The history of California State Route 142
What was to become California State Route 142 was added to the State Highway System via 1933 Legislative Chapter 767 as Legislative Route Number 177 (LRN 177). The original definition of LRN 177 was as follows:
"LRN 176 near Brea to LRN 77 near Chino"
LRN 177 appears for the first time on the 1934 Division of Highways Map. LRN 177 can be seen crossing the Chino Hills from LRN 176 in Brea via Carbon Canyon Road to LRN 77 south of Chino. LRN 177 was not assigned on of the initial Sign State Routes announced in the August 1934 California Highways & Public Works.
The 1935 Division of Highways Map of Orange County depicts LRN 177 beginning from LRN 176 at Loftus at LRN 176 via Carolina Street (now Kreamer Boulevard). LRN 177 is shown following Olinda Boulevard (now Birch Street) and Valenica Avenue to Carbon Canyon Road. LRN 177 is displayed following Carbon Canyon Road east through the Chino Hills to the San Bernardino County Line.