Marine and nonmarine strata in the upper part of the Iles and lower part of the Williams Fork Formations of the Mesaverde Group form the richest coal section between Rifle Gap and New Castle, Colorado. Within these strata, the ammonites Exiteloceras jenneyi and Didymoceras cheyennense indicate a late Campanian age for the section, which is 1,000-1,400 feet (305-430 meters) thick. This study distinguishes formal members, the Trout Creek Sandstone Member and Cozzette Sandstone Member of Young (1982) of the Iles Formation, and new informal units. Unit contacts coincide with horizons separating offshore marine, and fresh to brackish-water nonmarine strata. Differences in paleosalinity are indicated by marine mega-and microfossils, and great trace-fossil diversity; brackish-water gastropods and pelecypods (some occurring in bioturbated intervals); and fresh-water gastropods.Sedimentary structures provided evidence for reconstructing paleobathymetry. Outer-offshore deposits are structureless silty mudstone, bearing grain-lined tubes of Terebellina; inner-offshore deposits are storm-deposited, scour-based, hummocky-bedded sandstone, and silty mudstone, locally bearing a diverse trace-fossil assemblage. Shoreface sandstone contains low-angle trough crossbedding and Ophiomorpha.Seven depositional cycles are recorded in the stratigraphic section. Each of these cycles, from base to top, consists of offshore, shoreface, and onshore delta-plain strata. The latter are fluvial deposits with minor coal and brackish-water bayfill.Paleocurrent data indicate that shoreline-normal storm scour occurred in the offshore; shoreline-parallel sand transport to the south occurred in the shoreface; and seaward sediment transport occurred onshore. Coastal deposition was controlled by deltas supplying sediment to shallow, longshore-migrating, bar-trough systems. Delta shifting resulted in interfingering of marine and nonmarine.strata and in shoreline realignments recorded by paleocurrent indicators.New correlations of marine-sandstone members of the upper part of the Iles Formation along the central Grand Hogback presented here are based on field mapping. The sandstone commonly referred to as the Cozzette Sandstone Member in Rifle Gap can be traced to the Rollins Sandstone Member at New Castle, where the sandstone is overlain by the Wheeler coal bed. This interpretation differs from previous correlation of the Trout Creek Sandstone Member in Rifle Gap with the Rollins Sandstone Member at New Castle. The new interpretation presented here suggests that the Trout Creek and Manuscript approved for publication, March 23, 1988. Rollins sandstones are separated by 310-450 feet (94-135 meters) of strata along the central Grand Hogback, with the Rollins lying stratigraphically below the Trout Creek. The new correlation of these marine-sandstone members influences the paleogeographic reconstruction of the local, late Campanian shoreline.2 UPPER CRETACEOUS MESAVERDE GROUP, GRAND HOGBACK, COLORADO Outcrop of Mesaverde Group and equivalent strata O Locat...