Th    HOBACK FORMATION
Tfu   FORT UNION FORMATION

                                CENTRAL

Twr   WHITE RIVER FORMATION
Twru    Upper conglomerate member
Tid   DACITE AND QUARTZ LATITE INTRUSIVE AND EXTRUSIVE IGNEOUS
           ROCKS
Tai   ALKALIC INTRUSIVE AND EXTRUSIVE IGNEOUS ROCKS
Twb   WAGON BED FORMATION
Ta    AYCROSS FORMATION
Twdr  WIND RIVER FORMATION
Twim  WIND RIVER AND INDIAN MEADOWS FORMATIONS
Tim   INDIAN MEADOWS FORMATION
Tco   COALMONT FORMATION
Tfu   FORT UNION FORMATION
Tha   HANNA FORMATION
TKu   SEDIMENTARY ROCKS--Northern part of Wind River Basin
TKf   FERRIS FORMATION

                                 EAST

Twr   WHITE RIVER FORMATION
Twru    Upper conglomerate member
Twrb    Brule Member--Locally includes upper conglomerate member
Twrc    Chadron Member
Tie   INTRUSIVE AND EXTRUSIVE IGNEOUS ROCKS--Incorporates masses of
           Mississippian through Cambrian formations
Tw    WASATCH FORMATION
Twmo    Moncrief Member
Twk     Kingsbury Conglomerate Member
Tfu   FORT UNION FORMATION
Tftr    Tongue River Member
Tftl    Tongue River and Lebo Members
Tfl     Lebo Member
Tflt    Lebo and Tullock Members
Tft     Tullock Member