major subdivision of the Columbia Mountains, extending for 200 miles (320 km) in a southeasterly arc, mostly in British Columbia, Canada, and just across the U.S. border into northern Idaho and Montana. Bounded by the Purcell Mountains (east) and the Columbia River (west and north), they are sometimes considered part of the Rocky Mountain system. The summits are lowest in the south, where they average 7,500 feet (2,300 m), but many northern peaks exceed 10,000 feet (3,000 m), with Mount Sir Sanford (11,555 feet 【3,522 m】) being the highest. In many places the Selkirks rise abruptly more than 8,000 feet (2,400 m) above adjacent valley floors, affording wild and magnificent scenery. Glacier and Mount Revelstoke national parks, in the northern part of the range, are served by the Trans-Canada Highway, which crosses the mountains at Rogers Pass (4,354 feet 【1,327 m】). The 5-mile- (8-kilometre-) long Connaught Tunnel, just northeast of Glacier, was built under Mount Macdonald for the Canadian Pacific Railway. The mountains were named after Thomas Douglas, 5th Earl of Selkirk, philanthropic sponsor of Canadian settlements.