In these chapters, the surficial aquifers and the bedrock aquifers are shown on separate regional maps. Where aquifers are stacked atop other aquifers, the order of discussion is from shallowest to deepest. A variety of illustrations is used to describe each principal aquifer in each regional area. Where data are available, maps are used to show changes in aquifer water levels or the chemical quality of the water in the aquifer over time. Correlation charts list the geologic formations or parts of them that compose the aquifer, and show subdivisions that might exist in complex, layered aquifers or aquifer systems.
Hydrogeologic sections show the relation of the aquifer to the geology of the area.
Arrows are superimposed on the hydrogeologic sections and on the potentiometric-surface maps to show the direction of movement of water in the aquifer. Hydrographs are used to show the rise and fall of aquifer water levels in response to changes in the amount of precipitation or the rate of ground-water withdrawal. Pie diagrams are used to show the amount of water that is pumped for different uses or to illustrate the percentage of chemical constituents in the water. No new data were collected for the Atlas because the large amount of ground-water data available in the reports and files of the USGS and other agencies was sufficient for its preparation. Published illustrations and interpretations were merged, combined, modified, and simplified where necessary.