The biggest national parks of the United States

Kobuk Valley

Kobuk Valley has 61 miles (98 km) of the Kobuk River and three regions of sand dunes. Created by glaciers, the Great Kobuk, the Little Kobuk, and the Hunt River Sand Dunes can reach 100 feet (30 m) high and 100 °F (38 °C), and they are the largest dunes in the arctic. Twice a year, half a million caribou migrate through the dunes and across river bluffs that contain ice age fossils.