Santa Ana River

The Santa Ana River is the largest river of Southern California in the United States. Its drainage basin spans four counties. It rises in the San Bernardino Mountains and flows past the cities of San Bernardino and Riverside, before cutting through the northern tip of the Santa Ana Mountains and flowing southwest past Santa Ana to spill into the Pacific Ocean. The Santa Ana River is 96 miles (154 km) long, and drains a watershed of 2,650 square miles (6,900 km2).

For its size the Santa Ana drainage basin is quite diverse. It ranges from high peaks of inland mountains in the north and east, to the hot, dry interior and semi-desert basin, to flat coastal plains in the west. Its climates range from dry alpine to chaparral and desert, and the watershed as a whole is very arid. Relatively little water actually flows in the river or most of its tributaries. One of its largest tributaries, the San Jacinto River, rarely reaches the Santa Ana except in extremely wet years. The relative lack of vegetation also makes the river prone to flash flooding. Even so, a wide variety of animal and plant life has always been dependent on the river.

People have lived on the Santa Ana River for at least 9,000 years. There were four distinct indigenous groups in the area, all of which depended heavily on the river for their livelihoods. The river was first explored by Europeans in 1769, and received its name from Spanish mission fathers in the 19th century. Because it is one of the largest water sources in the four-county region, many large ranchos developed alongside the river and one of its major tributaries, Santiago Creek. This period of growth culminated in the establishment of many large cities on the river, including Santa Ana and Riverside, both of which derived their names from the River. In the early 20th century, devastating floods poured down the Santa Ana River, leading to much of the river being channelized and dammed in recent times.