The West Virginia. Cyclopedia
Monongahela is a term applied to Native Americans of a wide-ranging settlement area of the Ohio River system that included the Monongahela, Youghiogheny and Casselman tributaries. This occupation encompassed western Pennsylvania and the adjoining areas of eastern Ohio, West Virginia, and Maryland, roughly during the period of 900 to 1600 A.D.
The Monongahela People by Dennis Stahl, from website of the Somerset County Archaeology Society (PA).
The Golden Harvest of the Fort Ancient and Monongahela Cultures from Wonderful West Virginia.