California over the long haul does very well.
There's no way anybody can guarantee that home prices won't go down in any location. That's just not how the market works. We can only know that the trends we see are in place to continue driving prices up for several more years. If we get a depression, which nobody can predict, then prices may fall. But, even then, that doesn't mean there's a bubble here, since you could make the same argument about everything in a depression.