A surprising find on a ranch in southeastern Arizona has some archaeologists re-thinking a vital period of history in this corner of the Southwest.

In the desert upland just a few miles from both Mexico and New Mexico, researchers have uncovered a 3,000-year-old bison kill site, featuring hundreds of bones and bone fragments, along with dozens of cobblestones and flaked and ground stone tools.

Adding to the surprise is the fact that this location, known as Cave Creek Midden, near the town of Portal, is already well-known to archaeologists.

When it was first investigated in 1936, the site revealed stone tools and other artifacts that came to typify a critical phase in Southwestern history: the period from about 4000 and 500 BCE, when humans first started to re-settle the desert Southwest and develop methods for farming corn.

The discovery of a large bison kill here adds a whole new chapter to the story of the site, and a new understanding of the hunter-gatherers who lived here.

“We found a bunch of bison where we hoped to find corn,” said Dr. Jesse Ballenger, of the University of Arizona, who co-led the new study with Dr. Jonathan Mabry.

“The presence of bison at the Cave Creek Midden site opens interesting avenues of research,” added Francois Lanoe, an Arizona doctoral student who also took part in the study.

“If bison were a major component of people’s diet, well, it is unexpected in that region of the Southwest.

“If they were not, it is equally interesting: Why would people bypass such a highly-ranked resource?”

Very little has been found — and therefore little is known — from this phase of Southwestern history, known as the Middle Archaic or Chiricahua stage of the Cochise tradition, which is thought to be ancestral to the Mogollon culture.

So, Ballenger and his colleagues sought to re-investigate Cave Creek Midden and search for new clues about the region’s earliest corn farmers. [Read about an amazing maize discovery: “First Evidence of Corn Beer in Southwest Discovered“]

“[This site] is a huge deal, because it defined about 40 years of how people conceptualized that vague moment in prehistory,” noted Ballenger, who is also president of the Arizona Archaeological and Historical Society, which sponsored the research.

When the team began investigating Cave Creek Midden in the fall of 2014, they uncovered something that previous excavations had either missed or dismissed: a deep layer of dark soil about 45 centimeters (18 inches) thick, rich with cobbles, bison bones, and a few stone artifacts.

The dark soil marked the boundaries of what had been a spring-fed wetland, known regionally as a cienega.

The researchers were able to date this layer thanks to a small pit they found within it, containing ground stone tools, a bison bone that had been broken radially — as if with a hammerstone — and a bit of charcoal, which was radiocarbon dated to about 1,300 BCE.

“They may go a bit older,” Ballenger said of the bison bones, “but we don’t know.”

Some aspects of this artifact assemblage may be easier to understand than others, he said.

The cobbles, for example, may have been used for bludgeoning animals or breaking bones, or perhaps just as stepping stones across the marsh.

Shaped hand tools, called manos, were also present in large numbers.

But in addition to what they found, the researchers also took note of what seemed to be absent — namely, the butchering and cooking tools that are usually associated with bison kills.

“Those places are typically filled with the tools needed to kill and dismember the animals, such as projectile points, choppers, knives, pounders,” Ballenger said.

“It’s a fairly predictable assemblage.

“But once that meat, bone, and hide makes its way to the processing area, where boiling vessels would be handy, then ceramics are expected.”

And yet, all of these artifacts are either missing from the site, or are in short supply.

At the same time, an analysis of the bison bones themselves suggests that the animals were killed at the site.

“When we examine what skeletal parts are present at the Cave Creek Midden site, it’s clear that basically whole animals are present,” said Meredith Wismer, a doctoral candidate at the University of Iowa who took part in the study.

If the bison had been killed elsewhere and brought to Cave Creek Midden to be butchered, she said, only the processed parts of the animals would be found there.

“Since bison are such large animals, we expect that hunters would be selective in what carcass parts they would bring to a processing site, taking the most nutritionally valuable portions, for instance,” she said.

But even then, evidence that the animals were butchered at all has been, so far, hard to come by.

Out of the 83 bison-bones that contained marrow — a precious, calorie-rich resource usually extracted by hunters — only two were found to have been broken open, Wismer said.

“And any butchery marks that may be present on the bones are obscured due to the poor preservation of the bone surface,” she added.

So, Wismer speculated, it could be that at least some of the bison found in the ancient bone bed weren’t killed by hunters, but instead simply got stuck in the muck.

“This may have been an area on the landscape that bison frequented, and it is possible that at sometimes in the site’s history they were hunted and used by people, but at other times bison may have gotten trapped in the cienega, died of natural causes, and were not used by people,” she said.

Nonetheless, the fact that bison have been found here at all is an enlightening surprise, Wismer said. [Learn about bison hunting on the ancient Plains: “11,500-Year-Old Bison Butchering Site Discovered in Oklahoma“]

“Most sites in this region only have a handful of specimens of bison, and our site has over 200 specimens, coming from a minimum of 6 individuals,” she said.

“The presence of bison — that were clearly not traded in from other areas — can tell us about the environmental context of the local landscape.”

The researchers will continue to untangle the rather confusing clues they’ve uncovered at Cave Creek Midden.

But for now, Ballenger said, it’s clear that the history of the area is even richer and deeper than the historic excavations of the 1930s would suggest.

With the new data from Cave Creek, the picture of ancient life in these southern reaches of the Southwest may come into clearer focus. [See a recent discovery made nearby: “Oldest Human Footprints in the Southwest Discovered at Tucson Construction Site“]

“This re-investigation of a site that played a pivotal role in the development of concepts of the Archaic period in the Southwest borderlands is providing unexpected new information that is expanding our understanding of Middle Archaic adaptations,” said Mabry.

Ballenger agreed, adding, “We collected a lot of good information about the hydrology, vegetation, ecology, and archaeology of the Chiricahua Stage type site.

“As for what happened there, that’s a … story that we are trying to piece together.”

The team reported its findings this week at the 39th Annual Conference of the Society for Ethnobiology in Tucson, Arizona.