The Wall Street Journal, of all things, has this story at http://online.wsj.com/article/SB10001424052748704644404575482342261278092.html … in the early Holocene (or even during the Younger Dryas) humans migrated around the Tetons and Absoroka Mtns to tarry in the foothills and the plain that lies beneath the Bighorn and Owl Creek ranges. Near the centre of this basin stands Legend Rock, a cliff face 800 yards long and containing 300 images scattered along its length. The petroglyphs were made over the course of many years. The smaller images tend to show natural fauna – such as antelopes, human hands etc. The larger images stand around five feet tall and dominate the rock face. They depict fantastic anthropomorphic figures – but are only dated to a couple of thousand years ago. Historically, the region was inhabited by the Shoshone tribe – possible for thousands of years. So, they may have been responsible for some of the images. The Shoshone associate them with with the Spirits (shaman figures) which they represent and embody. One feature common to the site is a bird topped by a U shape – possibly representing horns (but see plasma images). In one image (below) a series of concentric circles is bisected vertically by an incised line and horizontally by a crack in the rock face.