The Canadian Rockies comprise the Canadian segment of the North American Rocky Mountains. They are the eastern part of the Canadian Cordillera, which is a system of multiple ranges of mountains which runs from the Canadian Prairies to the Pacific Coast. The Canadian Rockies mountain system comprises the southeastern part of this system, laying between the Interior Plains of Alberta and Northeastern British Columbia on the east to the Rocky Mountain Trench of BC on the west. The southern end borders Idaho and Montana of the USA. In geographic terms the boundary is at the Canada/US border, but in geological terms it might be considered to be at Marias Pass in northern Montana. The northern end is at the Liard River in northern British Columbia.