Gammon Formation

Dark gray mudstone and shale with numerous red-weathering ferruginous concretions, and thin, fine-grained sandstone or siltstone beds interbedded with shale. Offshore marine. Thickness as much as 260 m (853).
State Montana
Name Gammon Formation
Geologic age Cretaceous
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone (Bed)
Sedimentary > Clastic > Mudstone > Shale (Bed)
Minor
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Clastic > Siltstone (Bed)
References

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 Big Horn - Broadwater - Rosebud