The Campanian-Maastrichtian Baculite Zonal Sequence in the Pierre Shale, Berwind Canyon. Las Animas County, Colorado
— Paul L. Sealey, Keith Berry, and Spencer G. Lucas

At Berwind Canyon, northeast of Trinidad, Colorado, the upper 100 m of the Pierre Shale yield the most extensive upper Campanian-lower Maastrichtian record of fossil mollusks (primarily bivalves and ammonites) in the Colorado portion of the Raton Basin. This record includes the zonal baculitid ammonites (from oldest to youngest) Baculites compressus (Say, 1820), B. cuneatus Cobban, 1962, B. reesidei Elias, 1933, B. jenseni Cobban, 1962, B. eliasi Cobban, 1958, B. baculus Meek and Hayden, 1861, B. grandis Hall and Meek, 1855 and B. clinolobatus Elias, 1933, as well as other index mollusks (e.g., scaphitid ammonites, gastropods, and inoceramids). Thus, we identify eight ammonite zones in the condensed section of the Pierre Shale in Berwind Canyon, which record an important phase in the tectonic evolution of the basin.