Excavation (archaeology)

Chaco Canyon’s ancient civilization continues to puzzle

Pueblo del Arroyo
Recent research suggests that the ancient Chaco society of the U.S. Southwest was founded by locals and run by a female lineage for hundreds of years. The best-known Chaco structures are great houses, massive, multilevel buildings represented here by the remains of Pueblo del Arroyo.


Chaco Canyon is a land of extremes. Summer heat scorches the desert canyon, which is sandwiched between sandstone cliffs nearly two kilometers above sea level in New Mexico’s northwestern corner. Bitter cold sweeps in for winter. Temperatures can swing as many as 28 degrees Celsius during the course of a day. Through it all, Chaco Canyon maintains a desolate beauty and a craggy pride as home to one of ancient America’s most enigmatic civilizations.

Scientists have struggled to understand Chaco society since its first excavations in the late 1800s. Who first settled Chaco Canyon around 1,200 years ago is still a mystery. Many researchers suspect that it took a few hundred years for a fledgling city-state run by an elite social class to emerge. Political and cultural ties between the ancient society and Chaco-style communities outside the canyon also perplex. Then there’s the puzzle of how people survived from about 800 to around 1300 on the rough, parched terrain.

A new generation of Chaco studies and discoveries is under way, partly thanks to a young researcher’s skeleton reassembly project. This jigsaw job required a lot of travel, but not to Chaco Canyon.

That’s because bones of people excavated at Chaco in the 1890s and 1920s were packed away in boxes and drawers at museums in New York City, Chicago and Washington, D.C. Kerriann Marden visited all of these places to retrieve far-flung body parts from one site in particular — Pueblo Bonito, the oldest and largest of a dozen huge stone great houses in Chaco Canyon. The structure was built, along with a range of smaller structures, between about 800 and 1130.

Finds in a burial at the first and largest great house in Chaco Canyon, Pueblo Bonito, include turquoise jewelry and shell items placed alongside a presumably influential man interred between 800 and 850.

Pueblo Bonito was massive, rising at least five stories with around 650 rooms. It has yielded more human bones and artifacts than any other Chaco site. Research has focused on this great house presumably reserved for Chaco’s elite families; the lives of workaday folk have been largely unexplored, even in the latest studies.

During Chaco society’s heyday, other civilizations peaked elsewhere in the Americas, including the Maya in Central America. Just as present-day Maya groups trace their ancestry back to that ancient civilization, today’s Pueblo tribes, such as the Hopi and Zuni, consider Chaco people to have been their forebears. Navajo Nation also claims an ancestral tie to Chaco society.

Reassembly required

Archaeological excavations a century or more ago — at Pueblo Bonito and elsewhere — didn’t follow today’s rigorous standards for excavating and preserving remains. The work consisted of little more than mining for bones and artifacts, then carting the discoveries off to museums. As an anthropology graduate student at Tulane University in New Orleans, Marden journeyed back and forth between New York’s American Museum of Natural History, Chicago’s Field Museum and Washington’s Smithsonian National Museum of Natural History from 2005 to 2011. She painstakingly reunited long-dead Chaco individuals’ skulls with arms, legs with feet and so on. Marden is now a forensic anthropologist at Eastern New Mexico University in Portales.

As skeletons assumed their former shapes, a couple of peculiar things stood out. First, many individuals bore signs of disease, including tuberculosis and syphilis. That seemed peculiar for people who were buried in a great house typically thought to have been reserved primarily for society’s upper crust, not for the ill. Second, bodies had been manipulated in unusual ways and for unknown reasons. Comparisons of restored skeletons with field notes and photographs from original excavations indicated, for instance, that one woman was originally found with a fetus’s fragile remains in her pelvic cavity and her own bones below the knees missing. Her body lay across a room from several intact bodies.

“Nothing is simple at Pueblo Bonito,” Marden says. Her campaign to put Pueblo Bonito skeletons back together has enabled a couple of provocative new investigations. One concludes that members of a single maternal line wielded power in Chaco society from the start through an unexpected stretch of at least 330 years and perhaps 10 generations. Another study proposes that Chaco society’s founders were not outsiders with experience constructing huge buildings, as many researchers have assumed. People living in and near Chaco Canyon may have established a cliff-bordered society all on their own.

Other new findings suggest that Chaco residents contacted and traded with people living as far as 2,500 kilometers to the south in Central America and as close as 75 kilometers to the west and south. It’s debatable, though, whether Chaco Canyon’s 2,000 to 3,000 residents could raise enough crops to feed themselves or whether they had to trade for staples such as maize.

Less contentious — but far weirder — is evidence from graves and artwork that Chaco people revered community members with six toes and often created images of human feet and footprints with and without extra digits.

DNA dynasty

Fittingly, Chaco society’s archaeological footprint covers what was once an extensive regional system of buildings and roads. The largest great houses were clustered in a 2-kilometer-diameter downtown zone at the center of Chaco Canyon. Smaller great houses, ritual structures called kivas, groups of small family houses and other urban features, connected by a network of straight dirt roads, fanned out from the canyon across an area the size of Ireland.

After Chaco society dissolved around 1300, Pueblo groups may have rejected its centralized political system and social classes, says archaeologist Stephen Lekson of the University of Colorado Boulder. Pueblo people today live in small communities oriented around clans based on maternal lines of descent.

Therein lies a connection between past and present, says archaeologist Stephen Plog of the University of Virginia in Charlottesville. Many individuals buried in one of Pueblo Bonito’s oldest rooms, known to researchers as Room 33, shared maternal ancestry (SN Online: 2/21/17). Plog and colleagues — led by Penn State archaeologist Douglas Kennett — extracted mitochondrial DNA, which is typically passed from mother to child, from skeletons of nine of 14 individuals interred in Room 33. Marden’s reassembly project was crucial to identifying individuals whose DNA was analyzed.

Members of this Pueblo Bonito group, the researchers reported February 21 in Nature Communications, inherited mitochondrial DNA that was similar enough to signal shared kinship with a female line. Nuclear DNA recovered from six Room 33 skeletons identified two as mother and daughter and two others as a grandmother and grandson. Children inherit nuclear DNA from both parents.

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Pueblo Bonito
A years-long skeletal reassembly project has spurred new research into who was buried at a massive great house called Pueblo Bonito (remnant walls and foundation shown).

Room 33 is a crypt with a complex history. Two men were buried beneath the chamber’s wooden floor, one below the other. The lowermost body had a gash in the head. Plog suspects the man was bashed on the noggin during a fight. Marden thinks it’s more likely that someone with a shovel, perhaps a looter, broke the skull after the man had been buried.

Thousands of offerings, including turquoise and shell beads and pendants, were heaped around the two bodies under Room 33’s floor, with the lion’s share surrounding the bottommost man. Chaco people laid a wooden plank floor over the two men’s graves before additional bodies were buried in the chamber.

Radiocarbon dating conducted by Plog’s group gives a rough timeline for Room 33’s burials. The first two men were placed there as early as 800. Construction of the wooden floor occurred by about 900. Additional burials took place intermittently up to 1130, the new dating indicates. Activity in Room 33 occurred as civilizations flourished throughout the Americas, from what’s now the U.S. Midwest to Central and South America.

Plog regards the extravagantly buried man at the base of Room 33 as an early leader from a prominent Chaco family dynasty. Based on the exceptional treatment given to all deceased individuals placed…

Sticking Around: The La Brea Tar Pits

The following article is from the book Uncle John’s Bathroom Reader Plunges into California.

(Image credit: Jerrye & Roy Klotz, MD)

How much do you know about the Angelenos of the Pleistocene? Yeah, us either. Read on.


Hancock Park, an affluent area of Los Angeles, is well known for its celebrity sightings, million-dollar homes, and the famous Hollywood sign in the distance. But some of the neighborhood’s “residents” are even cooler. World-famous fossils—like the extinct dire wolf, saber-toothed tiger, and Columbia mammoth—are among the millions of specimens that have been excavated from the La Brea tar pits. Located on Wilshire Boulevard in the Miracle Mile, the tar pits contain one of the richest deposits of late Pleistocene era (the last ice age) fossils in North America. The fossils date from 10,000 to 40,000 years ago, and more than three million of them—including plants, mammals, birds, lizards, and insects—have been excavated since paleontologists first began digging there in the early 1900s.

The tar pits on display today were once excavation sites where workers dug for asphalt or scientists dug for fossils. Over the years, humans dug more than 100 pits throughout Hancock Park, but most of them have been refilled with dirt, debris, asphalt, and water. About 13 tar pits remain—the largest, called the Lake Pit, measures 28 square feet and is approximately 14 feet deep.


The La Brea tar pits formed thousands of years ago, when gas and oil beneath the ground came under pressure. The molten mixture pushed up through vents in the earth’s crust. Once it reached the surface, the oil pooled in natural depressions aboveground. The lighter part of the pooling oil evaporated—left behind was a heavy, sticky oil. Then rain and underground springs added water, forming ponds and lakes on top of the oil and creating what we now call the tar pits.

The water on the tar pits’ surface was especially attractive to thirsty animals, and during the warm spring and summer, the thick oil underneath was especially sticky. Animals that ventured into to the pits couldn’t escape. Often predators chased their prey into the pits and got stuck too. Paleontologists once found a large bison fossil surrounded by a pack of fossilized wolves. The dead animals eventually sank completely, and their bones and teeth turned brown from the oil. But otherwise, they were almost perfectly preserved for more than 30,000 years.


Hundreds of years ago, local Native Americans used the thick oil at the tar pits as waterproof caulking for their baskets and canoes. When the Spanish arrived in the 18th century, they used it to waterproof their houses. In 1828 the tar pits were part of a Mexican land grant called Rancho de la Brea (brea means “tar” in Spanish). When the United States took over California in 1848, the area was part of the deal, and ultimately, it came into the possession of lawyer and surveyor Henry Hancock…