Cal. Rev. & Tax. Code § 2297

In the event that the boundaries of a local agency are altered by a governmental reorganization, or that a local agency becomes responsible, as a result of a governmental reorganization, for providing a program or service it has not heretofore provided, the maximum property tax rate for such an agency, after the reorganization has occurred, shall continue to be the maximum property tax rate which had been established, pursuant to the provisions of this article or of Article 4, for such agency prior to the reorganization.