When crossing southern Idaho, there are several options. 20, 26, 84, 15, 93.

If you can figure Hiway 20 into your route, it will take you right through Craters of the Moon National Monument. As far as I know, there is nothing like it anywhere else in the Continental US. Take a couple minutes to Google it and consider if it would make a worthwhile addition to your trip.

I have spent an afternoon there on three different occasions, usually accompanying 4'th to 6'th grade school kids on field trips. I found something new to see each time. Cinder cones which look like they might have just quit spewing in the last week. Lava tube tunnels twenty feet in diameter where the outside of a lave flow cooled and hardened while the interior remained molten and flowed away.

About 1000 sq miles of naked lava flows just about like it was 2000 to 15000 years ago when it had barely cooled.

People who choose to brew up their own storms bitch loudest about the rain.