Landforms of British Columbia 1976 - Department of Geography

mentary rocks are folded and faulted. These crustal movements have been
localized largely in belts, in some of which there may have been recurrent activity
over a long period of time, during sedimentation and after. This localization of
movement has affected not only the character of the sedimentary rocks laid down
in each belt, but also the structures that are produced in them (see Plates XXXIIB
and =xIIIB). A variety of structures of difIerent ages and orientations has
been impressed upon the earth’s crust because of changes of position of the active
belts in the course of geologic time.
The present landforms are greatly influenced by the fact that regional uplift* in
the late Tertiary was differential in amount. The differential uplift accounts for the
contrast between the moderate to low topographic relief of the plateau areas of
central British Columbia and the strong relief of the adjoining Coast Mountains
and Columbia Mountains (see Plate XIB) . It also accounts for regional differences
in height of the surface of the Interior Plateau, for the low area in the Coast
Mountains between the Nass and the Bella Coola Rivers, and the low area in the
Rocky Mountains between the Peace River and Mount Sir Alexander.
[References: GeoZ. Surv., Cunu&, Map 932A, Geological Map of British
Columbia; Geol. Surv., Can&a, EC. Geol. Series No. 1, “ Geology and Economic
Minerals of Canada,” 1957, pp. 283-392, “ The Cordillera Region “; B.C. Nuturul
Resowces Conference Atlus of British Columbiu, 1956, Map No. 3, Geology;
White, W. H., “ Cordilleran Tectonics in British Columbia,” Bull., Am. Ass. Pet.
Geol., Vol. 43, No. 1, 1959, pp. 60-100; Wheeler, J. O., “ Mesozoic Tectonics
of South Central Yukon,” Proc., GeoZ. Ass. Cunudu, Vol. II, 1959, pp. 23-43;
Gabrielse, H., and Wheeler, J. O., “ Tectonic Framework of Southern Yukon and
Northwestern British Columbia,” GeoZ. Swv., Cunadu, Paper 60-24.1
SUMMARY OF PHYSIOGRAPHIC HISTORY OF BRITISH COLUMBIA
A very large part of the Canadian Cordillera in British Columbia-that part
lying west of the Rocky Mountain Trench - was involved in the Coast Range
orogeny, which lasted from earliest Jurassic time through to post Lower Cretaceous.
It was a time of mountain-building, invoIving foIding and faulting on a regional
scale and the intrusion of granitic batholiths in the Insular Mountains, Coast Moun-
tains, Cassiar-Omineca Mountains, and Columbia Mountains. Subsequent erosion
in the mountains was sufficiently deep to remove the cover of sedimentary rocks
from the batholithic cores. The unroofing of the batholiths took place contem-
poraneously with the deposition of Upper Cretaceous and early Tertiary sediments
in two basins, one of which included Vancouver Island, the Gulf of Georgia, and
the Queen Charlotte Islands, and the other occupied the Rocky Mountain area.
The Rocky Mountains occupy the site of a geosyncline, whose western border
roughly coincides with the line of the Rocky Mountain Trench. It was the site of
sedimentary deposition during the Paheozoic and Mesozoic eras. The Rocky
Mountain orogeny, post-Paleocene in age, terminated sedimentation in the basin
and buih the Rocky Mountains, and a cycle of erosion was initiated that has persisted
without interruption to the present.
During the Tertiary the entire Cordilleran region was subjected to erosion,
except for small basins of marine sedimentation in the Puget Trough and on the
northeast tip of Graham Island, and small basins of fresh-water sedimentation
through central British Columbia. By Miocene time it is known that in central
British Columbia there had been developed a land surface of moderate relief
* Note.-This late. Tertiary regional uplift and the consequent erosion and modification of the Tertiary
surface is a connnon denominator of all physiographic units of British Columbia. Further reference to it may
be found on pages 45 and 55.
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