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. They are limited on the eastern side by the Columbia River and Arrow Lakes, beyond which lie the Selkirk Mountains, and by the upper North Thompson River and the Interior Plateau on the west. The northern end of the range is at the southern end of the Robson Valley just south of the town of Valemount. The southern extremity of the range is in Washington State, where the Kettle River Range reaches just down to the confluence of the Kettle River and the Columbia, and also farther west to the southern extremity of the Okanagan Highland (spelled Okanogan Highland in the US) just northeast of the confluence of the Okanogan and Columbia rivers at Brewster and Bridgeport.