Greenhorn formation (MTKg;0)

State	Montana
Name	Greenhorn formation
Geologic age	Phanerozoic \| Mesozoic \| Cretaceous-Late
Original map label	Kg
Primary rock type	mudstone
Secondary rock type	limestone
Other rock types	bentonite
Lithologic constituents	Major Sedimentary > Clastic > Mudstone (Bed) Minor Sedimentary > Carbonate > Limestone (Bed) Incidental Sedimentary > Clastic > Mudstone > Claystone > Bentonite (Bed)
Map references	Ross, P.R., Andrews, D.A., and Witkind, I.J., 1955, Geologic map of Montana: U.S. Geological Survey, 2 sheets, scale 1:500,000.
Unit references	Viele, G.W. and Harris, F.G., III, 1965, Montana Group stratigraphy, Lewis and Clark County, Montana: American Association of Petroleum Geologists Bulletin, v. 49, no. 4, p. 379-417. Obradovich, J.D. and Cobban, W.A., 1975, A time-scale for the Late Cretaceous of the Western Interior of North America, in Caldwell, W.G., ed., The Cretaceous System in the Western Interior of North America: Geological Association of Canada S Richards, P.W. and Rogers, C.P., Jr., 1951, Geology of the Hardin area, Big Horn and Yellowstone Counties, Montana: U.S. Geological Survey Oil and Gas Investigations Map OM-111, 2 sheets, scale 1:63,360 (Reprinted 1975). [http://pubs.er.usgs.gov/publication/om111] Merewether, E.A., 1996, Stratigraphy and tectonic implications of Upper Cretaceous rocks in the Powder River basin, northeastern Wyoming and southeastern Montana, in Evolution of sedimentary basins--Powder River basin: U.S. Geological Survey Bul [http://pubs.er.usgs.gov/publication/b1917T] Knechtel, M.M. and Patterson, S.H., 1955, Bentonite deposits of the northern Black Hills district, Montana, Wyoming, and South Dakota: U.S. Geological Survey Miscellaneous Field Studies Map MF-36, 2 sheets, scale 1:48,000. [Also, U.S. Geologi [http://pubs.er.usgs.gov/publication/mf36] Robinson, C.S., Mapel, W.J. and Bergendahl, M.H., 1964, Stratigraphy and structure of the northern and western flanks of the Black Hills uplift, Wyoming, Montana, and South Dakota: U.S. Geological Survey Professional Paper 404, 134 p. [http://pubs.er.usgs.gov/publication/pp404] Vuke, S.M., Wilde, E.M., Bergantino, R.N., Colton, R.B., 2001, Geologic map of the Alzada 30' x 60' quadrangle, eastern Montana: Montana Bureau of Mines and Geology Open File Report 433, scale 1:100,000. Cobban, W.A., 1951, Colorado shale of central and northwestern Montana and equivalent rocks of the Black Hills: American Association of Petroleum Geologists Bulletin, v. 35, no. 10, p. 2170-2198. Rubey, W.W., 1931, Lithologic studies of fine-grained Upper Cretaceous sedimentary rocks of the Black Hills region, IN Shorter contributions to general geology, 1930: U.S. Geological Survey Professional Paper 165-A, p. A1-A54. [http://pubs.er.usgs.gov/publication/pp165A] Knechtel, M.M. and Patterson, S.H., 1962, Bentonite deposits of the northern Black Hills district, Wyoming, Montana, and South Dakota, in Contributions to economic geology, 1958: U.S. Geological Survey Bulletin 1082-M, p. M893-M1030. [http://pubs.er.usgs.gov/publication/b1082M]
Geographic coverage	Carter