California Code, Code of Civil Procedure - CCP § 1089

On the date for return of the alternative writ, or on which the application for the writ is noticed, or, if the Judicial Council shall adopt rules relating to the return and answer, then at the time provided by those rules, the party upon whom the writ or notice has been served may make a return by demurrer, verified answer or both. If the return is by demurrer alone, the court may allow an answer to be filed within such time as it may designate. Nothing in this section affects rules of the Judicial Council governing original writ proceedings in reviewing courts.