The pinkish-tan cliff soars 80 feet above Una Vida, the ruins of a 150-room multistory stone pueblo built when Europe was in the Middle Ages.

Una Vida is what archaeologists call a great house, a large planned public building with distinctive masonry and a great kiva, a chamber used for religious ceremonies. It lies in Chaco Canyon, the heart of an elaborate system of more than 150 great houses throughout the San Juan Basin of northwestern New Mexico built more than 800 years ago.

Chaco Canyon National Historic Park is in northwestern New Mexico, near Farmington. The canyon was the heart of an elaborate system of more than 150 great houses throughout the San Juan Basin of northwestern New Mexico built more than 800 years ago, and was the system's political, economic and ceremonial center for more than three centuries.

Chaco Canyon was the system’s political, economic and ceremonial center for more than three centuries. Remains of macaws and parrots, copper bells and seashells have been found in Chaco Canyon, evidence of trade that flourished between 1020 and 1120 and stretched hundreds of miles into Mexico.

Construction in Chaco Canyon ceased in the mid-1100s and the area declined.

The suggested reasons include drought and overpopulation in the fragile high desert ecosystem, but Russell Bodnar, the National Park Service’s chief of interpretation at Chaco, says there’s not a solid consensus about what happened. There could have been social and political reasons as well.

“I think of Chaco as a social experiment,” he says. “I like to think of it as a time when pueblos united under a unique vision that lasted 300 years, but eventually that way no longer worked and the pueblos went back to being autonomous units.

“I think Chaco is always going to be a mystery. … Chaco was unique, but people knew when it was time to move on.”

Chacoan influence continued in the 1100s and 1200s in places such as Aztec Ruins, about 60 miles north.

Chaco’s descendants are today’s Southwest Indians, many of whom consider the canyon a sacred place. The park service has signs at paths leading to the ruins: “Sacred sites, please enter with respect.”

Ceremonial centers

Despite the size of the great houses, there’s no evidence large numbers of people lived in them year-round, Bodnar says.

Ruins in Chaco Canyon show the evolution of the Chacoans' building techniques. The technologically advanced methods allowed buildings up to five stories high.

“The buildings were the public ceremonial centers that really swelled when people came into the canyon for the big events that happened throughout the year,” he says.

Una Vida, the ruin closest to Chaco’s visitor center, was built between the mid-800s and the mid-1100s, concurrent with construction at two other Chaco sites, Pueblo Bonito and Penasco Blanco.

Archaeologists say L-shaped Una Vida, Spanish for “One Life,” was two to three stories high and consisted of about 150 rooms and five kivas, similar to those modern pueblos use for religious purposes. Una Vida’s walls collapsed over time, and centuries of blowing sand covered the ruins, which have been left largely unexcavated.

By contrast, Pueblo Bonito, the largest of the great houses, has been extensively excavated and studied.

Pueblo Bonito, Spanish for “Beautiful Town,” is a D-shaped structure considered the center of the Chacoan world. Occupied from the mid-800s to the 1200s, it towered four stories and contained 600 rooms and 40 kivas.

Nearby Chetro Ketl was begun about 1020 and largely completed over about 30 years, with modifications in the 1100s. It has an estimated 500 rooms, 16 kivas and an immense earthen plaza.

Casa Rinconada is the largest known Great Kiva in the park. The trail to Casa Rinconada passes several “small house” sites.

“These more humble sites were what people would have to live in throughout the region while the great houses reflect something more special at Chaco,” Bodnar says.

Architectural engineering

The masonry of the great houses also is unique a technologically advanced core-and-veneer technique that enabled the Chacoans to build up to five stories. Chacoans designed the great houses’ construction with wider bases to distribute the weight of the massive walls.

Chaco’s masonry styles subtly changed with time, giving clues about when the great houses were built all with stone tools in relation to each other.

The earliest construction was simple: thick stone walls held together with mud mortar. As Chacoans began to build higher, they engineered walls with thick inner cores of rubble and fairly thin veneers of facing stone.

About half the ground floor of Pueblo Bonito was built in two styles employed about the same time courses of large stones chinked with flat, smaller stones to make patterns. Archaeologists say the attractive patterns were covered with plaster when the buildings were new.

The final style appears in Kin Kletso and other early 1100s architecture a thin inner core of rubble and thick outer veneers of shaped sandstone similar to the masonry of the Mesa Verde region about 100 miles away in southern Colorado.

Charting the heavens

Across the cottonwood-filled Chaco wash stands 443-foot Fajada Butte, home to the Sun Dagger. At the winter solstice the rays of the sun fell between two huge stone slabs bracketing a spiral petroglyph on the butte. At summer solstice, a sunbeam bisected the petroglyph.

Erosion possibly from people climbing up to see the Sun Dagger caused it to slip out of alignment in 1988, Bodnar says. It was not restored because of fears that an attempt would make things even worse.

The Sun Dagger is only one of many Chaco sites that chronicle the heavens.

“Even some buildings take their shape and location and orientation from the movement of the sun and moon and stars,” Bodnar says.