The fossils from the middle third of the lower shale and siltstone member consist mostly of a small smooth baculite and a large, flattened Inoceramus that becomes nearly smooth in the adult. This Inoceramus resembles I. sagensis Owen from the upper part of the Pierre shale in the western interior region. This resemblance suggests an age of late Campanian to early Maestrichtian. Another Inoceramus in collection 55AGz301 is probably an undescribed species. We obtained the identical species on Granite Creek at 55AGz13. It resembles I. amukusensis Nagao and Matsumoto from Japan which has about the same range as I. undulatoplicatus (equals I. japonicus). I suspect that the species in question from Matanuska formation occurs stratigraphically higher than I. undulatoplicatus Roemer.