Ravalli group (MTpCAr;0)

State	Montana
Name	Ravalli group
Geologic age	Proterozoic \| Mesoproterozoic
Original map label	pCr
Comments	The term "Ravalli Group" is an obsolete nomenclature, now replaced on more modern geologic maps by individually mapped formations. Appears to include the Burke Formation, Grinnell Formation, Spokane Formation, Revett Formation, St. Regis Formation, and perhaps the Empire Formation (see USGS Map I-2267).
Primary rock type	meta-argillite
Secondary rock type	quartzite
Other rock types
Lithologic constituents	Major Metamorphic > Metasedimentary > Metaclastic > Argillite (Greenschist) Minor Metamorphic > Metasedimentary > Metaclastic > Quartzite (Greenschist)
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	Lewis, R.S., 1998, Preliminary geologic map of the Butte 1° x 2° quadrangle: Montana Bureau of Mines and Geology Open File Report 363, 16 p, scale 1:250,000. Berg, R.B., Lonn, J.D., 1999, The preliminary geologic map of the Nez Perce Pass 30' x 60' quadrangle, Montana, revised 1999: Montana Bureau of Mines and Geology Open File Report 339, 14 p., scale 1:100,000. 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] Lewis, R.S., 1998, Geologic map of the Montana part of the Missoula West 30' x 60' quadrangle: Montana Bureau of Mines and Geology Open File Report 373, 20 p, scale 1:100,000. Lonn, J.D., and McFadden, M.D., 1999, Geologic map of the Wallace 30' x 60' quadrangle: Montana Bureau of Mines and Geology Open File Report 388, 15 p., scale 1;100,000. Harrison, J.E., Griggs, A.B., and Wells, J.D., 1986, Geologic and structure maps of the Wallace 1° x 2° quadrangle, Montana and Idaho: Montana Bureau of Mines and Geology Montana Atlas Series 4-A, scale 1:250,000. Harrison, J.E., Cressman, E.R., and Whipple, J.W., 1992, Geologic and structure maps of Kalispell 1° x 2° quadrangle, Montana and Alberta, British Columbia: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-2267, scale 1:250,000. [http://pubs.er.usgs.gov/publication/i2267] Harrison, J.E., 1972, Precambrian Belt basin of northwestern United States--Its geometry, sedimentation and copper occurrences: Geological Society of America Bulletin, v. 83, no. 5, p. 1215-1240. Connor, J.J., Reynolds, M.W., and Whipple, J.W., 1984, Stratigraphy of the Ravalli Group, Belt Basin, Montana and Idaho, in Hobbs, S.W., ed., The Belt--Abstracts with summaries, Belt Sympsium II, 1983: Montana Bureau of Mines and Geology Special Publicat White, B.G., Mauk, Jeff, and Winston, Don, 1984, Stratigraphy of the Revett Formation, in Hobbs, S.W., ed., The Belt--Abstracts with summaries, Belt Sympsium II, 1983: Montana Bureau of Mines and Geology Special Publication 90, p. 16-17.
Geographic coverage	Deer Lodge - Flathead - Granite - Lake - Lincoln - Mineral - Missoula - Powell - Ravalli - Sanders