Cal. Gov. Code § 33013

Whenever any municipal corporation elects to include its city police officers and city firemen in a county retirement plan pursuant to the provisions of this chapter, such city shall assume all cost and expense to the plan, arising out of all retirement, disability and death benefits payable, or to become payable to, or on account of its police officers and firemen to the same extent, in the same manner and at the same time or times as the county assumes and discharges its liabilities for the payment of retirement, disability and death benefits to county peace officers and county foresters, fire wardens and firemen, and administration expense shall be prorated each year between the county and any municipal corporation or corporations joining the county plan in the proportion that each of their active membership bears to the total active membership under the plan.