The California State Supreme Court has invalidated a 1977 state law, upheld in 2000 by Prop 22, that defined marriage as the union of a man and a woman. This paves the way for gays to marry in CA. See this and this.
How did Karl Rove manage this? Prop 22 won by over 1.2 million votes. This is a sure fire way to get conservatives to the ballot box in November.
Personally, I think the divorce lawyers are behind this. They see a section of the population that hasn't been paying them and want in on the action.