California Code, Corporations Code - CORP § 18035

(a) “Unincorporated association” means an unincorporated group of two or more persons joined by mutual consent for a common lawful purpose, whether organized for profit or not.

(b) Joint tenancy, tenancy in common, community property, or other form or property tenure does not by itself establish an unincorporated association, even if coowners share ownership of the property for a common purpose.

(c) Marriage or creation of a registered domestic partnership does not by itself establish an unincorporated association.