Cal. Penal Code § 3082

Each county board may make and establish written rules and regulations for the unconditional release of and may unconditionally release any prisoner who is an alien and who voluntarily consents to return or to be returned to his native land and who actually returns or is returned thereto. The necessary expenses of the transportation of such alien prisoner and officers or attendants in charge of such prisoner, may be paid by the county, upon order of the board of supervisors authorizing or ratifying the return of the prisoner at the expense of the county.