Kootenai Formation

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).
State Montana
Name Kootenai Formation
Geologic age Cretaceous
Lithologic constituents
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Clastic > Mudstone (Bed)
Sedimentary > Clastic > Siltstone (Bed)
Sedimentary > Clastic > Conglomerate (Bed)
Sedimentary > Carbonate > Limestone (Bed)

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.

NGMDB product
Counties Beaverhead - Big Horn - Blaine - Broadwater - Carbon - Cascade - Chouteau - Fergus - Flathead - Gallatin - Glacier - Golden Valley - Hill - Jefferson - Judith Basin - Lewis and Clark - Liberty - Madison - Meagher - Musselshell - Park - Petroleum - Phillips - Pondera - Stillwater - Sweet Grass - Teton - Wheatland - Yellowstone