The Columbia Mountains are a group of mountain ranges along the Upper Columbia River in British Columbia, Montana, Idaho and Washington. The mountain range covers 135,952 km². The range is bounded by the Rocky Mountain Trench on the east, and the Kootenai River on the south; their western boundary is the edge of the Interior Plateau. Seventy-five percent of the range is located in Canada and the remaining twenty-five percent in the United States; American geographic classifications place the Columbia Mountains as part of the Rocky Mountains complex, but this designation does not apply in Canada. Mount Sir Sandford is the highest mountain in the range, reaching 3,519 metres (11,545 ft).