The Mystery of Chaco Canyon by Doug Hocking

DaVinci Code meets the Wild West. Set against the historic background of the Civil War in the Southwest, four friends seek a fantastic treasure hidden in the unknown wilds where clues have been left by peoples long gone. They are pursued by Danites, Penitentes and Knights of the Golden Circle and assisted by mysterious native shamans and wanderers of strange origin. The clues are real, the solutions novel.