The term Great American Desert was used in the 19th century to describe the part of North America east of the Rocky Mountains to about the 100th meridian. It can be traced to Stephen H. Long's 1820 scientific expedition which put the Great American Desert on the map. The area is now usually referred to as the High Plains, and the original term is now sometimes used to describe the arid region of North America, which includes parts of northwestern Mexico and the American southwest.