California Code, Government Code - GOV § 31205

Whenever any public agency having a retirement system takes over and assumes any of the functions of any other public agency, and because of such assumption all or any employees of the second public agency become employees of the first public agency, such agencies, by contract, may agree that the second agency will pay either to the first agency or to the retirement fund of the first agency an amount of money to be agreed upon because of the retirement rights to be granted to such employees.