Sliderock Mountain volcanics

Gray, pale purplish gray, and pale greenish gray andesite lahar breccia with interbeds of andesitic conglomerate and coarse-grained sandstone. Subordinate flows of porphyritic andesite and basaltic andesite containing plagioclase, hornblende, and pyroxene phenocrysts.
State Montana
Name Sliderock Mountain volcanics
Geologic age Cretaceous
Lithologic constituents
Major
Igneous > Volcanic > Mafic-volcanic > Andesite (Volcaniclastic-lahar, Volcaniclastic-volcanic breccia, Flow)
Sedimentary > Clastic > Conglomerate (Bed)andesitic conglomerate
Sedimentary > Clastic > Sandstone (Bed)
Minor
Igneous > Volcanic > Mafic-volcanic > Basaltic-andesite (Flow)
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 Park - Stillwater - Sweet Grass