Cal. Gov. Code § 43616

If any proposition is defeated by the electors, the legislative body shall not call another election on a substantially similar proposition to be held within six months after the prior election. If a petition requesting submission of such a proposition, signed by 15 percent of the city electors as shown by the votes cast for all candidates for Governor at the last election, is filed with the legislative body, it may hold an election before the expiration of six months.