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 (154 km) long, and its drainage basin is 2,650 square miles (6,900 km2) in size.
The Rio Hondo is a tributary of the Los Angeles River in Los Angeles County, California, approximately 16.4 miles (26.4 km) long. As a named river, it begins in Irwindale and flows southwest to its confluence in South Gate, passing through several cities. Above Irwindale its main stem is known as Santa Anita Creek, which extends another 10 miles (16 km) northwards into the San Gabriel Mountains where the source, or headwaters, of the river are found.
The San Gabriel River is a mostly urban waterway flowing 58 miles (93 km) southward through Los Angeles and Orange Counties, California in the United States. It is the central of three major rivers draining the Greater Los Angeles Area, the others being the Los Angeles River and Santa Ana River. The river's watershed stretches from the rugged San Gabriel Mountains to the heavily developed San Gabriel Valley and a significant part of the Los Angeles coastal plain, emptying into the Pacific Ocean between the cities of Long Beach and Seal Beach.
The Arroyo Seco, meaning "dry stream" in Spanish, is a 24.9-mile-long (40.1 km) seasonal river, canyon, watershed, and cultural area in Los Angeles County, California. The area was explored by Gaspar de Portolà who named the stream Arroyo Seco as this canyon had the least water of any he had seen. During this exploration he met the Chief Hahamog-na (Hahamonga) of the Tongva Indians.
Ballona Creek is an 8.5-mile (13.7 km) tame and unsightly year-round stream in southwestern Los Angeles County, California, and in conjunction with neighboring estuary Ballona Wetlands a “prime bird-watching spot for cormorants, owls, and migrating ducks and geese.”
The Los Angeles flood of 1938 was one of the largest floods in the history of Los Angeles, Orange, and Riverside Counties in southern California. The flood was caused by two Pacific storms that swept across the Los Angeles Basin in February-March 1938 and generated almost one year's worth of precipitation in just a few days. Between 113–115 people were killed by the flooding. The Los Angeles, San Gabriel, and Santa Ana Rivers burst their banks, inundating much of the coastal plain, the San Fernando and San Gabriel Valleys, and the Inland Empire. Flood control structures spared parts of Los Angeles County from destruction, while Orange and Riverside Counties experienced more damage.
San Juan Creek, also called the San Juan River, is a 29-mile (47 km) long stream in Orange and Riverside Counties, draining a watershed of 133.9 square miles (347 km2). Its mainstem begins in the southern Santa Ana Mountains in the Cleveland National Forest. It winds west and south through San Juan Canyon, and is joined by Arroyo Trabuco as it passes through San Juan Capistrano. It flows into the Pacific Ocean at Doheny State Beach. San Juan Canyon provides a major part of the route for California State Route 74.
Aliso Creek is a 19.8-mile (31.9 km)-long, mostly urban stream in south Orange County, California. Originating in the Cleveland National Forest in the Santa Ana Mountains, it flows generally southwest and empties into the Pacific Ocean at Laguna Beach. The creek's watershed drains 34.9 square miles (90 km2), and it is joined by seven main tributaries. As of 2018, the watershed had a population of 144,000 divided among seven incorporated cities.
Oso Creek is an approximately 13.5-mile (21.7 km) tributary of Arroyo Trabuco in southern Orange County in the U.S. state of California. Draining about 20 square miles (52 km2) in a region north of the San Joaquin Hills and south of the Santa Ana Mountains, the creek is Trabuco Creek's largest tributary, and is part of the San Juan Creek drainage basin. Beginning in the foothills of the Santa Ana Mountains near the city of Mission Viejo, the creek is dammed twice to form Upper Oso Reservoir and Lake Mission Viejo. The creek is channelized and polluted along much of its length.
Laguna Canyon is a canyon that cuts through the San Joaquin Hills in southern Orange County, California, in the United States, directly south of the city of Irvine. The canyon runs from northeast to southwest, and is drained on the north side by tributaries of San Diego Creek and on the south by Laguna Canyon Creek. It is deeper and more rugged on the southwestern end near Laguna Beach.
San Diego Creek is a 16-mile (26 km) urban waterway flowing into Upper Newport Bay in Orange County, California in the United States. Its watershed covers 112.2 square miles (291 km2) in parts of eight cities, including Irvine, Tustin, and Costa Mesa. From its headwaters in Laguna Woods the creek flows northwest to its confluence with Peters Canyon Wash, where it turns abruptly southwest towards the bay. Most of the creek has been converted to a concrete flood control channel, but it also provides important aquatic and riparian habitat along its course and its tidal estuary.
Coyote Creek is a principal tributary of the San Gabriel River in northwest Orange County, southeast Los Angeles County, and southwest Riverside County, California. It drains a land area of roughly 41.3 square miles (107 km2) covering eight major cities, including Brea, Buena Park, Fullerton, Hawaiian Gardens, La Habra, Lakewood, La Palma, and Long Beach. Some major tributaries of the creek in the highly urbanized watershed include Brea Creek, Fullerton Creek, and Carbon Creek. The mostly flat creek basin is separated by a series of low mountains, and is bounded by several small mountain ranges, including the Chino Hills, Puente Hills, and West Coyote Hills.
Brea Creek is one of four principal tributaries of Coyote Creek, which is a lower tributary of the San Gabriel River. It drains parts of Orange, Riverside and San Bernardino counties in the southern part of the U.S. state of California. The creek flows 11.7 miles (18.8 km) from the cities of Brea and Anaheim to Whittier, where its mouth is on the left bank of Coyote Creek, at a point 481 feet (147 m) lower in elevation.
San Mateo Creek is a stream in Southern California in the United States, whose watershed mostly straddles the border of Orange and San Diego Counties. It is about 22 miles (35 km) long, flowing in a generally southwesterly direction. Draining a broad valley bounded by the Santa Ana Mountains and Santa Margarita Mountains, San Mateo Creek is notable for being one of the last unchannelized streams in Southern California.
Arroyo Calabasas is a 7.0-mile-long (11.3 km) tributary of the Los Angeles River, in the southwestern San Fernando Valley area of Los Angeles County in California.
Carbon Canyon Dam is a dam at the northern edge of Orange County, California. The dam is approximately 4 miles (6.4 km) east of the city of Brea and approximately 12 miles (19 km) north of the city of Santa Ana. The drainage area above the dam is 19.3 square miles (50 km2) and is encompassed entirely within the Puente and Chino Hills. The Carbon Canyon Creek flows in a generally southwesterly direction onto the coastal Orange County Plain, joins Coyote Creek, and then flows into the San Gabriel River.
Chino Creek is a major stream of the Pomona Valley, in the western Inland Empire region of Southern California. It is a tributary of the Santa Ana River.
San Antonio Creek is a major stream in Los Angeles County and San Bernardino County, California, draining southwards from Mount San Antonio in the San Gabriel Mountains into Chino Creek, a tributary of the Santa Ana River. Upon leaving San Antonio Canyon and entering the broad alluvial plain of the Pomona Valley, it is known as the San Antonio Wash or the San Antonio Creek Channel, the former referring to the creek's seasonal dry nature below the mouth of San Antonio Canyon.
Walnut Creek is an urban stream in the San Gabriel Valley of Southern California, and is a tributary of the San Gabriel River. The creek begins at the Puddingstone Dam of Puddingstone Reservoir in Frank G. Bonelli Regional Park and flows westward for about 13 miles (21 km), through San Dimas, Covina, West Covina and Baldwin Park, to join the San Gabriel River in El Monte.
