Although California-- and especially coastal California-- was the biggest place with skyrocketing housing prices, it was not the only place. Other enclaves, here and there, with severe housing restrictions also had rapidly rising housing prices to levels far above the national average.
If the housing boom was so localized, how did this become a national problem? Because the money that financed housing in areas with housing price booms was supplied by financial institutions across the country and even across the ocean.
Mortgages made in California were sold to nationwide financial institutions, including Fannie Mae and Freddie Mac, and to firms in Wall Street which bundled thousands of these mortgages into financial securities that were sold nationally and internationally. The problem was that, not only were these mortgages based on housing prices inflated by the Federal Reserve's low-interest rate policies, many of the home buyers had been granted mortgages under federal government pressures on lenders to lend to people who would not ordinarily qualify, whether because of low income, bad credit history or other factors likely to make them bigger credit risks.
This was not something that federal regulatory agencies permitted. It was something that federal regulatory agencies-- under pressure from politicians-- pressured and threatened lenders into doing in the name of "affordable housing."
The housing market collapse was set off when the Federal Reserve returned interest rates to more normal levels, but it was a financial house of cards that was due to collapse, sending shock waves through the economy. It was just a matter of when, not if.
A fuller account of all this appeared last year in my book "The Housing Boom and Bust." The revised and expanded edition, which has just been published, shows how more of the same kinds of policies today are making it harder for the economy to recover. It's not that politicians never learn. They learn how much they can get away with, when they can blame others.