Note the faint drawings on these outcrops. These are called petroglyphs and have been etched into the dark film covering the sandstone. This film is called "rock varnish" and is

predominantly clay and some iron and manganese oxides. The petroglyphs were pecked out hundreds of years ago by prehistoric inhabitants of the Tucson Mountains. Make a sketch of one of the petroglyphs:What do you think this petroglyph signifies?