Cal. Rev. & Tax. Code § 5103

Notwithstanding any other provision of law, a taxpayer and the county or city and county may enter into a written settlement agreement to substitute credits against a taxpayer’s future tax liabilities for the payment by the county or city and county to that taxpayer of refunds of tax and any interest accrued thereon. Interest may continue to accrue upon a substituted credit until that credit has been fully offset against future tax liabilities. The authority of a county or city and county to provide for tax credits in accordance with this section shall be vested in that branch of the county or city and county government that is authorized to settle legal disputes on behalf of the county or city and county.