You may rent horses from Wolfley horse rentals in Thayne Wyo. He
has an ad on this website! I was up there this last weekend! It's
awfully hot! Take plenty of bug spray for both you and the horses!
I don't think Gordon White has rented horses for quite some time. Try Chad at Yellowstone Horse rentals out of Afton.
E-mail me I can get you some more info if needed.