Arizona Hwy 89 ALT info please

The "drop-offs" between Fredonia and Vermillion are after you pass the exit to the North Rim. There's a long downgrade then. However, it is a good road, with shoulders, and the curves are not sharp. There are several viewpoint pullouts, also.
It's no problem in an RV towing, as long as you control your speed.

Plenty of RV's along that road.

We will be coming south from Utah and getting on Hwy 89A out of Fredonia, Arizona doing the Vermillion Cliffs National Monument. 89A is the only route. My question is what are the drop offs like that are mentioned in the Mountain Directory? We are a 40' diesel towing a Jeep Liberty.

Just don't go on 89A over the mountain, via Jerome, in anything bigger than a pickup truck.

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Traveled this scenic byway many times, only once while towing our rig. Being that there is such an elevation change from Flagstaff to Sedona, there are lots of challenging sections in either direction. Sure, it can be done but I prefer using I-17 south to Sedona area than traversing 89A in our 40' Class A. We will use our toad for going up and down from Flagstaff to Sedona via 89A, a truly breathtakingly beautiful panoramic drive that is certainly less stressful when travelling by car.