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.
Routes in favor of the Interstate Highways (designated in 1959), and the renumbering of State Routes that conflicted with Interstate numbers.
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.