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Willow Creek formation

Willow Creek formation: Variegated clay and soft sandstone, chiefly maroon to chocolate brown; local lenses of purple-gray nodular limestone.
StateMontana
NameWillow Creek formation
Geologic agePhanerozoic | Cenozoic | Cretaceous-Late
Original map labelTwc
Primary rock typemudstone
Secondary rock typesandstone
Other rock typeslimestone; conglomerate
Lithologic constituents
Major
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Clastic > Mudstone (Bed)I lumped mudstone and shale into this description, because much is described for this unit as "shaly mudstone" or "shale".
Minor
Sedimentary > Carbonate > Limestone (Bed)
Incidental
Sedimentary > Clastic > Conglomerate (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
Witkind, I.J., 1969, Geology of the Teepee Creek quadrangle, Montana-Wyoming: U.S. Geological Survey Professional Paper 609, 101 p., scale 1:62,500.
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.
Geographic coverageGlacier

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