Ch.3: Pre-Chacoan Architecture

URBAN GENESIS AT CHACO: Case Study of the Origin of Civilizations. Chapters: 1 2 3 4 5 6

3.3 The Best Response to a Harsh Environment

Several factors seem to have motivated ancient Puebloans to develop pithouses. Domesticated plants had been introduced to the region by the second century, and the nomads may have decided to stay put for the growing season in order to concentrate more effort on growing maize, beans, and squash. Initially, these Mesoamerican domesticates were probably planted in only a few places where a combination of local conditions made growing easy. In most parts of the southwest, though, the growing season is very short, so the timing of planting is critical. Rainfall across the basins and plateaus is also marginal, and arable soils are rare. Various methods of both irrigation and water-and-soil retention were used throughout the region, and these systems required not only initial labor but continuous maintenance. Raising crops in the Southwest has always been risky, and the additional labor required to reduce risk of famine meant a considerable commitment to agriculture as a way of life. "In the relatively food-poor and marginal environments in the Southwest, the production of crops is essential for the survival of even seasonally sedentary communities" (Cordell 1984:214). Another method of risk-reduction used in historic times by the Hopi was to plant fields in a wide variety of situations, with the expectation that in any given year, many of the fields would fail to produce. The investment of either labor or land into crops meant that growers would need to remain in the same place for at least a season, both to tend crops and to guard them against theft. Once a successful system of agriculture is established, though, one would also have to store the produce so that it lasts until the next harvest time. Food storage, more than agricultural activities in themselves, was a likely motive for permanent settlement.

Pithouses are very thermally efficient, which is probably why this design was developed as the first form of settlement. A small cooking fire could keep the dwelling heated throughout the winter (Farwell 1981:46; Cordell 1984:220). Thermal efficiency is critical in this region not only because the winters are very cold, but also because combustible fuel is scarce. Pithouse entrances were oriented south or southeast, which may have had sacred meaning to pithouse dwellers as it does to the Pueblo, Navajo, and Central Asian nomads today. In any case one likely reason for the orientation was to let morning sun into the room.

The structure of the pit-house itself was also an efficient use of wood. The use of a four-post frame within the space meant that load-bearing spans were short. Bending stress in horizontal members drops exponentially with a linear reduction in span length, so the slight reduction in span achieved by placing the upright supports within the room would have enabled the builders to use much smaller structural members. This gain in structural efficiency may have meant the difference between using relatively common pion and juniper trunks as beams versus using ponderosa trunks as the primary structural members. Ponderosa pines were both rare and much more difficult to fell and strip without metal tools.

Assessing the pithouse in terms of environmental conditions begs the question: has the climate changed in the Southwest over the last fifteen hundred years? The two main lines of evidence available to us indicate that it has not. Since 1929 a continuous dendrochronological sequence has been established back to at least the Chaco era. From this sequence it is clear that the degree of variation in rainfall from year to year has changed, but there is no evidence of a significant difference in the overall amount of rainfall. Secondly, plant pollens found in alluvial deposits have been dated and analyzed for the relative concentration of different plant species (Sebastian 1992:11-12). From these analyses we know that the climate and flora have changed very little in the Chaco cultural region over the last fifteen hundred years. Today, bunch grasses and sagebrush are the main ground cover, with occasional stands of juniper and piñon in shaded areas, and cottonwood and riparian vegetation in arroyos and washes.