CA Rev & Tax Code Section 454

The assessor may subpena and examine any person in relation to:

(a)

any statement furnished him, or

(b)

any statement disclosing property assessable in his county that may be stored with, possessed, or controlled by the person. He may do this in any county where the person may be found, but shall not require the person to appear before him in any other county than that in which the subpena is served.