Cal. GOV § 6599.10

All those local agencies that request membership in the authority and meet the standards established by the authority pursuant to Section 6599.09, for entry into and continued participation in the authority may become members of the authority. If the authority determines that a local agency requesting membership meets the underwriting standards of the authority, the authority, upon receipt of the premium prescribed by the authority, shall admit the requesting local agency to membership. No local agency may be denied membership unless the board determines the agency cannot be actuarially safely underwritten. Premiums shall be based upon all appropriate actuarial data, including, but not limited to, claims and loss experience of applicant member agencies. Local agencies may request membership individually or through insurance joint powers authorities.