When the US Route System was created during November 1926 the terminus of US Route 99 was located in El Centro via Imperial Avenue to US Route 80 at Adams Avenue. During June 1932, US Route 99 would be extended from El Centro to the Mexican Border in Calexico. US Route 99 would remain signed through El Centro until the highway was truncated to the southern end of the Golden State Freeway during June 1963. The blog examines the history of US Route 99 within the community of El Centro from inception to eventual replacement by California State Route 86. Pictured above as the blog cover is the multiplex of US Route 99 and US Route 80 on Main Street in downtown El Centro during the 1940s.
https://www.gribblenation.org/2022/12/former-us-route-99-in-el-centro.html?m=1