CA Gov't Code Section 66451.301

If any parcels or units of land merged under a valid local merger ordinance which was in effect prior to January 1, 1984, but for which a notice of merger had not been recorded before January 1, 1988, and one or more of the merged parcels or units of land is within one of the categories specified in paragraphs (1) to (5), inclusive, of subdivision (b) of Section 66451.30, the parcels or units of land shall be deemed not to have merged unless all of the following conditions exist:

(a)

The parcels or units are contiguous and held by the same owner.

(b)

One or more of the contiguous parcels or units do not conform to minimum parcel size under the applicable general plan, specific plan, or zoning ordinance.

(c)

At least one of the affected parcels is undeveloped by any structure for which a building permit was issued or for which a building permit was not required at the time of construction, or is developed only with an accessory structure or accessory structures, or is developed with a single structure, other than an accessory structure, that is also partially sited on a contiguous parcel or unit.

(d)

The parcels or units which do not conform to minimum parcel size were not created by a recorded parcel or final map. If all the conditions described in subdivisions (a), (b), (c), and (d) above exist, only a parcel or unit of land which does not conform to minimum parcel size shall remain merged with a contiguous parcel.