Chaco Culture National Historical Park is a United States National Historical Park in the American Southwest hosting a large concentration of pre-Columbian indigenous ruins of pueblos. The park is in northwestern New Mexico, between Albuquerque and Farmington, in a remote canyon cut by the Chaco Wash. Containing the most sweeping collection of ancient ruins north of Mexico, the park preserves one of the most important cultural and historical areas in the United States.
Building in the canyon
DNA evidence establishes the people of Picuris Pueblo once lived in Chaco Canyon. By AD 490, the descendants of those who lived in Chaco Canyon, of the Late Basketmaker II period, farmed lands around Shabik'eshchee Village and other pit-house settlements at Chaco. A small population of Basketmakers remained in the Chaco Canyon area. The broad arc of their cultural elaboration culminated around 800, during the Pueblo I period, when they were building crescent-shaped stone complexes, each comprising four to five residential suites abutting subterranean kivas, large enclosed areas reserved for rites.
Such structures characterize the Early Pueblo People. By 850, the Ancient Pueblo population had rapidly expanded: groups resided in larger, more densely populated pueblos. Strong evidence attests to a canyon-wide turquoise processing and trading industry dating from the tenth century. Around then, the first section of Pueblo Bonito was built: a curved row of 50 rooms near its present north wall.
Archaeogenomic analysis of the mitochondria of nine skeletons from high-status graves in Pueblo Bonito determined that members of an elite matriline were interred here for approximately 330 years between 800 and 1130, suggesting continuity with the matrilineal succession practices of many Pueblo nations today. The cohesive Chacoan system began to unravel around 1140, perhaps triggered by an extreme 50-year drought that began in 1130; chronic climatic instability, including a series of severe droughts, struck the region again between 1250 and 1450.
Great houses and their uses
Immense complexes known as "great houses" embodied worship at Chaco. The Chacoans used masonry techniques unique for their time, and their building constructions lasted decades and even centuries. As architectural forms evolved and centuries passed, the houses kept several core traits. Most apparent is their sheer bulk; complexes averaged more than 200 rooms each, and some enclosed up to 700 rooms. Individual rooms were substantial in size, with higher ceilings than Ancestral Puebloan works of preceding periods.
The great houses were well-planned: vast sections or wings erected were finished in a single stage, rather than in increments. Houses generally faced the south, and plaza areas were almost always girt with edifices of sealed-off rooms or high walls. The meticulously designed buildings composing the larger Chacoan complexes did not emerge until around 1030. The Chacoans mixed pre-planned architectural designs, astronomical alignments, geometry, landscaping, and engineering into ancient urban centers of unique public architecture.
Researchers have concluded that the complex may have had a relatively small residential population, with larger groups assembling only temporarily for annual ceremonies. Smaller sites, such as Hillside Ruin, apparently more residential in character, are scattered near the great houses in and around Chaco. The canyon runs along one of the lunar alignment lines, suggesting the location was originally chosen for its astronomical significance. This allowed alignment with several other key structures in the canyon.
Sunlight and architectural alignments
Two whorl-shaped etchings near the top of Fajada Butte compose what is called the "Sun Dagger" petroglyph that is tucked behind the eponymous rock panels of the "Three-Slab Site". They are symbolically focal. It consists of two spirals—one principal and one ancillary. The latter left-hand spiral captured both spring and fall equinoxes; its artifice was revealed by a descending spear of light, filtered through the slabs, that shone upon it and split it in two. The former and larger whorl to its right was lit by the titular "sun dagger", which bisected it through another interplay of slab and sunlight. Light struck it, brilliantly, as the summer sun attains its solstice midday peak.
Some parties have advanced the theory that at least 12 of the 14 principal Chacoan complexes were sited and aligned in coordination, and that each was oriented along axes that mirrored the passing of the Sun and Moon at visually pivotal times. The first great house known to evince fastidious proportioning and alignment was Casa Rinconada: the twinned T-shaped portals of its 10 m (33 ft) radius great kiva were north–south collinear, and axes joining opposing windows passed within 10 cm (4 in) of its center. The great houses of Pueblo Bonito and Chetro Ketl were found by the "Solstice Project" and the U.S. National Geodetic Survey to be sited along a precisely east–west line, an axis that captures the passage of the equinox sun.