The Purcell Trench, also known as the Kootenay River Valley is a large valley on the western side of the northern part of North America's Rocky Mountains. The trench extends approximately from Lake Pend Oreille, Idaho, down the Kootenay River (north) to Kootenay Lake, up the north arm to Duncan Lake. It joins the Rocky Mountain Trench another northward at the south tip of Kinbasket Lake, in British Columbia. The trench bottom is wide and is above sea level. The trench is nearly a straight north or south line. Some of its topography has been carved into U-shaped glacial valleys, it is primarily a product of geologic faulting. The trench splits the Columbia Mountains between the Purcell Mountains on the east and the Selkirk Mountains on the west.