It won't happen.
Based on the most recent precedent from 1863, it appears most likely that the U.S. Constitution requires a state's legislature—along with the Congress—to consent before that state is split into two or more new states. And I don't see either the California legislature nor Congress giving up the power California has as a whole state.
Texas is actually the only state with power to split itself into multiple states without Congressional approval. As many as five states, a privilege given to it as a unique condition of its annexation to the Union in 1845.