When the United States was dictating the terms of the Treaty of Guadalupe Hidalgo in 1848, after its successful war with Mexico, it made sure the southern boundary of its new California territory was just south of the port of San Diego. This is one of three splendid natural harbors on the Pacific Coast, and in 1914 the Marine Corps established a base on North Island. This was just the first of many military bases in San Diego, with its mild climate, deep harbor, and plentiful land for aircraft maneuvers. This has been the major West Coast U.S. Navy base for more than 50 years, the second-largest Navy port behind Norfolk, and home to about 30,000 active-duty Navy and Marine Corps personnel on shore. Also based here are the retired aircraft carriers Midway and Constellation, plus the Ronald Reagan, which was commissioned in 2003, with a flight deck that covers 4.5 acres.

The port and Navy base in the sheltered harbor remain the central focus of a rapidly growing metropolis that now stretches far inland and to the north. Downtown there are post-modern buildings like the Horton Plaza amid a few well-preserved early-20th-century relics like the Spreckels Theatre. Across the harbor, on the sand spit that guards it against the ocean, is the white frame castle of the Hotel Del Coronado, with its surprisingly dark wooden interior—the U.S.’s largest wooden structure, opened in 1888 and a favored resort of past American presidents; the town of Coronado has long been a favorite retirement mecca for Navy admirals and captains.

San Diego is not all harbor and Navy. To the north, the Pacific waves pound against the beach beneath erose cliffs of unique rock formations along the coast. Located here are some of San Diego’s great cultural institutions: the Scripps Institute of Oceanography, the University of California San Diego campus, the Salk Institute, and the Torrey Pines reserve, home of the unique, wide-spreading pine tree. To the south are raffish Mission Beach; Ocean Beach, with its strong rip currents; and Point Loma, overlooking the entrance to the harbor. The weather—a sunny 70 degrees most of the time—lures tourists and new residents. But this also is a working town, a sophisticated high-tech center with growing biotechnology, electronics, software, and telecommunications industries. It is a manufacturing center as well, with maquiladora factories clustering near the Mexican border. The city has had a long-running battle over proposals to expand or move Lindbergh Field, its landlocked airport, with options ranging from a floating airport in the ocean to a site nearly 100 miles away in Imperial County.

The 53rd Congressional District of California—and the only 53rd district in American history—consists of the center of San Diego, the San Diego beaches from Blacks Beach to Ocean Beach, the port, La Jolla beach (but not the neighborhood itself), and Balboa Park. It includes the heavily Latino neighborhoods south and east of downtown; the Gaslamp District, with its glitzy nightlife scene; and the older neighborhoods of University Heights and East San Diego. Altogether, 85% of the district’s population is within the city limits. It also includes Coronado and Imperial Beach, just north of the Mexican border, and the inland suburbs of La Presa and Lemon Grove, site of a celebrated school-desegregation case in the 1930s. The district is 30% Hispanic. Historically, this was a Republican district, but with coastal California’s trend toward cultural liberalism and with more Democratic areas added in the most recent redistricting, it is now solidly Democratic. In 2004, Democratic nominee John Kerry won the district 61%-38%, and in 2008, Democrat Barack Obama won it 68%-30%.