Coal resource classification system of the U.S. Geological Survey
Gordon H. Wood
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Thomas M. Kehn
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M. Devereux Carter
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William C. Culbertson
Timothy J. Rohrbacher
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James A. Luppens
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Lee M. Osmonson
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David C. Scott
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Philip A. Freeman
R. D. Merritt
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G. R. Eakins
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K. J. Johnson