Rock Art

Because of the recent opportunities to explore "rock art" I feel it necessary for myself and others to understand what is rock art? According to an article I read, there are in general, three basic categories:

• Petroglyphs are carved, pecked, chipped or abraded into stone. The outer patina covered surface of the parent stone is removed to expose the usually lighter colored stone underneath. Some stone is better suited to petroglyph making than others. Stone that is very hard or contains a lot of quartz does not work well for petroglyph making; however, a nice desert varnished basalt usually works very well. The rock art we saw yesterday falls into this category.
• Pictographs are painted onto stone and are much more fragile than petroglyphs. The paint is a mineral or vegetal substance combined with some sort of binder like fat residue or blood. If the paint was not properly mixed with a binder it would not adhere well to the stone and the pictograph would quickly flake away. Pictographs were painted in locations where they would be protected from the elements: in caves, alcoves, under ledges and overhangs. This is what we saw in Dinosaur National Monument.
• Intaglios are large ground drawings created by removing the pebbles that make up desert pavement. Intaglios are usually in the outline of animals (zoomorphs) or human-like figures (anthropomorphs). Intaglios are found on mesas along the Colorado River more so than in other places. We haven't seen this type yet.