There are many choices for Monument Valley back country tours. I can't imagine getting a better experience than the one we received from Monument Valley Safari. The tour is 3.5 hours, where others offer 1.5 and 2.5 experiences. Our guide Don Mose was very enlightening with lessons on Indian culture, history, hieroglyphs, geography, geology, and his own experiences. And he made the experience SO MUCH FUN. It was an absolute delight. Best decisions we made on our entire trip.
I will say that they are difficult to reach by phone because of cell service. But if you leave a message or emails them, you will hear back. I'm overwhelmed by my experience with them. Great company.