The Brooks Range lies north of the Arctic Circle (66°33' N), roughly straddling 68° N. The range begins in the Yukon Territory of Canada, about 120 miles (193 km) east of the international boundary with the United States. At this point the Continental Divide leaves the north-south trending Richardson Mountains and runs east-west, first through the Barn Range, with Mt Sedgwick (2057 ft/627 m) as one of the high points, and then into the British Mountains, which straddle the international boundary. Mt Greenough (7240 ft/2207 m) is the highest peak of this range. The Brooks Range stretches westward from the international boundary for some 600 miles (965 km), ending near Pt Hope on the Chukchi Sea. The Alaskan portion of the British Mountains, the Davidson Mountains, the Romanzof Mountains, and much of the Philip Smith Mountains lie within the Arctic National Wildlife Refuge. The highest peak of the entire Brooks Range is one of the Romanzof peaks, Mt Isto (9060 ft/2761 m). Atigun Pass, situated at the headwaters of the Sagavonirktok River, flowing north, and the Dietrich River, flowing south, separates the Philip Smith Mountains from the Endicott Mountains. The Endicott Mountains lie within the Gates of the Arctic National Park and Preserve. Cockedhat Mountain (7610 ft/2348 m) and Mt Doonerak (7457 ft/2273 m) are major Endicott peaks, the latter made famous by Robert Marshall.
The Trans-Alaska Pipeline and the Dalton Highway both cross the Brooks Range through Atigun Pass at 4752 ft (1448 m). At the western edge of Gates of the
Arctic, the Continental Divide turns sharply to the south, leaves the Brooks Range, crosses the Arctic Circle, and then heads west to the Seward Peninsula. The Schwatka Mountains begin in the western portion of the Gates of the Arctic and continue westward into the Noatak National Preserve. Glacial melt waters from Mt Igipak (8510 ft/2594 m), a Schwatka peak located in the Gates of the Arctic, give rise to the Noatak River that empties into the Chukchi Sea near Kotzebue, some 400 miles away. The Noatak River divides the Brooks Range into a northern half, the De Long Mountains, with Mt Bastille (4440 ft/1353 m) a major landmark, and a southern half, the Baird Mountains, before turning southward near the northeastern corner of Cape Krusenstern National Monument and the village of Noatak. The most westerly peak of note, Mt Hamlet (2034 ft/620 m), forms a headland that drops off into the Chukchi Sea at Cape Lisburne.
The major uplifting of the Earth's crust that led to the formation of the Brooks Range occurred some 160 million years ago when an oceanic plate rotated away from the Canadian High Arctic Islands and collided with what was then northern Alaska. The Kobuk River marks the southern boundary of these colliding landmasses. Granite spires such as the Arrigetch Peaks are derived from the magma cores of ancient (Devonian) volcanic intrusions. Portions of the range, especially those peaks on the Arctic Divide, are derived from limestone terranes that were once coral reefs in tropical seas. Gold-bearing quartz veins are found in the hills on the southern side of the range. Only a few small glaciers remain, even though all of the Brooks Range was glaciated, and most of these are on north-facing slopes.
There is too little snowfall (annual average 60-80 inches/152-203 cm in Gates of the Arctic) to support glacier production. Average annual precipitation on the south-facing slopes in Gates of the Arctic varies from 8 to 18 inches (20-46 cm). The climate is continental, with very cold winters and moderately warm summers. Winters are severe, the average January minimum in the Gates of the Arctic being -30°F (-34°C); the average maximum is -10°F (-23°C). The July minimum and maximum averages are 46°F (8°C) and 70°F (21 °C). Temperatures on the north-facing slopes of the Brooks Range average, winter and summer, about 10-15° colder than on the south side. Total average annual precipitation on the north-facing slopes rarely exceeds 10 inches (25 cm), including an annual average snowfall of about 45 inches (114 cm). Because the whole of the Brooks Range is underlain by permafrost, any rainfall runs off rapidly, producing dramatic changes in the water levels in the streams and rivers.
Except for the bare rock faces, the north side of the Brooks Range is clothed in vegetation characteristic of Arctic and alpine tundra. The higher elevations on the south side have similar vegetation, but at lower levels the vegetation mix includes tundra, often as vast expanses of cottongrass tussocks with intervening lichens, mosses, grasses, and dwarf shrubs, boreal forest (taiga), and scrub thickets. The treeline is extremely sinuous on the south slopes, but generally extends up to about 2100 ft (640 m) in the vicinity of latitude 67°30' N. The generally dense vegetative coverage of the Brooks Range supports a great variety of animal species, but usually in rather small numbers of individual kinds, the exceptions being the twice-annual concentrations of migrating caribou, small herds of Dall's sheep and mountain goats, and the cyclic population upsurges of snowshoe hares and lemmings, and their predators. Moose, grizzly bears, black bears (south slopes only), wolves, red foxes, many other kinds of smaller mammals, and many kinds of birds inhabit the Brooks Range. Permanent human residents, mostly native Americans (Inupiaq and Athapaskans) and all on the south side, number only about 1000, and they are largely concentrated in the tiny villages of Anaktuvuk Pass, Arctic Village, Bettles, Evansville, Kobuk, Noatak, and Wiseman. The town of Coldfoot, on the Dalton Highway about 75 miles (121 km) south of Atigun Pass, is a service center for traffic to and from the Prudhoe Bay oil production facilities. Several active gold mining operations are scattered across the southern slopes and in the river valleys flowing out of the Brooks Range.
J. Richard Gorham
See also Alaska; Trans-Alaska Pipeline
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