The Monashee Mountains are a mountain range lying mostly in British Columbia, Canada, extending into the U.S. state of Washington. They stretch 530 km (329 mi) from north to south and 150 km (93 mi) from east to west. They are a sub-range of the Columbia Mountains. The highest summit is Mount Monashee, which reaches 3,274 m (10,741 ft). The name is from the Scottish Gaelic monadh and sìth, meaning "moor" and "peace".

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).