Plateau Rhyolite

Central Plateau Member: Upper part: rhyolitic flows with abundant phenocrysts dominantly of quartz and sanidine, and lacking plagioclase. Lower part: light gray, dense, fine-grained to aphanitic rhyolitic ash-flow tuff, with angular to rounded phenocrysts of quartz, sanidine, pyroxene, and olivine that make up as much as 25 percent of rock volume.
State Montana
Name Plateau Rhyolite
Geologic age Quaternary
Lithologic constituents
Major
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow, Pyroclastic-ash flow, Pyroclastic-tuff)
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 Gallatin