Columbia subject headings:
Harvard subject headings:
Natural areas--Economic aspects--United States.
Natural resources--United States
Public lands--United States.
Recreation areas--Economic aspects--United States.
Wilderness areas--Economic aspects--United States.
Princeton subject headings:
Natural areas--Economic aspects--United States.
Natural resources--United States.
Public lands--United States.
Recreation areas--Economic aspects--United States.
Wilderness areas--Economic aspects--United States.