Peter Dobratz
ODOT's website shows the route of Route 120
http://gis.odot.state.or.us/transgis/
Layer Catalog => Road Network => Signed Routes

However, in the real world, the route is not signed.  I was able to take a bunch of photos by bicycle in the area and as best I can tell there are not nor have there ever been any OR 120 signs.
I posted the photos to Mapillary, but I haven't updated the map data.