Part 1; the history of the San Gabriel River Freeway and Interstate 605
The origin of what is now Interstate 605 begins during 1933 with the addition of Legislative Route Number 170 (LRN 170) to the State Highway System. The original definition of LRN 170 was as follows:
"LRN 179 near Seal Springs via Santa Fe Springs to LRN 26 near West Covina."
The August 1934 California Highways & Public Works announced the initial run of Sign State Routes. California State Route 35 was assigned completely concurrent with LRN 170 between US Route 99-60-70/LRN 26 in West Covina and California State Route 22/LRN 179 near Seal Beach.