- Bronowski, Jacob, Science and Human Values, Harper Torch Books, 1965. pp. 14–16.
- Krutch, Joseph Wood, ”Conservation Is Not Enough,” University of Utah Press, Salt Lake City, pp. 5–6.
- Marshall, Robert, “Wildlands, A Part of Man's Environment,” The Yearbook of Agriculture: 1963, Dept, of Agriculture, Washington, D.C., p. 348.
- Newhall, Nancy; Adams, Ansel, This Is the American Earth, Sierra Club/Ballantine Books, San Francisco, 1968, p. 84.
- Udall, Stewart L., The Quiet Crisis, Holt, Rinehart, and Winston, New York, 1963.
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