The Red Hills are unique to Kansas, and their distinctive color comes from iron in the soil that rusts. They were formed 100 million years ago from red shale, sandstone, siltstone, gypsum, dolomite, and salt. Much of the road was constructed using horses and mules, and part of Highway 160 was built as a Works Progress Administration (WPA) project. During World War II, the road was vital to moving war materials.