The combined routes continue northerly through another part of the forest and over Adin Pass into the Warm Springs Valley, where SR 139 splits to the northwest near Canby.

The route continues through Newell before cutting across the intermittent Tule Lake as the Lava Beds Highway through the city of Tulelake.

At an intersection right on the state line, SR 161 begins to the west, and Oregon Route 39 continues northwest towards Klamath Falls.

There travelers could head east on Route 28 to Alturas and south on the present US 395 (not a state highway north of Susanville until 1933) towards Reno.

[15] The road was in fact mostly paved by mid-1939,[16] and under construction or completed by mid-1940, when Oregon Route 58 opened, continuing the corridor northwest from Klamath Falls.

[27] It has remained a two-lane road,[3] despite being added to the California Freeway and Expressway System in 1959 (Canby to Oregon) and 1965 (Susanville to Adin).

[28][29] Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage.