Cal. Sts. & Hy. Code § 10603.1
In the event the city conducting the proceedings designates the county treasurer or tax collector to perform any service relating to collecting and receiving the money, including but not limited to, printing, servicing, or collecting any bonds, neither the treasurer nor the tax collector so designated shall perform any such service until there shall have been paid to him his estimate of the cost of the service or services, provided, however, the city conducting the proceedings, in lieu of the prior payment of the estimated cost, may enter into a written agreement with the county treasurer or tax collector. Such agreement shall provide for the payment of the cost or estimated cost of any service rendered by the designated county officer.
In the event such cost of estimated cost is not included in the assessment, the city conducting the proceedings shall be liable for payment thereof from the general fund.
Ca. Sts. and High. Code § 10603.1