Cal. Rev. & Tax. Code § 13503

If the personal representative files an amended federal estate tax return, he or she shall immediately file with the Controller an amended return with a true copy of the amended federal estate tax return. If the personal representative is required to pay an additional tax under this part pursuant to the amended return, he or she shall pay that additional tax, together with any interest as provided in Section 13550 at the same time the amended return is filed.