1. Type sections and stratigraphy of the members of the Blackleaf and Marias River Formations (Cretaceous) of the Sweetgrass arch, Montana : a report of a formal subdivision and age assignments of a classic Cretaceous area Publication/Creation: Washington : U.S. Govt. Print. Off, 1976 Resource Type: Book Is Part Of: U.S. Geological Survey professional paper, no. 970-975. Access & Availability: Loading