What Comprises the Canadian Rockies?
Looking at a map of North America, the
mountains of the western edge of the continent are usually clearly visible, and
labeled as the Rocky Mountains. Logically, the Canadian Rockies would consist of
that part of this extensive range falling within the boundaries of Canada. In a
simple sense, this is true. However, within this larger definition, there are a
multitude of smaller mountain ranges, each with unique characteristics of
landscape, moisture, plant and animal life. The mountains of the coast are very
different from the mountains along the eastern slope of the province of Alberta.
For this reason, more detailed definitions are necessary.
Of these western mountain ranges, the
‘genuine’ Rockies are the most easterly, stretching for approximately 150 km (93
miles) east to west. Along the Trans Canada Highway, they begin to west of
Calgary and extend to Golden, British Columbia. Further north, following the
Yellowhead Highway (Hwy. #16), they stretch from Hinton, Alberta to Valemount,
British Columbia. Within this narrow band of southeast–northwest trending
mountains, lie some of Canada's most famous peaks.
If you travel west from Calgary, transecting
the Rockies, you will notice landscape change, and with it, the vegetation and
wildlife. The mountain ecosystem works like a three layered sandwich. The
landscape defines which plants are able to survive. The plants in turn play a
vital role in determining which animals take refuge within a particular habitat.
They may use the plants as food, or themselves become the food of some of our
The Rockies are characterized by slabs of
sedimentary rock, bent, folded, and finally pushed many miles inland along a
shallow incline, only to be piled on top of other, often younger, rocks. Unlike
ranges further to the west, the Rockies do not contain significant amounts of
formerly molten rocks. They are made up principally of sedimentary rocks
deposited at the bottom of ancient western seas.
The Alberta plains are a land of rolling
grassland and agricultural wealth. Often, the plains are perceived as endless
and boring, something to cross as one travels to the more spectacular mountains.
Despite this common misconception, the plains are more than Canada's
agricultural centre. They provide a diverse landscape with unique collections of
plants and animals. In fact, they are more diverse than the Rockies. Look at the
birdlife! Prairie slough ponds are alive with all manner of waterfowl,
red-winged blackbirds and wading shorebirds. The fence posts provide perches for
red-tailed and Swainson’s hawks. Insect eating birds, like the mountain
bluebird and the cowbird, are attracted to the plentiful amounts of insects
churned up by the cattle.
Soon after leaving Calgary, heading west on
the Trans Canada Highway, the plains begin to fall under the influence of the
mountains. The landscape begins to exhibit a more rolling character, and the
foothills begin to push their way towards the surface.
If one thinks of the formation of the
mountains as a shockwave moving inland from the west coast, gradually piling up
the mountains, the foothills represent the point at which the wave began to run
out of steam. Think of picking up a long rope, and giving one end a rapid up and
down motion. A wave will move along the rope, gradually petering out. The last
expression of this wave would represent the foothills. This also makes the
foothills the youngest of our tectonic features.
The foothills range from 25-40 km (15-25 mi.)
in front of the mountains. Like the mountains, they were formed when layers of
rock were pushed on top of other layers. Today, the foothills are characterized
by ridges of sandstone and valleys of shale. Since sandstone is more resistant
to erosion, it tends to remain as the dominant highland rock. There is a marked
lack of limestone in the foothills, so sandstone is the hardest common rock
In many cases, the layers of sandstone have
been squeezed into dome like structures called anticlines. Moose Mountain is a
classic example with its domed summit. These domes often form reservoirs for
The Front Ranges
The rolling Foothills give way to the jagged
summits of the Rockies. Beginning with the Front Ranges, the most easterly of
the Rocky Mountain ranges, the landscape takes a sudden change for the vertical.
Along the Trans Canada Highway, Mount Yamnuska marks the transition. At the base
of its vertical face, lies the McConnell Thrust, the official start of the Front
Ranges of the Rocky Mountains. Although not obvious from a distance, the upper
limestone cliffs have been pushed more than 30 km (18 mi.) inland to their
present position atop much younger shale beds. Along the Yellowhead Highway, the
junction between Foothill and Front Range occurs at the eastern entrance to
Jasper National Park.
The rocks of the Front Ranges average in age
between 350 and 135 million years old. They are characterized by steeply bedded,
heavily folded sheets of primarily limestone. The average height of the Front
Ranges is 2,500 m (8,200 ft) with the highest Front Range peak being Mt. Brazeau
at 3,470 m (11,382 ft) in Jasper National Park.
Many Front Range Mountains show a three
layered sandwich of upper Livingstone Formation limestone summits overlying the
soft shales of the Banff Formation, which in turn lay atop the limestones of the
Palliser Formation. Another change upon entering the Front Ranges is the sudden
change to limestone summit and shale valley. This arrangement will persist
throughout the Main and Western Ranges.
Coal is another common discovery in the Front
Ranges, and has supported several mines over the years. Examples include
Pocahontas in Jasper, the Canmore Mines, and Bankhead and Anthracite near the
town of Banff.
The Main Ranges
The Main Ranges appear as suddenly as the
Front Ranges, and with as dramatic a change in shape and appearance. Along the
Trans Canada Highway, this junction is marked by the Simpson Thrust, just prior
to the Highway 93 junction. Along with this junction, the summits jump in height
by almost 500 m (1,640 ft). Simply look up at Castle Mountain, and the change is
instantly evident. Towering 2,728 m (8,948 ft) high, it exhibits similar layered
sediments, however rather than the steep bedding and intense folding of the
Front Ranges, the layers still remain almost horizontal. The resulting
‘castellate’ mountain form is characteristic of main range peaks. Further
north, in Jasper, the junction between Front and Main Ranges occurs just to the
east of the Icefields Parkway, and slightly east of the townsite of Jasper.
To rise so high, yet remain virtually
horizontal, these rocks had to be pushed a great distance, at a relatively
shallow incline. The Simpson Thrust provided just such a sliding layer as the
rocks were pushed more than 40 km (24 mi.) along a gentle incline. The Simpson
Thrust begins south of Lake Louise and continues north for 360 km (216 mi.),
extending beyond the town of Jasper. The Icefields Parkway follows the fault
line for much of its length.
The rocks are also very old, primarily of
Cambrian and Precambrian age (500-800 million years old). The eastern Main Range
peaks are capped with limestones, dolomites and quartzites. As you pass the town
of Field, the summits change to become dominated with crumbly shale. Thus begins
the western Main Ranges. The shale is actually slightly metamorphic, or hardened
due to heat and pressure, to form slate.
The Western Ranges
The term Western Ranges refers to a limited band of mountains running along the western margin of the Rockies from Radium Hot Springs to the town of Golden, British Columbia. Along this corridor, the character of the mountains changes yet again. Here, the rocks have been overthrust, essentially pushed eastward at a very steep angle and then folded back over themselves. With this change in character, the crumbly shale peaks differ slightly from the Western Main Ranges that line the Trans Canada and Yellowhead Highways. As a major thrust sheet moved inland from the Purcell Mountains, it impacted the soft shales so hard that they were thrust up very steeply and literally back over onto themselves. The western ranges are visible along Highway 95 running between Radium and Golden.
The Western Ranges end with the Rocky Mountain Trench. The city of Golden, British Columbia lies at the bottom of the Trench. The Trench was likely formed after mountain building had finished. When the pressure was finally released, a large area of rock collapsed to form a fault. On the other side of the Trench, the Purcell Mountains, part of the Caribou Mountains, rise.
All Material © Ward Cameron 2005