Calico Early Man Site facts for kids

The Calico Early Man Site is an important archaeological spot in the Mojave Desert of southern California. It's near Barstow in San Bernardino County. This area was once home to an ancient lake from the Ice Age (Pleistocene epoch). Scientists study the old rock layers here to learn about early human activity.

At the Calico Early Man Site, researchers have found:

• Stone tools from the Lake Manix area. These tools were found near the surface at an elevation of over 543 meters. This was the shoreline of a large freshwater lake (about 236 square kilometers) that dried up around 18,000 years ago.
• Objects found deep within older soil layers. One "rock ring" was dated to about 135,000 years old using a method called thermoluminescence. Other tests suggest it could be even older, around 200,000 years.
• A large stone tool called the Rock Wren Biface. This tool was found in a younger layer and is about 14,400 years old. Scientists are still digging in this area and finding more tools.

The tools and flakes found at Calico were likely made by early modern humans (Homo sapiens sapiens).

Discovering the Calico Early Man Site

This archaeological site is also known as "The Calico Mountains Archaeological Site" or "The Calico Hills Archaeological Site." It's located in the central part of California's Mojave Desert. Here, stone tools, unfinished tools, and rock flakes are found in old rock layers and younger river terraces. These tools are mostly made from a type of rock called chalcedony.

The Manix Basin: A Window to the Past

The Manix Basin is a large valley in the central Mojave Desert. It's the lowest part of the Mojave River system. This river starts in the San Bernardino Mountains, about 200 kilometers away.

About 400,000 to 500,000 years ago, a freshwater lake formed in this basin near the Calico site. This lake, called Lake Manix, existed until the late Ice Age. Its highest level was at 543 meters, covering about 236 square kilometers. The lake likely drained very quickly around 18,100 years ago. This might have happened because of a big increase in river water or movement along the Manix fault.

The Manix Basin is special because it has many layers of ancient soil and rock. These layers have been exposed by natural processes like mountain building, climate changes, and erosion. This makes it easier for archaeologists to study the area's history, which goes back more than 350,000 years.

Ancient Animal Fossils Found Here

The old lake and river sediments at Calico contain fossils of many Ice Age animals. These fossils range in age from about 20,000 years to over 350,000 years old.

Some of the animals found include:

• Camels
• Horses
• Mammoths
• Saber-tooth cats
• Dire wolves
• Short-faced bears
• Coyotes
• Various birds like flamingos, pelicans, eagles, swans, geese, ducks, and storks.

Are They Tools or Natural Rocks?

Thousands of rocks that look like prehistoric tools have been found at the Calico site. Some were on the surface, and others were up to 8 meters deep. One stone from a main excavation pit was thought to be over 200,000 years old. However, this date might have been affected by other materials in the soil. Scientists are now trying to date confirmed tools using a method called thermoluminescence. Early results suggest they could be 20,000 to 30,000 years old.

The main discussion among scientists is whether these "tools" were actually made by humans (called artifacts) or if they were shaped by natural processes (called geofacts). Most scientists agree that the objects found deep underground are likely geofacts.

The Debate: Artifacts or Geofacts?

Some scientists have questioned if the rocks found at Calico are truly human-made tools. They suggest that natural events could have broken the rocks in ways that make them look like tools. For example, rocks could have fractured due to:

• Earth movements (tectonic stresses)
• Weathering
• Rocks hitting each other in streams or mudflows
• Pressure on buried rocks
• Repeated cycles of erosion and redeposition

Archaeologists are still studying the rocks collected from the Calico site. Many have been confirmed as geofacts, but some are believed to be possible artifacts. These potential artifacts have been carefully recorded and sent for dating. As of March 2020, work is ongoing to publish the newest findings. These will be shared with local tribes, the community, and other scientists for review.

Studying Flake Angles

One way scientists try to tell if a rock is a tool or a geofact is by looking at the angles of its "flake scars." These are the marks left when a piece of rock breaks off. In 1939, a researcher named Barnes found that natural breaks often have more wide (obtuse) angles than human-made tools. He suggested that if more than 25% of the angles on a flaked tool are wide, it's probably not human-made.

A scientist named Payen studied the Calico specimens using this method. He found that the angles on the Calico rocks were very similar to those found on naturally broken rocks. This suggested that they might not be tools. Other researchers also examined the Calico objects and concluded they were naturally flaked rocks that just happened to have tool-like shapes.

What Most Scientists Think Now

While there have been arguments supporting the idea that the Calico objects are artifacts, the current general agreement among scientists is that there is no clear proof of human activity at the Calico Early Man site.

This agreement is based on several reasons:

• Lack of other evidence: There are no other signs of human activity, like human or animal bones, or other non-tool objects.
• Very old dates: The site suggests very ancient human presence. However, the next oldest accepted date for human tools in the Americas is around 30,000 years ago, and even that date is debated.
• Huge number of "tools": Up to 60,000 possible tools have been found. This large number makes it more likely that many are natural formations.
• Natural explanations: Research has provided good explanations for how these stone objects could have formed naturally.

History of the Excavations

The visitor center at the Calico Early Man Site, June 2010

The story of the Calico site began in 1959. Louis Leakey, a famous archaeologist, met Ruth DeEtte Simpson, an archaeologist from California. Simpson showed Leakey some rocks from the Calico Hills that looked like ancient scraping tools.

Leakey believed it was important to study the Calico site. He thought that the many different native languages in the Americas would have needed much more than 12,000 years to develop. In 1963, Leakey received money from the National Geographic Society and started digging with Simpson.

Leakey and Simpson believed they had found stone tools that were 100,000 years old or even older. This would mean humans were in North America much earlier than previously thought. Another archaeologist, Jeffrey Goodman, who worked with Leakey, also claimed the stones were human-made. Goodman even suggested they could be 500,000 years old, which would mean human origins were in the Americas. However, most scientists have rejected these very old claims.

A geologist named Vance Haynes visited the site in 1973. He concluded that Leakey's "artifacts" were actually naturally formed geofacts. Haynes believed the geofacts were created when stones broke apart in an ancient river at the site.

Louis Leakey's wife, Mary Leakey, who was also a famous archaeologist, later wrote that she lost respect for him because of his involvement with the Calico Hills site. She felt it hurt his career. Louis Leakey continued to visit the site until he passed away in 1972. After his death, the site was managed by California's Bureau of Land Management and opened to the public.

See also

In Spanish: Calico (sitio arqueológico) para niños