From purposes of approach of study: The purposes of this study were to: (1) Define, on a reconnaissance level, current (1979) water-quality conditions in major aquifers (water-yielding rock formations) in the eastern Snake River basin; (2) present available geologic and hydrologic data to assist in understanding the natural and man-caused factors that affect water-quality conditions; and (3) establish a hydrologic base upon which future comparisons can be made to evaluate changes.