The recognition of both depositional facies and diagenetic events is essential to understanding the creation and preservation of the carbonate reservoir in the North McElroy Unit of Crane and Upton Counties, West Texas. The North McElroy area is located on the eastern margin of the Central Basin Platform. During Middle Permian time the deeper waters of the Midland Basin lay farther to the east; immediately to the west lay mud flats, sabkhas, and siliciclastic dune fields of the higher platform. This lateral transition from low, coastal to open marine environments is represented by sabkha and intertidal muds that grade laterally eastward into lagoonal and normal marine shelf deposits. The distribution of land-derived clastics also reflects a west-to-east departure off the platform.