Paleontology, stratigraphy and biostratigraphy of the upper Cretaceous Lewis Shale near Waterflow, San Juan County, New Mexico
— Paul L. Sealey and Spencer G. Lucas

Marine invertebrate fossils collected from the lower and upper parts of the Lewis Shale near Waterflow, New Mexico are of late Campanian age. The fauna from the lower part includes cf. Anisomyon sp., "Inoceramus" subcircularis, "Inoceramus (Endocostea) barabini, and Baculites sp. Invertebrates are abundant in small limestone concretions in a 6-m-thick interval in the upper part of the Lewis Shale and include the following taxa: cf. Anisomyon sp., "Inoceramus" (Endocostea) barabini, Eutrephoceras dekayi, Baculites sp., Placenticeras placenta, Placenticeras syrtale, and Didymoceras nebrascense. The occurrence of D. nebrascense is particularly important because it indicates the presence of the Didymoceras nebrascense zone, which is of early late Campanian age. The Didymoceras nebrascense zone also occurs in the Lewis Shale on the eastern side of the San Juan Basin, New Mexico and in the Pierre Shale in northeastern New Mexico.