The Anasazi from A.D. 900 to A.D. 1150

Environmental conditions improved during the period known as Pueblo II (A.D. 900 - 1100), and people living on the Colorado Plateau experienced a gradual increase in effective moisture and floodplain aggradation. Climatic variability from year to year initially remained high and spatial variability continued to be low until the A.D. 1000s. In the face of gradual climatic improvement, Anasazi groups intensified their agricultural economies. In most parts of the Anasazi world, dry farming systems continued to be employed, as were akchin fields that took advantage of the runoff and deeper soils of alluvial fans. In some areas, greater investments were made in agricultural infrastructure that supplemented traditional farming methods. For example, in Chaco Canyon in northwestern New Mexico, impressive irrigation systems were built that channeled rainwater running from the canyon walls into gridded fields. Extensive water control systems were also used along the river basins of southwestern Colorado. Further to the west, the Virgin Branch Anasazi constructed check dams and canal irrigation systems.

Agricultural Resources

The number of cultigens used in the Southwest greatly increased after A.D. 950. Many of the crops previously restricted to Hohokam areas in southern Arizona became widespread as other people in the region developed more reliable farming systems. Cotton, tepary beans, sieva beans, and green striped cushaw squash seeds have been found in sites throughout the Southwest dating to this period. New cultigens were also introduced by A.D. 1100 to the Hohokam along the Salt and Gila Rivers, including the warty squash and the jack bean. The identification of quantities of grain amaranth, beeweed, little barley, pigweed, panic grass, sunflower, and devil's claw in a number of Southwestern sites has led many archaeologists to suspect that these plants were being locally domesticated. However, devil's claw is the only plant that can be clearly demonstrated to have been domesticated by Southwestern groups, for it was historically grown by the Papago of Arizona.

The diet of most Southwestern groups after A.D. 950 relied almost exclusively on cultigens. An analysis by Paul Minnis of 139 coprolites from several Anasazi sites in the San Juan Basin found that an average of 85% of each sample was composed of maize. Other domesticates were also found, but very few wild plant remains could be identified. On average, only five plant taxa were found in any given sample, and this number decreases to three for samples dating after A.D. 1200. In another study conducted by Matson and Chisholm, carbon isotope analyses of three Anasazi skeletons showed that almost 90% of the protein diet came from C4 plants such as maize, although other wild C4 plants may have also contributed to the diet. All of these investigations suggest that maize was a major contributor to Anasazi diet, even though small amounts of wild foods continued to be eaten.

Architecture and Settlement

Pueblo II marks the complete transition to above-ground architecture, and Anasazi village sites proliferated during this period. Most domestic structures were single-story and consisted of two tiers of rooms, with the back rooms serving as storage facilities and the front rooms for habitation. The pithouse of earlier periods was located in front of the roomblock and served a ceremonial function while also likely functioning as retreats for members of various religious organizations; archaeologists refer to these pit structures as kivas. As in earlier periods, Anasazi communities consisted of clusters of these domestic structures, and during Pueblo II some of these communities grew to substantial sizes, with populations in the hundreds. This settlement arrangement was found throughout the Colorado Plateau, and persisted in most areas until Pueblo III.

Anasazi Cultural Divisions

During Pueblo II, Anasazi groups occupying different parts of the Colorado Plateau continued to follow diverging evolutionary paths that first emerged in Pueblo I. Most archaeologists divide Pueblo II populations into several groups that are usually identified according to each group's characteristic material culture, including distinctive pottery styles. Of course, these groups are arbitrary constructs. In reality, Anasazi people in each group were certainly not identical, and the boundaries between them were not impermeable. In many cases, there was extensive cultural variability within each group as well as frequent migrations between adjacent groups. These group identifications, however, allow archaeologists to more easily identify and discuss patterns in prehistory.

The most frequently recognized groups include the Virgin Anasazi in what is now northwestern Arizona and southwestern Utah; the Kayenta Anasazi in northeastern Arizona; the San Juan Anasazi of southeastern Utah and southwestern Colorado; the Chaco Anasazi of northwestern New Mexico; and the Rio Grande Anasazi of north-central New Mexico. Some groups, such as the Virgin Anasazi, maintained very conservative economic and sociocultural traditions characterized by a mix of sedentism and mobility, horticulture and wild foods. Others, such as the Chaco Anasazi, began to rely on more intensive agriculture and experienced the emergence of sociopolitical differentiation. Because Pueblo II represents the most complex sociopolitical manifestation of the Chaco Anasazi, they will be examined in greater detail.

The Chaco Anasazi

The unique characteristics of the Chaco Anasazi developed during the Pueblo II period, beginning when sites within Chaco Canyon started on an evolutionary path different from the rest of Anasazi culture. Chronologies constructed for Chaco Canyon are therefore slightly different than the rest of the Colorado Plateau. The period from A.D. 900 to about 1040 is referred to as the Early Bonito Phase and is characterized by rapid architectural changes in Chaco Canyon. Most prominent is the appearance of "great kivas" and "great houses" in Chacoan communities, a development that most clearly marks the emergence of the Chaco Anasazi as a cultural tradition distinct from other Anasazi groups.

The formal Chacoan great kivas found in many Pueblo II communities apparently developed from the earlier oversized pit structures that appeared throughout the Anasazi region as early as Basketmaker III. Both great kivas and their ancestral forms generally exhibit more features of probable ritual function and fewer indicative of domestic activities in comparison to smaller "ordinary" pit structures or kivas. Because of this, great kivas and oversized pit structures have most often been defined as "integrative" facilities in which community-level ceremonial activities occurred. Recent studies by Eric Blinman of Pueblo I oversized pit structures in southwestern Colorado indicate that they tend to be associated with large quantities of nonlocal ceramics as well as evidence for feasting activities and trade involving large groups of people. His studies also suggest that two or more oversized pit structures were often built in the same community, with each associated with especially large habitations. His research suggests that oversized pit structures and their great kiva descendents were centers for social and ceremonial activities and that they were administered by separate residential groups.

Unlike great kivas, which have a long history of development, Chacoan great houses appear rather suddenly during the Pueblo II period. In general, great houses are defined as masonry structures that are usually larger than the average surrounding sites, although, as Andrew Fowler and his colleauges have pointed out, "[great house size] is largely an illusion: exceptionally massive, yet smaller in plan than other forms of contemporaneous Anasazi buildings." Actual structure size and room frequency also vary considerably. Great houses usually, but not always, exhibit labor-intensive core-veneer or compound masonry, and rooms and kivas in great houses are normally larger than those found in common habitations. They also tend to contain above-ground, blocked-in kivas built into the structure, some which may be elevated above the first story. Great houses are generally believed to have a more formal and planned appearance in comparison to domestic habitations, although this seems to be more characteristic of the great houses that appear in Chaco Canyon than those found in other parts of the Colorado Plateau. Great kivas, prehistoric roadways, and certain ceramic styles are also used to define a great house. The ambiguity of these criteria has led Steve Lekson to conclude:

to a very large extent, great house criteria have shifted from intrinsic traits to extrinsic contexts. Given the appropriate time period, evidence of a compact plan, and massive construction, the deciding criteria is this: Is the candidate great house a significantly bigger "bump" than other contemporaneous bumps in its vicinity?

At the same time that the great kivas and great houses were being constructed in Chaco Canyon, related settlements appeared in other parts of the Four Corners area. These sites, often called "outliers" or "great house communities," are identified by the presence of great houses that are architecturally similar but typically much smaller than those found in Chaco Canyon. These outlier structures were almost always built in previously existing communities. By A.D. 950, seven great house communities had been constructed, with at least nine more built by A.D. 1050. Almost all of these were located south and west of Chaco Canyon. Due to the lack of investigation at these outliers, their function and relationship to the Chaco core and to each other is unclear, although eventually, during the A.D. 1000s, the construction of roads connecting some outliers to Chaco Canyon suggests close interaction between the central canyon and outlying areas. Suggestions for the function of the Chaco Anasazi "system" parallel theories proposed for the function of great houses, as discussed above. Some scholars argue that the entire system was a well-integrated economic system, others believe that the roads and great houses were part of an extensive pilgrimage system, while David Wilcox has even proposed that the roadways were corridors down which Chaco Canyon armies moved to subjugate surrounding areas. Research evaluating all of these hypotheses continues.

One bit of evidence that does seem clear is that Pueblo II is the period with the best evidence for leadership and economic inequality, particularly in Chaco Canyon. Bioarchaeologist Nancy Akins has found evidence for achieved and perhaps hereditary positions of authority in the few burials recovered from great houses in Chaco Canyon, and Robert and Florence Lister note similar inequities in burial goods from the Aztec Great House. Recent skeletal analyses have further suggested that two different kin groups used distinct parts of Pueblo Bonito, the largest great house in Chaco Canyon. In many parts of the Chaco system, but especially in Chaco Canyon, the Pueblo II period is associated with increases in the flow of prestige goods and perhaps some craft specialization, the construction of relatively sophisticated water-control devices, and a strong religious focus with cosmological undertones that may have involved pilgrimages to Chaco Canyon from other areas in the Chaco system.

The Late Bonito Phase, which lasted from A.D. 1100 to about 1140, was a period of reorganization that is still not well understood by archaeologists. In Chaco Canyon, construction of the so-called "McElmo" structures started, including New Alto, Casa Chiquita, and Kin Kletso. These used a different masonry style resembling that used in the Mesa Verde area to the north. McElmo structures were enclosed rectangles as opposed to the earlier open U , D, and E shapes, and kivas were completely enclosed by the room blocks. At this time, many older great houses with the open design were enclosed with exterior walls, their interiors were remodeled, and many of the older kivas were filled with trash. The construction of small villages also appears to have increased during this period, with masonry styles and layouts similar to the larger McElmo structures. By the end of this period, over 3,500 rooms were apparently utilized in Chaco Canyon.

The settlement system outside of Chaco Canyon also experienced much change during the Late Bonito Phase. Although great house construction continued in the area around the San Juan River in the northern portion of the basin, most southern great house communities were completely abandoned after A.D. 1125. Some archaeologists believe that this period represented the height of Chaco Canyon's control of the San Juan Basin, while others argue that the regional power shifted to Aztec and Salmon Ruins in the northern portion of the basin along the San Juan River. In the latter scenario, Chaco was still occupied but now found itself serving as an "outlier" to a regional system centered at Aztec Ruin. Unfortunately, the chronological control for areas outside of Chaco Canyon is still too rudimentary to fully resolve this issue.

What is clear is that construction in Chaco Canyon soon ceased. Although the canyon continued to be occupied for probably another century, the major architectural projects that characterized most of Pueblo II ended quite suddently early in the 12th century. For example, a huge extension to the great house of Pueblo Bonito was never completed; all that was built were the foundations. Chaco Canyon never again saw much occupation, although it remains an important part of the landscape for Native American groups living in the Southwest today.