In contrast to the beautiful array of colorful layers and spectacular cliffs of the Triassic and Jurassic (251 to 148 million years ago [Ma]) sections in the San Rafael Swell of east-central Utah, most of the Upper Cretaceous (96 to 86 Ma) Mancos Shale produces a drab, barren landscape. However, lying within the Mancos, the Ferron Sandstone, is the most studied unit in the San Rafael Swell. The Ferron has world-class outcrops of rock layers deposited near the shorelines of a sinking, fluvial- (stream) dominated delta system. Along the west flank of the San Rafael Swell, the 80-mile-long (130 km) Ferron outcrop belt of cliffs and side canyons (e.g., the Coal Cliffs, Molen Reef, and Limestone Cliffs [not actually limestone, just misnamed]) provides a three-dimensional view of vertical and lateral changes in the Ferron’s rock layers (facies and sequence stratigraphy), and, as such, is an excellent model for fluvial-deltaic oil and gas reservoirs worldwide (e.g., Chidsey and others, 2004).
Ancient delta deposits in the Ivie Creek area, Ferron Sandstone member of the Mancos Shale, western San Rafael Swell, east-central Utah
