Massive Cretaceous-age Mesaverde Formation sandstone on the southeast flank of Grass Creek oil field along Wyoming Highway 171. Photo by Alan VerPloeg.

View to the east from Greybull Park across the Big Horn River of the Peay Sandstone Member and underlying black shale of the Cretaceaous-age Frontier Formation. Note the normal fault in the center of the photograph with the downthrown side on the left. Photo by Alan VerPloeg. View to the east from Greybull Park across the Big Horn River of the Peay Sandstone Member and underlying black shale of the Cretaceaous-age Frontier Formation. Note the normal fault in the center of the photograph with the downthrown side on the left. Photo by Alan VerPloeg.

Mowry Shale overlying tan Muddy Sandstone west of Thermopolis on Highway 120. Photo by Alan VerPloeg.

View of the Cretaceous-age Cloverly Formation along a secondary road east of Greybull, south plunge of Sheep Mountain along anticline. Photo by Alan VerPloeg.

Eocene aeolian sandstone at the base of the Wasatch Formation in the Powder River Basin. Aeolian sands are capped by a thin (less than 3 feet) well cemented arkosic fluvial sandstone. Photo was taken along highway 450 east of the Black Thunder and Jacob's Ranch surface coal mines. Photo by Nick Jones.

Conglomerates, volcanic breccias, ash beds and tuffs. Ash beds are less resistant to erosion. Photo by Ryan O’Donnell.

Massive sandstone from the Tongue River Member of the Fort Union Formation along county road 26 near Greybull, WY, picture by Nikolaus Gribb.

Muddy Sandstone with tree cover overlain by Mowry Shale west of Thermopolis on Highway 120. Photo by Alan VerPloeg.

Phosphoria Formation along U.S. Highway 20 in Wind River Canyon. Photo by Alan VerPloeg.

Tensleep Sandstone along U.S. Highway 20 near northern end of Wind River Canyon. Photo by Alan VerPloeg.

Thick, tertiary conglomerate in the Bighorn Mountains (note hammer for scale). Photo by Fred McLaughlin.

View to the north-northeast just north of the Park County lin on Wyoming Highway 120. The lower part of the outcrop is composed of thin-bedded sandstone and shale in the Cretaceous-age Meeteetse Formation and the upper part of the outcrop is thick-bedded buff to light gray sandstone in the Cretaceous-age Lance Formation. Photo by Alan VerPloeg.