We just drove last week from California to Arkansas via Idaho, Wyoming,South Dakota, then down to Arkansas.
Every place is different with regards to masks. Depends on the state and the city.
Lots of rest stops were closed (I think mainly Wyoming, but other places too.)
Take food with you, at least sandwiches, drinks, and snacks.
Lots of beautiful areas. Feels good to be out of California. People are more relaxed out of there.
I traveled through the area in the last couple of weeks. In Wyoming some of the rest stops on the interstate were closed but the ones on state highways were open. Montana had theirs open, even on the interstate. The mask situation very subjective. I didn’t wear one anywhere, and wasn’t challenged about it either. Not even in Colorado/ Denver.
It might just be me, however that’s my evidence. Perhaps anecdotal. YMMV.