Cal. Rev. & Tax. Code § 18505.6

If an individual is unable to make a return required under Section 18501, the return of that individual shall be made by a duly authorized agent, his or her committee, guardian, fiduciary, or other person charged with the care of the person or property of the individual. The preceding sentence shall not apply in the case of a receiver appointed by authority of law in possession of only a part of the property of an individual.