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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.

The Ranges

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 many predators.

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 Plains

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.

The Foothills

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 found here.

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 natural gas.

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