In this case, the only way to oppose same-sex marriage in California is by constitutional ammendment, since the state supreme court overruled the democratic will of the people (expressed through a ballot initiative).
Yes, I totally understand that. However, and I know I'm in the minority here on this one (even though I am not for gay marriage), I do not like the idea of banning behaviors by a classification of person, in state or federal constitutions. It's definitely a tough issue though, and totally unacceptable for judges to interpret law and overturn the will of the people time and time again.