California Code, Government Code - GOV § 53582

The proceedings of any local agency authorizing the issuance of bonds shall not require the deposit of any more moneys, obligations, and federal securities as are sufficient, taking into account both the principal amount of the moneys, obligations, and securities and the interest to become due thereon, to implement the refunding of those bonds.  Federal securities and the interest thereon shall be used to satisfy any requirement of cash, money, specie, or lawful money in any proceeding conducted by a local agency before September 19, 1975.