미국 네브라스카의 Sand Hill (빙기의 산물)
The Sand Hills cover about a quarter of the U.S. Great Plains state Nebraska. These ancient sand dunes are from the Pleistocene Epoch (the geologic time period spanning about 1.8 to about 10,000 years ago). They are made of sediment eroded from the Rocky Mountains by the monumental Pleistocene glaciers, washed out into the plains, and now mostly stabilized by grassland vegetation. Covering an ar..