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The Santa Ana River at the River Road bridge at the Eastvale/Norco border in Riverside County, California. Image is looking upstream.

The Santa Ana River begins in San Bernardino County, California in the San Bernardino National Forest. After traveling nearly 100 miles through San Bernardino, Riverside, and Orange Counties, it eventually reaches its terminus between Newport Beach and Huntington Beach where it spills into the Pacific Ocean. Despite much of the river being channelized in recent times, it still represents one of the largest river systems in Southern California.

Due to Southern California's dry climate, dam control, and confiscation by local water agencies, very little water flows throughout the year. However, the Santa Ana River is prone to flooding in wet seasons. The Army Corps of Engineers considers it to be the greatest flood hazard west of the Mississippi River. It produced devastating floods in 1862, 1938, and 1969.

The 1938 flood was caused by heavy rains in the area that started on February 27, 1938. The river spilled over its banks on March 3, sweeping away cars, homes, and bridges, including Pacific Coast Highway. A total of 2000 people were left homeless and 19 people perished ^[1]. As a result of this flood, the Prado Dam was built near Corona in 1941. Officials in Orange County felt further protection was needed. The Seven Oaks Dam was completed in 1999, located a few miles north of Redlands.

In early 2005, Southern California experienced one of its wettest periods in recent history, which placed unusual stress on the Santa Ana River system. Prado Dam, which was under construction for expansion at the time, seeped water, and residents of the local communities of Corona and Yorba Linda were evacuated as a precaution. The dam was damaged, but there was no major flooding as a result, and evacuated people were soon allowed to return.

A recreational bicycle trail runs along the river some 30 miles, from Prado Dam near Corona to the Pacific Ocean. Other partial trails exist along the river. In Riverside County, construction is expected to begin in January, 2007 for a 4.5 mile recreational path running through the Hidden Valley Wildlife Area. This project, funded by the state, county and Wildlands Conservancy, is expected to be completed by May. The path will have separate bicycle and equestrian trails.^[2]

1. ^ Hallan-Gibson, Pamela. (2002). Orange County - The Golden Promise. American Heritage Press, pp. 212. 
2. ^ Bowles, Jennifer. “Measure would boost parks, water supply”, The Press-Enterprise, October 9, 2006, retrieved November 13, 2006.

• List of California rivers