Idaho is updated and the route has changed. It still starts near Tremonton, UT and ends in Afton, WY. It goes through Emmett, ID (the junction with the Pacific Ocean Spur- the old Oregon) and then turns East to continue on to Afton, WY.
Most of the roads are dirt-based and muddy when wet, so keep that in mind. There is a good mixture of back road pavement, jeep roads, and forest service roads. The countryside is beautiful and includes lots of potato fields and if you arrive during harvest, it’s a sight to see. Enjoy Craters of the Moon National Monument, which is made up of 60 miles of lava rocks. You could think that you were really on the moon. Also check out Challis National Forest, Sawtooth National Forest, and the 20 mi section approaching Rocky Bar and Featherville for an overnight stay.
Visit Lava Hot Springs and Soda Springs if you have time and when you get to Afton, WY, you will only be 100 miles south of Yellowstone.
Enjoy the adventure and ride with care and respect.