Farmland plains meet the Nebraska Sand Hills just north of Lexington, Nebraska. This unique region, which covers roughly 20,000 square miles (51,000 square km), contains mixed-grass prairies and grass-stabilized sand dunes. Average elevation here gradually increases from 1,800 feet (550 m) in the east to nearly 3,600 feet (1,100 m) in the west, as the sand hills approach the foothills of the Rocky Mountains.