California State Route 72 is a State Highway located in the Los Angeles Metro Area and a component of early US Route 101. The Legislative definition of California State Route 72 presently begins at Interstate 605 in Whittier and follows Whittier Boulevard to California State Route 39 near La Habra. Prior to 1953 US Roue 101 followed Whittier Boulevard, Spadra Road (now Harbor Boulevard) and Los Angeles Street (now Anaheim Boulevard) from Los Angeles to Anaheim. The original surface corridor of US Route 101 was repurposed as California State Route 72 during the 1964 State Highway Renumbering.
https://www.gribblenation.org/2023/06/california-state-route-72-former-us.html?m=1