Cruising The Rocky Mountain Trench

We’re definitely making progress.

In the previous post about our four day epic drive from southern Utah to Canada’s Yoho National Park and its 515–million year old Burgess Shale fossils, our lively two–car caravan finally crosses the international border at the Roosville Port of Entry. We are still on Highway 93, only now we are in another country. And even though for the past three days we have found ourselves motoring along in some of the most spectacular scenery this side of the Arctic, on our fourth day we get to cruise through the even more impressive valley of the Rocky Mountain Trench.

This jewel of geology does not all of a sudden appear out of nowhere at the US/Canadian border, however. The valley itself averages from 2–10 miles (3–16 kilometers) wide and extends, according to www.britannica.com, from near Flathead Lake in northern Montana for nearly 900 miles (1400 km) north through British Columbia to the headwaters of the Yukon River. The narrow, elongated geologic depression that is the Rocky Mountain Trench separates the front ranges of the Canadian Rockies on the east from the Columbia Mountains on the west. North of the Yukon River it continues into Alaska as the Tintina Trench. Our plans do not call for driving that far on this trip.

A stunningly lengthy weakness in the Earth’s crust, the Rocky Mountain Trench has existed for around 45 million years. The tectonic activity that produced it, however, began probably 100 million years prior, when the eastern Pacific plate began a collisional tango with western North America. In the southwestern US we call this prolonged mountain–building boogie the Sevier/Laramide Orogeny. When all this tectonic pushing and shoving and subducting and thrusting ceased, the crust pretty much recoiled and relaxed itself. It stretched and thinned, causing the mountains on the west side of the Trench to rise in a tilted fault block orientation.

I ponder a possible connection between the crustal weakness where the Rocky Mountain Trench is located and the basin where the Belt Supergroup sediments were deposited, about which I wrote here.

We stay in the southern part of the Trench until we reach Golden, BC, a distance of nearly 200 miles (321 km) from the US/Canadian border. As I drive along admiring the mountain scenery I find myself doing some mental mathematical gymnastics. In Canada, distance is measured in kilometers where in the US we use miles:

1 mile = 1.6 kilometers (km)/ 1 km = .62 miles

I realize that those clever little kilometers are ticking away on my odometer quicker than ice cream melting on a hot day. The friendly voices in my head soon tell me that, although there are a whole lot more kilometers in any given distance, they sure do fly by a lot faster than miles!

We cruise ever onward. I am not inclined to use my camera while steering with my knees so JC/CO take turns snapping endless digi–pictures from behind their bug–splattered windshield. Somewhere along the route Windermere Lake offers a restful respite at yet another picnic table. Eventually we leave the Rocky Mountain Trench in Golden and turn east to pick up the Trans Canada Highway, following the Kicking Horse River upstream through contorted layers of shiny phyllite. This rock was mildly metamorphosed from clay–rich shale during all that raucous mountain building of ages past.

Fourteen hundred miles, four days, and one broken Subaru air–conditioning unit later we pull into Field, the small village located dramatically at the base of Mt. Stephen on a large alluvial fan of glacial outwash just west of the continental divide. We have arrived exhausted!