At Cumberland Gap four natural features combine to open the way through the Appalachian Mountain range. At one time this land was flat and Yellow Creek flowed south into Powell River. Then the earth began to push up, and as Cumberland Mountain rose, the creek cut in it a notch, or gap
(1, below). The mountain rose faster than the creek could enlarge the gap, and the creek was diverted northward into Cumberland River. North of the gap is Middlesboro Basin (2), a large flat area perhaps formed by the impact of a meteor or the collapse of a huge underground cavern. Yellow Creek Valley (3) leads to "the Narrows" (4), a gap that crosses Pine Mountain and opens into the Bluegrass region of Kentucky. These four features are a natural door through the mountains, allowing travel in either direction and joining the eastern seaboard with the Mississippi west.