Cal. Rev. & Tax. Code § 13302

Notwithstanding the provisions of Section 13301, whenever a federal estate tax is payable to the United States, there is hereby imposed a California estate tax equal to the portion, if any, of the maximum allowable amount of the Credit for State Death Taxes, allowable under the applicable federal estate tax law, which is attributable to property located in the State of California. However, in no event shall the estate tax hereby imposed result in a total death tax liability to the State of California and the United States in excess of the death tax liability to the United States which would result if this section were not in effect.