, and the Coast Moun-
tain Area.
The Outer Mountain Area comprises the St. Elias Mountains in the extreme
northwesterly corner of the Province and the Insular Mountains of the Queen Char-
lotte Islands and Vancouver Island.
The Coastal Trough is a low-lying area which is partly submerged beneath the
sea. It is flanked on the west by the mountains of Vancouver Island and the Queen
Charlotte Islands and on the east by the heights of the Coast Mountains. It in-
cludes the Georgia and Hecate Depressions; it extends northwestward through
southeastern Alaska as far as Chatham Strait and southeastward through Washing-
ton as the Puget Depression.
The Coast Mountain Area flanks the Coastal Trough on the east and extends
on the mainland for the full length of the Province, forming a barrier of mountains
as much as 100 miles across. It includes the Coast Mountains, which extend 900
miles northwestward from their southern boundary at the Fraser River, as well as a
small northern prong of the Cascade Mountains of Washington and Oregon that
crosses into British Columbia and extends north as far as Lytton.
The very large area of the Coast Mountains is divided into three smaller units
which are natural groupings of individual ranges. These are the Boundary Ranges,
lying between the Yukon Border and the Nass River; the Kitimat Ranges lying
between the Nass River and the Bella Coola River; and the Pacific Ranges lying
between the Bella Coola River and the Fraser River.
OUTER MOUNTAIN AREA
ST. ELIAS MOUNTAINS
The St. Elias Mountains lie in the curve of the Gulf of Alaska and are readily
visible from the sea in clear weather, when they are seen to rise abruptly to great
heights as a white wall of mountains. They extend northwestward from Cross
Sound and Lynn Canal to Cook Inlet. * These mountains include some of the most
rugged country in North America and include the summits of Mount Fairweather
* Brooks, A. H., U.S.G.S., Prof. Paper No. 45, 1906, p. 29.
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