San Diego , named after Saint Didacus (Spanish: San Diego de Alcalá), is the eighth-largest city in the United States and second-largest city in California. The city is located on the coast of the Pacific Ocean in Southern California, immediately adjacent to the Mexican border. The birthplace of California, San Diego is known for its mild year-round climate, its natural deep-water harbor, and its long association with the U.S. Navy.
Historically home to the Kumeyaay people, San Diego was the first site visited by Europeans on what is now the West Coast of the United States. Upon landing in San Diego Bay in 1542, Juan Cabrillo claimed the entire area for Spain, forming the basis for the settlement of Alta California 200 years later. The Presidio and Mission of San Diego, founded in 1769, were the first European settlement in what is now California. In 1821 San Diego became part of newly independent Mexico, and in 1850 became part of the United States with the admission of California to the union.
The city is the county seat of San Diego County and is the economic center of the San Diego–Carlsbad–San Marcos metropolitan area as well as the San Diego–Tijuana metropolitan area. San Diego's main economic engines are military and defense-related activities, tourism, international trade, and manufacturing. The presence of the University of California, San Diego (UCSD), with the affiliated UCSD Medical Center, has helped make the area a center of research in biotechnology.