California Code, Revenue and Taxation Code - RTC § 327

Where any county or county officer possesses a complete, accurate map of any land in the county, or whenever such a complete, accurate map has been made in compliance with Sections 27556 to 27560, inclusive, of the Government Code , the assessor may number or letter the parcels in a manner approved by the board of supervisors.  The assessor may renumber or reletter the parcels or prepare new map pages for any portion of such map to show combinations or divisions of parcels in a manner approved by the board of supervisors, so long as an inspection of such map will readily disclose precisely what land is covered by any particular parcel number or letter in the current or any prior fiscal year.  This map or copy shall at all times be publicly displayed in the office of the assessor.

Land may be described by a reference to this map except that land shall not be described in any deed or conveyance by a reference to any such map unless such map has been filed for record in the office of the county recorder of the county in which such land is located.

All such maps in the possession of county assessors on August 27, 1937, and used for assessment purposes only, are deemed to have been numbered or lettered and approved properly.