The Santa Ana River is 96 miles km long, [ 5 ] and its drainage basin is 2, square miles 6, km 2 in size. The Santa Ana drainage basin has a diversity of terrain, ranging from high peaks of inland mountains in the north and east, to the hot, dry interior and semidesert basins of the Inland Empire , to the flat coastal plain of Orange County.
Although it includes areas of alpine and highland forest, the majority of the watershed consists of arid desert and chaparral environments. Due to low regional rainfall, the river carries only a small flow except during the brief winter season, when it is prone to massive flash floods.
The San Jacinto River , which drains the southern half of the watershed, rarely reaches the Santa Ana except in extremely wet years. A wide variety of animal and plant communities depend on the riparian zones and remnant wetlands along the Santa Ana River. Humans have lived on the Santa Ana River for at least 9, years.
Because it was one of the only reliable sources of water in a wide region, many large ranchos developed along the river and one of its major tributaries, Santiago Creek.
After the area became part of the United States, the economy transitioned to agriculture, before urbanizing in the 20th century. Many cities established during this time including Santa Ana , Riverside and Anaheim derived their names from the river. In order to protect urban areas from the river's flood threat, major channelization and damming projects were undertaken, resulting in the loss of much of the natural river channel.
