“Throughout the Great Plains, images of men, horses and a nomadic way of life have been scratched into rock walls, a pictographic record whose precise meaning has long been a mystery to modern eyes. But researchers have recently unearthed documents that are helping them pry far more detail from the images found on rock faces from Writing-on-Stone Provincial Park in southern Alberta to the cactus-studded plains of northern Mexico. They say most of the images are a form of picture writing, a cross-tribal code that was widely recognized.”