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| Southern California coastal plain | |
|---|---|
| Name | Southern California coastal plain |
| Other name | Coastal Plain of Southern California |
| Country | United States |
| State | California |
| Region | Southern California |
| Largest city | Los Angeles |
Southern California coastal plain is the low-lying stretch of coastline and adjacent lowlands along the Pacific Ocean in Southern California, extending through parts of Los Angeles County, Orange County, San Diego County and portions of Ventura County, Riverside County and Imperial County. The plain includes major urban centers such as Los Angeles, San Diego, Long Beach, Santa Ana and Irvine and features major coastal infrastructure like the Port of Los Angeles, Port of Long Beach, and San Diego Bay. It is bounded by mountain ranges including the Santa Monica Mountains, San Gabriel Mountains, and Sierra Pelona Mountains and interfaces with estuaries such as Ballona Wetlands and San Dieguito Lagoon.
The coastal plain comprises contiguous lowlands from the Ventura Basin southeast through the Los Angeles Basin and Orange County plains into the San Diego Trough and Tijuana River Estuary. Major rivers crossing the plain include the Los Angeles River, Santa Ana River, San Gabriel River, San Diego River, and Sweetwater River. Prominent coastal cities and municipalities on the plain are Los Angeles, San Diego, Long Beach, Santa Monica, Venice, Huntington Beach, Newport Beach, Mission Bay, and La Jolla. The plain contains critical facilities such as the Los Angeles International Airport, John Wayne Airport, and San Diego International Airport and recreational areas like Santa Monica Pier, Balboa Park, and Coronado Beach.
The plain formed through interactions among the Pacific Plate, North American Plate, and regional fault systems such as the San Andreas Fault, San Jacinto Fault Zone, and Newport–Inglewood Fault. Marine terraces, alluvial fans, and sedimentary basins including the Los Angeles Basin and Santa Maria Basin record Pleistocene and Holocene sea-level changes associated with glacial cycles recognized by researchers from institutions like Scripps Institution of Oceanography and United States Geological Survey. Hydrocarbon-bearing formations underlie parts of the plain and have been exploited in fields such as Signal Hill and the Los Angeles City Oil Field, connected historically to companies like Union Oil Company of California and Chevron Corporation. Earthquake history linked to faults including the 2010 Baja California earthquake and paleoseismic studies by California Geological Survey inform hazard assessments for coastal infrastructure and reclamation projects in locales like Long Beach and Seal Beach.
The plain experiences a Mediterranean climate influenced by the Pacific Ocean, the California Current, and coastal upwelling studied by scientists at Scripps Institution of Oceanography and NOAA. Weather patterns include marine layer and coastal fog that affect areas such as Santa Monica, San Pedro, Encinitas, and Carlsbad, along with seasonal Santa Ana winds originating in the Inland Empire and Mojave Desert that impact air quality in Los Angeles County and Orange County. Sea-level rise linked to Intergovernmental Panel on Climate Change assessments threatens low-lying infrastructure including the Port of Los Angeles, Los Angeles International Airport, and historic resources in San Diego Bay and Old Town San Diego.
Historically, the plain hosted extensive coastal sage scrub, salt marshes, estuaries, and riparian corridors supporting species cataloged by institutions like the Natural History Museum of Los Angeles County and San Diego Natural History Museum. Habitats include Los Angeles River riparian zones, Ballona Wetlands salt marsh, Tijuana River Estuary mudflats, and dune systems at Bolsa Chica Ecological Reserve and Torrey Pines State Natural Reserve. Native flora and fauna recorded from the plain include coastal scrub specialists like Artemisia californica and Eriogonum fasciculatum, avifauna such as California least tern and brown pelican, amphibians like Pacific tree frog, reptiles including California legless lizard, and mammals such as gray fox and coyote. Conservation organizations active on the plain include the Nature Conservancy, Audubon Society, and California Department of Fish and Wildlife working with municipal agencies in Los Angeles, Irvine, Carlsbad, and San Diego.
Indigenous groups traditionally inhabiting the plain include the Tongva, Chumash, Luiseño, Kumeyaay, and Cahuilla peoples, who maintained villages along rivers and estuaries such as the Los Angeles River and San Luis Rey River. Spanish colonial institutions such as the Mission San Gabriel Arcángel, Mission San Juan Capistrano, and Mission San Diego de Alcalá reshaped settlement patterns during the Spanish colonization of the Americas and Mexican–American War era transitions that culminated in the Treaty of Guadalupe Hidalgo and incorporation into United States. Land grants like Rancho San Pedro and Rancho Los Alamitos influenced 19th-century development tied to figures such as Pío Pico, Juan Rodríguez Cabrillo, and Gaspar de Portolá. Archaeological and ethnohistorical studies by universities like University of California, Los Angeles and University of California, San Diego document village sites, trade networks, and resource use on the plain.
Since the late 19th century, the plain has undergone rapid urbanization driven by oil booms at Long Beach oil field, transportation expansion with the Pacific Electric system and interstate highways like Interstate 5, Interstate 405, and Interstate 10, and population growth in metropolitan areas including the Greater Los Angeles Area and San Diego–Tijuana metropolitan area. Land use includes dense urban cores in Los Angeles and San Diego, suburban planned communities in Orange County such as Irvine and Anaheim, industrial ports at Port of Los Angeles and Port of Long Beach, and military installations like Naval Base San Diego and Los Angeles Air Force Base. Major redevelopment and planning efforts involve agencies such as the Metropolitan Transportation Authority (Los Angeles County) and San Diego Association of Governments, addressing issues of housing in places like Skid Row and Chula Vista.
The plain hosts key transportation corridors including Interstate 5, Interstate 405, U.S. Route 101, California State Route 1, and freight rail links to BNSF Railway, Union Pacific Railroad and the ports. Airports such as Los Angeles International Airport, San Diego International Airport, and John Wayne Airport connect the region to domestic and international destinations including Mexico and the Pacific Rim. Public transit systems serving the plain include Los Angeles Metro Rail, San Diego Trolley, Metrolink, and regional bus networks operated by agencies like Metro (Los Angeles County) and Metropolitan Transit System (San Diego County). Infrastructure projects and resilience planning involve entities such as the Federal Emergency Management Agency, California Coastal Commission, and California Department of Transportation to address sea-level rise, seismic retrofitting, and port operations at Port of Long Beach and Port of Los Angeles.
Category:Geography of Southern California