West of the SR 104/SR 99 interchange, Twin Cities Road continues to Interstate 5 and then eventually end at State Route 160 north of Walnut Grove.

The route turns northeast, passing through Herald, near Rancho Seco Nuclear Generating Station and on to the community of Clay before entering Amador County.

It then continues past Mule Creek State Prison and begins a short overlap with SR 124 in Ione.

Ridge Road makes this exact connection, but it is not currently owned or maintained by Caltrans.

[5] 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.