Cal. PEN § 413

Every person wilfully present as spectator at any fight or contention prohibited in the preceding section, is guilty of a misdemeanor.

An information may be laid before any of the magistrates mentioned in section eight hundred and eight of this code, that a person has taken steps toward promoting or participating in a contemplated pugilistic contest, or fight, or ring or prize fight, or sparring or boxing exhibition, prohibited under the provision of section four hundred and twelve of this code, or is about to commit an offense under said section four hundred and twelve. When said information is laid before said magistrate, he must examine, on oath, the informer, and any witness or witnesses he may produce, and must take their depositions in writing and cause them to be subscribed by the parties making them. If it appears from the deposition that there is just reason to fear the commission of the offense contemplated by the person so informed against, the magistrate must issue a warrant directed generally to the sheriff of the county, or any constable, marshal, or policeman in the state, reciting the substance of the information and commanding the officer forthwith to arrest the person informed against and bring him before the magistrate. When the person informed against is brought before the magistrate, if the charge be controverted, the magistrate must take testimony in relation thereto. The evidence must be reduced to writing and subscribed by the witnesses. If it appears there is no just reason to fear the commission of the offense alleged to have been contemplated, the person complained against must be discharged. If, however, there is just reason to fear the commission of the offense, the person complained of must be required to enter into an undertaking in such sum, not less than three thousand dollars, as the magistrate may direct, with one or more sufficient sureties, conditioned that such person will not, for a period of one year thereafter, commit any such contemplated offense.