Sorry Zyph....but that is exactly what Prop 8 was about. The California Supreme Court specifically ruled that bans on gay marriage violated the California Constitution, thus recognizing it as a Constitutional right.
Prop 8 was a constitutional amendment in response to that. Unfortunately, in California, Constitutional Amendments do not require a 2/3's majority and require only a simple 50%+1 vote. Thus, in California, Constitutional rights can be eliminated by a simple majority.