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2. Sabloff, J. A. in The Classic Maya Collapse (ed. Culbert, T. P.) (University of New Mexico Press, Albuquerque, 1973).
3. Culbert, T. P. The Classic Maya Collapse (University of New Mexico Press, Albuquerque, 1973).
4. Willey, G. R. & Shimkin, D. in The Classic Maya Collapse (ed. Culbert, T. P.) (University of New Mexico Press, Albuquerque, 1973).
5. Sidrys, R. thesis Univ. California, Los Angeles (1976).