Columbia subject headings:
Frontier and pioneer life--United States.
Nature conservation--United States.
United States--Civilization.
Harvard subject headings:
Frontier and pioneer life--United States
Human ecology--United States--History.
Nature conservation--United States.
Nature--Effect of human beings on--United States
Nature--Social aspects--United States.
Philosophy of nature--United States.
United States--Civilization.
United States--Environmental conditions.
Values--United States
Princeton subject headings:
Frontier and pioneer life--United States.
Nature conservation--United States.
United States--Civilization.