Diffendal, R. F., Jr., Voorhies, M. R., 1994. Geologic Framework of the Niobrara River Drainage Basin and Adjacent Areas in South Dakota Generally East of the 100th Meridian West Longitude and West of the Missouri River (GSI-9) 13 pp., size 8.5" x 11". Description This report covers the geology of the eastern part of the Niobrara Basin in Nebraska and adjacent parts of South Dakota. This geology includes the present scene and the geologic history of the basin. Out of print, unbound copy available.