Millions of years ago, the flat floor of the sea became the landscape of the Great Plains as the seas were displaced, according to "The Geologic Story of the Great Plains" by Donald E. Trimble. Over the course of thousands of years, wind, streams and glaciers helped to create thick overlayers of sedimentary rock.
The underlying rock structure of most of the Great Plains is comprised mostly of sedimentary rock. The High Plains make up the largest portion. The Badlands of South Dakota have experienced deep erosion in the sedimentary rock.
The northern plains are home to extremely cold winters and hot, dry summers. Hail storms and blizzards are common occurrences. This region also experiences more tornadoes than any other region in the U.S.
