Columbia subject headings:
Conservation of natural resources--Mississippi River Valley.
Mississippi River Corridor Study Commission (U.S.)
Mississippi River Valley--Civilization.
Mississippi River Valley--Environmental conditions.
Natural areas--Interpretive programs--Mississippi River Valley.
Harvard subject headings:
Conservation of natural resources--Mississippi River Valley.
Cultural property--Protection--Mississippi River Valley.
Mississippi River Corridor Study Commission (U.S.)
Mississippi River Valley--Civilization.
Mississippi River Valley--Environmental conditions.
Natural areas--Interpretive programs--Mississippi River Valley.
Princeton subject headings: