page_title: Santa Ana River
section_title: Ecology
hierarchical_section_title: Santa Ana River / Ecology
caption_attribution_description: English: The Santa Ana River downstream from Seven Oaks Dam, CA
context_page_description: The Santa Ana River is the largest river entirely within Southern California in the United States. It rises in the San Bernardino Mountains and flows for most of its length through San Bernardino and Riverside Counties, before cutting through the northern Santa Ana Mountains via Santa Ana Canyon and flowing southwest through urban Orange County to drain into the Pacific Ocean. The Santa Ana River is 96 miles long, and its drainage basin is 2,650 square miles 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 semi-desert 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.
context_section_description: Hundreds of species of animals and plants characterize the Santa Ana River's diversity of climates and vegetation zones. There are over ten of these vegetation zones in the watershed—including the sparsely vegetated alpine and subalpine zones in the mountains, mid-elevation forests of pine, lodgepole and oak, chaparral, coastal sage scrub, the increasingly rare riparian forest and marshes along the river bed, lined with trees and rushes, and the thinly vegetated coastal areas virtually flush with sea level. The watershed supports up to 200 bird species, 50 mammal species, 13 reptile species, 7 amphibian species, and 15 fish species, including steelhead trout.
  The largest portion of the watershed, the Inland Empire portion, is dominated by a hot, dry desert climate that supports sparse wildlife, while the climate and vegetation of the San Jacinto River and Temescal Creek watershed is similar to that of the southern Central Valley. Downstream of the desert was once the coastal sage scrub and dry grassland community of the Orange County coastal plain, but that region has been almost entirely lost to urbanization. Rimming the arid portions of the watershed are the chaparral zones, consisting of sclerophyllous, thick, low bushes and small trees. The chaparral generally is found between elevations of 1,000 feet (300 m) and 6,500 feet (2,000 m), and occurs mainly closer to the coast on the windward side of the Peninsular Ranges. The scrub oak is one of the most common plants in chaparral regions, forming a dense groundcover that makes it difficult for humans and large animals such as mountain lions, coyotes, and bobcats to traverse. Chaparral growth is determined by wildfires and droughts, and depends on the semi-arid climate of the region.
  Perennial and seasonal streams often are lined with live oak and sycamore, which transition into the riparian zones of the main stem Santa Ana River. The largest unbroken riparian corridor is the 20-mile (32 km) stretch between Riverside and Prado Dam, where the river has been largely left in its natural state despite pollution from urban runoff. In addition, the flood control basin behind Prado Dam contains 6,600 acres (2,700 ha) of seasonal wetlands. The Santa Ana sucker, a small bottom-dwelling fish, was once found along most of the Santa Ana River, but is now rarely seen. Near the mouth, the river was once abundant in salt marshes, which stretched for miles on either side of the river, even near Upper Newport Bay, which has also served as an alternate mouth of the river.
  The alpine and subalpine zones, despite their high elevation (above 9500 feet, 2900 meters) and significant rainfall (at least 35 inches, 89 cm per year, except in drought years), are sparsely vegetated. The windswept terrain of the alpine zone is primarily small brush and weeds, while trees—mostly small gnarled pines and junipers—occur in canyons and shielded depressions in the subalpine zone. Inland elevations above 5,000 feet (1,500 m) support much denser forest. Jeffrey pine, ponderosa pine, black oak, lodgepole pine, and willow constitute most of the forested lands. The mountain habitats of the watershed support many animals typical of Californian mountain regions, including squirrels, chipmunks, black bears, mule deer, and many species of migratory birds. In the canyons of the San Bernardinos, the river is abundant in rainbow trout and is lined with alders, willow and cottonwoods. Where the river and its large upper tributaries empty out of the mountain canyons into the Inland Empire basin, they are surrounded by the alluvial scrub zone, a mix of desert and upper riparian vegetation. Along the main stem, this zone begins at the base of Seven Oaks Dam and ends at the Lytle Creek confluence.
  Historically, the Santa Ana was named "the best stream in Southern California [for steelhead trout habitat]". The steelhead is an anadromous fish, similar to salmon, that migrates up rivers and streams to spawn. Unlike salmon, which usually only reproduce once, steelhead may reproduce multiple times and have a much longer life sp
caption: This segment of the Santa Ana River just downstream of Seven Oaks Dam marks the beginning of the inland riparian zone
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