The dates for Pueblo I encompass about A.D. 700 to 900. The transition from BMIII to PI is not abrupt, nor does it involve an influx of new people, although in the past it was thought that there had indeed been a migration of people into the Four Corners area during PI. This was based on the fact that during PI, a new form of baby cradle was introduced that had the effect of compressing and deforming the head of a baby as it developed. (There is no effect of this on mental faculties or anything else, and PI people probably regarded the shape of their heads as perfectly normal and natural, if not downright attractive.) Thus, the idea of a migration was based on faulty interpretation of the cranial differences between BMII and BMIII people, and PI people; it did not reflect different physical type, merely a change in cradle style. Changes from BMIII to PI are thus gradual and evolutionary, though when we compare overall trends from the two time periods, many differences can be seen. These include:

During PI, there is a trend toward increased construction of above-ground architectural forms, often in the form of rectangular rooms made of jacal (pole and thatch, covered with mud); it is thought that many of these constructions were used for storage and not for habitation

Toward the end of PI, the above-ground architectural form shifts from insubstantial jacal structures to rectangular masonry rooms. These are often arranged end-to-end in "blocks" of rooms. There is evidence (hearths and other floor features, as well as artifacts found on the floors) that such room blocks were used for a combination of habitation, storage, and special activities such as food preparation and manufacture of crafts.

In PI, the first corrugated and black-on-white pottery appears (probably by about A.D. 800), along with black-on-red styles. There is evolution of designs from the crude an sparse designs of BMIII pottery (which often resemble the designs woven into BMIII baskets), to more elaborate and widely distributed styles of painted decoration (which do not match basketry designs -- clearly pottery has emerged by PI as an important medium for new symbolic expressions). The corrugated pottery usually consists of thick corrugations confined to the neck of the pot.

In a few places, large villages arise during PI, which exceed the size of the largest BMIII villages and reflect different and probably more complex forms of social organization. Many of these villages involve multiple units of linear, arc-shaped, or U-shaped rows of masonry rooms, with doorways facing an open area containing one or more kivas. In the larger villages, there are one or a few exceptionally large, circular structures that can be considered as great kivas. In some cases, it appears that these great kivas did not have roofs, and were large, open-air gathering places. The number of people living at some of these sites is difficult to estimate, but in a few cases it might have been as many as 200 or more. At one site, Grass Mesa Village near Dolores, Colorado, it has been estimated that 40 households (120+ people) lived there at the peak of occupation, and that there were other, larger villages in the area. Because of the limited amount of non-agricultural food resources in these areas, some (Orcutt, Blinman, and Kohler, Perspectives on Southwestern Prehistory, edited by Minnis and Redman, Westview Press) have proposed that large villages forrmed during climatic conditions that fostered consecutive years of adequate agricultural production. The dendroclimatic evidence (evidence of yearly rainfall values based on tree rings) did not indicate that such aggregations took place during years that might have produced agricultural surplus. Instead, it appears that aggregations took place during times when there were no severe droughts that would have forced people to disperse and move to more favorable agricultural locations. Not surprisingly, the abandonment of these PI villages does seem to have been correlated with periods of drought, implying that the social organizations that were formed during the good times (agriculturally speaking) were relatively fragile, and the social bonds were relatively easily broken. As with the BMIII villages, there is no good evidence for "elite" leaders with substantial political power. Again, in spite of the fact that there were intra- or inter-village ceremonial organizations (reflected in the great kivas), the religious and political power may have been dispersed among a number of individuals and households, and social organization was relatively egalitarian. There is much evidence that the room blocks surrounding the kivas were used for "potluck" feasting, wherein large quanitities of food were prepared and eaten on a periodic basis. This evidence may indicate something about periodic ceremonial events involving large numbers of people congretating at the great kivas.