How much was the rental on the horses, and how long are the tours? I can imagine, however long it was, it wasn't long enough.
Mark
They vary depending on who you use, there are quite a few in the area. A lot are an hour, waste of time IMO as that's far too short, then they do sunset treks which are 2 hours, awesome, a must do, how the light changes at Monument Valley every minute at that time is amazing. You can also bespoke if you're willing to pay outside the pre-organised tours.
We did a day trek, 4 hours, and a sunset trek, 2 hrs. If you haven't ridden before 4 hours may be a bit harsh!
They are pretty relaxed, not polished 'guided tours' like some with the rangers at national parks can be, but I actually prefer the less 'school teacher' approach, gives you time to really soak up the atmosphere. I took most of the more dramatic shots when on horseback.
I'll put a few pics of the trekking on too, you may as well see all our pics 