SUMMARY: This report presents the results of a cooperative study of geothermal systems in the region from Aurora, Nevada, and Bridgeport, California, south to Long Valley, California, by the Division of Mines and Geology and the Division of Earth Sciences of the University of Nevada, Las Vegas. The study is the initialreconnaissance phase of a project that was proposed to span several years. Magmatic and hydrothermal systems have been common in this region for the last 15 million years. The objectives of this study were to begin determination of the properties ~nd interactions of these systems and to develop hypotheses on the locations of undiscovered, active systems _in the region. SpeCial emphasis was given to the re~ional relationships and controls of the systems. New data presented include a Bouguer gravity map of the region, several gravity and magnetic profiles, a resistivity profile near Aurora, and a potassium-argon date on Mud Spring volcano, also near Aurora. New interpretations are presented regarding relative 8Qes and distributions of thermal fluids, gravity anomalies, d~pths to pre-Cenozoic: basement, structural controls of the geothermal systems, and the late Cenozoic tectonic-magmatic evolution of the region. The U.S. Department of Energy provided most of the funds for this project.