Absaroka Volcanics Supergroup

Calc-alkalic andesite and dacite extrusive rock with lesser amounts of potassic, alkalic, and mafic lava; minor amounts of rhyodacitic ash-flow tuff associated with mafic lava; and dark gray, very fine-grained basalt or andesite intrusive breccia.
State Montana
Name Absaroka Volcanics Supergroup
Geologic age Tertiary
Lithologic constituents
Major
Igneous > Volcanic > Felsic-volcanic > Dacite (Flow, Pyroclastic-ash flow, Pyroclastic-tuff, Volcaniclastic-volcanic breccia)
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Pyroclastic-ash flow, Pyroclastic-tuff, Volcaniclastic-volcanic breccia)
Minor
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow, Volcaniclastic-volcanic breccia)
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 - Gallatin - Park - Sweet Grass