Red Island Volcano, also known as Red Hill, is a lava-dome volcano in Imperial County, California, within the Salton Trough. Part of the Salton Buttes, the only active volcanoes in Southern California, it is made up of two domes, Prospect Dome and Alamo Dome. Though these domes have been dormant for roughly 2,000 to 8,000 years, the volcano remains within an active volcanic field. A saddle about 50 feet below the summit of each dome now serves park visitors. Once more clearly surrounded by the Salton Sea, it became connected to the mainland around 2006 to 2007 as the sea receded, and by 2022 land bordered it on three sides.