As originally defined US Route 99 terminated at US Route 80 in El Centro of Imperial County, California. US Route 99 was extended to the Mexican Border in Calexico by way of what was supposed to be temporary alignment through Heber during June of 1932. US Route 99 would remain aligned to the Mexican Border in Calexico until being truncated to Los Angeles during June 1963. Above US Route 99 can be seen terminating at the Mexican Border at the end of Heffernan Avenue in 1933. Below US Route 99 can be seen following 4th Street south of US Route 80/Main Street in El Centro, Corfman Road, Heber Road through Heber, Imperial Avenue into downtown Calexico, 3rd Street and Heffernan Avenue in Calexico to the Mexican Border on the 1935 Division of Highways Map of Imperial County.
Below the southern terminus of US 99 on Heffernan Avenue at the Mexican Border in Calexico can be seen on a 1933 postcard.
1933 Legislative Chapter 767 added LRN 201 to the State Highway System with the following defintion:
"From a point on LRN 26 approximately 2 mi W of Brawley to a point on said LRN 26 approximately 2 1/2 mi SW of Brawley" and "Calipatria to Brawley-Holtville Road.
LRN 201 first appears on the 1934 Division of Highways Map with the more simplistic definition of "Route 187 near Calipatria to Route 26 east of Heber." Despite LRN 201 being adopted over the planned streamlined route of US 99 north of Calexico to US 80/LRN 27 it never became part of the highway.
California State Route 111 ("CA 111") is announced with the initial run of Sign State Routes announced in the August 1934 California Highways & Public Works. The initial southern terminus of CA 111 is shown to be in Brawley at US 99.
US 99/LRN 26 from El Centro to the Mexican Border in Calexico can be seen in detail on the 1935 Division of Highways Map of Imperial County.
The new definition of CA 86 incorporating former US 99 in the Indio-Heber corridor is announced in the March/April 1964 California Highways & Public Works.