The Napa Sonoma Marsh is a wetland at the northern edge of San Pablo Bay, which is a northern arm of the San Francisco Bay in California, United States. This marsh has an area of 48,000 acres (194 km²), of which 13,000 acres (53 km²) are abandoned salt evaporation ponds. The United States Government has designated 13,000 acres (53 km²) in the Napa Sonoma Marsh as the San Pablo Bay National Wildlife Refuge.