Dating the Hueyatlaco Archaeological Site (Valsequillo)

There are several sites in the Americas that show evidence for human habitation well prior to the Last Glacial Maximum. Of these Pre-LGM sites, each of the sites is not without some controversy, though none rise to the level of the Hueyatlaco site in the Valsequillo Basin of Mexico.  This project has attracted comments of the type we see in social media (this one from Julian Dorey):

"Archaeological COVERUPS are not myth! They've been happening and one site completely BROKE the timeline and was erased from history once academia found out. Hueyatlaco didn’t get rejected because it lacked evidence. It got rejected because the evidence didn’t fit the story".

The background can be judged from this useful informed and well-referenced text: Carl Feagans, 'Dating the Hueyatlaco Archaeological Site (Valsequillo)' A Hot Cup of Joe October 7, 2024.

The Hueyatlaco archaeological site, nestled within Mexico’s Valsequillo Basin near Puebla, presents an intriguing puzzle for archaeologists due to its contested dating. Initial excavation in the 1960s unearthed stone tools right alongside the remains of extinct Pleistocene mammals. This obviously suggests a human presence.

That part isn’t really controversial though. The real challenge was, and still is, pinning down a definitive date. Through various methods, the site was, back then, dated to as young as 25,000 years old and as old as 370,000 years.

A vast discrepancy to be sure, but you have to remember: this was the 1960s. Tom Dillehay still hadn’t excavated Monte Verde to obtain his then controversial dates of 14,800 years BP for this site in Southern Chile!
The first team to excavate at Hueyatlaco did so in 1962, led by Cynthia Irwin-Williams. She was a remarkable archaeologist and a genuine ground-breaker for women in archaeology. Because of the controversy surrounding the site, Irwin-Williams never published a final report despite the decades of research she and her colleagues put into it.

[...] When Barney Szabo, Harold Malde, Cynthia Irwin-Williams published their first paper on the site, they arrived at radiocarbon dates for animal remains at over 35,000 BP and Uranium dates of between 200,000 and 320,000 BP. [...]

In 1973 Virginia Steen-McIntyre joined the excavation team and brought with her a new technique for dating that she developed called tephra hydration. [...] the tephra in the tool-bearing strata [produced] [...] a date around 260,000 BP. In addition, C.W. Naeser used fission track dating on ash samples from the same strata and arrived at a date of 370,000 BP (+/- 240,000 yrs). [...]

The dating of Hueyatlaco remains a subject of debate within the archaeological community. Recent studies point toward a Late Pleistocene age, but the site’s complex stratigraphy, potential for reworked materials, and the limitations of some dating techniques contribute to this ongoing controversy. [...]

                                               Recent work on site                                     

Further research using a variety of dating techniques and a thorough understanding of the site’s geological context is essential to truly arrive a reliable conclusion for its earliest date of human occupation. [...] While it’s true there are some questions about the age of the site, most of the conclusions about dates were obtained when the dating methods were still being refined.

I’m hopeful that some day new data will be obtained for these strata and their deposits using modern dating methods and that we’ll have a better understanding of what was really going on at this site and when. In fact, this site is a good example of why it’s important to not completely destroy a site through excavation since so much has changed in the way of archaeological and geological sciences since the 1960s.

In light of these issues, the wide discrepancies in the proposed dates for Hueyatlaco are best understood as the cumulative result of methodological limitations rather than as evidence of any deliberate suppression or “cover-up.” The early excavations were conducted before the routine integration of high-resolution geoarchaeology, and sampling protocols were not always capable of securely isolating primary depositional contexts from reworked sediments. At the same time, the physico-chemical dating methods applied to the site were, in many cases, at or beyond their effective limits and relied on assumptions about stratigraphic integrity and post-depositional stability that could not yet be adequately tested. When large error margins, open-system behavior, and complex site formation processes are taken into account, the apparent contradictions between dates lose much of their force. Rather than reflecting nefarious intent, the controversy surrounding Hueyatlaco illustrates the nature of the process of establishing archaeological chronologies and the extent to which interpretations are constrained by the technical and theoretical tools available at the time of investigation.