Landforms of British Columbia 1976 - Department of Geography

The boundary between the Rocky Mountains and foothi& follows a structural
line between belts that differ in both lithology and rock structure. As a consequence,
there may be fundamental topographic differences between the two.
Specifically, the boundary between the Rocky Mountains and the Rocky
Mountain Foothills for the most part is along the easternmost fault on which
Devonian and (or) Permo-Carboniferous limestones are thrust over Mesozoic
formations. The boundary &tends southeastward from the Liard River at Sulphur
Creek, past Stone Mountain and through Mile 389 ~II the Alaska Highway, thence
more southerly to pass just east of the Tuchodi Lakes and just east of Redfern
Lake on Baa River, crosses the Peace River at the mouth of the Nabesche River,
and crosses the Pine River at the upper Pine River bridge east of Mount Solitude.
The boundary then veers more to the southeast, and crosses the Alberta-British
Cohunbia Boundary 15 miles northeast of Mount Ida. Southeast of Mount Ida
the interprovincial boundary follows the continental divide between Pacific and
other drainage, and the eastern margin of the Rocky Mountains is in Alberta.
In Alberta the boundary between the Rocky Mountain Front Ranges and the
western margin of the foothiIls is taken as the McDonnell thrust north of the High-
wood River, and the Livingstone and Lewis thrusts south of the Highwood River.
The Rocky Mountains are underlain very largely by sedimentary and meta-
morphic rocks, which range from Proterozoic to Cretaceous in age. The youngest
rocks are exposed in the foothills, and progressively older rocks lie to the west.
The predominant rocks of the Rocky Mountains are Palzeozoic and Proterozoic
limestones, quartzites, schists, and slates. In contrast, the foothills contain a
predominance of Mesozoic, especially of Cretaceous, formations. Two formations
of volcanic origin are known to occur, one of possible Mississippian age and the
other Lower Cretaceous. The intrusive rocks are so few that they have no regional
geomorphic significance.
During the Pleistocene the ranges were covered to heights of 7,000 to 8,000
feet by continental ice, the erosional effects of which are slight compared to the
modifications wrought by alpine and valley glaciers. These have produced charac-
teristic glaciated alpine scenery comparable to famous localities in Europe. In the
southern Rocky Mountains there is an area where the Cordilleran ice reached a
height of only 6,500 feet. There are as a consequence considerable areas above
that elevation that were onglaciated.*
There are four divisions of the Rocky Mountains in Canada in their 850-&e
length between the International Bowday at the 49th parallel and the Liard.
These arc the Border Ranges between the International Boundary and a liie be-
tween Elko and North Kootenay Pass; the Continental Ranges extending north-
westward from a line between Elko and North Kootenay Pass to Jarvis Creek just
north of Mount Sir Alexander; the Hart Ranges between Jarvis Creek and the
Peace River; and the Muskwa Ranges between the Peace River and the Liard
River.
Border Ranges
The southernmost ranges of the Rocky Mountains in Canada are the Border
Ranges, They lie south of a line running from Elko along the southern edge of the
Fernie Basin to North Kootenay Pass and are an extension north of the Inter-
national Boundary of the Montana Ranges of the physiographic subdivision named
in the United States the Northern Rocky Mountain Provh~ce. Along the Inter-
national Boundary from west to east the Border Ranges in Canada are the G&on,
MacDonald, Clarke, and Lewis Ranges. The extensions into Montana of the
* staker, A M., Gd. SW”., Gmd~, MW 31-wa
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