Wednesday, June 29, 2005
Reptile footprints preserved in the Coconino Sandstone of the Grand Canyon. Roughly 260 million years ago, a reptile clambered upthe side of what was then a sand dune. It may have been early in the morning when the sand was wet with dew, or perhaps later in the day following a cloudburst. Later, dry wind-blown sand filled the tracks, preserving them over the millenia as the pure quartz sand was transformed by the enormous pressure of strata forming above into sandstone. Erosion exposed the tracks, and one day will erase them, as well, perhaps exposing other hidden tracks below the present surface.