Devils Glen through Flathead Formation: Devils Glen, Switchback, Steamboat, Pentagon, Pagoda, Dearborn, Damnation or Elko, Gordon, and Flathead Formations

Devils Glen Formation: Light gray dolomite with subordinate algal limestone and shale. Shallow marine. Thickness as much as 200 m (656ft). Switchback Formation: Green and gray, locally calcareous, fissile shale or mudstone, interbedded with thin beds of gray, flaggy limestone or dolomite. Shallow marine. Thickness as much as 95 m (312 ft). Steamboat Formation: Tan, thick-bedded, hard limestone with thin layers of green fissile shale and nodular shaly limestone. Shallow marine. Thickness as much as much as 90 m (295 ft). Pentagon Formation: Black fissile shale and brownish gray, platy limestone beds. Laterally replaced by Pagoda Formation. Shallow marine. Thickness as much as 88 m (289 ft). Pagoda Formation: Green shale interbedded with maroon calcareous mudstone and gray limestone, and lower fissile black shale and thin limestone-pebble conglomerate. Shallow marine. Thickness as much as 120 m (394 ft). Dearborn Formation: Upper brownish gray to gray limestone and lower interbedded green shale, shale-pebble conglomerate, and calcareous sandstone. Shallow marine shelf. Thickness as much as 115 m (377 ft). Damnation Formation: Brownish gray or bluish gray fossiliferous, locally oolitic limestone and subordinate dark gray shale. Shallow marine. Thickness as much as 70 m (230 ft). Elko Formation: Light brownish gray dolomite and subordinate mudstone. Thickness as much as 220 m (722 ft). Gordon Formation: Upper part of formation: dark green to dark brown, fissile shale with thin beds of sandstone and gray, glauconitic limestone. Lower part of formation: ferruginous sandstone, sandy shale, and grayish green shale. Shallow marine. Thickness as much as 90 m (295 ft). Flathead Formation (CAf): Pinkish gray to light gray sandstone or quartzite. Locally very glauconitic, pebbly, arkosic, or iron-stained. Marine shoreface. Thickness as much as 100 m (328 ft).
State Montana
Name Devils Glen through Flathead Formation: Devils Glen, Switchback, Steamboat, Pentagon, Pagoda, Dearborn, Damnation or Elko, Gordon, and Flathead Formations
Geologic age Cambrian
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Shale (Bed)
Sedimentary > Carbonate > Limestone (Bed, Glauconitic)
Sedimentary > Carbonate > Dolostone (Bed)
Minor
Sedimentary > Clastic > Sandstone (Calcareous, Glauconitic, Arkosic)
Sedimentary > Clastic > Conglomerate (Bed)
Sedimentary > Clastic > Mudstone (Bed, Calcareous)
Sedimentary > Clastic > Mudstone > Shale > Black-shale (Bed)
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 Flathead - Lewis and Clark - Lincoln - Pondera - Powell - Teton