Named as one of six members of the Madison Limestone for exposures at Little Tongue River in NW1/4 sec 26, T56N, R87W, Sheridan Co., WY in the Powder River basin. Subsurface data suggests this member is present in the Bighorn, Wind River, and Powder River basins. These exposures are also the type section. Consists of cliff-forming, medium- to thick-bedded, cherty, crinoidal limestone and dolomitic limestone, but at some localities is predominately or entirely crinoidal dolomitic limestone and dolomite. At most localities is marked by a solution breccia that represents an interval of evaporite, carbonate, and terrigenous rocks. Anhydrite occurs at this level in the subsurface. Ranges in thickness from 24 to 87 m. Rests conformably on Big Goose Member (new name) of Madison. Is overlain conformably either by Bull Ridge Member of Madison or disconformably by Amsden Formation where Bull Ridge eroded. Is fossiliferous (spiriferoid brachiopods, corals, forams). Assigned a Meramecian or Late Mississippian age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

As a member of the Madison Limestone overlies Big Goose Member of Madison; unconformably underlies Darwin Member of Amsden Formation north of Fremont Canyon, Natrona Co, WY in the Wind River basin; underlies Bull Ridge Member of Madison on Casper Mountain., Natrona Co; unconformably underlies Darwin Sandstone Member of Amsden Formation at Banner Mountain and Box Elder Canyon, Converse Co, in the Powder River basin; underlies Darwin Sandstone Member (new affiliation) of Hartville Formation, in Hartville Canyon, Platte Co in the Denver basin. Replaces use of Guernsey Formation (part) in southeast WY (as do Fremont Canyon Sandstone and Englewood Formation). Is 50 ft (15.3 m) thick at Casper Mountain to 93.5 ft (28.6 m) thick at Fremont Canyon. Thickens east and west from Casper Mountain. Is the most widespread of the three members of the Madison. Includes crinoidal debris, brachiopods, forams, bryozoans, gastropods, corals, and ostracods. Is of late Osagean or Early Mississippian age. Thought to be a leached evaporite, terrigenous, and carbonate sequence deposited in a shallow subtidal offshore marine environment.

Source: GNU records (USGS DDS-6; Denver GNULEX).