Opeche Shale  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Paleozoic
 ...Permian
 ....Lower Permian
 .....Opeche Shale
RTWyoming
 Montana
 Nevada
 South Dakota
SNSE Montana, NW Nevada, W South Dakota and Wyoming. Added to Thesaurus in 1989.