Volcanic rock: locally includes Challis Volcanics in southwestern Montana

Volcanic rock; In southwestern Montana - Challis Volcanics: Basaltic andesite, andesite, quartz latite, latite, rhyodacite, and rhyolite flows, and tuff, most of which is nonporphyritic and commonly spherulitic; glassy to devitrified. Subordinate water-laid tuff.
State Montana
Name Volcanic rock: locally includes Challis Volcanics in southwestern Montana
Geologic age Tertiary
Lithologic constituents
Major
Igneous > Volcanic (Flow, Pyroclastic-tuff)volcanic rock
Minor
Igneous > Volcanic > Felsic-volcanic > Latite (Flow, Pyroclastic-tuff)
Igneous > Volcanic > Felsic-volcanic > Quartz-latite (Flow, Pyroclastic-tuff)
Igneous > Volcanic > Mafic-volcanic > Basaltic-andesite (Flow, Pyroclastic-tuff)
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow, Pyroclastic-tuff)
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow, Pyroclastic-tuff)
Igneous > Volcanic > Felsic-volcanic > Dacite (Flow, Pyroclastic-tuff)rhyodactie
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 - Granite - Lake - Madison - Mineral - Missoula - Ravalli - Sanders