Santa Ana River

Course and watershed

The river begins in San Bernardino County and crosses a wide and varied landscape as it moves through Riverside County and Orange County before emptying into the Pacific Ocean. Its watershed covers about 2,650 square miles (6,863 square kilometers), gathering runoff from mountain slopes, foothills, and urbanized valleys. Major tributaries include Lytle Creek, Temescal Creek, and Santiago Creek.

• Length: roughly 100 miles (160 km)
• Drainage area: about 2,650 square miles
• Major tributaries: Lytle Creek, Temescal Creek, Santiago Creek

Flood control and engineering

Like the Los Angeles and San Gabriel rivers to the north, the Santa Ana River has been channelized in many places and lined with concrete to reduce flood risk in densely populated areas. This kind of modification reflects the river’s history of sudden high flows, which can be dangerous after heavy rain or mountain runoff. One of the best-known structures in the basin is Seven Oaks Dam, a major flood-control dam on the upper river. At 632 feet (193 m) tall, it is the sixth tallest dam in the United States.

Importance today

Even in a heavily managed form, the Santa Ana River remains important for groundwater recharge, flood protection, recreation, and habitat. In some stretches, the river corridor supports trails and open space, including the well-known Santa Ana River Trail. The river’s mix of natural flow, engineered channels, and reservoir-and-dam management makes it a useful example of how water systems in arid and crowded regions must serve both environmental and urban needs.