Pennsylvanian sedimentary rocks in the Sandia Mountains, New Mexico, compose an ~586 m thick stratigraphic section. The Atokan–Desmoinesian Sandia Formation at the base of this section is dominated by shallow marine deposits but also contains terrestrial beds, including thin coals; it was deposited in a fluviodeltaic to shallow marine environment. The overlying Desmoinesian Gray Mesa Formation records deposition of marine carbonate rocks. Above that, the Desmoinesian–Virgilian Atrasado Formation and Virgilian Bursum Formation are mixed siliciclastic-carbonate strata that represent shallow marine and nonmarine paleoenvironments. Fossilized remains of animals and plants occur throughout the section. Plant remains record a significant environmental change across the Middle–Late Pennsylvanian boundary from largely wetland taxa to mixed floras with xeromorphic elements, such as conifers, paralleling changes in the coal basins of central Pangea. Unit age determinations are primarily based on fusulinid and conodont
