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The Hueyatlaco site is located in the Valsequillo Basin in central Mexico, and it has been the subject of a great deal of controversy and debate in the field of archaeology. Discovered by Cynthia Irwin-Williams in the 1960s, the site contains a range of artefacts and remains that have challenged traditional theories about the history of human habitation in the Americas. The site’s significance lies in its potential to provide insights into the earliest human migrations into the Americas, but the controversy surrounding its age and origin has made it a focal point for archaeologists and researchers since its discovery.

The History of Archaeology in the Americas
Archaeology in the Americas has a long history, dating back to the arrival of European explorers and settlers in the late 15th and early 16th centuries. Many early explorers, such as Hernán Cortés and Francisco Pizarro, were interested in the ancient ruins and artefacts they encountered, but their focus was primarily on treasure hunting rather than scientific investigation.

Valsequillo: The area of the findings.
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In the 19th century, however, archaeology began to emerge as a discipline, focusing on the study and interpretation of ancient cultures and their material remains. Some of the key figures in the development of American archaeology include Thomas Jefferson, who conducted excavations of Native American mounds in Virginia in the late 1700s, and John Wesley Powell, who explored and documented the archaeology of the American Southwest in the late 1800s.

The Importance of Understanding Early Human Migration
The study of early human migration is important for several reasons. First, it provides insights into the origins and development of human societies and cultures, including the spread of languages, technologies, and ideas. Secondly, it sheds light on the genetic and biological diversity of human populations and the factors that have influenced this diversity over time. Finally, the study of early human migration has implications for modern issues such as population movements, immigration policies, and the preservation of cultural heritage.

Background on the Valsequillo Basin and its Geological History
The Valsequillo Basin is located in central Mexico, east of Mexico City. It is a closed basin that has been filled by sediment deposits from the surrounding hills and mountains over millions of years.

The basin is bordered by the Sierra Madre Oriental mountain range to the east and the Trans-Mexican Volcanic Belt to the west. The basin contains several important archaeological sites, including the Hueyatlaco site. The geology of the basin is complex, with a variety of sedimentary deposits, volcanic rocks, and tectonic activity over the past several million years. The basin is known for its rich fossil record, which includes evidence of extinct megafaunas such as mammoths and other mastodons[2], camels, and horses. The geology of the basin and its fossil record provides important insights into the region’s history and the evolution of its flora and fauna over time.

Overview of the Excavation
Cynthia Irwin-Williams led the team that first excavated the site in 1962.[3] The dig is often associated with Virginia Steen-McIntyre because of her continuing efforts to publicise her findings and opinions. However, the excavation site was discovered by Professor Juan Armenta Camacho and Irwin-Williams. Steen-McIntyre joined the team in 1966 as a graduate student, at the request of project geologist Harold E. (Hal) Malde. The excavation was associated with the US Geological Survey.

Picture: Cynthia Irwin-Williams in 1964
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The region, about 75 miles southeast of Mexico City, was known for its abundance of animal fossils, and Irwin-Williams described Hueyatlaco as a “kill site” where animals were hunted and butchered.[4]

The Hueyatlaco site consists of several layers of sediment, each containing artefacts and remains of horses and extinct animals, such as mammoths. Cynthia Irwin-Williams’ initial discoveries at the Hueyatlaco site in the 1960s included a variety of stone tools (including bifaces, scrapers, and choppers) and other artefacts that suggested the presence of early humans in the area. The tools were found in association with the remains of extinct animals, such as mammoths and horses, and this led to early theories about the age and origin of the artefacts. The initial discoveries at the site sparked interest and excitement in the archaeological community, setting the stage for later investigations.

The discovery of early human artefacts in the Valsequillo Basin of Mexico has been the subject of much debate and controversy among archaeologists and anthropologists. Hueyatlaco is one of the most significant sites in this area, dating back to more than 250,000 years ago. This finding challenged the conventional theory of the arrival of humans in the Americas, which posits that humans first arrived in the continent around 15,000 years ago. The Hueyatlaco site, therefore, has played a crucial role in our understanding of the history of human habitation in the Americas and the broader context of early human migration. However, the age estimates were controversial, and many scientists questioned the accuracy of the dating methods used and have seen only occasional discussion in the literature[5].

Human artefacts have been discovered in several layers of sediment at the site, with more simple tools in the lower levels and more complex tools in the upper levels.

The Hueyatlaco Site
Irwin-Williams and her team found numerous stone tools and other artefacts at the site, leading them to believe that early humans had once inhabited the area. The site’s discovery was significant because it suggested that humans had been present in the Americas much earlier than previously thought.

The stone tools found at the site were made of quartzite[6], a hard, dense rock that is difficult to work on. The tools included various types of scrapers, blades, and points, which were likely used for multiple activities, such as butchering animals, scraping hides, and cutting plants. In addition to the stone tools, the team also found charcoal, animal bones, and other artefacts, providing evidence of early human habitation and activity.

Dating Methodology
The age and origin of the artefacts found at the Hueyatlaco site have been the subject of much debate and controversy. The initial carbon-14 dating[7] of the artefacts suggested that they were around 250,000 years old, making them some of the oldest artefacts ever found in the Americas. However, subsequent dating techniques, such as thermoluminescence and electron spin resonance, have yielded much younger ages, ranging from 30,000 to 200,000 years old.

There is also disagreement about whether the sediment layers at the site have been disturbed or not, which could affect the accuracy of the dating techniques.

Significance of the Hueyatlaco Site
Despite the controversy and uncertainty surrounding the Hueyatlaco site, it remains an important site for understanding the history of human habitation in the Americas.

If the artefacts are around 250,000 years old, as the initial carbon-14 dating suggested, it would challenge the traditional view that humans first migrated to the Americas around 13,000 years ago. Instead, it would suggest that humans arrived much earlier and possibly via a different route than previously thought.

Even if the artefacts are not as old as initially believed, the Hueyatlaco site still provides valuable insights into the history of human habitation in the Americas. The site has yielded evidence of the extinct animals that once roamed the area, such as mammoths and giant sloths, as well as evidence of the plants and other resources that early humans may have used. By studying the artefacts and remains found at the site, scientists can gain a better understanding of the lifestyle, technology, and behaviour of early humans in the Americas.

The controversy surrounding the Hueyatlaco site has made it a focal point for researchers interested in the early human history of the Americas. The site has the potential to provide important insights into the earliest human migrations into the region, and the artefacts and remains found there could shed light on how early humans adapted to new environments. Additionally, the remains of extinct animals found at the site could provide valuable information about the climate and environmental conditions in the region during the time of early human habitation.

Despite the initial excitement around the discoveries at the Hueyatlaco site, controversy and debate quickly followed. One of the major debates centred around the age of the Hueyatlaco artefacts and their origin. Some scientists argued that the artefacts were evidence of early human habitation in the Americas, while others argued that they resulted from natural processes or by other animals, such as ancient hominids.

The Hueyatlaco and the Traces of Early Man
Hueyatlaco is an archaeological site located in the Valsequillo Basin in Mexico. The Valsequillo Basin is located near the city of Puebla, in Mexico. Situated in the central part of the country, this basin has been the focus of much interest for geologists, archaeologists and the scientific world as a whole. This interest was sparked due to the presence of numerous megafaunal remains and evidence of very early human habitation. Megafauna is the term commonly used for large animals that roamed the landscapes of the Pleistocene, such as mammoths, woolly rhinoceroses, and cave lions. However, although rich in important discoveries, the site has always been the cause of much controversy, simply because some of the theories surrounding it are very hard to grasp fully.

The Chiquihuite Cave in the Astillero Mountains in Northern Mexico
In 2020, a team of researchers led by Ciprian Ardelean, an archaeologist at the Autonomous University of Zacatecas, Mexico, discovered evidence of human activity at the Chiquihuite Cave in the Astillero Mountains in northern Mexico. The findings included stone tools and other artefacts dated to be around 26,000 to 30,000 years old – much older than the widely accepted timeline of human presence in the Americas (around 15,000 years ago).

These findings sparked debate among archaeologists and palaeontologists as they challenged the widely accepted “Clovis-first” theory, which posited that the Clovis people were the first to populate the Americas. Further research and discoveries are needed to confirm the implications of these findings and to build a more accurate understanding of early human migration and settlement in the Americas.

Review and Concluding Words
Current evidence suggests that the earliest human settlers in Mexico arrived between 33,000 and 13,000 years ago, during the last Ice Age. These early settlers are thought to have been hunter-gatherers who migrated to Mexico from Asia via a land bridge that once connected the two continents across the Bering Strait. These early settlers may have followed the migration of large game animals, such as mammoths and bison, which also crossed the land bridge.

The Hueyatlaco site remains a fascinating and controversial subject in the field of archaeology. Despite ongoing debates and controversies, the site has the potential to provide important insights into the earliest human migrations into the Americas, and it serves as a reminder of the complexity and richness of the human past. As new research and exploration at the site continue, the controversies and debates will likely continue as well, making the Hueyatlaco site an ongoing and dynamic subject of interest for archaeologists and researchers.

Future research and exploration at the site could help to shed more light on the controversy surrounding the age and origin of the artefacts found there. Advances in dating methods and techniques could help to provide a more accurate estimation of the age of the artefacts and provide a more comprehensive understanding of the history of human habitation in the Americas. The Hueyatlaco site, therefore, remains an important site for ongoing research and exploration, and it has the potential to uncover new information about the history of human migration to the Americas.

Before I finish this paper, it is worth mentioning the Cuicuilco Archaeological Site, which is among the oldest excavated ancient cities in the Valley of Mexico and the oldest that you can visit. It was occupied by the Cuicuilca people from 700 BC to 150 AD and was home to around 20,000 people in its heyday. When the Xitle volcano began a series of devastating eruptions between 245 and 315 AD, most of the area was covered in lava, and the population fled to safer places. It is often noted that this time corresponds to the rise of Teotihuacán, and some Cuicuilca people are known to have migrated to the city. A corresponding ceremonial centre to the north, at Copilco, was almost entirely buried by the eruptions.

Picture: Comparison of a woolly mammoth (left) and an American mastodon (right).
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Sources and Further Reading

Books/Scholarly Papers:


CAUTION: This paper is compiled from the sources stated but has not been externally reviewed. Parts of this paper include information provided via artificial intelligence which, although checked by the author, is not always accurate or reliable. Neither we nor any third parties provide any warranty or guarantee as to the accuracy, timeliness, performance, completeness or suitability of the information and materials covered in this paper for any particular purpose. Such information and materials may contain inaccuracies or errors and we expressly exclude liability for any such inaccuracies or errors to the fullest extent permitted by law. Your use of any information or materials on this website is entirely at your own risk, for which we shall not be liable. It shall be your own responsibility to ensure that any products, services or information available through this paper meet your specific requirements and you should neither take action nor exercise inaction without taking appropriate professional advice. The hyperlinks were current at the date of publication.

End Notes and Explanations
  1. Source: Compiled from research using information at the sources stated throughout the text, together with information provided by machine-generated artificial intelligence at: [chat] and
  2. Explanation: A Mastodon is any proboscidean belonging to the extinct genus Mammut. Mastodons inhabited North and Central America from the late Miocene up to their extinction at the end of the Pleistocene (often referred to colloquially as the Ice Age) 10,000 to 11,000 years ago. Source:
  3. Source:  Irwin-Williams, C., et al., Comments on the Associations of Archaeological Materials and Extinct Fauna in the Valsequillo Region Puebla Mexico, American Antiquity, Volume 34, Number 1, Pages 82-83, Jan 1969. Cited at:
  4. Source:  Irwin-Williams, Cynthia. (1978) Summary of Archeological Evidence from the Valsequillo Region, Puebla, Mexico. In Cultural Continuity in Mesoamerica, David L. Browman, ed. The Hague: Mouton Publishers. Cited at:
  5. Source:  Gonzalez, Silvia; Huddart, David; and Bennett Matthew. (2006) Valsequillo Pleistocene archaeology and dating : ongoing controversy in Central MexicoWorld Archaeology, 2006, vol. 38, no4, pp. 611-627. Cited at:
  6. Explanation: Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure, usually related to tectonic compression within orogenic belts. Source:
  7. Explanation: Carbon-14 Dating, C-14, ¹⁴ C or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues to date archaeological, geological and hydrogeological samples. Source: Put more simply, an explanation of Carbon-14 Dating is as follows: Carbon-14 (C-14) is a special type of carbon that scientists can use to assess how old things are. C-14 is a tiny little part of carbon that is found in things that were once alive, like plants and animals. When plants and animals are alive, they take in carbon from the air and food they eat, and this includes C-14. Over time, the C-14 in their bodies starts to break down and turn into other elements. Scientists use the amount of C-14 left in a sample to work out how long ago something died. This is called radiocarbon dating. By knowing how quickly C-14 breaks down, scientists can estimate how long it has been since an animal or plant was alive. This is scientifically useful for dating things like old bones or ancient artefacts that were made from organic materials.

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