Preliminary studies indicate that the Imperial Valley has a large geothermal potential. In order to delineate additional geothermal systems a chemical and isotopic investigation of samples from water wells, springs, and geothermal wells in the Imperial Valley and Yuma areas was conducted. Na, K, and Ca concentrations of nearly 200 well water, spring water, hot spring, and geothermal fluid samples from the Imperial Valley area were measured by atomic absorption spectrophotometry. Fournier and Truesdell's function was determined for each water sample. Suspected geothermal areas are identified. Hydrogen and oxygen isotope abundances were determined in order to determine and to identify the source of the water in the Mesa geothermal system. (JGB).