The Brooks Range includes the northernmost of the major mountain systems of the North American Cordillera, and extends along an east-west axis across northern Alaska from near the northern opening of the Bering Strait to the northern Yukon Territory. Major subranges include the British Mountains and Richardson Mountains, towards their eastern end, and at their farthest west is the small subrange that De Long Mountains. The Brooks Range forms the northern flank of the lower Yukon River basin, separating it from Alaska's North Slope region, facing the Beaufort Sea. The Brooks Range is considered part of (or an extension of) the Rockies. South of the Brooks Range are the Mackenzie Mountains, and the Canadian Rockies.