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There is a Monongahela River and the Monongahela National Forest in the state of West Virginia.
Allegheny River (from the North East) and the Monongahela River (from the South East) meet to form the Ohio River.
The Allegheny, The Monongahela and the Ohio.
The Monongahala River (i'm not quite sure i spelled that right), and the Allegheny River
The Allegheny River and the Monongahela River