The “varnish” here, looking a little like apparitional tree trunks, is made up of clay, iron and manganese oxides, and some organic material. And time. The darker it is, the more manganese, a mineral rare on the planet.
In some accessible areas, this thin layer can be chipped off to reveal the lighter rock beneath. We call the resulting designs petroglyphs (from the Greek words for “stone” and “to carve”) when made by human hands. Here are some of the ones at Newspaper Rock, which is actually made up of several boulders, in Petrified Forest National Park in Arizona — and is not to be confused with Newspaper Rock State Historical Monument in Utah:These, whose meaning remains unknown, are thought to have been made by people farming in the Puerco River Valley some 600-2,000 years ago. The area, as stark and arid as it is (of course, sometimes such conditions are excellent for preservation), has evidence of people dating back 8,000 years.
There are a lot of designs here, and it is fun to try to guess what they are, and mean, but I think I like the circles most of all. What is fully, dare we say perfectly, circular in this world? Perhaps nothing at all, but Sun, Moon (periodically), the eye (both iris and pupil, but not in the case of all mammals) certainly look like they are. What else?