Lower Missoula Group: Shepard and Snowslip Formations; or Shepard Formation and unresolved Snowslip Formation equivalent

Shepard Formation: Tan-weathering, dolomitic, green siltite and argillite in couplets and microlaminae. In the west formerly considered part of the “upperWallace.” Thickness as much as 1,100 m (3,609 ft). Snowslip Formation: Green and red siltite and argillite in couplets. Western Snowslip equivalent is black siltite and argillite in couplets and microlaminae, formerly considered part of the “upper Wallace.” A new name is under consideration for the western Snowslip equivalent. Thickness as much as 1,200 m (3,937 ft).
State Montana
Name Lower Missoula Group: Shepard and Snowslip Formations; or Shepard Formation and unresolved Snowslip Formation equivalent
Geologic age Middle Proterozoic
Lithologic constituents
Major
Metamorphic > Metasedimentary > Metaclastic > Metasiltstonesiltite
Metamorphic > Metasedimentary > Metaclastic > Argillite
References

Vuke, S.M., Porter, K.W., Lonn, J.D., and Lopez, D.A., 2007, Geologic Map of Montana - Compact Disc: Montana Bureau of Mines and Geology: Geologic Map 62-C, 73 p., 2 sheets, scale 1:500,000. This map was digitized in 2012 as a result of a contract between the U.S. Geological Survey and the Montana Bureau of Mines and Geology.

NGMDB product
Counties Beaverhead - Deer Lodge - Flathead - Glacier - Granite - Lake - Lewis and Clark - Lincoln - Mineral - Missoula - Powell - Ravalli - Sanders