She climbed up behind him on the horse and they rode off.
The ride was uneventful. . .except, every few minutes the Indian would let out a whoop so loud that it would echo from the surrounding hills.

When they arrived in town, he let her off at the local service station, yelled one final, "Yahoo!" and rode off.
"What did you do to get that Indian so excited?" asked the service station attendant.
"Nothing. I merely sat behind him on the horse, put my arms around his waist, and held onto his saddle horn so I wouldn’t fall off."
"Lady," the attendant said, "Indians ride bareback"