The Brooks Range is an immense mountain system located in the far reaches of the North American continent. This remote chain forms a major geographic feature deep within the Arctic Circle. Its presence defines the geography, climate, and ecology of the vast northern region it occupies.
Pinpointing the Geographical Extent
The Brooks Range stretches for approximately 700 miles (1,100 km) in an east-west arc across northern Alaska. This mountain chain originates near the Chukchi Sea and extends eastward toward the Canadian border. Upon crossing into Canada’s Yukon Territory, the system continues, often referred to as the British Mountains or Richardson Mountains. The range spans a width of up to 200 miles (300 km) from north to south.
The Brooks Range creates a clear boundary between northern Alaska’s physiographic regions. To the north lies the flat Arctic Coastal Plain, also known as the North Slope. The southern boundary meets the Interior Plains, which encompass the Yukon River system’s drainage basin. The entire formation is situated almost entirely north of the Arctic Circle.
Distinct Sub-Ranges and Geological Features
The Brooks Range is a complex system composed of several distinct sub-ranges that vary in elevation and topography. In the westernmost sections, such as the Baird Mountains, peaks are generally smoother and lower, averaging around 3,000 feet. Moving eastward, the mountains become more rugged, with central and eastern sections averaging heights closer to 5,000 feet.
The highest points are concentrated in the eastern portion, particularly within the Romanzof Mountains near Canada. Mount Isto, the highest peak, reaches an elevation of 8,976 feet (2,736 m). The range’s geology is characterized by tightly folded and faulted sedimentary rocks, including shale, carbonate, and conglomerate, compressed during the Mesozoic era.
Past extensive glaciation shaped the modern landscape, leaving behind sharp glacial cirques and U-shaped valleys. Only small, scattered glaciers remain on the highest peaks today.
Environmental Role as a Continental Divide
The Brooks Range serves as the northernmost continental drainage divide in North America. This barrier separates the region’s watersheds, directing water flow in two opposing directions. Waters originating on the northern slopes flow into the Arctic Ocean, specifically the Beaufort and Chukchi Seas. Conversely, precipitation falling on the southern slopes drains south and west, eventually feeding into the Bering Sea or the Yukon River system.
The mountain chain also acts as a substantial climatic and ecological barrier, roughly delineating the summer position of the Arctic front. The land north of the range, the North Slope, experiences an extremely cold and dry Arctic climate. South of the mountains, the climate is slightly moderated, falling into the subarctic zone. This divide also marks the northern limit of the tree line. The northern side is dominated by tundra ecosystems, while the south supports the northern reaches of black spruce and other boreal forest species.