The Rocky Mountain Trench, also known as the Valley of a Thousand Peaks or simply the Trench, is a large valley on the western side of the northern part of North America's Rocky Mountains. The Trench is both visually and cartographically a striking physiographic feature extending approximately 1,600 km (1,000 mi) from Flathead Lake, Montana, to the Liard River, just south of the British Columbia–Yukon border near Watson Lake, Yukon. The trench bottom is 3–16 km (1.9–9.9 mi) wide and is 600–900 m (2,000–3,000 ft) above sea level. The general orientation of the Trench is an almost straight 150/330° geographic north vector and has become convenient as a visual guide for aviators heading north or south.
Although some of its topography has been carved into U-shaped glacial valleys, it is primarily a byproduct of geologic faulting. The Trench separates the Rocky Mountains on its east from the Columbia Mountains and the Cassiar Mountains on its west. It also skirts part of the McGregor Plateau area of the Nechako Plateau sub-area of the Interior Plateau of British Columbia. It is up to 25Â km (16Â mi) wide, if measured peak-to-peak, and varies in valley relief, but is clearly visible by air and satellite/remote sensing and is easily discernible to those ascending any of the mountains or ridges lining it.