You can understand why – were their city a little less perfectly located, were the climate anything other than unerringly benign, were the alluring parallel universe of the biggest nation in the Spanish-speaking world more than a $2 tram ride away – the average citizen of California's southernmost city might feel miffed. Irked enough, perhaps, to sink another happy-hour San Diego Sunset from the open-air bar that is not merely called Altitude – it is at an altitude of about 300ft above street level. From atop the Marriott Hotel, you can watch the day close over the Pacific. As the sun's final scarlet flourish inflames the mountains then melts into the haze, the horizon, and – ultimately – the Pacific, consider San Diego's mild exasperation about primacy.
California is the richest state in the wealthiest nation on earth, and San Diego is among its most opulent locations. Yet the city has to cede to Los Angeles in scale and population – and suffers the further irritation that most travellers, when asked to name California's second-biggest city, award the title to the smaller but higher-profile San Francisco (which is actually fourth, behind San Jose). Poor San Diego, tucked down on the Mexican border where California ends. Yet this is also the place the state began.
For an exact fix on the birthplace of modern California, go to Point Loma. This rocky outcrop, draped in rough, scrawny vegetation, lies at the tip of the peninsula that curls around anticlockwise from downtown. Here, on 28 September 1542, Juan Rodriguez Cabrillo landed and claimed the coast for Spain (though he was Portuguese, he was serving the Spanish crown). From his statue you can get your bearings beautifully. You may also wonder why San Diego has yet to join Sydney, Hong Kong and, yes, San Francisco, in the global super-league of great waterside cities.
The steel-and-glass skyline of downtown rises in the east. In the foreground, a big naval base, home of America's Pacific Fleet; in the background, the roasted rock that makes California such a scenic dream. In contrast, Coronado, a low-lying neck of indulgent territory, lies to the south. Beyond it, the busiest international frontier in the world: where America meets Mexico, and splashes out on a Tequila Sunrise. Northwards, a wave of beaches ripple their way up the coast, with names reverberating from the Beach Boys songbook. And to the west, simply the biggest ocean in the world.
For a couple of centuries after Cabrillo breezed in, California remained a backwater (gold would not be discovered in seductive quantities until 1849). But the Spanish became concerned about incursions from the Russians, who regarded the west coast of North America as Siberia's back yard. So Spain dispatched a "sacred expedition" from Mexico to establish roots, and a route, through California.
The man with a mission was Junípero Serra, a Franciscan friar from Mallorca, who established a Catholic settlement a few miles east of the present city centre, now swathed in suburbia yet still retaining a sense of serenity. You can explore Serra's spartan dwelling, built around 1774 (long before adobe became a brand of computer software), amid a complex of religious buildings that marks one end of California's original highway. This is the start of the Camino Real, the King's Highway, which runs north for 600 miles, connecting 21 missions. Each is a day's journey apart on horseback, making it ideal for a fly-ride holiday.
San Diego's global ambitions are most visible close by in Balboa Park, named after another adventurous Spaniard: Vasco Nuñez de Balboa, the first European to see the Pacific. This extravagant collection of architecture, gardens and wilderness began life as a piece of commercial opportunism. After the Panama Canal opened in 1914, the city wanted to show how the shortcut between the Atlantic and Pacific put San Diego on the map. So they launched a Panama-California Exposition here, and named the park after Balboa, who saw the world's biggest ocean from a peak in the Darié*region of present-day Panama.
Park life does not get better than this: San Diego has borrowed the best ideas from around the world, such as Washington DC's concept of a boulevard lined with museums, from fine art to photography – and a copy of the Alcázar gardens from Seville. If you prefer to commune with Californian nature, more than 1,000 acres of wilderness provide the chance to get lost in the middle of America's eighth-largest city. You will not stray, though, before you discover a place that features on the cover of what may be the finest pop album ever recorded.
When, in 1966, the Beach Boys sought the location that provided the best vibrations for the artwork for their greatest LP, Pet Sounds, San Diego Zoo provided the solution. If it slithers, sprints, splashes or simply sits and snacks, you can probably find it here, at a zoo nearly a century old and still one of the best in the world. On the average day, human visitors to San Diego Zoo outnumber by more than two to one the animal residents – which include giant pandas, polar bears, orang-utans and 800 other species.
Creatures at the zoo; culture in the park; but for cuisine, you should head downtown – specifically, to a place devoted to another music legend, Jim Croce. Half a lifetime ago, in 1973, I was lucky enough to see the rising star perform. Two months later, the singer-songwriter was killed in a plane crash. He and his wife, Ingrid, had made San Diego their home. Ingrid still lives here, and has created the city's most celebrated restaurant: Croce's. u o It offers fresh takes on Southwestern and Mexican dishes, plumb in the middle of the area known, thanks to some ornate Victorian ironwork, as the Gaslamp Quarter.
But first Ingrid Croce had to deal with sex and drugs. Twenty years ago, that is about all you would have found in the historic core of the city. Largely because of her energetic work, these 16 blocks now comprise the most appealing urban concentration in California – yes, San Francisco, that includes you. Highlights include the William Heath Davis House, a prefabricated New England home shipped around Cape Horn and now housing a museum; and the Horton Grand Hotel, which takes you instantly back to the Thirties and includes a Chinese museum in the foyer. The other handsome redbrick structures in the Gaslamp Quarter no longer deliver prostitution and tattoos; they now house inspirational enterprises such as Le Travel Store, precisely the place to get kitted out for an adventure south of the border to Tijuana or Tierra del Fuego. A few doors down, the Cheese Shop deli serves up a quick, nutritious and cheap lunch. The special, paradoxically, is pork, Californian dietary fads having rendered the original dairy-based menu obsolete.
The other surprise in downtown San Diego is that you can go shopping – proper, extravagant American shopping – in the city. As out-of-town strip malls sucked the commercial life out of city centres across the US, San Diego shrewdly decided to build a first-rate mall in the middle of town. And despite the slide in the pound, they won't scoff at your sterling in the Horton Plaza Mall, where Macy's offers overseas visitors an 11 per cent discount. (Just ask for the card – but remember that price tags don't include California sales tax, adding 8 per cent or so to the final bill.)
International trade is what built San Diego, as you discover at the Maritime Museum, which celebrates the city's seagoing heritage. The star attraction is the Star of India, which was launched on the Isle of Man in 1863 to bring immigrants to America and is now the oldest ship in the world with a regular sailing schedule.
An even more impressive piece of maritime history is tied up along the waterfront. The Panama Canal opened the year the First World War broke out, but it wasn't until the year the Second World War ended that a ship was built that was too big to fit through the canal. And here she is: the aircraft carrier USS Midway.
For a decade, she was the biggest vessel in the world. She saw service in Korea, Vietnam and the first Gulf War. Since 2004, she has been one of San Diego's biggest visitor attractions, giving you the inside story on a giant war machine. The ship was able to be away from base for almost a year at a time. You can see what life was like on board for the 4,500 men, up to 300 of them sharing a single dormitory. To match the vast scale of the ship, a gigantic sculpture of a sailor sweeping his sweetheart off her feet stands on the shore.
God only knows whence the Beach Boys' "Sloop John B" has drifted off these days, but if you want a pleasurable boat ride from downtown then step aboard the San Diego Bay Ferry to Coronado, the spit of land that adds the "merry" to "isthmus". Greater San Diego offers a total of 33 public beaches, some of them featured in Beach Boys lyrics, but the most sought-after sands shimmer beneath the grande-dame bulk of the Hotel del Coronado.
When this hotel first opened in 1888, the emphasis was more on what you would not find than on what you would: "No extreme heat. No mosquitoes. No malaria" – that was the promise at the "Del", as it is known. New arrivals were tutored in the art of a seaside vacation, exhorted into activity by rhymes such as "Oh, sleeper, do not lengthen night/ By wasting early morning light/ On idle dreams with eyes shut tight/ When fairy pictures wait your sight./ Arise and watch the sunbeams play".
You can find that epistle in the Del's museum – this is one hotel that has an official historian. The director of heritage projects maintains a celebrity register. The most notable was Marilyn Monroe, who filmed Some Like it Hot here half a century ago; Bill Clinton, Madonna and Humphrey Bogart have also been guests. If you unaccountably find yourself staying somewhere cheaper, at least get here before 11am, so you can feast on the $22 buffet (children 7-12 pay $13.50, six-year-olds and younger pay their age in dollars).
No charge is payable for San Diego's final treat, still in Coronado: the home of L Frank Baum, creator of The Wizard of Oz. A short road, made of brick and dull yellow in colour, leads to this neat, concise, detached house. Although it is now a private home, the owners celebrate the Dorothy connection – you will even find a pair of ruby slippers on the doormat. Kansas this isn't.
As you discover when you devote a couple of days to San Diego, being the second city in the most powerful state in the world's supreme nation isn't so bad after all, especially when the city in first place just does not have the looks and location. You know who I'm talking about, LA. Give me San Diego anytime: an oasis of indulgence between the desert and the ocean.
The Independent Traveller's new film, '48 Hours in San Diego', presented by Simon Calder, is available to download free at www.independent.co.uk/sandiego
State lines: California
Population 34 million
Area 20 times the size of Wales
Date in Union 9 December 1850
Flower California poppy
Motto 'I have found it'
Nickname Golden State
Could you fly no-frills to the west coast of the US?
Pressure: Europe's leading no-frills airline has been under plenty of it this week, after a loss of cabin pressure aboard a Ryanair Boeing bound for Spain triggered a steep descent and diversion to Limoges in France – and discussion of the airline's safety regime.
Ryanair is also the talk of the town in San Diego, where it is rumoured that executives from the airline have had preliminary talks about a possible air link from Britain. This would be nothing like the current no-frills European operation; it would use bigger planes and offer a business-class cabin.
San Diego is the ideal gateway. Besides providing a much easier arrivals experience to the vast LAX further north, the city's Lindbergh Field airport gives almost instant access to San Diego.
Most visitors to San Diego fly into Los Angeles International Airport (LAX), but this involves a road journey down Interstate 5 to San Diego. It is probably easier to change planes at a US gateway and continue on a domestic flight to San Diego's airport, not least because it is on the doorstep of the city and makes a superb arrival point.
All points of interest in and around the city are easily accessible on San Diego's network of trams and buses. An all-day pass is $5 (£2.85).
The San Diego Bay Ferry to Coronado departs hourly from Broadway Pier, $3.50 (£2).
Hotel del Coronado, 1500 Orange Avenue (001 619 435 6611; www.hoteldel.com). Doubles start at $302 (£159), room only.
William Heath Davis House, 410 Island Street (001 619 233 4692; www.gaslampquarter.org).
Maritime Museum of San Diego, 1492 North Harbor Drive (001 619 234 9153; www.sdmaritime.com).
USS Midway, 910 North Harbor Drive (001 619 544 9600; www.midway.org); $17 (£8.90).
Eating and drinking there
Cheese Shop Deli, 627 4th Avenue (001 619 232 2303; www.cheeseshopdeli.com).
Altitude Sky Lounge, 660 K Street (001 619 446 6086; www.altitudeskybar.com).
www.sandiego.org; 001 619 236 1212