|Geologic age||Phanerozoic | Paleozoic | Permian|
|Comments||Pu? is not a unit shown on the source paper map, but was assigned by Raines and Johnson (1995) for unlabeled polygons thought to be this unit.|
|Primary rock type||fine-grained mixed clastic|
|Secondary rock type||carbonate|
|Other rock types||chert; phosphorite; black shale; oil shale|
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.
Raines, G.L. and Johnson, B.R., 1995, Digital representation of the Montana stage geologic map: a contribution to the Interior Columbia River Basin Ecosystem Management Project: U.S. Geological Survey Open-File Report 95-691, 21 p.; http://pubs.usgs.gov/