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BTChronostratigraphic Units
 .Phanerozoic
 ..Mesozoic
 ...Cretaceous
 ....Upper Cretaceous
 .....Lewis Shale
RTNew Mexico
 Wyoming
 Colorado
SNLewis and Meeteetse formations throughout N central Wyoming considered stratigraphic equivalents with Lewis being applied generally in areas where marine strata are present and Meeteetse in areas where rocks are nonmarine in character. W Colorado, NW New