The Cosumnes River

The Cosumnes River is one of California’s natural treasures — and the last free-flowing river from the Sierra Nevada to the Sacramento–San Joaquin Delta. Unlike most rivers in the Central Valley, the Cosumnes remains undammed, allowing it to rise and fall with the seasons much as it has for thousands of years.

Originating in the Sierra Nevada foothills, the river flows more than 80 miles westward before joining the Mokelumne River and ultimately the Delta. Along its journey, it nourishes a mosaic of habitats — from oak woodlands and riparian forests to vast seasonal wetlands. These floodplains provide essential habitat for Chinook salmon, migratory birds, and countless other species, while also recharging groundwater and supporting agriculture.

The Cosumnes River is at the heart of the Preserve’s mission: protecting and restoring a living floodplain where people, wildlife, and water continue to move together with the natural rhythms of the land.