how to determine the age of a river
List of rivers by age Generally, the age is estimated based primarily upon the age of any mountains it dissects; the age of the sea or ocean to which it eventually outflows can be irrelevant; for example, several rivers of the east side of the Appalachian Mountains of the Atlantic Ocean, which did not exist 130 million years ago.[citation needed] If a river fully dissects a mountain range, then this generally indicates that the river existed at least at the time that the mountain range rose.