US 99 ran 917 miles through the heart of California. It entered the state from Oregon near Siskiyou Summit and left the state (and country) at Calexico. Prior to 1964, all California State Highways were also known internally by what were called “legislative route numbers” or “LRN” for short. Those numbers are also shown in the description below.
Pacific Highway Section (LRN 3)
Following I-5, State 263, I-5, State 265, and US 97
Hornbrook, Yreka, Weed (Junction US 97), Mt. Shasta City, Dunsmuir, Redding (Crossing US 299), Red Bluff
At Red Bluff, US 99 split into US 99E and US 99W.
US 99E (LRN 3)
Following current SR-36, SR-99, SR-20, SR-70, SR-65, I-80:
- Los Molinos, Chico, Yuba City, Marysville, Lincoln, Roseville, Sacramento
US 99W (LRN 7 and LRN 6)
Following current I-5, SR-113, I-80:
- Corning, Maxwell, Arbuckle, Woodland, Davis, Sacramento
The routes rejoined in downtown Sacramento. US 50 also joined. From there, US 99 followed this routing:
Golden State Highway Section (LRN 4)
Following State 99
Sacramento, Stockton (US 50 leaves), Modesto, Merced, Madera, Fresno, Tulare, Delano, Famoso (US 466 joins), Bakersfield (US 466 leaves, US 399 joins), Greenfield (US 399 leaves), Lebec, Gorman, Castaic, Santa Clarita, Los Angeles
Ocean to Ocean Highway Section (LRN 26)
Following I-10, State 86
In Los Angeles, Former US 99 leaves I-5, joins I-10 (Former US 60 and US 70), and goes through:
El Monte, West Covina, Pomona (US 60 leaves), Ontario, Colton, Redlands, Beaumont (US 60 rejoins), Banning, Indio
In Indio, former US 99 leaves I-10 (former US 60/US 70) to follow SR-86:
Valerie Jean, Oasis, Salton City, Kane Springs, Westmorland, Brawley, Imperial, El Centro (Joining US 80 for a few blocks – Ocean to Ocean Highway continues east on US 80), Heber, Calexico.
At Calexico, US 99 left SR-86 to follow SR-111:
Heading south on current SR-111, US 99 ended at the border in Calexico at 1st St and Heffernan Ave.
Thus is the routing of US 99 through the State of California.
US 99 spur routes in California:
US 199 (LRN 1) (still existing) runs from US 101 near Crescent City to I-5 (former US 99) in Grants Pass, Oregon.
US 299 (LRN 20 and LRN 28) (Current State 299) ran from US 101 near Eureka to US 395 in Alturas.
US 399 (LRN 138, LRN 57, LRN 140, and LRN 4) (Current State Highways 33 and 119) ran from US 101 in Ventura to Jct US 99/466 in Bakersfield, cosigning with US 99 from Greenfield to Bakersfield.
Routing Courtesy SoCalRegion.com