PHOTO CREDITS

Frontispiece courtesy Anthropology Department, Southern Methodist University (SMU)

Cover photo courtesy U. S. Geological Survey (USGS)

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[11] USGS
[12] USGS
[14], [16], [17] Willard F. Libby
[18] University of Arizona
[21] Massachusetts Institute of Technology
[22] Graduate Research Center of the Southwest
[23] Graduate Research Center of the Southwest
[25] Robert L. Fleischer
[26] Perkin-Elmer Corporation
[30] University of Texas
[32] Graduate Research Center of the Southwest
[36] Massachusetts Institute of Technology
[40] Des Bartlett, Armand Denis Productions
[43] Anthropology Department, SMU
[44] USGS
[47] USGS
[59] Author’s photo courtesy Graduate Research Center of the Southwest