Custer National Forest

                     DESCRIPTION OF MAP UNITS

                         Pryor Mountains

Qs   Surficial deposits (Quaternary)--Alluvium, colluvium,
          slope-wash, mudflows, landslides, and pediment gravel

JPs  Jurassic, Triassic, and Permian sedimentary rocks--Includes
          Morrison Formation (Jurassic); Ellis Group (Jurassic)
          including the Swift, Rierdon, and Piper Formations;
          Chugwater Formation (Triassic); and Phosphoria Formation
          equivalents (Permian)

Ps   Pennsylvanian sedimentary rocks--Includes Tensleep Sandstone
          and Amsden Formation

Mm   Madison Limestone Group (Mississippian)--[Stratigraphic units
          A-D proposed by Richards (1955) and summarized by
          Blackstone (1975)].  

Ds   Devonian sedimentary rocks--Includes Jefferson Formation
          (Dolomite) and Beartooth Butte Formation

Ob   Bighorn Dolomite (Ordovician)

Cs   Cambrian sedimentary rocks--Includes Gallatin Limestone, Gros
          Ventre Shale (Formation), and Flathead Quartzite

pCr  Precambrian rocks--Includes granitic gneiss; hornblende
          schist; quartz veins; and aplite dikes


                         REFERENCES CITED

Blackstone, D.L., Jr., 1975, Geology of the East Pryor Mountain
quadrangle, Carbon County, Montana: Montana Bureau of Mines and
Geology Special Publication 69, 13 p., 1 plate, scale 1:24,000.

Richards, P.W., 1955, Geology of the Bighorn Canyon-Hardin area,
Montana and Wyoming: U.S. Geological Survey Bulletin 1026, 93 p.,
7 plates.