The Muddy Sandstone forms a stratigraphic trap at the Bell Creek field. The sandstone is very fine to fine grained, well-sorted, lenticular, and has an average thickness of 20 feet. Generally, the grain size increases upward. The quartz content ranges from 50 to 99 percent and averages 86 percent. The porosity and permeability of the unit are as much as 33 percent and 13,500 md., respectively. The bedding changes upward from massive to laminated and crossbedded. The sandstone is laminated and burrowed, in the basal two feet, and is apparently gradational with the underlying shale. The mineral composition, vertical textural change, bedding, and gross morphology are evidence that the Muddy Sandstone is a barrier bar. The updip permeability barrier may be the lagoonal siltstone and shale to the southeast.