Editing Ohio River (section)

==Geology==
[[File:Historical Collections of Ohio- An Encyclopedia of the State; History Both General and Local, Geography with Descriptions of Its Counties, Cities and Villages, Its Agricultural, Manufacturing, Mining (14770614544).jpg|thumb|upright=1.5|Glacial Lake Ohio]]

From a geological standpoint, the Ohio River is young. Before the river was created, large parts of [[North America]] were covered by water forming a saltwater lake about 200 miles across and 400 miles in length. The [[bedrock]] of the Ohio Valley was mostly set during this time.<ref name="McNeese-2004" /> The river formed on a piecemeal basis beginning between 2.5 and 3&nbsp;million years ago. By the movement of [[glacier]]s during the earliest [[Laurentide Ice Sheet|ice ages]], the contemporary river [[drainage]]s of the [[Kanawha River|Kanawha]], [[Big Sandy River (Ohio River tributary)|Sandy]], [[Kentucky River|Kentucky]], [[Green River (Kentucky)|Green]], [[Cumberland River|Cumberland]] and [[Tennessee River|Tennessee]] rivers northward created the Ohio system and the course of early [[tributaries]] of the Ohio River, including the [[Monongahela River|Monongahela]] and the [[Allegheny River|Allegheny]] rivers, were set.<ref name="McNeese-2004" /> The [[Teays River]] was the largest of these rivers. The modern Ohio River flows within segments of the ancient Teays. The ancient rivers were rearranged or consumed.

The section of the river that runs southwest from Pittsburgh to [[Cairo, Illinois]], is around tens of thousands of years old.

===Upper Ohio River===
The upper Ohio River formed when one of the glacial lakes overflowed into a south-flowing tributary of the [[Teays River]]. Prior to that event, the north-flowing Steubenville River (no longer in existence) ended between [[New Martinsville]] and [[Paden City, West Virginia]]. The south-flowing Marietta River (no longer in existence) ended between the present-day cities. The overflowing lake carved through the separating hill and connected the rivers. The floodwaters enlarged the small [[Marietta, Ohio|Marietta]] valley to a size more typical of a large river. The new large river subsequently drained glacial lakes and melting glaciers at the end of the ice ages. The valley grew during and following the ice age. Many small rivers were altered or abandoned after the upper Ohio River formed. Valleys of some abandoned rivers can still be seen on satellite and aerial images of the hills of Ohio and West Virginia between Marietta, Ohio, and [[Huntington, West Virginia]].

===Middle Ohio River===
The middle Ohio River formed in a manner similar to that of the upper Ohio River. A north-flowing river was temporarily dammed by natural forces southwest of present-day [[Louisville]], creating a large lake until the dam burst. A new route was carved to the Mississippi. Eventually, the upper and middle sections combined to form what is essentially the modern Ohio River.