How Old Are Petroglyphs, Pictographs, and Inscriptions?

“How old is it?” is a common question about petroglyphs, pictographs, and inscriptions. The answer depends on who you ask and how they know.

Age or Time

Native and Western peoples may have differing conceptions of age or time. Indigenous and Native peoples may see time as circular or cyclical, with no beginning or end. Historians, archeologists, and scientists seek chronological sequences and points in linear time. These perspectives complement each other.

For Native peoples, rock markings are part of cultural traditions and ways of knowing that extend to time immemorial. Generations passed oral traditions about rock markings and their significance. These traditions contextualize rock markings within broad patterns of life over significant time.

Western disciplines including anthropology, archeology, chemistry, geology, and history study rock markings. Their methods involve the collection and analysis of information. They tend to seek absolute dates and chronologies. Many work with Native peoples to incorporate their knowledge.

These approaches together provide a sense of the age of rock markings in North America. Rock markings in the Pyramid Lake Indian Reservation in Nevada date to between 14,800 and 10,500 years ago. Markings at the Paisley Caves in Oregon date to 14,300 BP or roughly 12,000 BCE on the basis of radiocarbon dates from DNA found nearby. The caves are on lands ceded by the Klamath Tribes. Petroglyphs at Tlingit Aaní (“kling-it") on Kaachxaan.akw’w (how to pronounce), part of Petroglyph State Park in Alaska, are between 8,000 and 10,000 years old. The Tlingit (“kling-it"), ancestors of the Alutiiq (“al-yoot-eek"), created them.

Style

Style is another way to date rock markings. Motifs and techniques are compared from place to place, and over time. In some places, the style changed from abstract shapes to representational figures. Nonrepresentational designs were constant. Archeologists infer age by finding parallels with motifs on artifacts from nearby sites. It is not clear why the styles changed or the degree to which the changes were linear over time.

Two styles of rock markings from different time periods at Canyon de Chelly National Monument.

NPS photos.

Content

The content of rock markings can provide an approximate or precise date.

"Approximate dates" draw on the principle that rock markings cannot show something not yet introduced.

Around 1300, the katsina (“katsi-na”) and the religion around it developed among Pueblo cultures in the Southwest. Only then did pictographs begin to depict katsina dancers and masks, and cloud terraces and parrot motifs. Katsina are benevolent spirits who act as intermediaries between the gods and people.

People hunt bighorn sheep from horseback at Arches National Park.

NPS photo.

Circa 1540, Spanish explorers arrived in the Southwest. They introduced horses, a new language, written numbers, and Christian symbols. These motifs appear in petroglyphs only after their arrival.

"Precise dates" are when rock markings have a date or year or describe a specific known event.

A pictograph on the Penasco Blano trail at Chaco Canyon may depict a star that exploded on July 5, 1054. The supernova appeared in the constellation Taurus next to a waning crescent moon. It could be seen during the day for over three weeks. The pictograph shows the waning moon and the exploding star. The hand may point to the horizon where the supernova rose an hour and forty-five minutes before sunrise. The concentric circles may represent the sun before it rose or, possibly, a comet.

Inscriptions left by the Spanish at El Morro National Monument.

NPS photo.

Layering

New rock markings may be carved or painted over old ones. This creates a sequence from back to front. The oldest images are at the back – they are painted over or cut through by new markings. The newest images at the front have no lines or shapes cutting into them. It is often difficult to know the time depth between the oldest and newest markings.

“Desert varnish” is a darkening, or patination, of rock. Petroglyphs carved into desert varnish expose the lighter rock color below the surface. Over time, the rock surface will re-varnish in a process called “repatination.” Repatination occurs at various rates and degrees. A great degree of repatination indicates greater age than an image that shows only some. As a result, the degree of repatination provides a relative idea of how old an image may be.

Newer petroglyphs at Petrified Forest National Park have brighter lines than older ones.

NPS photo.

Lichens

Green lichen regrow over a petroglyph at Petrified Forest National Park.

NPS photo.

Lichens consist of fungi and algae that grow on rock. Fungi grow around the algae to buffer it from the weather. It takes a long time for them to cover a surface, but when they do, the coating is very durable. Many lichen grow less than a millimeter per year, but lichens can live for thousands of years.

Lichenometry is a technique to date rock markings using indices of lichen growth. It analyzes the age of the lichen’s thallus. It provides the best data for the most recent millennia and is most precise up to 500 years. A rock marking is younger than the lichen when the carving goes through it. It is older when the lichen grows over the carving.

Radio Carbon Dating

Radiocarbon dating is also called carbon dating, carbon-14 dating, or C14 dating. All plants and animals need carbon to survive. When a living thing dies, it stops exchanging carbon with the environment. The amount of C14 it contains undergoes radioactive decay. Over time, it contains less and less C14. The remaining C14 can be measured to determine when the plant or animal died. The older the sample, the less C14 there will be. C14 dating is most reliable for dates up to approximately 50,000 years ago.

One way to radiocarbon date pictographs is to analyze organic pigment. For example, charcoal (the pigment most often used for black painting) dates to the death of the plant from which it was made. It may not, however, date the pictograph itself. As a result, the charcoal or the wood used to make it could date much older than the pictograph. C14 thus provides a ballpark date for when a pictograph was made.

Comparative Evidence

Oral history, archeological data, and historical documents provide comparative evidence for dating rock marks. Working from multiple perspectives strengthens our understanding of rock markings.

Oral history from Indigenous or Native perspectives draws on memories and information passed from generation to generation. It can help interpret the content and age of rock images and place them in a cultural context.

Archeologists extrapolate dates from evidence found at nearby sites and analysis of collections. Archeological data includes findings from site excavations and collections analysis. Charcoal, diagnostic artifacts (such as lithic tools or ceramic types), and tree rings are some ways archeologists place a site in chronological time.

The location of rock markings near buildings provides another clue. When archeologists know the date of a building, they may assume that the images were made while the building was in use.

Archeological sites may be associated with rock markings.

NPS photo.

Historical documents kept by Europeans recorded their observations and travels. They correlate the creation of rock markings with Europeans’ movements through a place. Historical documents also help to place rock markings into context by tying them to larger currents and trends.