The central Brooks Range is a remote area of rugged, glaciated east-trending ridges that rise to elevations of 8,000 feet. This range is part of the Rocky Mountain system that stretches completely across the northern part of Alaska. Gates of the Arctic National Park and Preserve spreads across three land classifications: Arctic Foothills, Arctic Mountain, and Western Alaska. Two primary mountain ranges make up the central Brooks Range — the Endicott and Schwatka mountains. Several episodes of uplift, deformation, and intrusion have produced complex patterns of foldings, fracturing, and overlapping thrust fault blocks. Uplift, erosion, and heavy glaciation account for the rugged mountain profiles and U-shaped valleys evident today. Metamorphic rocks, primarily quartz mica schist and chloritic schists, belt the south flank of the range. There are also a few small bodies of marble and dolomites. Granitic intrusion created the rugged Arrigetch Peaks and Mt. Igikpak areas.

Ridge to Cickedhat from Pass 2
© MacGill Adams, Wilderness Alaska

Four major glaciations have been recognized within this region of the Brooks Range. The first glaciation (Anaktuvuk River) took place more than one-half million years ago. The second (Sagavanirktok River) is thought to be broadly equivalent to the Illinoian glaciation of central North America. The last two glacial periods (Itkillik and Walker Lake) are thought to correlate with the Wisconsin advance in central North America. Glaciers were generated at relatively high altitudes near the crest of the range during the more extensive glaciations. Ice flowed from these sources southward through the major valley systems to terminate at and beyond the south flank of the range. Terminal glacial moraines created dams that formed large lakes along the southern foothills.

The primary metallic minerals found within the region include copper, gold, lead, and zinc. The major known deposits of minerals occur in a schist belt that generally lies south and west of the park in the Ambler mining district and may extend into the park. The only known mineral produced in the park is gold. Placer mines operated historically in the Nolan-Hammond River areas near Wiseman, the North Fork, Wild Lake, and Mascot Creek. There has also been some limited gold production in the Noatak River drainage near Midas Creek.

The northern portion of the park has petroliferous rocks within drilling depths. The principal reservoir rock in this area is the upper Paleozoic Lisburne formation. There are some potentially large hydrocarbon-bearing structures north of the range front, and petroleum may also exist in Cretaceous or Devonian formations. The current economic situation will not encourage a great deal of interest in this petroleum potential in the near future; however, eventually it may be more economically feasible to investigate further.

The federal lands within the park and preserve have been withdrawn from additional mineral location, entry, and patent under the United States mining laws and disposition under the mineral leasing laws. However, the unit was also established subject to valid existing rights, including existing recorded unpatented mining claims established under the U.S. mining laws. Federal lands in the unit are closed to oil and gas leasing.

The paleontological resources of Gates of the Arctic National Park and Preserve consist of small fossils of invertebrates, shells, and corals found in the metamorphosed rocks of the Brooks Range. A few plant fossils have been found in sandstones near the divide. Most of these fossils are inconspicuous and difficult to identify.

The value of these fossils is largely scientific. They have been examined and collected by scientists, particularly by members of the U.S. Geological Survey, over the past 30 years. They provide information useful in dating rocks and establishing the geological sequence related to life forms.

The entire Noatak River drainage, of which the headwaters are in Gates of the arctic is internationally recognized as a biosphere reserve in the United Nation's"Man in the Biosphere" program.

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