The California Redistricting Commission has completed it's work, drawing new Congressional, State Senate, State Assembly and Board of Equalization (whatever the hell that is or does) districts.
You'd think that might be the end of it, barring Federal or State court challenges. But no. The dumb as a rock authors of the initiative that made the Commission -- instead of the Legislature -- responsible for drawing new districts also saw fit to allow the Commission's work to be challenged by referendum in the same way that many laws passed by the Legislature can be challenged (Section 3, clause (i)).
In California anyone can attempt to get sufficient signatures (about half a million) to challenge some kinds of laws. If they succeed, the new law is put on hold or, if already in effect, temporarily undone, until an election is held. The voters may approve or reject the law by majority vote. It's a so-called people's veto -- such as is to be held in Ohio this year on SB 5, an anti-union law, and was held in Maine in 2009 to overturn its legislature's legalization of same-sex marriage.
Each of the four maps the Commission has drawn is subject to this process. Each one individually can be challenged by gathering enough signatures, and by doing so at least temporarily nullifying the map. What happens if the map is nullified? The California Supreme Court must appoint 'special masters' (sounds kinky) to draw the lines. If the voters eventually approve of the commissions' map, the Supreme Court lines goes away, replaced by the Commission's districts. If the voters reject the Commission's work, the Supreme Court-drawn lines stay in effect until the next redistricting.