A chain of
valleys in the
Rocky Mountains stretching
1600 km (1000 mi) from the southeastern corner of
Yukon Territory, down
the entire length of
British Columbia and into
Montana, ending at
Flathead
Lake.
The trench is occasionally interrupted by high mountains, and different
stretches of valley display different characters. Most are filled in with
alluvium to form flat-bottomed valleys 5-8 km wide with mountains rising
1,000-2000 meters on either side. In the valleys lie stretches
of many of the most important rivers of northwest North America: Kootenay, Columbia, Fraser,
Peace, Liard.
The valleys' configuration is a civil engineer's dream: The Peace
River has been dammed to form Williston Lake, the Columbia to form
Mc Natughton Lake, and a dam on the Kootenay backs Lake Koocanusa north
across the Canadian border. Some have tried to fill the entire valley up with water, to implement the vast NAWAPA scheme.
Although the valleys appear to have been shaped by a mixture of faulting
and glacial scouring, the fact that they line up at all indicates
that the entire system has some structural underpinning. One theory
places an old tectonic plate boundary there.
Although natives had lived in the region for thousands of years, and
European explorers and trappers had visited the trench for hundreds, the
valley was first described to the Geological Survey of Canada by George
Dawson in 1886.