Swiss gold in San Francisco

When the gold-diggers arrived in San Francisco in 1849, intoxicated by tall tales of a contemporary Eldorado, they must have been sorely disappointed by what they found. The tiny town of single-storey shacks was dwarfed by the hulks of ships abandoned by the early prospectors in their haste to plunder the richest seams. There is a powerful echo of those rusty hulks in the city's newest monument, the stunning de Young Museum beached on a hill in Golden Gate Park.

On the morning I encountered the building, one of the fogs that are so characteristic of the city enveloped the site. The museum's delicate, perforated copper façade revealed itself only slowly, its twisted tower emerging like the stripped-down, rusted bridge of one of the battleships they used to build in the docks below.

The proposals for the radical new building, which has been designed by the Swiss architectural firm Herzog and de Meuron, met such vehement opposition from locals that the trustees decided to raise the whole of the $190m (£107m) cost from private donations. The second incarnation of the de Young museum (the first was an Egyptian revival pile from 1894), a curiously blank tower embraced by bland wings, was demolished to make way for the new structure. In its later years it had been supported by a kind of architectural Zimmer frame after it sustained structural damage in an earthquake. If the old building retained a sense of the picturesque pavilion in the park, Herzog and de Meuron's grittier design did not, and people were worried about how its bulk would sit in their carefully manicured park.

The de Young Trustees visited Herzog and de Meuron's extraordinary Dominus winery, with its caged stone walls, in the nearby Napa Valley, and the architects' native Basel to see an exquisite copper-clad signal box. Combined with the extraordinary power and popularity of their Tate Modern in London (now the world's most visited contemporary art museum), the trustees were convinced.

The de Young, however, is almost the diametric opposite of Tate Modern. While the latter is contained within an impermeable shell of solid brick, the de Young is sheathed in a fragile skin of copper panels perforated in patterns derived from those made by light filtering through trees in the surrounding park. And whereas the London building is defined by its cavernous turbine hall, still presenting artists with the ultimate challenge of filling it, the de Young is entered through a long, low lobby, a self-effacing space that defers to two huge commissions, an Ed Ruscha triptych and an abstract photographic work by Gerhard Richter of the atomic structure of strontium titanate. The lobby itself is preceded by an angular courtyard populated by a series of cut rocks arranged by Andy Goldsworthy. They are scarred by a continuous rupture, a fissure that strikes towards the entrance and across the ground - an eloquent acknowledgement of the city's precarious position on a geological faultline.

These works of art have been knitted into the fabric of the structure. Just as the architects have sought to bring the landscape into the building through a complex series of courtyards and views, so they have tried to allow the art to influence the form of the building. Jacques Herzog compares the art to software and the architecture to hardware and talks of the extent to which the former can define the latter. It is an apt analogy in a city that has made its latest fortune as the hub of micro-technology.

Herzog is also, however, obviously unhappy with the way the collection has been presented. It is true that the huge collection, which has historically embraced ethnic and tribal art, challenges coherent display, and that too much has been crammed in. Yet that is almost certainly more apparent to Herzog than to thevisitors, who seem mightily impressed. The naturally top-lit galleries are varied and effective, and the architects maintain a sense of movement through the dullest of exhibits - of which, unfortunately, there are plenty. Colonial furniture mingles with Tiffany glass, and fine 20th-century US art competes with walls of mawkish garbage and an awesomely bad crafts display.

The galleries also offer views across the surrounding park, although these are as nothing compared with the outlook from the nine-storey viewing tower, which has already become a destination for a city confident of its beauty. The tower rotates on its axis, so that from some angles it appears to swell towards the top, while from others it presents a pyramid.

The bulky cantilevered canopy that shelters the café at the back offers further opportunities for contemplating the beautiful grounds, now being thoughtfully landscaped by Walter Hood, one of the few black designers ever to win a commission of this scale. Theday I saw it, the intended effect of the sun being filtered through the canopy in a simulacrum of tree cover was stymied by the clouds but it looks as if it would work.

San Francisco has a voracious appetite for culture. It is only a decade since another Swiss architect, Mario Botta, completed the downtown monumental Museum of Modern Art. This monolithic block of brick is everything the de Young is not; dogmatic, inflexible, massive and attention-seeking. For years San Francisco has bemoaned its lack of a world-class museum, a destination gallery. In the de Young, it may not have one of the world's great collections but it does, in the new building, have one of its finest museums.