Cosumnes River Preserve in California’s Central Valley protects more than 51,000 acres along the lower Cosumnes River near the Sacramento–San Joaquin Delta, preserving a rare remnant of oak savanna, riparian forest, wetlands, floodplain, and marsh in a valley largely transformed by agriculture. Its river is the last remaining free-flowing one in the Central Valley, still flooding in wet years and sustaining deep alluvial soils and natural ecological processes. Long shaped by Miwok communities and later disrupted by colonization, the area became a major conservation effort beginning in the 1980s. Today it is an Important Bird Area on the Pacific Flyway and a key refuge for diverse and threatened species.