fall line boundary between an upland region and a coastal plain across which rivers from the upland region drop to the plain as falls or rapids http://bungakubu.kokushikan.ac.jp/chiri/EarthWacht/Nov2003/FallLine.jpg
Cities sprang up east of the Fall Line, because ships needed a place to unload and switch their cargo to land- based carriers. http://photo.pds.org:5005/student/extmedia?id=ar190640&st=appalachian+mountains&em=lr005123
There was even a “Fall Line Road.” http://freepages.genealogy.rootsweb.ancestry.com/~bruckner/maps/colonial_roads_1750.jpg
natural boundary a boundary based on a natural feature of the land – for example, a river, a mountain range, a cliff, or a coast http://wwp.greenwichmeantime.com/time-zone/usa/virginia/map.htm
http://wwp.greenwichmeantime.com/time-zone/usa/oklahoma/ Are any of Oklahoma’s borders natural boundaries?
Google earth image of Red River at Okla/Tx border http://www.notsogreen.com/images/3230812955_GoogleLarge.jpg
artificial boundary a boundary decided without a natural feature of the land to guide the boundary This usually is based on longitude or latitude. http://wwp.greenwichmeantime.com/time-zone/usa/utah/