San Diego (, Spanish: [san ˈdjeɣo]; Spanish for 'Saint Didacus') is a city in the U.S. state of California on the coast of the Pacific Ocean and immediately adjacent to the Mexican border. With a 2020 population of 1,386,932, San Diego is the eighth most populous city in the United States and second most populous in California (after Los Angeles). The city is the county seat of San Diego County, the fifth most populous county in the United States, with 3,338,330 estimated residents as of 2019. The city is known for its mild year-round climate, natural deep-water harbor, extensive beaches and parks, long association with the United States Navy and Marine Corps, and recent emergence as a healthcare and biotechnology development center. Historically home to the Kumeyaay people, San Diego is frequently referred to as the "Birthplace of California", as it was the first site visited and settled by Europeans on what is now the West Coast of the United States. Upon landing in San Diego Bay in 1542, Juan Rodríguez Cabrillo claimed the area for Spain, forming the basis for the settlement of Alta California 200 years later. The Presidio and Mission San Diego de Alcalá, founded in 1769, formed the first European settlement in what is now California. In 1821, San Diego became part of the newly declared Mexican Empire, which reformed as the First Mexican Republic two years later. California became part of the United States in 1848 following the MexicanAmerican War and was admitted to the union as a state in 1850. San Diego's main economic engines are military and defense-related activities, tourism, international trade, research, and manufacturing. The city is the economic center of the San DiegoTijuana conurbation, the second most populous transborder metropolitan area in the western hemisphere (after DetroitWindsor), home to an estimated 4,922,723 people as of 2012. The primary border crossing between San Diego and Tijuana, the San Ysidro Port of Entry, is the busiest international land border crossing in the world outside of Asia (fourth-busiest overall). The city's primary airport, San Diego International Airport, is the busiest single-runway airport in the world.

La Jolla ( lə HOY-ə, American Spanish: [la ˈxoʝa]) is a hilly, seaside neighborhood within the city of San Diego, California, occupying 7 miles (11 km) of curving coastline along the Pacific Ocean. The population reported in the 2010 census was 46,781.La Jolla is surrounded on three sides by ocean bluffs and beaches and is located 12 miles (19 km) north of Downtown San Diego and 45 miles (72 km) south of the Orange County line. The climate is mild, with an average daily temperature of 70.5 °F (21.4 °C).La Jolla is home to many educational institutions and a variety of businesses in the areas of lodging, dining, shopping, software, finance, real estate, bioengineering, medical practice and scientific research. The University of California, San Diego (UCSD), is located in La Jolla, as are the Salk Institute, Scripps Institution of Oceanography (part of UCSD), Scripps Research Institute, and the headquarters of National University (though its academic campuses are elsewhere).

Temecula (; Spanish: Temécula, [te'mekula]) is a city in southwestern Riverside County, California, United States. The city is a tourist and resort destination, with the Temecula Valley Wine Country, Old Town Temecula, the Temecula Valley Balloon & Wine Festival, the Temecula Valley International Film Festival, championship golf courses, and resort accommodations for tourists which contribute to the city's economic profile. Although Temecula is geographically closer to downtown San Diego than downtown Los Angeles, it is considered part of the Greater Los Angeles area. The city of Temecula, forming the southwestern anchor of the Inland Empire region, is approximately 58 miles (93 km) north of downtown San Diego and 85 miles (137 km) southeast of downtown Los Angeles. Temecula is bordered by the city of Murrieta to the north and the Pechanga Indian Reservation and San Diego County to the south. With a population of 110,003 during the 2020 census, Temecula is the 5th most populous city in Riverside County. It was incorporated on December 1, 1989.

Coronado is a resort city located in San Diego County, California, United States, across the San Diego Bay from downtown San Diego. It was founded in the 1880s and incorporated in 1890. Its population was 24,697 at the 2010 census, up from 24,100 at the 2000 census. Coronado is a tombolo connected to the mainland by an isthmus called the Silver Strand. The explorer Sebastian Vizcaino gave Coronado its name and drew its first map in 1602. Coronado is Spanish term for "crowned one," and thus it is nicknamed The Crown City. Its name is derived from the four offshore islands, Los Cuatro Mártires Coronados (Spanish for "The Four Crowned Martyrs"). These other islands are still known as the Coronado Islands, and are now located within Tijuana Municipality of Mexico. Three ships of the United States Navy have been named after the city, including USS Coronado.