Pursuant to the authority provided by Section 22358 of the Vehicle Code of the State, it is hereby determined upon the basis of an engineering and traffic survey that the speed limit of sixty-five (65) miles per hour is more than is reasonable or safe under the conditions found to exist upon the streets and parts of streets of the County set forth in this article, and it is hereby declared that the prima facie speed limit shall be as set forth in this article on such streets and parts of streets. Such declared prima facie limit shall be effective when appropriate signs giving notice thereof are erected upon such streets. (§ 1, Ord. 410, § 1, Ord. 458, § 1, Ord. 498, § 1, Ord. 504, § I, Ord. 533, § I, Ord. 537, § I, Ord. 544, § I, Ord. 560, § I, Ord. 562, § 1, Ord. 564, § 1, Ord. 565, § I, Ord. 568, § 1, Ord. 570, § 1, Ord. 571, § 1, Ord. 577, § 1, Ord. 579, § 1, Ord. 589, § 1, Ord. 593, § 1, Ord. 601, § 1, Ord. 602, § 1, Ord. 609, and § 1, Ord. 614)