"Along the face of the stone bluffs were old pictographs of men and animals and suns and moons as well as other representations that seemed to have no referent in the world although they once may have"
Pictographs at Arroyo de los Monos
Permission Granted by Copyright Owner for Use on Book DrumPictographs at Arroyo de los Monos - Credit: RAEchel Running (www.raechelrunning.com)

Billy may well be passing the ancient petroglyphs found within the Arroyo de los Monos, a canyon located near the Casas Grandes region.

These etchings were probably left behind by former residents of Paquimé or the surrounding area (see bookmark p.194 - 'they rode past...').