This forms the most densely populated region of the county, which has a mild Mediterranean to semiarid climate and extensive chaparral vegetation, similar to the rest of the western portion of Southern California.

The area which is now San Diego County has been inhabited for more than 12,000 years by the Kumeyaay (also known as 'Iipai-Tiipai or by the historical Spanish name Diegueño), Luiseño, Cupeño, Cahuilla, and the Acjachemen people and their local predecessors.

[14] In November 1602, Sebastián Vizcaíno surveyed the harbor and what are now Mission Bay and Point Loma and named the area for Saint Didacus, a Spaniard more commonly known as San Diego.

San Diego County became part of the United States as a result of the Treaty of Guadalupe Hidalgo in 1848, ending the Mexican–American War.

The Cleveland National Forest is spread across the central portion of the county, while Anza-Borrego Desert State Park occupies most of the northeast.

Signs posted in numerous spots of the county provide information on the level of threats from fires based on weather conditions.

Western San Diego's climate is characterized by warm, dry summers and mild winters with most of the annual precipitation falling between November and March.

The climate in the San Diego area, like much of California, often varies significantly over short geographical distances resulting in microclimates.

In San Diego's case this is mainly due to the city's topography (the Bay, and the numerous hills, mountains, and canyons).

[24] The city of El Cajon, just 10 miles (16 km) northeast of downtown San Diego, averages January lows of 42 °F (6 °C) and August highs of 89 °F (32 °C).

[27] Rainfall along the coast averages about 10 inches (25 cm) of precipitation annually, which occurs mainly during the cooler months of December through April.

It contains all or most of the cities of Carlsbad, Encinitas, Solana Beach, Del Mar, and Poway in addition to a substantial portion of northern San Diego.

Local governments may not prohibit adults, who are in compliance with state laws, from growing, using, or transporting marijuana for personal use.

Its numerous tourist destinations include Westfield UTC, Seaport Village, and Fashion Valley for shopping.

The region is host to the second largest cruise ship industry in California which generates an estimated $2 million annually from purchases of food, fuel, supplies, and maintenance services.

Present-day culture includes many historical and tourist attractions, a thriving musical and theatrical scene, numerous notable special events, a varied cuisine, and a reputation as one of America's premier centers of craft brewing.

[86] The county is home to several universities whose teams compete in various NCAA Division I sports, most notably the San Diego State Aztecs.

San Diego is the largest American city not to have won a championship in a "Big Four"[a] major professional league.

[88] Some chartered cities such as San Diego and Chula Vista provide municipal services such as police, public safety, libraries, parks and recreation, and zoning.

[90][91]) That pattern was broken in 2013 when Slater-Price retired; she was replaced by Democrat Dave Roberts, who won election to the seat in November 2012 and was inaugurated in January 2013.

In 2008, Barack Obama became the first Democratic presidential candidate to win a majority of votes in San Diego County since World War II.

Supporters and political observers gather to watch the results come in; supporters of the various candidates parade around the hall, carrying signs and chanting; candidates give their victory and concession speeches and host parties for campaign volunteers and donors at the site; and television stations broadcast live from the floor of the convention center.

[110] Naval Base San Diego is principal home to the Pacific Fleet (although the headquarters is located in Pearl Harbor).

NAS North Island is located on the north side of Coronado, and is home to Headquarters for Naval Air Forces and Naval Air Force Pacific, the bulk of the Pacific Fleet's helicopter squadrons, and part of the West Coast aircraft carrier fleet.

[111] It is located on the Southern California coast, bordered by Oceanside to the south, San Clemente to the north, and Fallbrook to the east.

[115] As of the 2020 census, San Diego County includes 18 incorporated cities, 18 Indian reservations, and 39 census-designated places.

[116] Although they are typical in size to other Indian reservations in California (many of which are termed "Rancherías"), they are relatively small by national standards,[citation needed] and all together total 200.2 sq mi (519 km2) of area.

[117][118] † county seat incorporated removed The communities of Del Dios, Elfin Forest, Harmony Grove, and Pala were newly-designated as CDPs in the 2020 census.

Alpine, Bonita, Fallbrook, Lakeside, Ramona, Rancho Santa Fe and Spring Valley have each been tied to various incorporation studies, organized efforts and discussions in the past.

[148] Encinitas and Solana Beach in 1986 are the most recent examples of successful campaigns for incorporation within the County of San Diego.