Diagrammatic restored section of the Inyan Kara group, Morrison formation, and Unkpapa sandstone of the western side of the Black Hills, Wyoming and South Dakota

The Inyan Kara group of Early Cretaceous age and the underlying Morrison formation and Unkpapa sandstone of Late Jurassic age comprise about 300 to 850 feet of gently dipping predominantly nonmarine rocks that crop out along the flanks of the Black Hills in northeastern Wyoming and western South Dakota. Detailed mapping and stratigraphic studies of these rocks were made from 1952 to 1957 by the U.S. Geological Survey on behalf of the Division of Raw Materials of the U.S. Atomic Energy Commission. One of the results of the studies is a correlation of formational and intraformational units along the western side of the Black Hills for a distance of about 140 miles. The generalized section above, which has a greatly exaggerated vertical scale, shows the main lithologic units that have been traced and correlated, and the stratigraphic position of uranium deposits in various parts of the Black Hills in relation to these units. Geologists who have contributed to the diagrammatic section are listed on another part of this sheet and the areas for which each is responsible are shown on the accompanying map. The brief text below summarizes some of the broad stratigraphic relations within the Inyan Kara group and underlying formations.