DARBY FORMATION--Yellow and greenish-gray shale and dolomitic siltstone underlain by 
     fetid brown dolomite and limestone.  MD, MDO, Pzr
THREE FORKS FORMATION
  Northern Yellowstone area--Pink, yellow, and green dolomitic siltstone and shale.  MD, DO
  North Wyoming--Yellow and greenish-gray shale and dolomitic siltstone.  MDO, DO 
JEFFERSON FORMATION
  Northern Yellowstone area--Massive siliceous dolomite.  MD, DO
  North Wyoming--Fetid brown dolomite and limestone.  MDO, DO