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: KootenayColumbia, 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.