The Upper Cretaceous-lower Tertiary Ferris and Hanna formations in south-central Wyoming constitute an interval of continental rocks that contain principal coal beds in the Hanna and Carbon intermontane basins. The interval in the Hanna foreland basin consists of plane-bedded arkosic and lithic conglomerate with sandstone and mudstone interpreted as piedmont slope deposits. They wedge southward into central basin planar and trough cross-bedded sandstone and coeval parallel bedded sandstone and siltstone, dark-colored mudstone and shale, and coals interpreted as fluvial and floodplain deposits. The adjacent Carbon basin contains the fluvial and floodplain deposits. Deposition occurred in a syncline situated between systems of uplifts that resulted from compressional deform tion. Upper Cretaceous sediments were derived mostly from uplifts to the south, and Paleocene and lower Eocene sediments were derived mostly from north of the Hanna basin. Lower Eocene and older rocks were folded into the footwalls of large, east-west-trending middle Eocene uplifts that were thrust southward over the northern Hanna basin margin.

Increased structural complexity from Late Cretaceous through middle Paleocene to middle Eocene time resulted from increasing uplifts and associated counterclockwise rotation from east-west- to north-south-directed couple stresses. This rotation paralleled the movement of the North America plate as it overrode the Farallon plate. The north-south couple stresses produced thrusting of middle Eocene uplifts surrounding the basins, separation of the Hanna and Carbon basins, and thrusting that was at about right angles to Late Cretaceous thrust patterns. Crustal shortening was followed by extensional deformation and general regional uplift.