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Coso Rock Art | archeology / surveying sites / dating rock art
archeology Dating rock art

Hiking through the isolated canyon, its walls covered with bighorn sheep, swirling patterns and otherworldly human figures, the archeologist can't escape the sense that the images are speaking to her. But what are they saying?

This is a special problem for the archeology of rock art: understanding images that cry out in a language no one remembers.

It is clearly a language, a system of communication. These are not merely random images, nor is it certain that they record anything so straightforward as actual events. Somehow, this select set of symbols is infused with meanings so important that people for thousands of years dedicated time and effort to their production.

Archeologists who worked on the 1960s surveys developed the chronology of both the production of rock art as well as the order in which different symbols were created. By associating symbols with sites that could be dated, archeologists believed that most Coso rock art was produced during the last few thousand years with a marked flurry of production about one thousand years ago.

Over time, artists seemed to turn away from the production of curving and rectangular abstracts and focused on representational forms. Men, dogs, and particularly sheep, proliferated. more >>


(photo) Heavily varnished panel showing degrees of repatination on individual images.  By TOMOL.


The degree of weathering one design exhibits compared to that of another suggests a difference in age. Here, weathering has caused re-patination of the large, complex anthropomorph, while the smaller, simpler ones seem vivid and new.

To accurately correlate weathered images, however, they must have been subjected to similar conditions. A panel protected by an overhang, for instance, may show much less weathering than one made at the same time but exposed to the sun and rain.

(photo) Petroglyph panel with bighorn image superimposed over visibly older medicine bag.  By TOMOL.


Archeologists have found that certain patterns often overlay other types. If one type is consistently superimposed upon another, the underlying type would likely be older than the upper type.

Superimposition analysis can be complicated by factors such as the artist's ideology: does the sheep cover the medicine bag simply because of chronology and limited canvas space, or might there have been a specific reason to juxtapose the two patterns in this way? Relative age differences between instances of superimposition, for instance, would suggest an ideological reason for this phenomenon.

(photo) Simple, stick-figure-like bighorn sheep.  Far Western Anthropological Research Group, Inc. (photo) Gracefully curving bighorn figure.  Far Western Anthropological Research Group, Inc.


Stylistic analysis is used to determine the development of particular styles of rock art. In the case of Coso bighorns, archeologists have determined that so-called "simple" bighorns predate the more famous boat-shaped sheep. Here, the simple sheep shows only hints of the stylization that culminates the boat-shaped sheep below.

(photo) Closeup of stone with lightly scratched grid.  Far Western Anthropological Research Group, Inc.


Archeologists sometimes find that particular styles of rock art are associated with sites of a certain age range, but never with sites of any other. Such inter-site patterning is notable in the case of scratched styles. Scratched rock art is almost exclusively found in association with recent upland sites. In fact, other relative dating results have led some archeologists to conclude that scratched art is the most recent type.

(photo) Image of an anthropomorph hunting bighorns with a bow and arrow.  By TOMOL.


Historical analysis looks for images of objects or events that occur at well-known points in the past. A hunter with a bow, for instance, could only have been drawn within the past 1,500 years, since that is when the bow and arrow were adopted in California.

This type of analysis is complicated by the fact that older objects or events may still be depicted for centuries afterwards. For instance, images of atlatls could well post-date the introduction of the bow and arrow, because the richness of its symbolism might not have been easily superseded by that of the newer device.

(photo) Bighorn petroglyph with lichen growing on it.  By TOMOL.


Lichenometry looks at the growth of lichens to determine a minimum age. Because each species of lichen grows at a specific rate, the relative development of a lichen can indicate its age, and thus, the most recent possible age for the petroglyph on which it is growing.

(photo) Petroglyph panel showing varying degrees of patination.  By TOMOL.


Bob Higgins, NPS Chief Geologist

Geochemists have been instrumental in identifying what desert varnish is, how rocks weather, how ancient artists' paints have been preserved, and how best to preserve rock art. Yet perhaps geologists' biggest contribution to the study of rock art involves solving the mystery of how old the images are.

While most archeologists have focused on the relative ages of the artwork, geologists have worked to develop "absolute" age dating methods. Absolute or chronometric age dating methods are based on the principle that when a petroglyph is created it disturbs the rock surface and a natural clock begins to tick. These dating techniques reveal the time that has elapsed since the artwork was created. Absolute methods produce a quantifiable date range during which the images were created.

All absolute methods of dating petroglyphs are highly complex, requiring sophisticated laboratories and precise sampling techniques. As such they are all considered experimental.