The Cahuilla gold-silver deposit is a Plio-Pleistocene epithermal hot springs highgrade deposit that covers an ~4 square kilometer area at the southern end of the Santa Rosa Mountains on the western Salton Trough in southern California. The Cahuilla deposit is closely related to the northeast-southwest trending Modoc fault which is a down-to-thesoutheast normal fault. Field work focused on the kinematics of the Modoc fault and hydrothermal near-surface alteration. Mineralization is restricted to units within the hanging wall of the fault that encompass Plio-Pleistocene non-marine fluvial and alluvial fan deposits of the Palm Spring Group and Canebrake conglomerate formation. The footwall of the Modoc fault comprises Upper Cretaceous tonalite/granodiorite of the eastern Peninsular Ranges batholith intruded into a schist-quartzite-limestone package of prebatholithic sedimentary rock. The Cahuilla deposit comprises silicified sediment with disseminated gold and high-grade steeply dipping banded quartz-chalcedony adularia veins and stockwork. Siliceous sinter was deposited as part of this hot spring deposit. Thomas Dibblee (1954) defined and mapped the “Truckhaven Rhyolite” from the Cahuilla deposit; however, petrography, whole rock and trace element geochemistry and zircon U-Pb geochronology identify this rock unit as silicified Palm Spring Group which eliminates the possibility that the Cahuilla deposit hydrothermal activity is related to it as a local volcanic source. The Palm Spring Group is determined to be a proximally derived unit from the eastern Peninsular Ranges based on nearly identical zircon U-Pb age distribution to footwall basement granitoids. Whole rock major and trace element compositions from X-ray fluorescence analysis documents elemental mobility associated with silicic alteration of the strata. X-ray diffraction analyses document the formation of kaolinite, expandable and illite clays and alunite in response to hydrothermal mineralization. The Cahuilla deposit can be alternately interpreted as 1) the result of hanging wall mineralization associated with the nearby Western Salton Detachment fault ( ?5 to ?2 Ma), or 2) hydrothermal activity associated with a stepover within the San Jacinto fault system (~1.1 to ~1.3 Ma). The recognition of primary vapor phase jarosite in veins provides a means by which Cahuilla mineralization could be dated by 40Ar/39Ar methods and thus resolve between these two options.