By almost any standards, Chaco Canyon, in the San Juan Basin of northwestern New Mexico, is a harsh and inhospitable region. Summers are hot and dry, winters are cold and windy, and vegetation is largely limited to desert scrub, semi-arid grasslands, and limited pinyon-juniper woodlands on the mesa tops. Average annual precipitation within the basin is a mere 20 cm.
Yet a thousand years ago Chaco Canyon was the epicenter of the complex Eastern Anasazi culture, associated with as many as 400 nearby and outlying Chacoan Anasazi villages and settlements. Originally developed within the Chaco Canyon core in the 10th century A.D., this sociocultural system quickly spread over a 65,000 km2 area of the Four Corners region, an occurrence now known as the Chaco Phenomenon. Today, the spectacular great houses, kivas, pueblos and other archaeological remains of Chaco Canyon are protected within Chaco Culture National Historic Park.
Humans have occupied the San Juan Basin for at least 7000 years, possibly even longer. Palynological data indicate that the climatic and ecological conditions of the San Juan Basin have varied significantly during the time period of human occupation. Packrat middens dated to 8600-7400 B.C. suggest that a mixed conifer forest of Douglas fir, Rocky Mountain juniper, and limber pine dominated the region at that time. Middens from the period 3550-2480 B.C. indicate a shift toward warmer and wetter conditions, along with a change in vegetation pattern to pinyon-juniper woodland with a ponderosa pine forest on the uplands. Since approximately 2000 B.C., conditions have been essentially the same as they are in modern times. It appears that it may have been relatively short-term climatic fluctuations in temperature and moisture that had important ramifications for the prehistoric peoples inhabiting the basin.
The earliest evidence of human existence is limited to isolated Clovis and Folsom projectile points and not actual sites, suggesting that the highly mobile Paleo-Indians were present to some extent in and around the basin, following and hunting large game such as mammoth and bison. Archaic sites are more common and extensive in the San Juan Basin, and indicate that Archaic occupation of the region was continuous from about 5500 B.C. until approximately 500 B.C. Two Early Archaic and three Late Archaic phases have been defined for this area, demonstrating a gradual progression toward a more sedentary lifestyle in which dependence on hunting decreased and plant foraging increased. During these millennia, preferred campsite and settlement locations shifted throughout the basin, but were largely concentrated in localities that had permanent water.
Cultigens such as maize were introduced to the area as early as 1000 B.C., but widespread agriculture and the corresponding cultural and organizational impacts did not develop until about 200 B.C. While the exact nature of the transition between Archaic and Puebloan traditions is debated, many experts believe that the Puebloan Anasazi developed over time from the Archaic peoples and were not the result of a cultural displacement. In any case, by 400 A.D., the first Puebloan tradition of the Pecos Classification, Basketmaker III, was on the rise in the San Juan Basin.
The period between 400 and 700 A.D. is characterized by more permanent architecture, widespread use of ceramics and a greater degree of sedentism as dependence on agriculture became prevalent. This was also a period of increased moisture, instigating a general population shift to the Chaco Basin, where water drainage from the mesa tops could support an agricultural subsistence to a greater extent than ever before in this arid region. By 700 A.D., moisture and groundwater levels began a steady decline that lasted for several centuries, culminating in a 50-year drought that ended in 900 A.D. This was a difficult time for the Anasazi of the San Juan Basin, forcing them to make social and technological changes to cope with poor climatic conditions. Exchange systems expanded, populations dispersed to find agriculturally productive niches and large, well-designed storage facilities were built to house any surplus foodstuffs.
By the early 900s conditions began to improve, and the Chaco Anasazi culture began what anthropologists call a fluorescence--a remarkable cultural and sociological explosion. During the next few centuries, Chaco Canyon was the setting for the development of one of the most complex societies in pre-contact North America, a place of power and wealth, and the center of an architectural and technological revolution that influenced the entire region.