Landforms of British Columbia 1976 - Department of Geography

The lowland consists of many low, wooded cuesta-like ridges separated by
narrow valleys. The northwesterly elongation of the ridges and of the Gulf Islands
is the result of differential erosion of the Upper Cretaceous sedimentary rocks. The
ridges are underlain by hard sandstone and conglomerate beds, and the valleys are
eroded in shales and softer rocks or along fault zones. In the south between Saanich
Inlet and Jordan River, the lowland is underlain by granitic and other older rocks,
which are more resistant to erosion. This fundamental difference in bedrock is
reflected in somewhat greater elevations and in different topographic forms.
The lowland was overridden by ice during the Pleistocene, and the direction of
ice movement is shown by the form of many rock surfaces. The already low relief
was further reduced by glacial erosion and by the deposition of a fairly thick mantle
of glacial and fluvio-glacial materials. Uplift of the land since the ice retreat has
led to rejuvenation of streams and in many instances to the cutting of narrow box
canyons in the lower courses of streams approaching the sea.
[References: Clapp, C. H., “Geology of Victoria and Saanich Map-areas,”
GeoZ. ,!?urv., Cunu&, Mem. 36, 1914; Clapp, C. H., “Geology of the Nanaimo
Map-area,” GeoZ. Surv., Cur&u, Mem. 51, 1914; Clapp, C. H., “Sooke and
Duncan Map-areas,” Geol. Surv., Canada, Mem. 96, 1917; Fyles, J. G., “ Sur-
ficial Geology, Oyster River,” GeoZ. &rv., Cunudu, Map 49-1959; Fyles, J. G.,
“ Surficial Geology, Courtenay,” GeoZ. &4rv., Canudu, Map 32-1960; Fyles, J. G.,
“ Surficial Geology of Horne Lake and Parksville Map-areas,” GeoZ. surv., Cunudu,
Mem. 318, 1963.1
[Photographs: B.C. 673:40, 52; B.C. 1206: 102; B.C. 1555: 79.1
COAST MOUNTAIN AREA
COAST MOUNTAINS
The Coast Mountains extend along the mainland coast of British Columbia as
an unbroken mountain chain, from their south end at the Fraser River northwest-
ward for about 950 miles to the northern boundary of the Province. The mountains
extend a further 50 miles into the Yukon, giving them a total length of approximately
1,000 miles. Their width ranges from a minimum of 35 miles to a maximum of
100 miles.
On.the west the Coast Mountains, between the mouth of the Fraser River and
Chatham Strait, are flanked by the Coastal Trough, whose eastern boundary is the
2,000-foot contour line. Between Lynn Canal and the Yukon Border the Coast
Mountains are separated from the St. Elias Mountains on the west by the valleys of
Chilkat River in Alaska and of Kelsall and Tatshenshini Rivers in British Columbia.
The eastern boundary of the Coast Mountains is the boundary between the
Western and Interior Systems. For the greater part of its length, from the Yukon
Border to Lytton, the boundary is drawn between mountains on the west and
plateaus and highlands on the east. Although in places there may be transition
between the two systems, the separation of one from the other is along a fairly easily
determined line. In the extreme north the Coast Mountains are flanked by a transi-
tional belt of highlands (Tagish and Tahltan Highlands) extending south to the
Iskut River. Between the Iskut River and the head of the Bell-Irving River the
Coast Mountains for 25 miles are flanked by a range which is part of the Interior
System-the Klappan Range of the Skeena Mountains. Farther south the border
is against the Nass Basin and Hazelton Mountains. From Eutsuk Lake to the head
of the Yalakom River the Coast Mountains border the Nechako and Fraser Plateaus
with a sharply defined front rising above the plateau surface. On the extreme south
the Yalakom and Fraser Rivers mark the eastern boundary of the Coast Mountains.
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