… Protected and restored by the Nature Conservancy, Cosumnes River Preserve is south of Sacramento along I-5. The last undammed, free-flowing river originating in the Sierra Nevada is one of California’s richest wildlife areas. The cranes migrate into the Sacramento–San Joaquin Delta and the surrounding Central Valley each winter, arriving from far northern nesting grounds, seeking refuge and food. The migration has been repeating for thousands of years. … From its source in the Sierra Nevada counties of El Dorado and Amador, the Cosumnes watershed comprises 940 square miles from the Sierra crest to the Sacramento-San Joaquin Delta. … Uniquely undammed, the Cosumnes’ winter floods still spread across the floodplain, naturally recharging the groundwater. Native forests regenerate. Salmon still spawn.