Cal. RTC § 327.5

Notwithstanding any other provision of law, the assessor shall not assign any parcel numbers or prepare a separate assessment or separate valuation to divide any existing residential structure into a subdivision, as defined in Section 66424 of the Government Code, until a subdivision final map or parcel map, as described in Sections 66434 and 66445, respectively, of the Government Code has been recorded as required by law. If the requirement for a parcel map is waived pursuant to subdivision (b) of Section 66428 of the Government Code, then the assessor shall not assign any parcel numbers or prepare a separate assessment or separate valuation, unless the applicant provides a copy of the finding made by the legislative body or advisory agency, as required by that subdivision.