Chaco Canyon is a pretty dry place. Its position in the rain shadow of the Chuska Mountains to the west gives it a semiarid climate with an average of about eight and a half inches of precipitation per year. While it does snow, and that provides some moisture, the major source of water is the summer storms which come during the “monsoon season” from late July to early September and provide about a third of the annual precipitation in most years.
This is not the kind of environment in which a spectacular cultural flowering is generally expected. And yet, the Chaco phenomenon that was centered in the canyon but spread throughout the region in the eleventh and early twelfth centuries was nothing if not spectacular. Looking at the remains of the great houses in the canyon today, it’s hardly a surprise that many of the most common questions visitors ask are about water. Where did they get it? How did they store it? Was it wetter then than it is now?
The answer to the last question is no, which comes as a considerable surprise to many visitors. Some of them even seem very skeptical, like I’m trying to trick them. It defies common sense to think that anything like what we see at Chaco could have arisen in an environment as dry as what we see today. And, indeed, many early archaeologists who worked on Chaco assumed that the climate must have been more favorable, and there has been a considerable amount of research into this topic over the past few decades, much of it using the precision available through tree-ring studies to great effect.
Rather surprisingly, what that research has shown is that the climate has not changed significantly in at least the past several thousand years. There were variations in the amount of precipitation on the order of decades, but always within the range seen in modern records. So while there were wetter periods and drier periods, and these may have corresponded to important events in the development of the Chacoan system, it was always pretty dry, and never an attractive environment for a sedentary agricultural society displaying the level of complexity seen in the archaeological remains.
In that case, then, if Chaco wasn’t a more attractive place to live then than it is now, why on earth did people choose to live there and do the things they did there? This is, in some ways, the biggest question out there about Chaco, and also one of the most difficult to answer. There have been various answers proposed, but none of them seems totally convincing to me. This is one of the most enduring mysteries about Chaco, and it’s likely to remain so for a long time to come.
Okay, so, given that there was no more water available to the Chacoans than there is now, where did they get the water to do everything they did? This is another very interesting question that has been the subject of considerable research, and in this case we do have some answers (although a lot of questions remain).
The main scholar who has worked extensively on this issue is R. Gwinn Vivian, who taught at the University of Arizona for many years until his retirement. He has probably spent more time at Chaco than anyone else alive today; his father, R. Gordon Vivian, was the park archaeologist for decades, and Gwinn literally grew up at the park and went on to devote his career to the study of Chaco. His theories about the Chacoan system are in some ways a throwback to an earlier era of archaeological thought, and in recent years whatever consensus there has been about Chaco has largely moved away from him, but his studies of the water control systems in the canyon have been widely considered the most extensive and reliable work on the issue available.
In a short but important paper published in 1992, Vivian laid out what is probably the most concise and accessible account of the various activities for which the Chacoans would have needed water and the probable ways they fulfilled them. He divides the needs into three categories: domestic, construction, and agricultural. While these were all important, they involved different amounts of water and different levels of immediate necessity.
The most immediate and constant need would have been for domestic water, largely for drinking, washing, and cooking. The amount required would of course depend heavily on the population of the canyon, which is one of the most contentious issues in discussions of Chaco. Vivian tends to favor a higher population estimate, and he runs through a series of calculations to get a rough sense of how much water would have been required at different times of year for domestic purposes. He argues that the main source for domestic water would have been the various seeps and springs in the side canyons, which in historic times were heavily utilized by the local Navajo population and today provide water for the park wildlife as well. Even given a fairly high population estimate, Vivian concludes that with sufficient maintenance these springs would likely have produced enough water for domestic use except during period of extreme drought. While domestic use is the most necessary and constant of the needs for water, it also involves by far the least water.
The next main need for water would have been construction. The Chacoan style of masonry architecture required considerable quantities of water for mud mortar and plaster. While this is obviously not necessarily a constant need, and could easily be postponed if necessary, Vivian points out that it seems to have been more or less continual in the canyon during the height of the Chaco Era, and some of the building projects at the great houses were of sufficient scale to require vast amounts of water over relatively short periods of time. While it would certainly have been possible for construction water to have come from the same springs that supplied domestic water, Vivian notes that domestic use would surely have been the priority in times of shortage, and he considers it likely that water from these sources would only have been used in small, low-level construction projects (if, indeed, it was used for construction at all). He considers it most likely that construction water came from runoff impounded in reservoirs or left in pools, either natural or man-made, in the bed of the Chaco Wash after the high flow from the summer storms had subsided. With the amount of water that flows through the canyon during the summer, it would take just a bit of ingenuity to divert an amount that, in any given year, would likely have easily been sufficient for construction needs. It is also possible, though hard to determine, that for construction purposes it was mud rather than standing water that was collected. The amount of mud left in the bed of the wash (and elsewhere) following a large rain would have been considerable, and using it directly would have conserved any remaining liquid water for other uses. In either case, it seems quite clear that there would generally have been enough water for construction, although the construction events would likely have needed to be timed just right to take advantage of it.
The third major use of water, and perhaps the most contentious among archaeologists today, was agriculture. The Chacoans were certainly an agricultural people, and abundant amounts of corn, beans, and squash have been found at sites in the canyon. While there is recent evidence that at least some of the corn was being imported from elsewhere, it has generally been assumed that there was at least some agriculture in the canyon itself. The main source of water for this, as for construction, would have been the runoff from the summer rains. Vivian has put considerable effort over the years into studying the elaborate water control systems on the north side of the canyon, involving diversion dams at the base of the cliffs that lead to canals that lead to fields laid out in very formal grids. While the best-known of these is one just east of Chetro Ketl and can be seen clearly on aerial photography, Vivian argues that there are many other examples of this sort of pseudo-irrigation elsewhere in the canyon, and mentions one example near Peñasco Blanco in particular. He runs through a number of possible runoff amounts from rainfall events based on modern measurements of annual precipitation, and finds that the amount available for the fields would vary considerably depending on the parameters set for the calculation. Thus, while the dams, canals, and fields are certainly there, how they would have actually worked is a subject for debate. Vivian also argues that other sorts of farming, such as planting directly in the path of runoff and on terraces on the mesa tops, would have supplemented the gridded fields. In the end, despite the ambiguous nature of the runoff calculations, he notes that the very existence and size of the water-control systems suggests that they must have handled quite large amounts of runoff at least some of the time.
However it was managed and used, and however many people were using it, water was the limiting factor at Chaco. Anything else the Chacoans needed they could have imported from elsewhere, and there is a growing amount of evidence showing that they did import all kinds of things: wood, corn, pottery, and even stone for tool manufacture (though not for construction). With the technology they had, however, they couldn’t effectively transport large volumes of water over any significant distance. They didn’t have the technology to build aqueducts or other sorts of long-distance pipelines, and while they could certainly carry water in jars, and likely did for short distances within the canyon, those jars would both too heavy and too likely to break to carry over the long distances necessary to reach Chaco from any better-watered area. As a result, they put as much effort as they could into harnessing every drop of water they could find in the canyon, and they seem to have done a fantastic job of it. Whatever the situation with agriculture, the sheer amount of construction that they were obviously able to accomplish testifies to their success in controlling, managing, and using the scarce water in their dry location.