page_title: Rocky Mountain Trench
section_title: Geography
hierarchical_section_title: Rocky Mountain Trench / Southern Rocky Mountain Trench / Geography
caption_attribution_description: English: Purcell and Rocky Mountain Trenches within the US
context_page_description: 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 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 wide and is 600–900 m 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.
context_section_description: The southern Rocky Mountain Trench comprises approximately one half of the Trench in British Columbia and includes three regions, the Robson Valley, Columbia Valley and East Kootenay (from north to south). It hosts dozens of communities and two major reservoirs - Kinbasket Lake, and Lake Koocanusa (an acronym of Kootenay/Canada/USA.) There are intersections with two other trench features. At the approximate midpoint of Kinbasket Lake, the now submerged Columbia River exits the Trench in an almost southerly direction toward Revelstoke and flows beyond to its point of exit from Canada south of Trail BC. West of Donald BC, the Beaver river flows in from the south - but it represents the intersection of the lesser but impressive feature called the Purcell Trench.  The Purcell Trench as it proceeds southward becomes the valley of the Duncan River and Duncan and Kootenay Lakes.
  There are four geographic segments of the Southern Rocky Mountain Trench:
  The segment of the Trench encompassing the uppermost court of the Fraser River from east of Prince George and continuing southeastward to the town of Valemount is known as the Robson Valley, named after Mount Robson which overlooks its southern end. Valemount is the Westerly portal to the Yellowhead Pass.
  From Valemount and Canoe Southeastward to the eastern egress of Rogers Pass at Donald, BC just north of the town of Golden the Trench cradles the waters of Kinbasket Lake the reservoir created by Mica Dam; this region before the reservoir was part of the route of the interprovincial highway, once known as the Big Bend Highway, prior to the 1960s opening of the Roger's Pass section of the Trans-Canada.
  The Trench from Golden extending SE to the headwaters of the Columbia River at Columbia Lake is known as the Columbia Valley. Golden is the westerly portal to the Kicking Horse Pass on Highway #1 eastbound to Alberta.
  The southernmost Canadian part of the Trench is the core of a region known as the East Kootenay, comprising the upper of the two Canadian portions of the valley of the Kootenay River.  Here, near Cranbrook, British Columbia, the Trench is much wider than to the northwest, forming more of a broad basin than the U-shaped valley which typifies most of the Trench elsewhere from Columbia Lake northwards to the Liard. This segment bifurcates near Wasa 100 km north of the US border. The off-shooting western fork contains the City of Cranbrook affords access to the nearby City of Kimberley. Elko is the westerly portal to the Crowsnest Pass on Highway 3 eastbound to Alberta.
  The southward transborder extension of the Trench into Montana is the primary containment for Lake Koocanusa, a Kootenay River reservoir created by the Libby Dam near Libby, Montana.
caption: Geologic map of the Purcell and Rocky Mountain Trenches within the U.S.
exif: {}