Legal Question in Real Estate Law in California

Was there an agreement? Was it in writing, Without a written agreement the person living there would not likely be successful claiming an ownership interest.

The resident has a legal claim as a tenant, nothing more.

I think Mr. Selik has it backwards. WITHOUT an agreement, the resident is developing a potential adverse possession ownership claim. His claim will be ripe for presentation to a court as an action to quiet title as soon as he has paid five years of property taxes. If, however, the owner HAS an agreement with the occupant, the possession is NOT adverse and the occupant is a guest, not an adverse possessor. Also, no written agreement is necessary to make the occupant a guest rather than an adverse possessor. All that is required is conduct showing that the record owner consented to the possession of the occupant.