Tertiary sedimentary rocks, undifferentiated (MTTs;0)

Tertiary sedimentary rocks, undifferentiated: clastic deposits in western Montana, mostly in valleys, and in most places not divided into formations; mostly poorly consolidated gravel, sand, silt, and clay; includes some tuffaceous material and locally lenses of lignite and bentonite; a little hot spring tufa; and in areas not yet mapped in detail, lava may be included. These rocks were in part laid down in lakes but a large part was formed in streams and alluvial fans. These rocks are Tertiary in age and as now mapped may even include some beds of Cretaceous age. Some late Tertiary terrace deposits may be included.

State	Montana
Name	Tertiary sedimentary rocks, undifferentiated
Geologic age	Phanerozoic \| Cenozoic \| Tertiary
Original map label	Ts
Primary rock type	medium-grained mixed clastic
Secondary rock type	coarse-grained mixed clastic
Other rock types	lava flow; ash-flow tuff; tuff; coal; bentonite; carbonate
Lithologic constituents	Major Sedimentary > Clastic > Mixed-clastic (Bed)Conglomerate, sand, silt, and clay layers. Minor Igneous > Volcanic (Pyroclastic) Igneous > Volcanic (Flow) Incidental Sedimentary > Carbonate (Lense)Hot spring deposits Sedimentary > Clastic > Mudstone > Claystone > Bentonite (Bed) Sedimentary > Coal (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	Fields, R.W., Rasmussen, D.L., Tabrum, A.R. and Nichols, Ralph, 1985, Cenozoic rocks of the intermontane basins of western Montana and eastern Idaho--A summary, in Flores, R.M., and Kaplan, S.S., eds., Cenozoic paleogeography of the west-central Hanneman, D.L. and Widemann, C.J., 1991, Sequence stratigraphy of Cenozoic continental rocks, southwestern Montana: Geological Society of America Bulletin, v. 103, no. 10, p. 1335-1345. 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]
Geographic coverage	Beaverhead - Broadwater - Deer Lodge - Flathead - Gallatin - Glacier - Granite - Jefferson - Lake - Lewis and Clark - Lincoln - Madison - Meagher - Mineral - Missoula - Park - Pondera - Powell - Ravalli - Sanders - Silver Bow - Sweet Grass - Teton - Wheatland