Brooks Range

Lore & Background

The Brooks Range stretches across northern Alaska into Canada’s Yukon Territory, forming the northernmost drainage divide in North America. Its peaks, including the highest, Mount Isto, are composed of rocks originally formed in an ancient seabed, yielding fossils of marine organisms such as corals, trilobites, and brachiopods. The range is roughly 126 million years old and marks the northern limit of the tree line; beyond the continental divide, only isolated balsam poplar stands occur, while trembling aspen and white spruce appear only on sites disturbed by human activity. Southern slopes support black spruce. As the climate warms, the tree line has been observed moving northward, and shrub abundance is increasing in formerly tundra-dominated areas. The mountains are home to Dall sheep, grizzly and black bears, gray wolves, moose, and porcupine caribou. The Western Arctic Caribou herd, numbering 490,000 in 2004, traverses the range during its annual migration, as do the smaller Central Arctic herd and the 123,000-animal Porcupine Caribou herd, whose migration is the longest of any terrestrial mammal. The range is mostly uninhabited, with only a few small settlements and the Dalton Highway and Trans-Alaska Pipeline crossing Atigun Pass. The Red Dog mine, the world’s largest zinc mine, lies in the far west. The range is federally protected as wilderness and refuges, including Gates of the Arctic National Park and the Arctic National Wildlife Refuge.

Reader's Guide

The Brooks Range forms the northernmost drainage divide in North America, separating rivers that flow into the Arctic Ocean from those reaching the North Pacific. It roughly delineates the summer position of the Arctic front and represents the northern extent of the tree line, with only isolated balsam poplar stands occurring north of the continental divide. Trembling aspen and white spruce are also found north of the range, but only in sites disturbed by human activity. Southern slopes support some black spruce, marking the northern limit of that species. As global temperatures rise, the tree line has been observed moving northward, and shrub abundance is increasing in areas once dominated by tundra, altering the local ecology. The range is one of the most remote and least-disturbed wildernesses in North America, home to Dall sheep, grizzly bears, black bears, gray wolves, moose, and porcupine caribou. The Western Arctic Caribou herd, numbering 490,000 in 2004, traverses the Brooks Range during its annual migration, as do the smaller Central Arctic herd and the 123,000-animal Porcupine Caribou herd, whose migration is the longest of any terrestrial mammal on Earth. The range’s rocks, formed in an ancient seabed, contain fossils of marine organisms, including corals, trilobites, and brachiopods from the middle Cambrian. During the mid-Cretaceous, the thrust belt underwent significant regional extension. Remains of a woolly mammoth that died about 17,100 years ago were found north of the range, with a research report on its movement published in 2021. The range is federally protected in the United States as a series of national wildernesses and refuges, including Gates of the Arctic National Park, Arctic National Wildlife Refuge, and Noatak National Preserve. In the far west, near the Wulik River in the De Long Mountains, lies the Red Dog mine, the largest zinc mine in the world. The only settlements within the range are the Alaska Native villages of Anaktuvuk and Arctic Village, along with the small communities of Coldfoot, Wiseman, Bettles, and Chandalar. The Dalton Highway and Trans-Alaska Pipeline System pass through Atigun Pass on their way to the oil fields at Prudhoe Bay.

Did You Know?

• The Brooks Range is listed as a section of the North American Cordillera, stretching 1,100 km (680 mi).