San Diego, port and city, seat (1850) of San Diego county, southern California, U.S. It lies along the Pacific Ocean at San Diego Bay, just north of the international border with Mexico and some 120 miles (195 km) southeast of Los Angeles. The city consists of two portions of unequal size: the much larger part extends north and east of San Diego Bay, and the smaller one stretches southeastward from the bay to the Mexican border. The city site is characterized by varied topography of broad mesas, canyons, and wide valleys. The landscape becomes hillier to the north (notably in the La Jolla section) and eastward toward a line of mountains along the edge of the main built-up area. The region has a mild, sunny climate year-round; the little precipitation it receives comes mainly during the winter.