General provisions governing unincorporated associations are found in the California Corporations Code, commencing with section 18000.

An unincorporated association is an unincorporated group of two or more persons joined by mutual consent for a common lawful purpose, whether organized for profit or not. These associations may file with the Secretary of State a statement designating the location and complete address of the association's principal office in this state. If the association does not have an office in this state it may designate the complete address of the association to which the Secretary of State shall send any notices required to be sent, and designate as agent of the association for service of process any natural person residing in this state or any corporation which has complied with section 1505 of the California Corporations Code and whose capacity to act as such agent has not terminated. The Statement by Unincorporated Association form is available in PDF file format and can be viewed and printed from your computer using the most current version of the Adobe Reader (available for free from Adobe's website).