The purpose of this study was to investigate multiple methods used to locate and identify sources of submarine groundwater discharge (SGD) along the coastline of Santa Catalina Island (Catalina) in Los Angeles, California. The driving hypothesis is that SGD may be identified by higher temperature/lower salinity plumes. To test this hypothesis, temperature and conductivity measurements were made along the shoreline of Catalina and compared with previously collected airborne thermal infrared images. In some locations where potential zones of SGD were identified, samples were collected from the surface water within the plume and analyzed for the presence of radon. Radon in ocean water can be used as a tracer to identify the presence of terrestrial groundwater. The analysis was complicated by dynamic variables including tides, weather, and sample collection. In spite of this uncertainty, one potential zone of SGD was identified using sea surface temperature, electrical conductivity, and radon at Toyon Bay. This zone of SGD is consistent with the location of warm water shown in airborne infrared imagery. These results suggest that high-resolution thermal imagery may be useful for identifying diffuse SGD in southern California, but further field tests will be necessary to confirm this conclusion.