The most remarkable aspect of California's demographic patterns is their consistency. Beginning about a quarter-century ago, the state began experiencing a new wave of immigration from other nations and with that wave - roughly 300,000 people a year - has come a new spurt of population growth.

This is what typically happens in California every year:

As 300,000 foreign immigrants - legal and illegal - arrive in California, another 500,000-plus babies are born (60 percent of them to immigrant mothers, incidentally), and 200,000 or so Californians die. The state's net population growth is 600,000.

Adding 600,000 new souls a year translates into 6 million each decade. That's exactly how much the state expanded in the 1980s and how much it would have expanded in the 1990s except that a million-plus Californians packed up and left the state as the economy dipped into a very severe recession, so our growth was more like 5 million. But we're right on track to add another 6 million in this decade.

The state Department of Finance last week produced its most recent population survey and found that California grew by 598,000 during the 2002-03 fiscal year, almost exactly what it had grown during the preceding year. If this trend continues, we should top 40 million by 2010.

This massive movement of human beings and an equally impressive production of babies does not fall evenly on California. While immigrants tend to concentrate in urban areas - also the locale of most births - there's an offsetting shift of population from those urban centers into suburban and even rural areas. Thus, the state's fastest-growing regions are on the urban periphery, especially counties in the interior valleys north and south. Riverside was the state's fastest-growing county at 4.53 percent - nearly three times the statewide rate - in the latest Department of Finance study, followed by Placer County at 4.43 percent.

These two trends mean that the fundamental impacts of growth - such as traffic and school crowding - are being felt most heavily in the suburbs, but the urban centers are undergoing a demographic transformation as immigrants settle in and others pack up for the suburbs. There's an obvious ethnic component to that exchange, with the cities becoming dominated by non-white residents and the suburbs taking on mostly white newcomers from cities. And there's even a political aspect: the urban areas and older suburbs becoming more Democratic and the fast-growing suburbs more Republican.

The politics of growth are daunting. Most of the major political issues facing the state - water distribution, housing, economic development, traffic congestion, health-care access, etc. - directly stem from the fact that we have a high, immigration-driven rate of growth. Our needs for 200,000 new housing units and a quarter-million new jobs a year, the growth of K-12 and college enrollment, the impacts of 1,000 new cars each day and so forth are growth-related.

We and the politicians we elect, however, tend to avoid talking about fundamental growth issues even as we heatedly debate its impacts. Both of the major factors in California's growth, immigration and births, are political third rails, burning anyone who touches them, as a current struggle within the Sierra Club attests.

While the Sierra Club beats the drums constantly about restricting development to serve growth, whether it be new housing, commercial buildings or transportation, it has adopted a policy of never talking about immigration, the major driver of growth.

Why? The Sierra Club, like most environmental organizations, is overwhelmingly white and upper middle class and it wants to maintain political relations with Latino organizations, which oppose curbs on immigration.

An anti-immigration faction within the Sierra Club, however, is mounting a new drive to gain control of the club's board and change its immigration policies. The battle is heated; last week, the dissidents filed a lawsuit accusing the club's leadership of illegally using club funds to campaign against them through mailers.

It's a microcosm of California's reluctance to seriously debate growth in its most fundamental terms even as we cope with its massive impacts.