In 1963 and 1964, the California Division of Highways, at the behest of the California State Legislature, implemented a major renumbering of its state highways. The majority of sign routes—those marked for the public—kept their numbers; the main changes were to the legislative routes, which had their numbers changed to match the sign routes. Many formerly unsigned routes received sign numbers corresponding to their new legislative numbers. A smaller change was the removal and truncating of many U.S. Routes in favor of the Interstate Highways (designated in 1959), and the renumbering of State Routes that conflicted with Interstate numbers. Some U.S. Routes that were officially removed continued to be signed until the replacement Interstates were completed. The state law authorizing the renumbering was passed by the Legislature on September 20, 1963. Signage changes took place by July 1, 1964.

Changes in sign routes

U.S. Routes

State Routes

All available numbers up to and including State Route 255 were assigned in 1964; State Route 256 and above were assigned starting in 1965.