The streams of the San Bernardino Mountains are also prone to flash floods, a danger that has prompted the construction of numerous flood control dams throughout the range. The largest of these is Seven Oaks Dam - the sixth highest dam in the United States - on the Santa Ana River. In 1969, the U.S. Army Corps of Engineers deemed the Santa Ana the greatest flood threat in the United States west of the Mississippi River because of its course through heavily developed areas. Completed in 1999, the dam is designed to completely contain a 350-year flood. Many other dams, including Mojave Forks Dam on the Mojave River and various retention basins and check dams on smaller drainages, provide more localized flood and sediment control.