About a quarter half of Nebraska is covered by the Sand Hills, so called because the hills are entirely made of sand. The Sand Hills made up of Pleistocene sand dunes derived from glacial outwash eroded from the Rockies, and now (mostly) stabilized by vegetation. The most attractive part of this hills are although they look like a sheet of clouds, while watching a winter photo of these Hills covered with snow makes to think for a while whether they are really sand hills.