Columbia subject headings:
Erosion.
Geology--Appalachian Mountains.
Physical geography--Appalachian Mountains.
Rivers--United States.
Harvard subject headings:
Erosion.
Geology--Appalachian Mountains.
Physical geography--Appalachian Mountains.
Rivers--United States
Princeton subject headings:
Erosion.
Geology--Appalachian Mountains.
Physical geography--Appalachian Mountains.
Rivers--United States.