Cal. PEN § 1484

The party brought before the Court or Judge, on the return of the writ, may deny or controvert any of the material facts or matters set forth in the return, or except to the sufficiency thereof, or allege any fact to show either that his imprisonment or detention is unlawful, or that he is entitled to his discharge. The Court or Judge must thereupon proceed in a summary way to hear such proof as may be produced against such imprisonment or detention, or in favor of the same, and to dispose of such party as the justice of the case may require, and have full power and authority to require and compel the attendance of witnesses, by process of subpoena and attachment, and to do and perform all other acts and things necessary to a full and fair hearing and determination of the case.