Otter Formation

Green, grayish green, gray, and subordinate reddish brown shale interbedded with light brown or gray limestone. Open and semirestricted marine. Thickness as much as 150 m (492 ft).
State Montana
Name Otter Formation
Geologic age Mississippian
Lithologic constituents
Sedimentary > Carbonate > Limestone (Bed)
Sedimentary > Clastic > Mudstone > Shale (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 Cascade - Fergus - Golden Valley - Judith Basin - Lewis and Clark - Meagher