in which part of the u.s. is the majority of state boundaries based upon natural features
List of river borders of U.S. states Because of its unique history, many of the boundaries of the political divisions of the United States were artificially constructed (rather than being permitted to evolve and drawn using natural features of the landscape). Therefore, many U.S. states have straight lines as boundaries, especially in the West. However, there are a number of states, particularly in the Midwest, North and South with at least partial river borders.