FRONTIER FORMATION
  Thrust belt--White to brown sandstone and dark-gray shale; oyster coquina in upper part;
     coal and lignite in lower part.  Kf
  Northern Yellowstone area--Yellowish- to medium-gray sandstone; tuffaceous and car-
     bonaceous in lower part.  Kft
  North and south Wyoming--Gray sandstone and sandy shale.  Kf, Kcf, Knt, Kft
STEELE SHALE (AGE ABOUT 78 TO 82 Ma)--Gray soft marine shale containing numerous
     bentonite beds and thin lenticular sandstone.  Ks, Ksn
PIERRE SHALE (AGE 72 TO 78 Ma)--Dark-gray concretionary marine shale; contains
     several bentonite beds.  Kp
NIOBRARA FORMATION (AGE ABOUT 83 Ma)--Light-colored limestone and gray to yellow
     speckled limy shale.  Kn, Ksn, Knt, Knc
CARLILE SHALE--Dark-gray sandy shale; Sage Breaks Member at top; Turner Sandy Member
     in middle.  Kcl, Knc
GREENHORN FORMATION--Light-colored limestone, marl, and limy sandstone interbedded 
     with gray concretionary shale.  Kgb, Kgbm
BELLE FOURCHE SHALE--Black soft bentonitic concretionary shale.  Kgb, Kgbm