Chaco Culture

Chaco Culture National Historical Park is a United States National Historical Park hosting the densest and most exceptional concentration of pueblos in the American Southwest. The park is located 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 United States' most important precolumbian cultural and historic areas.

Between AD 900 and 1150, Chaco Canyon was a major center of culture for the Ancient Pueblo Peoples. Chacoans quarried sandstone blocks and hauled timber from great distances, assembling 15 major complexes which remained the largest buildings in North America until the 19th century. Evidence of archaeoastronomy at Chaco has been proposed, with the Sun Dagger petroglyph at Fajada Butte a popular example. Many Chacoan buildings may have been aligned to capture the solar and lunar cycles, requiring generations of astronomical observations and centuries of skillfully coordinated construction. Climate change is thought to have led to the emigration of Chacoans and the eventual abandonment of the canyon, beginning with a 50-year drought in 1130.

Composing a UNESCO World Heritage Site located in the arid and sparsely populated Four Corners region, the Chacoan cultural sites are fragile; fears of erosion caused by tourists have led to the closure of Fajada Butte to the public. The sites are considered sacred ancestral homelands by the Hopi and Pueblo people, who maintain oral accounts of their historical migration from Chaco and their spiritual relationship to the land. Though park preservation efforts can conflict with native religious beliefs, tribal representatives work closely with the National Park Service to share their knowledge and respect the heritage of the Chacoan culture.

Chaco Canyon lies within the San Juan Basin, atop the vast Colorado Plateau, surrounded by the Chuska Mountains in the west, the San Juan Mountains to the north, and the San Pedro Mountains in the east. Ancient Chacoans drew upon dense forests of oak, piñon, ponderosa pine, and juniper to obtain timber and other resources. The canyon itself, located within lowlands circumscribed by dune fields, ridges, and mountains, runs in a roughly northwest-to-southeast direction and is rimmed by flat massifs known as mesas. Large gaps between the southwestern cliff faces—side canyons known as rincons—were critical in funneling rain-bearing storms into the canyon and boosting local precipitation levels. The principal Chacoan complexes, such as Pueblo Bonito, Nuevo Alto, and Kin Kletso, have elevations of 6,200 to 6,440 feet (1,890 to 1,960 m).

The alluvial canyon floor slopes downward to the northeast at a gentle grade of 30 feet (9.1 m) per mile (6 meters per kilometer); it is bisected by the Chaco Wash, an arroyo that rarely bears water. Of the canyon's aquifers, the largest are located at a depth that precluded ancient Chacoans from drawing groundwater: only several smaller, shallower sources supported the small springs that sustained them. Aside from occasional storm runoff coursing through arroyos, significant surface water is virtually non-existent.

After the Pangaean supercontinent sundered during the Cretaceous period, the region became part of a shifting transition zone between a shallow inland sea—the Western Interior Seaway—and a band of plains and low hills to the west. A sandy and swampy coastline oscillated east and west, alternately submerging and uncovering the area atop the present Colorado Plateau that Chaco Canyon now occupies.

As the Chaco Wash flowed across the upper strata of what is now the 400-foot (120 m) Chacra Mesa, it cut into it, gouging out a broad canyon over the course of millions of years. The mesa comprises sandstone and shale formations dating from the Late Cretaceous, which are of the Mesa Verde formation. The canyon bottomlands were further eroded, exposing Menefee Shale bedrock; this was subsequently buried under roughly 125 feet (38 m) of sediment. The canyon and mesa lie within the "Chaco Core", distinct from the wider Chaco Plateau, the latter a flat region of grassland with infrequent stands of trees. Because the Continental Divide is only 15.5 miles (25 km) east of the canyon, geological characteristics and different patterns of drainage differentiate these two regions both from each other and from the nearby Chaco Slope, the Gobernador Slope, and the Chuska Valley.


An arid region of high xeric scrubland and desert steppe, the canyon and wider basin average 8 inches (200 mm) of rainfall annually; the park averages 9.1 inches (230 mm). Chaco Canyon lies on the leeward side of extensive mountain ranges to the south and west, resulting in a rainshadow effect fostering the prevailing lack of moisture in the region. Four distinct seasons define the region, with rainfall most likely between July and September; May and June are the driest months. Orographic precipitation, resulting from moisture wrung out of storm systems ascending mountain ranges around Chaco Canyon, is responsible for most precipitation in both summer and winter; rainfall increases with higher elevation. Occasional abnormal northward excursions of the intertropical convergence zone may boost precipitation in some years.

Chaco endures remarkable climatic extremes: temperatures range between -38 to 102 °F (-39 to 39 °C), and temperatures may swing 60 °F (33 °C) in one day.[8] The region averages less than 150 frost-free days per year, and the local climate swings wildly from years of plentiful rainfall to prolonged drought. The heavy influence of the El Niño-Southern Oscillation contributes to the canyon's fickle climate.

Chacoan flora typifies that of North American high deserts: sagebrush and several species of cactus are interspersed with dry scrub forests of piñon and juniper, the latter primarily on mesa tops. The canyon is far drier than other parts of New Mexico located at similar latitudes and elevations, and it lacks the temperate coniferous forests plentiful to the east. The prevailing sparseness of plants and wildlife was echoed in ancient times, when overpopulation, expanding cultivation, overhunting, habitat destruction, and drought may have led the Chacoans to strip the canyon of wild plants and game. It has been suggested that even during wet periods the canyon was able to sustain only 2,000 people.

The canyon's most notable mammalian species include the ubiquitous coyote (Canis latrans); mule deer, elk, and pronghorn also live within the canyon, though they are rarely encountered by visitors. Important smaller carnivores include bobcats, badgers, foxes, and two species of skunk. The park hosts abundant populations of rodents, including several prairie dog towns. Small colonies of bats, are present during the summer. The local shortage of water means that relatively few bird species are present; these include roadrunners, large hawks (such as Cooper's hawks and American kestrels), owls, vultures, and ravens, though they are less abundant in the canyon than in the wetter mountain ranges to the east. Sizeable populations of smaller birds, including warblers, sparrows, and house finches, are also common. Three species of hummingbirds are present, including the tiny, but highly pugnacious, rufous hummingbird; they compete intensely with the more mild-tempered black-chinned hummingbirds for breeding habitat in shrubs or trees located near water. Western (prairie) rattlesnakes are occasionally seen in the backcountry, though various lizards and skinks are far more abundant.

Carl Sagan on the Anasazi peoples' calendrical devices
http://www.youtube.com/watch?v=Yw1plQa5-Hs&feature=related