Bordes et al. (2020) bring us an interesting and methodologically strong update on the Cerutti Mastodon site, which has been claimed (Holen et al. 2017) to show 130 000 year old archaeological material in Southern California. If confirmed as archaeological, the Cerutti Mastodon site would push back the earliest material remains of human activity in the Americas by more than 110 000 years over the currently well documented 14-16kya.

The initial claim was heavily criticized (see Bolger 2019 for a recent analysis), mostly rejected in fact, mainly because the material claimed as archaeological by the team, while it could have been the result of human activity, certainly doesn’t have to be, at least as it was presented in the original report. There is little doubt that the site itself is 130ky old, and that it contains Mastodon bones and rocks. The key question is whether it is a geological or an archaeological location.

The claim

Did the production of the Cerutti Mastodon site require human activity? Bordes et al seek to resolve that question by examining the relationship between the claimed stone anvils, hammer-stones, and the mastodon bones claimed to have been broken and worked by humans using those tools. Specifically, they look at microscopic bone residue found on the surface of the rocks.

To put it simply, they conclude that there is bone residue on the upward-facing surfaces of the rocks, and/or the surfaces that show wear. They found no bone residue on the downward facing surfaces, and/or on surfaces that show no wear. This would suggest that the bones were in contact with certain surfaces of the rocks but not others, primarily the faces that were pointing upward when the rocks and bones were found. It suggests that the contact had enough force to transfer residue, but that residue was not transferred as a result of simple environmental exposure, since it would then be distributed all over the rocks.

The simplest explanation for this pattern, according to the authors, is that humans used the rocks as hammers and anvils to break the bones. Since the damaged surfaces of the rocks and the bone residue are found under a carbonate crust which developed over time, they conclude that the damage was done and the bone residue deposited at the time the site was first formed 130ky ago.

What we know

Bordes et al.’s results definitely don’t rule out that the Cerutti Mastodon site is archaeological, however, they don’t quite show that it isn’t just geological. They show quite clearly that mastodon bones were in forceful contact with rocks at the location sometime in the past. If we grant the carbonate crust argument, that contact occurred in a relatively remote past, much too old to be related to modern construction work and damage from heavy machinery (about which see Ferrell 2019).

But the structure of the argument, and its main weakness, remains the same as in the original 2017 claim. According to the authors, human activity is the simplest explanation for the presence of bone residue on some rock surfaces and not on others. This is softened from the 2017 claim that human activity is the only possible explanation for the patterns found at the site.

As we know from the eolith debate, however, humans are not the only agents that can exert force, and telling force applied by humans from force applied by other biological or geological agents is not easy.

Bordes et al. tell us at the end of their article that experiments are underway to evaluate whether the pattern observed in the Cerutti Mastodon site material must be blamed on humans. I look forward to seeing the results of those experiments. At the very least, I would like to see whether simulated trampling of bones on a rock strewn surface by large animals can produce the kind of impact that leaves the observed residue pattern. Another important question is whether longer-term application of a constant pressure, perhaps combined with small migrations or movements across a surface, has the same effect as breaking a bone with hammer and anvil stones.

Bordes et al present some solid work, and it definitely goes in the right direction for the study of the Cerutti Mastodon site, but it doesn’t in itself make the point they are pursuing. Perhaps combined with replication experiments, it could.


Bolger B 2019. The Perfect Storm: an analysis of the scientific credibility of the archaeological claims for the Cerutti Mastodon site and the public interaction with those claims, Masters Thesis, University at Buffalo.

Bordes L, E Hayes, R Fullagar, T Deméré 2020. Raman and optical microscopy of bone micro-residues on cobbles from the Cerutti Mastodon site, Journal of Archaeological Science: Reports 34.

Ferrell PM 2019. The Cerutti Mastodon site reinterpreted with reference to freeway construction plans and methods. PaleoAmerica.

4 thoughts on “Cerutti Mastodon 2020: Interesting new results, more experiments needed

  1. Extraordinary claims need extraordinary evidence, no? The Bayesian prior for having humans there at 120K before present is low, it takes a really impressive evidence to raise that prior to a reasonable posterior. They’re going to need more than this.


  2. I knew it! I was sure when I saw the site years ago that it was human created. The position of the teeth, ball joints…looks like boys playing. The were breaking bones but also wanted to set aside interesting remnants of the animal. Who wouldn’t?


  3. The Cerutti Mastodon Site has a lot of evidence pointing to human activity. First of all there is the very unusual distribution of bone and stone. The site was preserved in original context cemented within undisturbed Pleistocene fluvial overbank deposits, untouched by heavy machinery contrary to Ferrell et al. , who by the way never visited the site . Anomaly #1. The thick heavy femur bones were smashed into small fragments while the ribs and vertebrae were mostly intact. Many of the femur fragments exhibit impact points and spiral fracturing. Why are biggest, most indestructable bones smashed to bits while the dainty ribs and vertebrae a meter or two away are untouched? Anomaly #2. Micro fragments of stone, teeth and bone occurring though out the siltstone of “Bed E”, including “cone flakes,” like the ones produced by a BB hitting a glass window. Anomaly#3. The ball joints of the femora were discovered in perfect condition side by side, one side up and the other down, each with a small part of the femoral neck still attached, removed in nearly the same exact manner from the rest of the femora. Anomaly#4. Fragments of spirally fractured bone, teeth and stone surrounding the anvil stones. These anvil stones have impact marks only on the up sides with bone residue occurring only in those marks. The matching hammer stones also present exhibited similar use wear. Bordes et al 2020. Now for the other anomalies. #5. The vertically emplaced tusk extending 60 centimeters below the main stone and bone bearing horizon of the “E Bed” into the underlying fine grained sandstone. The south side of that tusk has sediment drag from the upper layers preserved along it’s surface still cemented to it, indicating direct vertical force that was applied to the tusk into then soft sediment. Anomalies. #6 and #7. Refitting granitic boulder fragments of concentration 2 separated by as much as 3 meters horizontally from the large main granitic block. Refitting fragments of an andesite cobble of concentration 1. All of this was preserved in original context, cemented within the carbonate rich siltstone of Bed E. There’s much more. I could go on for centuries, but you get the point.


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