The recent discovery of oil in the Mesaverde formation in the Powder River Basin, Wyoming, has placed new economic emphasis on the intertonguing relation of the Mesaverde and adjacent formations in central Wyoming. Surface studies in the southeastern part of the Wind River Basin and subsurface studies along the southwestern margin of the Powder River Basin and southern part of the Big Horn Basin have outlined several regressive and transgressive pinch-outs within the Mesaverde and adjacent formations that may have possibilities as oil and gas traps.

The basal unit of the Mesaverde formation, the Parkman sandstone member, reflects a widespread regression of the Late Cretaceous sea. Minor oscillations of the shoreline during this regression produced interfingering of off shore and littoral type sediments in the Cody-Mesaverde contact zone. The marine part of the unnamed middle member of the Mesaverde formation, which appears to be a tongue of the Pierre shale, represents a fairly widespread re-advance of the Late Cretaceous sea. The stratigraphic relations of the uppermost member of the Mesaverde formation, the Teapot sandstone, member, are inconsistent with the normal pattern of regressive and transgressive deposition. No satisfactory explanation for its mode of deposition can be made without further study; however, its stratigrap ic relations are similar to those of the Castlegate sandstone of Utah.

The marine Lewis shale, which can be correlated with the Bearpaw shale of northern Wyoming and Montana, was found to intertongue with the Meeteetse formation in the Wind River and Big Horn basins.