Large tilted mountain with may layers and person standing in the foreground

NPS/Rachel Sullivan

Gates of the Arctic National Park and Preserve protects a landscape encompassing the central Brooks Range, a mountain range located completely north of the Arctic Circle. Like much of Alaska, these mountains were formed when large sections of the Earth's crust called terranes were transported here by the process of plate tectonics. Hiding within the layers of these terranes there can be fossils of once-living organisms from throughout history, some as old as 400 million years!

In addition to this tectonic activity, many of the peaks in the park, like the Arrigetch Peaks, started out as magma below the earth’s surface and slowly cooled overtime to become solid rock called granite. As this granite was uplifted by the collision of the plates, the rocks above it were eroded away by forces on the earth’s surface.

One of those forces that has helped shape the landscapes of the park is glaciation. The Brooks Range was mostly covered by ice during the last Ice Age unlike Interior Alaska that was mostly ice-free. Glaciers carved out sharp peaks, ridges, valleys, and lakes, while leaving behind deposits that trace the history of glacial retreat, shaping the landscape into the rugged mountains of today.

All of these fascinating natural processes came together to create the beautiful and scenic Gates of the Arctic Natural Park and Preserve. When you visit the park remember to take only pictures and leave the rocks and fossils where they are so they can continue to be a part of this dynamic landscape.

Color coded geologic map of Gates of the Arctic

Map modified from Wilson et al. (2015)

The Geologic Map above reflects the history of geology in northern Alaska described above.

The Arrigetch Peaks are made of granite, a type of igneous rock, that is distinctive from the schist belt, a type of metamorphic rock, that surrounds the peaks.

Much of the park is underlain by the Endicott Group, a group of ancient sedimentary rocks that formed on the ocean floor millions of years ago.

To delve into more detail about park geology visit the resources below!
Connecting Further

Additional NPS Resources

Arctic Geodiversity Atlas

Arctic Park Paleontological Inventory

Last updated: April 4, 2023

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