Landforms of British Columbia 1976 - Department of Geography

streams tend to develop a trellis pattern, with long stretches parallel to the strike
of the rocks and short lateral tributaries that are parallel to the direction of dip
and enter the main streams at right angles. Ridges and ranges follow the strike
of the formations. Topography of this type is particularly well displayed in the
foothills of the Rocky Mountains, at the heads of the Sikanni Chief, Prophet,
Tuchodi, and Tetsa Rivers (see National Topographic System* Sheets 94~ and
94K).
Figure 5. Diagram showing the main areas of folded and faulted sedimentary rocks.
The main areas of folded and faulted sedimentary rocks, shown on Figure 5,
are in the Selkirk, Purcell, and Rocky Mountains in the southeastern part of the
Province, in the Rocky Mountains and their foothills in the northeast, and west of
the Rocky Mountain Trench in north central British Columbia. A belt of such rocks
lies along the east side of Vancouver Island, extending southeastward from Campbell
River to the Gulf Islands.
(5) During most of post-Devonian time in British Columbia, both sedimentary
and volcanic materials were deposited in the central and western parts of the
Province, in a general area stretching from Vancouver Island and the Queen
Charlotte Islands to the Rocky Mountain Trench and west of a line running south-
eastward to Kootenay Lake. The rocks in this general area comprise heterogeneous
sedimentary rocks, including greywackes, argillites, limestones, and cherts, all inter-
calated with lavas and fragmental volcanic rocks. Such successions of mi,xed rocks
differ markedly from the entirely sedimentary successions farther east, and erode
somewhat differently because of their diversity. Within areas of such rocks there
* In the body of this report a National Topographic System Sheet will be designated N.T.S. Sheet.
19