Legal Question in Real Estate Law in California

Without a lot more information there is no possible way even to begin to guess what it means.

It may depend upon who told you the lots aren't "legal," or what you had in mind when discussing them with that person. Often, in informal parlance among owners or developers, a "legal" lot is one that meets current zoning requirements for a particular use that the owner or developer may have in mind at the moment, such as construction of a single-family home without getting a variance.

Occasionally, adjoining parcels held in common ownership are merged by the county, resulting in (for example) two lots shown on an asessor map in 2011 becoming a single lot in 2012. It's possible this might be what the person using the expression "not legal" had in mind. For further information on involuntary lot mergers, you can look up Government Code sections 66451.10 to about 66451.21, or for an important decision on the merger process, try the California Supreme Court decision in Morehart v. County of Santa Barbara (1994) 7 Cal.4th 725 -- both can be accessed on line.

Other meanings of the inexact expression "not legal" are also possible, and before buying, selling or deciding to develop such parcels it is important to get a clear and accurate understanding of their legal status and the zoning laws and procedures that will apply.

Your question is too ambiguous. It would help knowing who told you or where you are getting the "not legal" description from. For example, you may be looking at a form that states the apn numbers, but states that those are not the legal description, meaning they are not the legal description of the properties. Or it may mean the lot sizes are too small, and not the minimum size under the Subdivision Map Act.

Other than the obvious, 'something's wrong', none of us can answer why or what without knowing all the facts and reviewing all the documents. Contact the controlling building dept and ask them what it means, and contact whoever told you that and ask what 'they' mean.