A petroglyph is rock carvings, ¹ made by the removal of part of the rock surface to create the art work. This was normally done by carving, chiseling, incising, or picking at the surface in order to leave the desired art form.

Normally, the petroglyph artist uses a hard hammerstone, which is battered against the stone surface. In other instances, the rock art is pecked out through indirect percussion, as a second rock is used like a chisel between the hammerstone and the panel where the art is to be created.

A third and much rarer form of creating rock art was through incision, or scratching, into the surface of the stone with a lithic flake or other type of blade. The art produced using this technique are fine lined and often difficult to see.

There are at least two types of petroglyph created by the ancient people here on the North American continent.

Whatever the method used or the media of the art work, the finished result was what is now called a petroglyph.

The first type was accomplished in some locations where the rock carving was done when the ancient people would inscribing with a tool into sandstone and removing some of the sandstone material in order to leave an impression (or recess) for the artwork desired.

This type was accomplished when the darker weathered surface attached to a rock, called desert varnish was removed. Ancient people pecked, scratched, abraded, and carved their art into stone by removing portions of that dark weathered surface to expose the lighter rock beneath and in doing so, the resultant dark and light pattern remaining became their rock art.

The petroglyph at many locations are inscribed into the dark surface coating of the rock, which is called desert varnish or patina. The varnish is mainly made up about seventy percent of clay materials and gets its blackish color from manganese oxide deposits that gradually form on exposed sandstone cliff faces and also owing to the action of rainfall and bacteria. Higher iron content cause the varnish to be somewhat lighter, from brown to even a brown-orange.

Desert varnish is an brown to black coating found on rock surfaces in arid environments. The varnish is approximately one micrometer thick and exhibits nanometer size layering.

The ancient artists produced the many types of figures and patterns by carefully chipping the coated rock surfaces with sharpened tools to remove the desert varnish and expose the lighter rock beneath. Older figures are themselves becoming darker in color as new varnish slowly develops.