THE NEIGHBORHOOD BONEBED

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In order to protect the fragile bones from the elements, the small site is covered in Quonset hut-like fashion by a durable plastic material. Bison bones were discovered during construction of a housing development near Denver. Little did the construction workers know they had stumbled upon the single largest Late Archaic bonebed in North America. Working in the shadow of new homes, excavators are learning the story of the people and animals that lived here nearly 3,000 years ago.

By Catherine Dold Photography by Willie Gibson

Not many archaeological excavations come complete with a brand new sidewalk, curbside mailbox, and a few swing sets nearby. But then, most excavations are not located smack in the middle of a large new housing development.

Some 60 miles north of Denver, out among the rapidly disappearing farms and rangelands that surround the tiny prairie town of Windsor, Colorado, the Kaplan-Hoover Bison Bonebed site perches on a hillside. Just a few feet to the east sits a new house. Directly west is another new house, along with piles of construction materials. Eventually, yet another home may sit on the Kaplan-Hoover lot, but for the moment only a large white tent adorns the hillside.

Inside the tent, a small propane heater wards off the chill of an approaching snowstorm, and 10 students from nearby Colorado State University (CSU) lie sprawled across planks of wood, suspended above a hole in the ground. Covered in dust and dirt, bamboo digging tools at hand, each student carefully reaches into the hole and slowly extricates one bone at a time from what appears to be a bottomless cauldron. They use bamboo tools rather than metal because the former do far less damage to the fragile bones. Plainly visible below them is a dense jumble of body parts—several complete skulls, snaking spines, dozens of legs and ribs, and more. Most are bison remains; a few are from wolves or other carnivores.

The bones, explains Larry Todd, an archaeologist at CSU and director of the excavation, are the leftovers of a single bloody event that took place late one summer some 2,700 years ago: a bison kill, in which human hunters trapped scores of animals in a small gulch or arroyo, killed them, butchered them for food, and left the carcasses behind to rot. Scavengers, decay, and hundreds of years of water flowing to the Cache la Poudre River below reassembled the bones into the tightly packed jumble seen today, the bonebed.

Bison kill sites are fairly common on the plains, Todd says. But most kills involved no more than 30 animals. When he first started exploring this site, he says, “I thought

This bison skull is one of more than 120 that have been recorded. The archaeologists can see that there are many more skulls in the bonebed.

Though this hammer stone (left) was not found at the site, it’s believed to be the type of tool used by hunters to break the bones, from which they occasionally extracted marrow. This is one of the few bones recovered from the site that contained marrow. I’d go out on a limb and say there might be 50 animals here. We soon found out how wildly wrong we were.”

Standing at the edge of the pit, watching his students work, Todd says, “At a bare minimum there are 250, maybe 300 animals here. That makes this the single largest bonebed in North America for the time period.” To date, thousands of bones have been extricated from the 55-square-foot pit, including more than 120 complete skulls, and the bottom is nowhere in sight. The sheer number of animals makes the site significant. But it is also expected to reveal substantial information about the lives of the people and the animals who lived on the Colorado prairie in the Late Archaic period.

The entire site was nearly lost forever. The bonebed had settled to at least 18 feet below the surface when, in 1997, construction workers began grading the land for roads and homes. Carving out a hillside with heavy equipment, they nicked the top of the bonebed. The workers saw the bones, but they continued to develop the site. Later, a volunteer with the Denver Museum of Nature & Science happened to stumble upon the site. Word traveled, and soon Todd went looking for the bonebed along with a student. They didn’t have much luck at first. “We spent the day driving from one new housing development to another, and we couldn’t find it,” laughs Todd, waving a hand at the sea of new homes that can be seen from the hillside.

During a second search they found the site and knew immediately it was worth exploring. “We walked up the hill and saw bison bones. One of the first ones we picked up had cut marks on it. That was pretty good evidence that they’d been butchered by humans, rather than getting trapped in a blizzard or something.”

Todd tracked down the property owner, Lester Kaplan, and got permission for an initial excavation. “We were lucky that the construction plans didn’t call for the grade to go deeper, because I’m sure they would have just dug it all out,” says Todd. “We were also lucky that Kaplan was willing to let us work here. He could have just sold the bones at a flea market.” Later, when it became clear that the bonebed was larger and more important than originally suspected, Kaplan agreed to let the researchers use the site until 2004. It was named in recognition of Kaplan and Gary Hoover, the owner of the construction company.

Since the excavation began an entire community, River West, has been built around it. Construction crews have paved miles of roads, installing nearby Meander Road and Pioneer Place, houses ranging from modest duplexes to “prairie palaces” have sprung up on the hillsides, and scores of new residents have arrived. And just a few feet from the edge of the new suburban landscaping, students in the tent have pulled more than 10,000 bones and artifacts from the ground.

The work is slow going. Erin Baker, an undergraduate student, says she has removed and catalogued just two bones so far this morning. Now working on a wolf scapula, she hangs over the pit and uses a small brush and a pointed bamboo stick to carefully clear away dirt that is encasing the bone. Once she works it free, she’ll wrap it in tinfoil, label it, and send it to a laboratory at CSU. Already she has recorded 29 different data points on the scapula—its location, position, length, width, whether or not it was articulated, and more. Some of the bones are in good shape and are easily ex-

tricated in one piece. Some are broken into many pieces. Some, says Todd, are like “excavating oatmeal.”

Not all of the bones will be taken out of the ground. This year, the researchers plan to excavate a three-footwide cross section of the bonebed to get an idea of how deep it is and how it is shaped below the surface. Whatever bones remain after this season will stay there. The site might then be preserved with a homeowner’s covenant. Or it might just disappear under more suburban landscaping. “We thought about trying to buy the lot, but it was too expensive,” says Todd. Kaplan is donating the excavated bones to the university, but there are no funds to secure the site for future research.

As with Baker’s bones, every single one of the thousands of items excavated to date has generated 29 points of data. Todd estimates that he and his students could spend the next 10 years analyzing it all. He has already spent considerable time analyzing the initial findings—the first 4,000 bison bones extracted—and has developed some theories about just what happened here.

“The arroyo ran north-south and made a steep-sided natural corral 12 to 15 feet deep,” he explains. The bison were likely grazing near the river, to the north, and were quietly herded into the trap. “You put a couple of people at the edge of the herd and the animals will slowly graze away from them, into the arroyo. You don’t want to start a stampede.” Once the animals were contained, perhaps by a wooden gate at the end of the arroyo, he says, the hunters probably stood above them and killed them with spears topped with stone projectile points. “It was like shooting fish in a barrel.”

Radiocarbon dating of bone and charcoal found in the bonebed— likely from hearths built along the top of the arroyo—shows that the kill happened about 2,700 years ago. Analysis of teeth found there indicate it took place in late summer-early fall, and that it was a single event. Most bison calves are born during a twoweek period in late spring, Todd explains. Looking at the teeth of the youngest animals found—which molars have erupted, how worn the teeth are—reveals the age of the calves which in turn tells him that the kill occurred five months after the calving period, or late summer. The fact that all the young animals were the same age tells him that they were slaughtered at the same time.

“It looks like this was a fairly large kill to get meat for winter storage,” says Todd. “There might have been 150 people working on this site. They would have had to process the animals quickly because the meat would start to go bad. Plus, it would attract grizzlies and wolves, making it a dangerous place.”

Looking at cut marks on the bones—nicks left behind by butchering tools—gives him a good idea of how the hunters processed the animals. “They probably started by stripping off the big meat masses to dry and store,” Todd says. “They probably went for the hump first, because there are 40 to 50 pounds of meat there.” Indeed, 40 percent of the higher vertebrae examined have cut marks, while few lower vertebrae show signs of butchering. A high number of cut marks on jaw bones indicates the hunters also removed many tongues.

Not all parts of the animals were processed, however.

Having slaughtered the bison, the Yonkee then performed the difficult work of removing the meat from the bones and preparing it for storage.

Larry Todd addresses students who are reconstructing bison bones in a laboratory. The lab work is painstaking, and Todd estimates it could take another five years to process all of the recovered bones. A replica of a six-month-old bison skeleton commands the students' attention. Todd has noted a resemblance between part of the bison’s thoracic vertebrae and the ears of a mouse. This prompted a student to crown the skeleton with Mickey Mouse ears.

The hunters apparently paid little attention to the brains or bone marrow. And in contrast to what has been seen at other kill sites, they left behind large amounts of usable meat.

Not surprisingly, the site was very popular with carnivores. Nearly 99 percent of the bison front leg bones examined show damage by other animals. According to the researchers, this degree of carnivore modification is far higher than at any other plains kill site.

More definitive answers to what the people did at the Kaplan-Hoover site, and how that reflects their social and environmental interactions, will come only after processing all of the more than 10,000 bones and artifacts extracted and several years of studying the data.

“The real excitement of archaeological discovery these days usually takes place late at night in front of the computer screen, when the data starts coalescing in a way that the patterns start to make sense, when the cut marks and skull frequencies and animal ages and the tools used all start to bring out some coherent picture,” says Todd. “The fieldwork is only the beginning.”

At the CSU laboratory, graduate student Paul Burnett demonstrates how the bones are processed. Each one is cleaned with a toothbrush and water, then left to dry. Broken bones are painstakingly glued back together. All are labeled with a felt tip marker, sorted by type, and filed away in clear plastic boxes. Already, some 80 boxes are stacked floor to ceiling in the lab, full of femurs, vertebrae, and other bones. Intact skulls line the shelves. Dozens more foil-wrapped bones are piled in a corner, fresh from the field and awaiting their turn at the sink. The most fractured bones, the ones that the researchers haven’t been able to reassemble, lie on the counter.

Each bison bone is eventually scrutinized under magnification, says Burnett. “We look for cut marks from tools, breakage, tooth marks from carnivores, pathologies such as arthritis. We need to sort out the human and nonhuman patterns of modification.” They will also carefully examine all of the non-bison bones found on the site, the stone projectile points, and the thousands of sharpening flakes they have found—the tiny shards of stone that break off from points when they are sharpened.

One of the most intriguing issues that Todd would like to explore, once all the data is assembled, is why two distinct types of projectile points were found at the site. Some of the points appear to be linked to the Yonkee culture, which is more commonly found further north, in Wyoming and Montana. They show a characteristic Yonkee style and are made of a type of stone found in Wyoming. Their presence at the site seems to indicate that the Yonkee people were traveling further south than was previously known. Other points show a different style and were quarried from a stone source much closer by.

Finding both styles at one kill site raises some interesting questions, says Todd. First, if two separate cultural groups were at the site, how did they interact? “It could be that the Yonkees came down and made the kill and were butchering the animals in another group’s territory and the other people came over and chased them away,” he says. “Or, we could be seeing communal hunting between the Yonkees and the other group. So it could have been regional conflict or regional cooperation.” Analyzing the thousands of flakes of each style found at the site, seeing how many there are of each, will give them a rough measure of how many people of each group were at the site and may help them to figure out what was going on.

Second, what might have prompted the Yonkees to travel to a new area? Data on climatic conditions, garnered from tooth analysis, might help answer that question. As teeth grow they lock in clues about temperature and rainfall, in the form of specific ratios of oxygen and carbon isotopes. Todd plans to chemically analyze the teeth of animals from several age groups, which will allow him to reconstruct the conditions for several years before the kill. “We can figure out the monthly temperatures for about 15 years before the kill,” he says. That will help him to evaluate two possible environmental triggers for their travel. Were the Yonkee people coming further south because environmental conditions were bad and bison were getting harder to hunt? Or was it for the opposite reason: a period of increased rainfall resulted in more grass and bison, and the Yonkee traveled there in pursuit of the expanded herds?

The researchers also hope to learn more about the hunting and butchering strategies of the people and what that says about the animal populations. These hunters were not known to store large amounts of food. So why did they kill so many bison—clearly more than they could use—at this site? If it was a small, local population of animals it would not have made sense to kill them all at once. Could it be that the bison were part of a large migratory herd that presented a one-time bountiful hunting opportunity, and the extra meat left behind in the arroyo was seen as a bit of winter insurance? On the other hand, bison are smart. “Maybe the hunters knew that if any survivors got away they wouldn’t be able to pull the same trick on them next year, so they got as many as possible this year,” speculates Todd. DNA analysis might help to answer those questions, by showing whether the animals were from a small, genetically homogenous population, or from a larger, more diverse group.

A Native American visitor to the site has suggested another scenario for the seeming wastefulness: Perhaps the humans killed extra bison to help out their other “relatives,” the coyotes, wolves, and bears. Some of the other animals found at the site, in fact, might not have been scavengers; the wolf bones found could be from wolf-dog hybrids that were used as pack animals. Those bones will be examined for signs of arthritis that could indicate they were carrying heavy loads.

All of these possible relationships between the humans and the animals intrigue Todd. “I try to get people to think of humans as part of the ecosystem, rather than separate from it,” he says. Clearly, the scavengers that fed at the site had diets that were closely related to human behavior. “Prehistoric wolves probably relied on these leftovers. There would have been hundreds of thousands of pounds of meat left here.

“The implications of that are if you want to talk about modern wolf or bear management, somewhere you need to take into account that these animals adapted in large part to interacting with humans. The notion that a wolf is a wild animal out there not interacting with people, and that is how we have to preserve it today, is not the truth. They’ve been interacting with people for years.”

Human interaction played a role in the evolution of bison, too. “For the last 10,000 years, bison have been getting smaller and more agile,” says Todd. “The evolutionary force that could create that is predator avoidance. We tend to think of bison as this romantic image of wild North America, but those living today are the way they are in part because of interactions with humans.” DNA analysis of the Kaplan-Hoover bison may help to further clarify this relationship by yielding information about herd sizes and their movements, two consequences of being hunted.

The Kaplan-Hoover excavation concluded in April. The bones that were extracted will remain at the university. Todd hopes the bones left in the ground will remain undisturbed, right in the middle of River West, near the swing sets.

CATHERINE DOLD lives in Boulder, Colorado. Her work has appeared in Discover, Smithsonian, and the New York Times.