Petroglyphs are rock carvings (rock paintings are called pictographs) made by pecking directly on the rock surface using a stone chisel and a hammerstone. When the desert varnish (or patina) on the surface of the rock was chipped off, the lighter rock underneath was exposed, creating the petroglyph. Archaeologists have estimated there may be over 25,000 petroglyph images along the 17 miles of escarpment within the monument boundary.
