PREUSS SANDSTONE OR REDBEDS--Purple, maroon, and reddish-gray sandy siltstone and 
     claystone; contains salt and gypsum in thick beds in some subsurface sections.  Jst
TWIN CREEK LIMESTONE--Greenish-gray shaly limestone and limy siltstone.  Includes
     Gypsum Spring Member.  Jst
GYPSUM SPRING FORMATION--Interbedded red shale, dolomite, and gypsum.  In north
     Wyoming wedges out south in T. 39 N.  KJg, K@, Jsg, J@, J@gn, J@gc, MzPz