The Big Bend is the northernmost section of the Columbia River, which changes from a northwestward course along the Rocky Mountain Trench to curve around the northern end of the Selkirk Mountains to head southwest between that range and the Monashee Mountains, which lie to the west. The area is part of the larger Columbia Country, which includes the Columbia Valley and upper Arrow Lakes of eastern British Columbia. The north of the railway line, and enclosed by the river, roughly defines the Big Bend. However, in earlier eras, the descriptive was more narrowly understood.