Kootenai Formation (Kk, Kku, Kkm, Kkl): Red, maroon, and olive gray mudstone, tan or gray siltstone, calcareous concretions, limestone beds, and several prominent sandstone beds that include the Greybull Member (top of the formation in south-central Montana) and the Sunburst Member (middle to lower part of the formation in northwest-central Montana), both dominantly quartzose sandstone. Basal Cutbank or Pryor Conglomerate. Alluvial plain with local marine influence in the north. Thickness as much as 335 m (1,099 ft). Morrison Formation (Jm): Green, gray, or red mudstone and marlstone with subordinate limestone and sandstone beds. Upper part Neocomian age in central Montana and contains carbonaceous black shale and coal. Fluvial, paludal, and lacustrine. Thickness as much as 180 m (590 ft). Thaynes Formation: Gray and tan limestone with interbedded siltstone, shale, and tan sandstone. Locally with red shale tongues. Marine. Thickness as much as 290 m (950 ft). Woodside Formation: Maroon and red siltstone, dolomite, and shale. Tidal flat. Thickness as much as 250 m (820 ft). Dinwoody Formation (TRd): Interbedded green siltstone, shale, sandstone, and carbonate that grades eastward into red shale, siltstone, and anhydrite. Nearshore and restricted marine. Thickness as much as 330 m (1,083 ft).
Vuke, S.M., Porter, K.W., Lonn, J.D., and Lopez, D.A., 2007, Geologic Map of Montana - Compact Disc: Montana Bureau of Mines and Geology: Geologic Map 62-C, 73 p., 2 sheets, scale 1:500,000. This map was digitized in 2012 as a result of a contract between the U.S. Geological Survey and the Montana Bureau of Mines and Geology.