Southern California (colloquially and locally known as SoCal) is a geographic and cultural region that generally comprises California's southernmost counties, and is the second most populous urban agglomeration in the United States.^[3][4] The region contains ten counties: Imperial, Los Angeles, Orange, Riverside, San Bernardino, San Diego, Santa Barbara, San Luis Obispo, Ventura, and Kern counties.

The Colorado Desert and the Colorado River are located on southern California's eastern border with Arizona, and the Mojave Desert is located north on California's Nevada border. Southern California's southern border is part of the Mexico–United States border.

Southern California includes the heavily built-up urban area which stretches along the Pacific coast from Ventura through Greater Los Angeles down to Greater San Diego (the contiguous urban area in fact continuing into Tijuana, Mexico), and inland to the Inland Empire and Coachella Valley (Palm Springs area). It encompasses eight metropolitan areas (MSAs), three of which together form the Greater Los Angeles Combined Statistical Area (CSA) with over 18 million people, the second-biggest CSA after the New York CSA. These three MSAs are: the Los Angeles metropolitan area (Los Angeles and Orange counties, with 13.3 million people), the Inland Empire ((Riverside and San Bernardino counties, including the Coachella Valley cities, with 4.3 million people), and the Oxnard–Thousand Oaks–Ventura metropolitan area (0.8 million people). In addition, Southern California contains the San Diego metropolitan area with 3.3 million people, Bakersfield metro area with 0.9 million, and the Santa Barbara, San Luis Obispo, and El Centro (Imperial County) metropolitan areas.

The Southern California Megaregion (or megalopolis) is larger still, extending east into Las Vegas, Nevada and south across the Mexican border into Tijuana.^[5]

Within southern California are two major cities, Los Angeles and San Diego, as well as three of the country's largest metropolitan areas.^[6] With a population of 4,042,000, Los Angeles is the most populous city in California and the second most populous in the United States. South of Los Angeles and with a population of 1,307,402 is San Diego, the second most populous city in the state and the eighth most populous in the nation.

The counties of Los Angeles, San Diego, Orange, Riverside, and San Bernardino are the five most populous in the state, and are in the top 15 most populous counties in the United States.^[7]

The motion picture, television, and music industry are centered in the Los Angeles area in southern California. Hollywood, a district of Los Angeles, gives its name to the American motion picture industry, which is synonymous with the neighborhood name. Headquartered in southern California are The Walt Disney Company (which owns ABC), Sony Pictures, Universal Pictures, MGM, Paramount Pictures, 20th Century Fox, and Warner Bros. Universal, Warner Bros., and Sony also run major record companies.

Southern California is also home to a large homegrown surf and skateboard culture. Companies such as Vans, Volcom, Quiksilver, No Fear, RVCA, and Body Glove are all headquartered here. Skateboarder Tony Hawk; surfers Rob Machado, Tim Curran, Bobby Martinez, Pat O'Connell, Dane Reynolds, and Chris Ward live in southern California. Some of the most famous surf locations are in southern California as well, including Trestles, Rincon, The Wedge, Huntington Beach, and Malibu. Some of the world's largest action sports events, including the X Games,^[8] Boost Mobile Pro,^[9] and the U.S. Open of Surfing, are held in southern California. The region is also important to the world of yachting with premier events including the annual Transpacific Yacht Race, or Transpac, from Los Angeles to Hawaii. The San Diego Yacht Club held the America's Cup, the most prestigious prize in yachting, from 1988 to 1995 and hosted three America's Cup races during that time. The first modern era triathlon was held in Mission Bay, San Diego, California in 1974. Since then, southern California, and San Diego in particular have become a mecca for triathlon and multi-sport racing, products and culture.

Southern California is home to many sports franchises and sports networks such as Fox Sports Net.

Many locals and tourists frequent the southern California coast for its beaches. The inland desert city of Palm Springs is also popular.

Southern California is not a formal geographic designation and definitions of what constitutes southern California vary. Geographically, California's North-South midway point lies at exactly 37° 9' 58.23" latitude, around 11 miles (18 km) south of San Jose; however, this does not coincide with the popular use of the term. When the state is divided into two areas (northern and southern California), the term southern California usually refers to the 10 southernmost counties of the state. This definition coincides neatly with the county lines at 35° 47′ 28″ North latitude, which form the northern borders of San Luis Obispo, Kern, and San Bernardino counties. That closely matches the lower one-third of California's span of latitude. Another definition for southern California uses Point Conception and the Tehachapi Mountains as geographical landmarks for the northern boundary.

Though there is no official definition for the northern boundary of southern California, such a division has existed from the time when Mexico ruled California and political disputes raged between the Californios of Monterey in the upper part and Los Angeles in the lower part of Alta California. Following the acquisition of California by the United States, the division continued as part of the attempt by several pro-slavery politicians to arrange the division of Alta California at 36 degrees, 30 minutes, the line of the Missouri Compromise. Instead, the passing of the Compromise of 1850 enabled California to be admitted to the Union as a free state, preventing southern California from becoming its own separate slave state.

Subsequently, Californians (dissatisfied with inequitable taxes and land laws) and pro-slavery Southerners in the lightly populated "cow counties" of southern California attempted three times in the 1850s to achieve a separate statehood or territorial status separate from Northern California. The last attempt, the Pico Act of 1859, was passed by the California State Legislature and signed by State Governor John B. Weller. It was approved overwhelmingly by nearly 75 percent of voters in the proposed Territory of Colorado. This territory was to include all the counties up to the then much larger Tulare County (that included what is now Kings, most of Kern, and part of Inyo counties) and San Luis Obispo County. The proposal was sent to Washington, D.C. with a strong advocate in Senator Milton Latham. However, the secession crisis following the election of Abraham Lincoln in 1860 and the subsequent American Civil War led to the proposal never coming to a vote.^[10][11]

In 1900, the Los Angeles Times defined southern California as including "the seven counties of Los Angeles, San Bernardino, Orange, Riverside, San Diego, Ventura and Santa Barbara." In 1999, the Times added a newer county, Imperial, to that list.^[12]

Southern California was the name of a proposed new state which failed to get on the 2018 California ballot. It proposed to split the existing state into three parts.^[13]

The state is most commonly divided and promoted by its regional tourism groups, consisting of northern, central, and southern California regions. The two American Automobile Association (AAA) Auto Clubs of the state, the California State Automobile Association, and the Automobile Club of Southern California, choose to simplify matters by dividing the state along the lines where their jurisdictions for membership apply, as either northern or southern California, in contrast to the three-region point of view. Another influence is the geographical phrase South of the Tehachapis, which would split the southern region off at the crest of that transverse range, but in that definition, the desert portions of north Los Angeles County and eastern Kern and San Bernardino Counties would be included in the southern California region due to their remoteness from the central valley and interior desert landscape.

Southern California consists of a heavily developed urban environment, home to some of the largest urban areas in the state, along with vast areas that have been left undeveloped. It is the third most populated megalopolis in the United States, after the Great Lakes Megalopolis and the Northeastern Megalopolis. Much of southern California is famous for its large, spread-out, suburban communities and use of automobiles and highways. The dominant areas are Los Angeles, Orange County, San Diego, and Riverside-San Bernardino, each of which are the centers of their respective metropolitan areas, composed of numerous smaller cities and communities. The urban area is also host to an international metropolitan region in the form of San Diego–Tijuana, created by the urban area spilling over into Baja California.

Traveling south on Interstate 5, the main gap to continued urbanization is Camp Pendleton. The cities and communities along Interstate 15 and Interstate 215 are so interrelated that Temecula and Murrieta have as much connection with the San Diego metropolitan area as they do with the Inland Empire. To the east, the United States Census Bureau considers the San Bernardino and Riverside County areas, Riverside-San Bernardino area as a separate metropolitan area from Los Angeles County. Newly developed exurbs formed in the Antelope Valley, north of Los Angeles, the Victor Valley, and the Coachella Valley with the Imperial Valley. Also, population growth was high in the Bakersfield-Kern County, Santa Maria and San Luis Obispo areas.

The climate is Mediterranean-Like, with Warm/dry Summers, Mild/wet Winters, where cool weather and freezing temperatures are rare. Southern California contains several different types of climate, including Mediterranean, semi-arid, desert and mountain, with infrequent rain and many sunny days. Summers are hot or warm, and dry, while winters are mild, and rainfall is low to moderate depending on the area. Although heavy rain can occur, it is unusual. This climatic pattern was alluded to in the hit song "It Never Rains (In Southern California)". While snow is very rare in the southwest region of the state, it occurs occasionally in the southeast region of the state.

Southern California consists of one of the more varied collections of geologic, topographic, and natural ecosystem landscapes in a diversity outnumbering other major regions in the state and country. The region spans from Pacific Ocean islands, shorelines, beaches, and coastal plains, through the Transverse and Peninsular Ranges with their peaks, and into the large and small interior valleys, to the vast deserts of California.

Southern California is divided into:

Each year, southern California has about 10,000 earthquakes. Nearly all of them are so small that they are not felt. Only several hundred have been greater than magnitude 3.0, and only about 15–20 have been greater than magnitude 4.0.^[24] The magnitude 6.7 1994 Northridge earthquake was particularly destructive, causing a substantial number of deaths, injuries, and structural collapses as well as the most property damage of any earthquake in U.S. history at an estimated $20 billion.^[25]

Many faults are able to produce a magnitude greater than 6.7 earthquake, such as the San Andreas Fault, which can produce a magnitude 8.0 event. Other faults include the San Jacinto Fault, the Puente Hills Fault, and the Elsinore Fault Zone. The United States Geological Survey (USGS) has released a California earthquake forecast,^[26] which models earthquake occurrence in California.

Southern California is divided culturally, politically, and economically into distinct regions, each containing its own culture and atmosphere, anchored usually by a city with both national and sometimes global recognition, which is often the hub of economic activity for its respective region and being home to many tourist destinations. Each region is further divided into many culturally distinct areas but as a whole, combine to create the southern California atmosphere.

*Part of multiple regions

As of the 2010 United States Census, southern California has a population of 22,680,010. Despite a reputation for high growth rates, southern California's rate grew less than the state average of 10.0 percent in the 2000s. This was due to California's growth becoming concentrated in the northern part of the state as result of a stronger, tech-oriented economy in the Bay Area and an emerging Greater Sacramento region.

Southern California consists of one Combined Statistical Area, eight Metropolitan Statistical Areas, one international metropolitan area, and multiple metropolitan divisions. The region is home to two extended metropolitan areas that exceed five million in population. These are the Greater Los Angeles Area at 17,786,419, and San Diego–Tijuana at 5,105,768.^[27][28] Of these metropolitan areas, the Los Angeles-Long Beach-Santa Ana metropolitan area, Riverside-San Bernardino-Ontario metropolitan area, and Oxnard-Thousand Oaks-Ventura metropolitan area form Greater Los Angeles;^[29] while the El Centro metropolitan area and San Diego-Carlsbad-San Marcos metropolitan area form the Southern Border Region.^[30][31] North of Greater Los Angeles are the Santa Barbara, San Luis Obispo, and Bakersfield metropolitan areas.

Los Angeles (with a 2017 census-estimated population of 4.0 million people) and San Diego (at 1.4 million people) are the two largest cities in all of California and are in the top eight largest cities in the United States. In southern California, there are also 12 cities with more than 200,000 residents and 34 cities over 100,000 residents. Many of southern California's most developed cities lie along or in close proximity to the coast, with the exception of San Bernardino and Riverside.

Southern California has a diverse economy and is one of the largest economies in the United States. It is dominated and heavily dependent upon the abundance of petroleum, as opposed to other regions where automobiles are not nearly as dominant, due to the vast majority of transport that runs on this fuel. Southern California is famous for tourism and the entertainment industry. Other industries include software, automotive, ports, finance, biomedical, and regional logistics. The region was a leader in the housing bubble from 2001 to 2007 and has been heavily impacted by the housing crash.

Since the 1920s, motion pictures, petroleum, and aircraft manufacturing have been major industries. In one of the richest agricultural regions in the U.S., cattle and citrus were major industries until farmlands were turned into suburbs. Although military spending cutbacks have had an impact, aerospace continues to be a major factor.^[32]

Southern California is home to many major business districts. Central business districts (CBD) include Downtown Los Angeles, Downtown San Diego, Downtown San Bernardino and South Coast Metro. Within the Los Angeles Area are the major business districts of Downtown Pasadena, Downtown Burbank, Downtown Santa Monica, Downtown Glendale and Downtown Long Beach. Los Angeles itself has many business districts, such as Downtown Los Angeles and those lining the Wilshire Boulevard Miracle Mile, including Century City, Westwood, and Warner Center in the San Fernando Valley. The area of Santa Monica and Venice (and perhaps some of Culver City) is informally referred to as "Silicon Beach" because of the concentration of financial and marketing technology-centric firms located in the region.

The San Bernardino-Riverside area maintains the business districts of Downtown San Bernardino, Hospitality Business/Financial Centre, University Town which are in San Bernardino and Downtown Riverside.

Orange County is a rapidly developing business center that includes Downtown Santa Ana, the South Coast Metro, and Newport Center districts, as well as the Irvine business centers of The Irvine Spectrum, West Irvine, and international corporations headquartered at the University of California, Irvine. West Irvine includes the Irvine Tech Center and Jamboree Business Parks.

Downtown San Diego is the CBD of San Diego, though the city is filled with business districts. These include Carmel Valley, Del Mar Heights, Mission Valley, Rancho Bernardo, Sorrento Mesa, and University City. Most of these districts are located in Northern San Diego and some within North County regions.

Los Angeles

Orange County

Riverside & San Bernardino

San Diego

Southern California is home to Los Angeles International Airport, the second-busiest airport in the United States by passenger volume (see World's busiest airports by passenger traffic) and the third-busiest by international passenger volume (see Busiest airports in the United States by international passenger traffic); San Diego International Airport, the busiest single-runway airport in the world; Van Nuys Airport, the world's busiest general aviation airport; major commercial airports at Orange County, Bakersfield, Ontario, Burbank and Long Beach; and numerous smaller commercial and general aviation airports.

Six of the seven lines of the commuter rail system, Metrolink, run out of Downtown Los Angeles, connecting Los Angeles, Ventura, San Bernardino, Riverside, Orange, and San Diego counties with the other line connecting San Bernardino, Riverside, and Orange counties directly.

Southern California is also home to the Port of Los Angeles, the country's busiest commercial port; the adjacent Port of Long Beach, the country's second busiest container port; and the Port of San Diego.

The following table shows all airports listed by the Federal Aviation Association (FAA) as a hub airport:^[33]

Sections of the southern California freeway system are often referred to by names rather than by the official numbers.

The Tech Coast is a moniker that has gained use as a descriptor for the region's diversified technology and industrial base as well as its multitude of prestigious and world-renowned research universities and other public and private institutions. Amongst these include five University of California campuses (Irvine, Los Angeles, Riverside, Santa Barbara, and San Diego), 12 California State University campuses (Bakersfield, Channel Islands, Dominguez Hills, Fullerton, Los Angeles, Long Beach, Northridge, Pomona, San Bernardino, San Diego, San Marcos, and San Luis Obispo); and private institutions such as the California Institute of Technology, Azusa Pacific University, Chapman University, the Claremont Colleges (Claremont McKenna College, Harvey Mudd College, Pitzer College, Pomona College, Scripps College, Claremont Graduate University and Keck Graduate Institute), Loma Linda University, Loyola Marymount University, Occidental College, Pepperdine University, University of Redlands, University of San Diego, and the University of Southern California.

Many cities in the region have world class medical facilities such as Imperial, Los Angeles, Orange, Riverside, San Bernardino, San Diego, San Luis Obispo, Santa Barbara, and Ventura.

Numerous parks provide recreation opportunities and open space. Locations include:

Major professional sports teams in southern California include:

Southern California also is home to a number of popular NCAA sports programs such as the UCLA Bruins, the USC Trojans, and the San Diego State Aztecs. The Bruins and the Trojans both field football teams in NCAA Division I in the Pac-12 Conference, and there is a longtime rivalry between the schools.