Kobuk Valley National Park provides protection for several important geographic features, including the central portion of the Kobuk River, the 25-sqaure-mile Great Kobuk Sand Dunes, and the Little Kobuk and Hunt River dunes.Sand created by the grinding action of ancient glaciers has been carried to the Kobuk Valley by both wind and water. Dunes now cover much of the southern portion of the Kobuk Valley, where they are naturally stabilized by vegetation. River bluffs, composed of sand and standing as high as 150 feet, hold the fossils of Ice Age mammals.Nearly half a million caribou migrate through the Park twice a year ñ north in the spring, south in the fall. Their tracks crisscross the 25 square miles of the Great Kobuk Sand Dunes. The lofty dunes are a sculpted desert in the middle of a wilderness of wetlands. The Kobuk River on the north side of the dunes winds roughly 61 miles through the park, providing a travel path for people and wildlife.