Chaco Canyon and Pueblo Bonito: Ancestral Puebloan Centre

Chaco Canyon, in the dry San Juan Basin of northwestern New Mexico, was the centre of the Ancestral Puebloan world between about 850 and 1150. Its people built massive multi-storey “great houses”, the largest of which, Pueblo Bonito, held some 600–800 rooms, and linked the canyon to dozens of distant communities by straight engineered roads. Chaco is one of the most impressive achievements of pre-Columbian North America and a UNESCO World Heritage Site.

Background: the Ancestral Puebloans

The Ancestral Puebloans were farming peoples of the Four Corners region, where Arizona, New Mexico, Colorado and Utah meet today. They grew maize, beans and squash in a harsh environment with short growing seasons and unreliable rain. Over the first millennium AD they moved from pit-house villages to above-ground stone and adobe buildings, the “pueblos” that gave them their name.

Chaco Canyon itself is not an obvious place for a great centre. It is about 15 km long, lies at around 1,900 metres above sea level, has cold winters and receives only about 20–25 cm of rain a year. The Chaco Wash flows only occasionally. Yet from the ninth century onwards it became the focus of building on a scale not seen anywhere else in the region.

The older name “Anasazi” comes from a Navajo word often translated as “ancient ones” or “ancestors of enemies”. Many Pueblo people prefer “Ancestral Puebloans”, the term now generally used by archaeologists and the National Park Service.

The great houses

Construction of the first great houses began around 850–860, at Pueblo Bonito, Peñasco Blanco and Una Vida. These were planned buildings, much larger than ordinary villages, with hundreds of rooms built in a few major stages. Between about 1020 and 1130, often called the Chaco florescence, building accelerated and new great houses such as Chetro Ketl, Pueblo Alto, Pueblo del Arroyo, Hungo Pavi and Kin Kletso were raised or enlarged.

Great houses share a recognisable style. Their walls have rubble cores faced with finely shaped sandstone, laid in banded patterns that were usually hidden by plaster. Rooms are large and arranged in blocks around plazas containing round, partly underground ceremonial rooms called kivas. Great kivas, some more than 15 metres across, such as Casa Rinconada, served larger gatherings.

The amount of material involved was enormous. Archaeologists estimate that some 200,000 trees, mainly ponderosa pine, spruce and fir, were used as roof beams. Because no suitable forest grew near the canyon, many logs were carried on foot from mountains such as the Chuska Mountains and Mount Taylor, roughly 50–80 km away. Tree-ring dating of these beams gives Chaco one of the most precise building chronologies in the ancient world.

Pueblo Bonito

Pueblo Bonito, Spanish for “beautiful town”, is the largest and most studied great house. Built in stages from the mid-800s until the early 1100s, it grew into a D-shaped structure covering roughly 0.8–1.2 hectares (2–3 acres). Its curved back wall rose to four and in places perhaps five storeys, and it contained roughly 600–800 rooms and more than 30 kivas, including great kivas in its plaza.

Many rooms seem to have been used for storage rather than living, and estimates of the building’s permanent population are surprisingly low, sometimes only around 100 people. This has led some archaeologists to argue that Pueblo Bonito was above all a ceremonial and elite centre, perhaps the residence of leading families and a place for great seasonal gatherings.

Excavations uncovered rich burials and caches, especially in a group of rooms in the oldest part of the building. They contained thousands of turquoise beads and pendants, shell ornaments, carved wooden staffs and painted objects. A DNA study published in 2017 showed that individuals buried in one crypt, Room 33, belonged to a single maternal lineage over roughly 330 years, evidence for a hereditary elite.

Pueblo Bonito stood beneath a large, cracked block of cliff known as Threatening Rock. The Chacoans braced it with timbers and masonry, but it finally fell in 1941, destroying part of the back wall and about 30 rooms.

Roads, trade and the Chaco world

Chaco was the centre of a wider network. More than 150 “outlier” great houses built in Chacoan style have been identified across the San Juan Basin and beyond, some more than 100 km away. Many were connected to the canyon by roads, which are among Chaco’s most striking features.

The Chaco roads are often about 9 metres wide and run in nearly straight lines across the landscape, cutting stairways into cliffs instead of going around them. The best-known, the Great North Road, runs north from the canyon for about 50 km. Because they are so wide and straight in a society without wheeled vehicles or pack animals, many archaeologists think they had ceremonial or symbolic meaning as well as practical use.

Trade reached far beyond the Southwest. Turquoise from mines such as Cerrillos near Santa Fe was worked at Chaco. Pueblo Bonito yielded skeletons of scarlet macaws, birds native to tropical Mexico, and copper bells from West Mexico. In 2009 chemical analysis of pottery cylinder jars detected traces of cacao, which must have been brought from Mesoamerica, more than 2,000 km to the south.

Astronomy and ritual

Chacoans paid close attention to the sky. Several great houses and great kivas are aligned to cardinal directions or to solar and lunar events. The most famous example is the “Sun Dagger” on Fajada Butte, identified in 1977 by the artist Anna Sofaer, where slabs of rock channel daggers of sunlight across spiral petroglyphs at the solstices and equinoxes.

Some researchers have argued that buildings were also aligned to the 18.6-year cycle of the moon’s extreme rising points. A painted handprint, crescent and star near Peñasco Blanco has often been linked to the supernova of 1054, which created the Crab Nebula, though this interpretation cannot be proved. What is clear is that calendar-keeping and ceremony were central to Chaco’s role.

Decline and migration

Major construction at Chaco ended in the early to mid-1100s. Tree-ring records show a severe drought from about 1130 to 1180, which would have made farming in and around the canyon extremely difficult. The regional system centred on Chaco broke up, and influence moved north to new centres such as Aztec Ruins on the Animas River, built in Chacoan style from about 1110.

People did not vanish. Many moved to the Mesa Verde region and other areas, where building flourished in the 1200s at sites such as Mesa Verde’s Cliff Palace. A further crisis, the Great Drought of 1276, drove migrations south towards the Rio Grande, Zuni and Hopi areas, where modern Pueblo communities live today.

Rediscovery and protection

The ruins were described in 1849 by Lieutenant James H. Simpson of the US Army, who recorded several great houses during a military expedition against the Navajo, using names given by his Mexican and Pueblo guides. From 1896 to 1900 the Hyde Exploring Expedition, with the rancher Richard Wetherill and the archaeologist George Pepper, dug extensively in Pueblo Bonito and sent many objects to New York.

Concern about digging led President Theodore Roosevelt to proclaim Chaco Canyon National Monument in 1907 under the new Antiquities Act. Neil M. Judd excavated Pueblo Bonito for the National Geographic Society from 1921 to 1927. In 1980 the area became Chaco Culture National Historical Park, and in 1987 it was inscribed on the UNESCO World Heritage List together with Aztec Ruins and other Chacoan sites. In 2013 it was designated an International Dark Sky Park.

Timeline

• c. 850–860: Construction begins at Pueblo Bonito, Peñasco Blanco and Una Vida.
• c. 1020–1130: Peak of building; Chaco becomes the hub of a regional network of great houses and roads.
• c. 1110: Chacoan-style construction begins at Aztec Ruins to the north.
• c. 1130–1180: Severe drought; major building at Chaco ends.
• 1849: Lieutenant James H. Simpson describes and names several great houses.
• 1896–1900: The Hyde Exploring Expedition excavates Pueblo Bonito.
• 1907: Chaco Canyon National Monument is proclaimed.
• 1921–1927: Neil M. Judd excavates Pueblo Bonito for the National Geographic Society.
• 1941: Threatening Rock falls and destroys part of Pueblo Bonito.
• 1987: Chaco Culture is inscribed as a UNESCO World Heritage Site.

By the numbers

Myths and facts

Chaco is sometimes described as a “lost civilisation” whose people mysteriously disappeared. In fact archaeology and Pueblo oral tradition agree that the Chacoans’ descendants migrated and became the Pueblo peoples of Arizona and New Mexico, who continue to regard Chaco as a sacred ancestral place.

Another popular idea is that Chaco was a dense city of many thousands. Estimates for the canyon’s population range from around 2,000 people to more than 5,000, and some archaeologists argue for far fewer permanent residents with much larger numbers arriving for ceremonies. The question remains one of the central debates in Southwestern archaeology. Comparison with the contemporary Mississippian city of Cahokia shows how differently large centres could develop in North America.

Why it matters

Chaco Canyon shows that farming communities in one of North America’s harshest landscapes could organise labour, astronomy, trade and ritual on a regional scale. Its great houses, roads and alignments remain among the most remarkable monuments of the pre-Columbian Americas, and it continues to be a living heritage for the Pueblo peoples who descend from its builders.