The word petroglyph comes from the Greek petro (rock) and glyph (carving or engraving). They are made by pecking or scraping off the dark layers of "desert varnish" that accumulate on rocks in dry climates, thus exposing the lighter-colored underlying stone.

The desert varnish coating is the result of airborne particles of certain minerals, such as iron oxide and manganese oxide, that settle on the surface of the rock. In a complex natural process involving microbial and bacterial action, the dust particles are turned into a concrete-like substance that adheres to the surface. This takes centuries. Once the varnish is removed, new varnish immediately begins to form in the scar. This is called "repatination." The amount of varnish that has built up over a petroglyph is one of the means archeologists use to date them, although this is an inexact science. The petroglyphs in the Agua Fria National Monument are typically seven to eight hundred years old.

Most petroglyphs are made by holding a pointed rock against the drawing surface and hitting it with a hammerstone, much as a modern carpenter would use a hammer and chisel. Some petroglyphs are abraded or scraped off, and some use a combination of techniques. A few petroglyphs show evidence of having been colored in using various pigments (animal blood, berry juice, charcoal), but the paints have weathered off in locations not protected from the elements. Rock art made entirely using pigments (without removing the varnish first) are called pictographs, and are very rare.

There are millions of petroglyphs in the Arizona desert, and they have been studied extensively by archeologists. There are several distinct "styles" that are characteristic of particular geographic locations and time periods. In Arizona, we have the Anasazi Style in the Four Corners region (300 AD to AD 1300 AD), the Hohokam Style in the vicinity of Phoenix and along the Salt River (essentially the same time period), and the much older Archaic style throughout the state (5000 BC to 300 AD). The Agua Fria petroglyphs are most similar to the Hohokam style, although the differences can be difficult to distinguish.

What do the petroglyphs mean? Some are obvious: a bighorn sheep with arrows in its side and a bunch of hunters running after it, for example, requires little explanation. Some pictures are interpreted by contemporary Native Americans, many of whom claim a common cultural heritage with the ancient petroglyph makers, as having spiritual or religious significance. But the fact is we don't have any idea what most of the pictures mean, and likely never will.

In additon to hundreds of ruins, the Agua Fria National Monument contains many thousands of ancient petroglyphs. Most of the ones shown on this page are located within a few hundred yards of each other.

These photos are arranged in four groups. The first group shows panels that contain many petroglyphs in one place. The second group -- the biggest -- shows animals. The third group shows people and human/animal hybrids such as the ubiquitous "Lizard Man" (a lizard figure with a round, man-like head). The final group contains abstract figures, geometric designs and unidentified objects.

A few of the petroglyphs in this collection show some rather bright colors. This is caused by modern-day petroglyph hunters who press chalk into the markings in order to obtain rubbings on a piece of paper. Unfortunately, both the application of the chalk and the subsequent rubbing process can damage subtle details of the work, and leaves unsightly chalk stains that can last for decades. Don't do it. Take a picture instead.

Click on each thumbnail to see a full-sized version.