It is the best of times for urbanism and urbanists in Southern California. The region is being transformed into one of the most prosperous, most livable and most urbane in the United States.

Only a decade ago, the Los Angeles of smog, riots, lost jobs and broken opportunities dominated the national news. But since the early 1990s, Southern California has experienced a physical and social transformation so rapid and extensive that it has been hard to comprehend. Its emergence as a paradigmatic polycentric region - socially diverse, entrepreneurial, culturally confident - has been a surprise.

How did this monumental shift from urban decay to urban renaissance take place in such a short period of time?

Not being able to see the mountains, and not being willing to imagine the oneness of this region, were central to the culture of L.A. Los Angeles, pioneer of auto mobility through freeway construction, leader in growth by formless subdivision, source of universal and perpetual urban expansion, was rightfully branded the Mother Lode of Sprawl.

Since the 1950s, the rest of the United States has seen Southern California as a frightening place of declining livability and environmental quality. This view of outsiders eventually became Los Angeles' corrosive view of itself. Sprawl and smog were too overwhelming a reality to deny or to overcome. A region founded on boosterist self-promotion was reduced to pessimism and low expectations of itself.

Beginning in the early 1990s, the planning and development culture of Southern California began to shift away from sprawl. This was not accomplished by a sudden reversal of citizen attitudes, political climates and professional practices. It was instead induced by a variety of trends, slowly and steadily leading the region toward a more positive view of its culture, its livability prospects and its financial outlook.

Small cities within the region have prospered. Effective planning and development enabled cities such as Pasadena, Santa Monica, Culver City and many others to regenerate. Real estate values in these small cities soared.

After 50 years of doubting, it has finally become clear that freeways don't relieve congestion but induce it. The promise of free and rapid mobility by car through the L.A. basin has been dashed. Commuting across the region is out of control. The half-hour freeway ride between Pasadena and Santa Monica is now a distressing 11/2 hours in the morning and evening.

As a result, alternative means of mobility have emerged and prospered. In the past decade, bus and rail systems have become regional in their reach. Working at home or closer to home is increasingly seen as a preferred way of living in Los Angeles. Transit-oriented development is becoming an alternative to extensive car ownership and time-wasteful commuting by car.

One of the most unexpected developments of the past decade has been the dismantling of malls in many Southern California cities. In Pasadena, Long Beach, Sherman Oaks and elsewhere, malls have been converted to open-air, multi-use, multi-building places.

The end of the mall has hastened the localization of retail. Living anywhere within this vast basin, it is possible to meet a family's total retail needs within a five-mile radius.

There is no fact more characteristic of the age of sprawl than the dominance of the single-family house configured in endless subdivisions. Most of the land left for large-scale land development now exists in the outer reaches of the region. Commuting back and forth from there to the center is impractical.

The price of land in the core areas of this polycentric L.A. has soared. As a result, the condominium in mixed-use or middle-density housing projects has become a viable commodity. So much so, that in most prosperous Southern California towns and cities, the price of condominiums has caught up with the price of single-family houses.

Los Angeles is one of the most densely populated metropolises in the United States. The scarcity of open space and landscape at the neighborhood level has become more acute as development becomes more dense. Greening streets and parks has become a priority. More and more municipalities are choosing to carry out public works projects that reclaim streets into city-wide networks of green places.

This emphasis on designing high-quality thoroughfares in balance between the needs of pedestrians and cars is beginning to affect the form of buildings. Regionwide, housing projects are being designed to form streets, and to invite their residents to walk them.

Large-scale parks projects are also underway, such as the recovery of the L.A. River as a regional park and the conservation of the Santa Monica Mountains.

As a new urban culture begins to dominate the life of the region, civic buildings are being designed that express its aspirations and its presence. The L.A. Philharmonic Hall, the Staples Center and the proposed transformation of the L.A. County Museum of Art suggest a resurgence in the design of monumental building.

In the right locations, of appropriate program and well -ntegrated into the city around them, such buildings, both small and large but particularly small, can act as catalysts of urban redevelopment.

While sprawl has been slowed, it has not ceased. Throughout the L.A. region, conventional subdivision-based development is still being built on agricultural land. Reaction to this has been pointed. In Ventura County, a citizen-led referendum, Save Our Agricultural Lands, has imposed growth limits over a 20-year period.

Farther north, in the coastal counties of Santa Barbara and San Luis Obispo, conventional development is severely constrained. Agriculture, particularly viniculture, has been built up as an antidote to sprawl. Weekly farmers markets have sprung up in virtually every Southern California town. The amazing proliferation of places to eat throughout the region, both high and low, famous and family-run, has elevated Los Angeles to the highest realms of food culture in the country and the world.

The 50-year reign of sprawl generated both an abandonment of city centers and unchecked growth at the edge of the metropolis. The attempt in the 1950s and '60s to radically restructure the region's downtowns unleashed the most extensive pro-preservation movement the republic has ever known.

Organizations such as Pasadena Heritage and the Los Angeles Conservancy, among others, flourished in response to the ravages of clearance. Citizens organized around these preservation organizations to protect the character of their streets, neighborhoods and downtowns, and to fight insensitive projects. Eventually, the care to preserve led to a radical shift in planning theory and in building codes, toward the enhancement of existing landscapes.

The age of sprawl was also the age of the supremacy of modernism. For 60 years, we have been served triumphant and undecipherable modernist buildings. Traditional buildings of declining quality were delivered in a climate of cultural repression and increasing ignorance.

But there's a new elite in Los Angeles today: migrants and immigrants, ambitious, educated, entrepreneurial. These leaders of business and culture are sponsoring buildings as diverse as the cultures of their native lands. In this climate, there is no possibility for "an architecture of our time," a singular style that represents the aspirations of all.

The recent triumph of architectural eclecticism in Southern California has generated an unprecedented freedom of expression. Authentic modernist and traditional new buildings have become more common, almost expected. And the common currency that makes them of the same place is their urbanist and sustainable design content. For the first time in many decades, we now expect buildings here to be both unique and rooted.

Much remains to be done. The public school system in California is in a state of decline. Mechanisms for delivering affordable housing are not producing the results desired. There is still too much emphasis on road-building. There is a fast-food epidemic afflicting those who don't know or can't afford better. The trends described above don't extend into many suburban and exurban reaches of the region. The socially damaging consequences of mass immigration need to be addressed with both dignity and firmness. The environmental review process needs to be urgently reformed. There is more.

Yet the news from 2005 is that Southern California is emerging, one decision, one investment, one project, one policy at a time, as one of the most distinguished places in the world.