Ordovician, undifferentiated (MTOu;0)

State	Montana
Name	Ordovician, undifferentiated
Geologic age	Phanerozoic \| Paleozoic \| Ordovician
Original map label	Ou
Primary rock type	dolostone (dolomite)
Secondary rock type	arenite
Other rock types	medium-grained mixed clastic; limestone; chert
Lithologic constituents	Major Sedimentary > Clastic > Sandstone > Arenite (Bed) Sedimentary > Carbonate > Dolostone (Bed) Minor Sedimentary > Carbonate > Limestone (Bed) Sedimentary > Clastic > Mixed-clastic (Bed) Incidental Sedimentary > Chemical > Chert (Lense)
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	Van Gosen, B.S., Elliott, J.E., LaRock, E.J., du Bray, E.A., Carlson, R.R., and Zientek, M.L., 2000, Generalized geologic map of the Absaroka-Beartooth study area, south-central Montana: U.S. Geological Survey Miscellaneous Field Studies Map MF-2338, sca [http://pubs.er.usgs.gov/publication/mf2338] Ruppel, E.T., O'Neill, J.M., and Lopez, D.A., 1993, Geologic map of the Dillon 1o x 2o quadrangle, Idaho and Montana: U.S. Geological Survey Miscellaneous Investigations Series Map I-1803-H, scale 1:250,000. [http://pubs.er.usgs.gov/publication/i1803H] O'Neill, J.M., Christiansen, R.L., 2002, Geologic map of the Hebgen Lake quadrangle: Montana Bureau of Mines and Geology Open File Report 464, 21 p, scale 1:100,000. Dahl, G.G., Jr., 1971, General geology of the area drained by the North Fork of the Smith River, Meagher County, Montana: Butte, Montana College of Mineral Science and Technology, M.S. thesis. Wilson, A.B., and Elliott, J.E., 1997, Geologic maps of western and northern parts of Gallatin National Forest, south-central Montana: U.S. Geological Survey Geologic Investigations Series Map I-2584, 2 sheets, scale 1:126,720. [http://pubs.er.usgs.gov/publication/i2584] Lopez, D.A., 2000, Geologic map of the Bridger 30' x 60' quadrangle, Montana: Montana Bureau of Mines and Geology Geologic Map 58, scale 1:100,000. Blackstone, D.L., Jr., 1975, Geology of the East Pryor Mountain quadrangle, Carbon County, Montana: Montana Bureau of Mines and Geology Special Publication 69, 13 p., 1 plate, scale 1:24,000. Kellogg, K.S., and Williams, V.S., 2000, Geologic map of the Ennis 30' x 60' quadrangle, Madison and Gallatin Counties, Montana, Park County, Wyoming: U.S. Geological Survey Miscellaneous Geologic Investigations Series Map I-2690, scale 1:100,000. [http://pubs.er.usgs.gov/publication/i2690] Richards, R.W., 1955, Geology of the Bighorn Canyon-Hardin area, Montana and Wyoming: U.S. Geological Survey Bulletin 1026, 93 p., 7 plates. [http://pubs.er.usgs.gov/publication/b1026] Macke, D.L., 1993, Cambrian through Mississippian rocks of the Powder River basin, Wyoming, Montana, and adjacent areas, in Evolution of sedimentary basins--Powder River basin: U.S. Geological Survey Bulletin 1917-M, p. M1-M174 [http://pubs.er.usgs.gov/publication/b1917M] Sloss, L.L., and Moritz, C.A., 1951, Paleozoic stratigraphy of southwestern Montana: American Association of Petroleum Geologists Bulletin, v. 35, no. 10, p. 2135-2169 Fuller, J.G., 1961, Ordovician and contiguous formations in North Dakota, South Dakota, Montana, and adjoining areas of Canada and the United States: American Association of Petroleum Geologists Bulletin, v. 45, no. 8, p. 1334-1373. Lochman-Balk, Christina, 1956, The Cambrian of the Rocky Mountains and southwest deserts of the United States and adjoining Sonora province, Mexico, in Rodgers, John, ed., El Sistema Cambrico, su paleogeografia y el problema de su base; Symposiu Lochman-Balk, Christina, and Wilson, J.E., 1967, Stratigraphy of Upper Cambrian-Lower Ordovician subsurface sequence in Williston basin: American Association of Petroleum Geologists Bulletin, v. 51, no. 6, p. 883-917.
Geographic coverage	Beaverhead - Big Horn - Blaine - Carbon - Gallatin - Judith Basin - Park - Phillips - Stillwater - Sweet Grass