The Hydrogeologic Atlas enhances exploration and development activities by illuminating the relationship between the flow of water and the migration and accumulation of petroleum. Map units were defined that include all significant oil and gas reservoirs in the basin. Ideally the map units form relatively thin units of permeable strata over-and underlain by poorly permeable sediments. However, some map units (e.g., the Mississippian System) comprise multiple permeable formations grouped together. Ultimately, 23 map units were adopted, ranging from the Upper "Belly River" Formation to the Basal Cambrian Sandstone. Three maps were created for each of the stratigraphic units comprising: i) A Hydraulic Head Map, ii) A Total Dissolved Solids (TDS) or Water Salinity Map, iii) A Water Force Vector Map. Head maps reveal useful information about the pre-production pressure distribution, reservoir heterogeneities, water-saturated "wet zones", and oil and gas shows. TDS maps reveal useful information about reservoir continuity, indicate locations of reservoir discontinuities, and can help resolve patterns of water flow. TDS concentrations are often linked to reservoir lithology, so TDS patterns can also aid geologic mapping. Force vector maps can be used to infer patterns of lateral water flow. Force vector maps can also be used to calculate water flow rates in areas where the hydraulic characteristics of the formation are known.