The Santa Ana River is a major river in southern California, in the United States. It begins in San Bernardino County and flows west about to the Pacific Ocean, through Riverside and Orange counties. It has a watershed of 2,650 square miles (6,863 square kilometers). Its biggest tributaries include Lytle, Temescal, and Santiago Creeks. Like the Los Angeles and San Gabriel rivers to the north, it is lined with concrete in many places. A notable feature on the river is the Seven Oaks Dam, which, at tall, is the 6th tallest dam in the United States.