Canadian Rockhound: A Rocky Mountain Mystery

Home

A Rocky Mountain Mystery
By Murray Nicholson

Imagine, if you can, a chain of valleys, each different from the next, but all stretching in a straight line over more than 1,600 kilometres, leaving a scar so distinctive it is visible from outer space. Add to this, the discovery that the east wall rocks are sedimentary while the west wall rocks are much older intrusive and metamorphic rocks. These are the mysteries of the Rocky Mountain Trench.

Extending from Flathead Lake, Montana to the Liard Plain near the Yukon border, the Trench marks the western boundary of the Rocky Mountains. The width of individual valleys ranges from 5 to 13 kilometres. Mountain summits on each side rise steeply some 1,000 to 2,000 metres above the flat-bottomed floor. Nine rivers, including the Fraser and Columbia drain the Trench, most entering and leaving through canyons.

The Trans-Canada Highway crosses the Trench at Golden, British Columbia. From here, the traveler can see the Trench to the north and the south. Another highway follows the east wall for 100 kilometres south to Radium Hot Springs. More small communities can be found in the valleys to the south.

Since George Dawson first described the Trench in his 1886 report to the Geological Survey of Canada, several geologists have studied different sections. They have concluded that while all of the valleys show signs of glaciation some were formed by erosion and others by faulting. To date however, there is no comprehensive explanation of the origins of the Trench as a whole. Could it be the result of mountain-building, or an old tectonic plate boundary, or perhaps the evidence of something we don't yet understand? More than 100 years after its discovery, the Rocky Mountain Trench remains a mystery.

This article may not be copied, distributed or reprinted in any form without the author's permission. To contact the author, please use the e-mail address provided. If you are unable to contact the author, please contact the Canadian Rockhound. Authorized reprints must acknowledge the author, original source and the Canadian Rockhound, and include the website URL address of the Canadian Rockhound.

The preceding article was first published in the October 1991 issue of the Calgary Lapidary Journal, the official newsletter of the Calgary Rock & Lapidary Club. Reprinted in the Canadian Rockhound with permission from the author.