Jefferson and Bighorn Formations: locally includes Beartooth Butte Formation in central Montana

Jefferson Formation (Dj): Birdbear Member (upper part of formation): light to medium gray, sucrosic dolomite. Lower part of formation: grayish black, commonly petroliferous dolomite or limestone that may be interbedded with light gray quartzite. Marine. Thickness as much as 520 m (1,706 ft). Bighorn Formation (Ob): Yellowish gray to very pale orange crystalline dolomite with local basal sandstone. Marine shelf. Thickness as much as 120 m (394 ft). In central Montana - Beartooth Butte Formation: Light gray and grayish red dolomite and limestone breccia and conglomerate, sandy and silty dolomite, and dolomitic siltstone, sandstone, and shale. Isolated outcrops throughout central Montana. Estuarine. Thickness as much as 50 m (164 ft).
State Montana
Name Jefferson and Bighorn Formations: locally includes Beartooth Butte Formation in central Montana
Geologic age Devonian and Ordovician
Lithologic constituents
Major
Sedimentary > Carbonate > Limestone (Bed)
Sedimentary > Carbonate > Dolostone (Bed)
Minor
Sedimentary > Clastic > Mudstone > Shale (Bed)
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Clastic > Conglomerate (Bed)limestone breccia and conglomerate
Sedimentary > Clastic > Siltstone (Bed)dolomitic siltstone
Incidental
Metamorphic > Metasedimentary > Metaclastic > Quartzite
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 - Carbon