The May 1913 California Highway Bulletin notes LRN 9 had been partially surveyed in Los Angeles County and fully surveyed in San Bernardino County. LRN 9A is noted as the Riverside County extension of LRN 9 and fully surveyed.
The May 1913 California Highway Bulletin notes the combined route of LRN 9 and LRN 9A had a planned 105 miles of highway.
In April of 1912 the National Old Trails Road (NOTR) was organized with the goal of signing a trans-continental highway between Baltimore and Los Angeles. Building a modern road for automotive use through the Mojave Desert of California would prove to be particularly difficult as State Highway Maintenance didn't exist, and the general path of travel was alongside the service routes of railroads. The first Auto Trail through Cajon Pass was the Santa Fe-Grand Canyon Needles National Highway which was first signed in Cajon Pass by 1913. NOTR organizers later adopted the routing of the Santa Fe-Grand Canyon Needles National Highway in the western United States by 1914. The NOTR was able secure funding to pave the route through Cajon Pass and construct the 1914 Crowder Canyon Bridge.
FHWA.dot.gov National Old Trails Road
From San Bernardino beginning at Mount Vernon Avenue/4th Street the NOTR followed existing LRN 9 westbound to Pasadena. Upon reaching Pasadena the NOTR branched away from LRN 9. The NOTR westbound jogged south on Santa Anita Avenue to Colorado Boulevard in Pasadena and departed towards Los Angeles via Fair Oaks Avenue. The NOTR followed Fair Oaks Avenue, Huntington Drive and Broadway into downtown Los Angeles where it terminated at the intersection of Broadway and 7th Street. The early NOTR can be seen on the 1916 National Old Trails Road map below.
The July 1914 California Highway Bulletin notes the progress of LRN 9. LRN 9 Los Angeles County Segment A is noted to have been surveyed from LRN 4/San Fernadno Road to La Canada Flintridge. LRN 9 Los Angeles County Segment B is noted to have been surveyed from La Canada Flintridge to Pasadena. LRN 9 San Bernardino County Segment A from Upland to Cirtus Avenue is stated to be approximately 36% complete. LRN 9 San Bernardino County Segment B is noted to be surveyed from Citrus Avenue to Rialto. LRN 9 San Bernardino County Segment C from Rialto to San Bernardino is stated to be 82% complete. LRN 9 San Bernardino County Segment D from the Los Angeles County Line to Upland is stated to be 15% complete. The July 1914 California Highway Bulletin is unclear what happened to LRN 9A to Riverside.
The January 1915 California Highway Bulletin noted 17.9 miles of LRN 9 was completed whereas 31.8 miles was surveyed.
What became LRN 26 and LRN 27 were added to the State Highway System as part of the 1916 Second State Highway Bond Act. The initial definition of LRN 26/LRN 27 was as follows:
"an extension of the San Bernardino county State Highway lateral (LRN 9) to the Arizona State line near the town of Yuma, Arizona, via the cities of Brawley and El Centro in Imperial County by the most direct and practical route..."
The addition to LRN 26 and LRN 27 can be seen in the July 1916 California Highway Bulletin. LRN 26 by proxy connected San Bernardino to Redlands via 3rd Street, E Street, Colton Avenue and Redlands Avenue.
The NOTR and National Park-to-Park Highway can be seen following LRN 9 from San Bernardino to Pasadena on the 1924 Rand McNally Map of California. Both highways are shown splitting from LRN 9 in Pasadena towards downtown Los Angeles.
The new Pacoima Wash Bridge on LRN 9 near San Fernando is featured in the June 1924 California Highways & Public Works.
The October 1924 California Highways & Public Works features paving operations on LRN 9/Foothill Boulevard in Azusa.
The October 1925 California Highways & Public Works references LRN 9 between San Fernando and La Canada Flintridge as the "Foothill Boulevard."
The October 1925 California Highways & Public Works notes 5.49 miles of LRN 9 between San Bernardino to Redlands was contracted to widened from 12 feet to 20 feet.
The January 1926 California Highways & Public Works notes a realignment project was underway on LRN 9 between San Fernando and La Canada Flintridge.
The initial draft of the US Route System was approved by the Secretary of Agriculture during November of 1925. The US Route System within California was approved by California Highway Commission ("CHC") with no changes recommended which can be seen in January 1926 California Highways & Public Works. US Route 99 (US 99) is given a vague description which had it multiplex with US 60 (not quite yet US 66) from Los Angeles to San Bernardino via LRN 9. US 99 is shown following LRN 26 from San Bernardino to Redlands onwards to the Sonoran Desert.
Thusly planned US 99 and US 60 appear on the 1925 Rand McNally Map of California. Both US 99 and US 60 are shown diverging from LRN 9 towards downtown Los Angeles. The divergence of US 99 and US 60 from State Maintained LRN 9 is likely due to Los Angeles being used as a control point in both of their route descriptions.
The California State Highway Engineer noted in a letter to the AASHO Executive Secretary dated April 13th, 1931, that the Eherenburg Bridge was to be purchased by the States of California and Arizona.
California Highways Highway Chronology Chapter 3; A Significant System is Created 1933-1946
Prior to the fourth Figuroa Street Tunnel being completed during 1936 US 99 used an interim alignment to reach downtown Los Angeles multiplexed with US 66. US 99/US 66 followed Solano Avenue and Broadway into downtown where they met US 101/LRN 2 at Sunset Boulevard.