Rising to 1,112 feet above Vallejo, Sulphur Springs Mountain offers sweeping views of San Francisco Bay and the Napa River from its basalt and serpentine ridges. Trails from Hiddenbrooke lead up the slopes, where hikers can explore unique rock outcrops and habitats that support rare native plants. The mountain also holds deep cultural significance, with evidence of village sites once inhabited by the Suisunes, Coastal Miwok, and Patwin peoples, making it a place of both natural beauty and historic resonance.