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Ravalli group

Ravalli group: a diverse assemblage with numerous subdivisions, only a few of which have been recognized over large enough areas to be distinguished here. Near Idaho the rocks are light colored and siliceous, ranging from pure white quartzite to siliceous shale, mostly in subdued tones of gray, green, purple, and red. Near Missoula the rocks are dark-gray quartzite and quartzitic argillite. In and near Glacier National Park the Grinnell, Appekunny, and Altyn formations are distinguished.
State Montana
Name Ravalli group
Geologic age Proterozoic | Mesoproterozoic
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
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.
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.
Counties Deer Lodge - Flathead - Granite - Lake - Lincoln - Mineral - Missoula - Powell - Ravalli - Sanders