The Kobuk Valley National Park contains, not one but three active sand dunes: the Great Kobuk Sand Dunes, the Little Kobuk Sand Dunes and the Hunt River Dunes, that together cover 20,000 acres of land, but at one time covered as many as 200,000 acres immediately after the retreat of Pleistocene glaciation. The dunes were believed to have formed by the grinding action of glaciers and subsequent deposition of sand by glacial-outwash streams emptying into what was once a large lake in the Kobuk valley, some 150,000 years ago. The 25-square-km Great Kobuk Sand Dunes constitute the largest active sand dunes found in the Arctic.
Wind have sculpted the sand into dunes that rise as high as 100 feet and are stabilized by the area's vegetation. Although the dunes are located close to the Arctic Circle, summer temperatures there can soar to 100 degrees Fahrenheit.
The rest of the park is wetlands formed by the Kobuk River that runs through the park. A great variety of wildlife is found in the Kobuk Valley, including grizzly and black bears, moose, foxes and other small fur-bearing mammals, wolves, and numerous waterfowl. The Western Arctic caribou herd, the largest in Alaska at 490,000 animals, travels through the park during its migration from its calving grounds on the northern slopes of the Brooks Range to where the herd winters south of the range.