Sand Dune Pony is the story of a boy named Pete and a wild mustang pony set in what is now Great Sand Dunes National Park in Colorado. At the center of the story is a sinister individual who is seemingly dedicated to causing random harm. Pete and an old cowboy by the name of Hatsy get to the bottom of the mystery as they come across the remains of long-dead humans and the bodies of slain animals. The recurrent themes of the books in the Wilderness Mystery Series are natural phenomena-caves, canyons, mountains, sand dunes, and forests-and a sense of the past as seen through archaeology. In many of the narratives, events of long ago are seen to have left traces of their passing. Notwithstanding the fact that the books were written in the 1950s, the progressive Franklin Folsom (alias Troy Nesbit) had refreshing views of women, Native Americans, and the environment, and he was prescient in having his characters often oppose corporate and government efforts to develop wilderness areas.

Chapter 1: No Horse to Ride Chapter 2: Mysterious Visitor Chapter 3: Hatsy's Scheme Chapter 4: Horse Trap Chapter 5: A Break in the Fence Chapter 6: The Chase Chapter 7: The Young Stallion Chapter 8: Sandy Gets His Name Chapter 9: "Take it Easy!" Chapter 10: Sacking Out Chapter 11: Assorted Bad Hombres Chapter 12: Ski-jaw and Salami Chapter 13: Duck-Pond Raider Chapter 14: Sandy Disappears Chapter 15: Murdered Mustangs Chapter 16: Pete's Discovery Chapter 17: Danger in the Dunes Chapter 18: Sandy Spooks Again Chapter 19: Rendezvous at Night Chapter 20: Wrapped in Cellophane Chapter 21: Twenty-Dollar Questions Chapter 22: Sandy's Choice