Proceeding westward, the Appalachian Plateau topography gradually gives way to gently rolling hills and then (in central Ohio) to flat lands converted principally to farms and urban areas. This is the beginning of the vast Interior Plains of North America. As a result, prairies cover most of the Great Plains states. Iowa and much of Illinois lie within an area called the prairie peninsula, an eastward extension of prairies that borders conifer and mixed forests to the north, and hardwood deciduous forests to the east and south.