Oregon Route 273 in Jackson County contains segments of the Pacific Highway and the original US Route 99 alignment over Siskiyou Pass. The first road over Siskiyou Pass was the Siskiyou Mountain Wagon Road which surprisingly persisted as a toll facility until the emergence of the Pacific Highway in the 1910s. The Pacific Highway was improved by 1920 over Siskiyou Pass which was then inherited by US 99 in 1926. The original alignment of US 99 between the Siskiyou rail siding north to Ashland included a jog through the 1914 Steinman Overcrossing and what is now Emigrant Lake. US 99 north of Siskiyou Pass north to Ashland was shifted onto a new alignment by 1940. The original route of US 99 through the Steinman Overcrossing and Emigrant was partially added to OR 66 in addition to being partially retained as unnumbered State Highway. I-5 was constructed over Siskiyou Summit by 1966 tracked west of the 1920 Siskiyou Pass Route. The unnumbered former segments of US 99 over Siskiyou Pass and the Steinman Overcrossing were assigned Oregon Route 273 in 2003.
https://www.gribblenation.org/2020/12/oregon-route-273-early-us-route-99-over.html
Drove this a few months ago. The thing that surprised me most was the Tehachapi Curve-like overcrossing at Steinman.