Dating the Hueyatlaco Archaeological Site (Valsequillo)

The Hueyatlaco archaeological site, nestled within Mexico’s Valsequillo Basin near Puebla, presents an intriguing puzzle for archaeologists due to its contested dating.

For a long time, the prevailing idea was that humans arrived in the Americas with the opening of the Ice Free Corridor (IFC) between the Laurentian and Cordilleran Ice Sheets. This was after they already crossed the Bering Land Bridge which, by the way, was probably as wide as Texas.

When the (IFC) first opened up between 15,000 and 13,000 years ago, it allowed for megafauna and humans to migrate in as they hunted these animals. However, there are several sites in the Americas that show evidence for human habitation well prior to the Last Glacial Maximum. We’ll call these Pre-LGM sites.

A Few Pre-LGM Sites

• White Sands, New Mexico – human footprints in ancient lake sediments initially dating to between 26,000 and 18,000 years ago. Now revised to a date “up to 23,000 years” ago.
• Chiquihuite cave, Mexico – dated to as old as 26,000 years.
• Meadocroft Rockshelter, Pennsylvania – Dates to between 19,000 and 16,000 years ago for its earliest habitation.
• Gault Site, Texas – a site in Florence, Texas that dates to as early as 20,000 years
• Cactus Hill, Virginia – Dated to between 20,000 and 16,000 years ago.

Each of the sites above is not without some controversy, though none rise to the level of the Hueyatlaco site in the Valsequillo Basin of Mexico.

A Brief Overview

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.

The Controversy

You might think the controversy was due to the Clovis-First consensus of archaeology in the Americas during the 1960s. And you’d be correct. But only partially.

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.

They really had no definite explanation for extreme dates other than there may have been some contamination contemporary to the tools found in the stratum were the animal remains were recovered. That contamination from an older stream bed might have given the uranium dates.

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 principle is similar to obsidian hydration, in that volcanic tephra take up water through time at a regular rate which can be calculated to produce exact dates. Assuming certain controls exist.

Steen-McIntyre and Malde worked Roald Fryxell on the site at this point and tested the tephra in the tool-bearing strata, arriving at 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).

Irwin-Williams criticized Malde and Fryxell after they announced their extreme dates during the Geological Society of America meeting as “irresponsible.” Steen-McIntyre, probably hoping to write a doctoral dissertation on Hueyatlaco ended up with one on dating volcanic ash instead. To this day, there isn’t a consensus on what the earliest date is for human occupation of Hueyatlaco.

Ongoing Debate and Significance

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.

At one time–particularly in the 1960s and 70s when this site was initially being worked, the possibility of a pre-Clovis occupation at Valsequillo held significant implications for our understanding of early human migration routes and the timing of human arrival in the Americas. And even the dates that Irwin-Williams thought were more conservative and realistic in the 20,000 years BP range were once considered extreme by the archaeological consensus.

Fortunately, science is a able adapt and, with new data and new evidence, revisions to the consensus happen. Discoveries of sites like White Sands, with foot prints as old as 23,000 years BP put Irwin-Williams’ preferred dates in good company. With the dates preferred by Steen-McIntyre still firmly in the fringes of scientific acceptance.

That’s not to say these dates are wrong. But they are improbable for various reasons.

Criticisms of Steen-McIntyre’s Conclusions

Virginia Steen-McIntyre and others argue that the dates important to the early occupation of this site include those that are a full order of magnitude greater than those of Irwin-Williams. She sees the site as dating to at least 260,000 to 300,000 years BP.

Criticisms of Steen-McIntyre’s conclusions about the age of the Hueyatlaco site can be grouped into a few main points:

• Uranium Dating Methods: Critics argue that the uranium-series dates might be inaccurate due to leaching of uranium from the bones, which could lead to an overestimation of the age. They point to the fact that uranium-series dating on bone can be unreliable in situations where there’s potential for the movement of uranium in the surrounding environment. Similarly, the large statistical errors associated with the fission-track dating method raised concerns about the precision and usefulness of these dates in the context of the archaeological findings.
• Fission Track Dating Methods: Irwin-Williams pointed out that the fission-track dates obtained for deposits near Hueyatlaco (600,000 and 370,000 years old) were not only inconsistent with the uranium-series dates but were also in reverse stratigraphic order, where the Tetela Brown Mud, apparently overlying the Hueyatlaco Ash, yielded an older date. This stratigraphic inconsistency raises doubts about the accuracy of these specific dates.
• Tephrochronological Dating: Irwin-Williams criticized Steen-McIntyre’s tephrochronological studies for not adequately considering how the chemical composition of volcanic glass and environmental temperature could affect hydration rates, which are crucial for determining the age of the deposits.
• Inconsistency with Tool Technology: A major point of contention lies in the implication that if the older dates are accepted, it would mean that sophisticated tools like bifacially worked knives, scrapers, and projectile points were being used in the New World long before similar tools appeared in the Old World. Critics find this scenario highly improbable and suggest that the tools found at Hueyatlaco are “entirely too modern” to have been manufactured by hominids 250,000 years ago. They argue that the tools align more closely with those found in later periods, such as the last glacial maximum (approximately 18,000 to 20,000 years BP).
• Lack of Comparable Sites: The lack of other archaeological sites in the Americas showing similarly old ages for human presence contributes to the skepticism surrounding Hueyatlaco’s early dates. Critics argue that the findings contradict the widely accepted timeline for the peopling of the Americas, which generally points to human arrival no earlier than 20,000-30,000 years BP. Proponents will lean on claims for sites like the Cerutti Mastodon site in California, alleged to be 130,000 years BP, the Calico Early Man site, also in California and supposed to be 130,000-200,000 years BP, and the Topper site in South Carolina, believed by some to be at least 50,000 years old. But each of these have problems of their own.
• ? Absence of early hominid fossils in the New World: The old age suggested by the uranium-series dating would also require evidence of early hominid presence in the New World to account for the toolmakers, but Irwin-Williams noted that no such fossil evidence existed.
• ? General Consistency With Other Evidence: Irwin-Williams pointed to the consistency of the archaeological evidence, faunal analysis, and limited radiocarbon dating, all of which supported a Late Pleistocene age (greater than 9,000 and less than 22,000 years old) for the Valsequillo deposits. She specifically mentioned a personal communication from Russell Graham, who conducted a faunal analysis and concluded that the assemblage was likely between 10,000 and 30,000 years old.
• Reliance on Relative Dating: Critics question the heavy reliance on relative dating methods, such as tephra hydration and mineral etching, to support the older radiometric dates. While these techniques can provide valuable insights, they argue that these methods are not as precise as absolute dating methods, and their accuracy is heavily dependent on factors like environmental conditions and the specific properties of the materials being analyzed.

These criticisms don’t necessarily mean Steen-McIntyre was wrong, but they definitely highlight the need for a cautious approach when interpreting the data. 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.

This site will possibly play a part in Season 2 of Graham Hancock’s Ancient Apocalypse, a speculative documentary (speculamentary) of dubious value to anyone interested in #RealArchaeology. 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.

What I didn’t cover in this article are the alleged human footprints found in the region. That’ll be a topic for another day…

References and Further Reading

Irwin-Williams, C., et al (1969). Comments on the Associations of Archaeological Materials and Extinct Fauna in the Valsequillo Region Puebla Mexico, American Antiquity, 34(1), pp. 82-83.

Irwin-Williams, Cynthia. (1978) Summary of Archaeological Evidence from the Valsequillo Region, Puebla, Mexico. In Cultural Continuity in Mesoamerica, David L. Browman, ed. The Hague: Mouton Publishers.

Malde, Harold E.; Steen-McIntyre, Virginia; Naeser, Charles W.; and VanLandigham, Sam L. (2007). The stratigraphic debate at Hueyatlaco, Valseillo, Mexico. Palaeontologica Electronica, 14(3), pp. 1-26.

Steen-McIntyre, Virginia (2008). A review of the Valsequillo, Mexico early-man archaeological sites (1962-3004) with emphasis on the geological investigations of Harold E. Malde. Presentation at 2008 Geological Society of America Joint Annual Meeting, Oct. 5-9, Houston, TX.

Steen-McIntyre, V., R. Fyxell and H. Malde. (1981) Geologic Evidence for Age Deposits at Hueyatlaco Archaeological Site Valsequillo Mexico, Quaternary Research, 16, pp. 1-17.

Szabo, B.J., Malde, H.E., and Irwin-Williams, C (1969). Dilemma Posed By Uranium-Series Dates On Archaeologically Significant Bones From Valsequillo Puebla Mexico. Earth and Planetary Science Letters, 6(6), pp. 237-244.