Because their culture changed continually (and not always gradually), researchers have divided the occupation into periods, each with its characteristic complex of settlement and artifact styles. Since 1927 the most widely accepted nomenclature has been the "Pecos Classification," which is generally applicable to the whole Anasazi Southwest. Although originally intended to represent a series of developmental stages, rather than periods, the Pecos Classification has come to be used as a period sequence:
Basketmaker I: pre-1000 B.C. (an obsolete synonym for Archaic)
Basketmaker II: c. 1000 B.C. to A.D. 450
Basketmaker III: c. A.D. 450 to 750
Pueblo I: c. A.D. 750 to 900
Pueblo II: c. A.D. 900 to 1150
Pueblo III: c. A.D. 1150 to 1300
Pueblo IV: c. A.D. 1300 to 1600
Pueblo V: c. A.D. 1600 to present (historic Pueblo)
The last two periods are not important to this discussion, as the Pueblo peoples had left Utah by the end of the Pueblo III period.
As the Anasazi settled into their village/farming lifestyle, recognizable regional variants or subcultures emerged, which can be usefully combined into two larger groups. The eastern branches of the Anasazi culture include the Mesa Verde Anasazi of southeastern Utah and southwestern Colorado, and the Chaco Anasazi of northwestern New Mexico. The western Anasazi include the Kayenta Anasazi of northeastern Arizona and the Virgin Anasazi of southwestern Utah and northwestern Arizona. To the north of the Anasazi peoples - north of the Colorado and Escalante rivers - Utah was the home of a heterogeneous group of small-village dwellers known collectively as the Fremont.
Although they continued to move around in pursuit of seasonally available foods, the earliest Anasazi concentrated increasing amounts of effort on the growing of crops and the storage of surpluses. They made exquisite baskets and sandals, for which reason they have come to be known as "Basketmakers." They stored their goods (and often their dead) in deep pits and circular cists - small pits often lined with upright stone slabs and roofed over with a platform of poles, twigs, grass, slabs or rocks, and mud. Basketmaker II houses were somewhat more sturdy than those of their Archaic predecessors, being rather like a Paiute winter wickiup or a Navajo hogan. Very few have been excavated.
By A.D. 500 the early Anasazi peoples had settled into the well-developed farming village cultural stage that we know as Basketmaker III. Although they probably practiced some seasonal traveling and continued to make considerable use of wild resources, they primarily had become farmers living in small villages. Their houses were well-constructed pit structures, consisting of a hogan-like superstructure built over a knee-or waist-deep pit, often with a small second room or antechamber on the south or southeast side.
Settlements of this time period are scattered widely over the canyons and mesas of southern Utah; they consist of small hamlets of one to three houses and occasionally villages of a dozen or more structures. By about A.D. 700 evidence of the development of politico-religious mechanisms of village organization and integration appears in the form of large, communal pit structures. One such structure, with a diameter of forty feet, has been excavated next to the old highway in Recapture Creek by archaeologists from Brigham Young University.
Three important changes took place before A.D. 750: the old atlatl (spear thrower) that had been used to propel darts (small spears) from time immemorial was replaced by the bow and arrow; the bean was added to corn and squash to form a major supplement to the diet; and the people began to make pottery. By A.D. 600 the Anasazi were producing quantities of two types of pottery - gray utility ware and black-on-white painted ware.
By A.D. 750 these farming and pottery-making people in their stable villages were on the threshold of the lifestyle that we think of as being typically Puebloan, and from this time on we call them Pueblos.
Perhaps the most significant developments in Pueblo I times (A.D. 750 to 900) were 1) the replacement of pithouse habitations with large living rooms on the surface; 2) the development of a sophisticated ventilator-deflector system for ventilating pitrooms; 3) the growth of the San Juan redware pottery complex (red-on-orange, then black-on-orange, pottery manufactured in southeastern Utah); and 4) some major shifts in settlement distribution, with populations concentrating in certain areas while abandoning others.
The two-hundred-fifty-year period subsequent to A.D. 900 is known as Pueblo II. The tendency toward aggregation evidenced in Pueblo I sites reversed itself in this period, as the people dispersed themselves widely over the land in thousands of small stone houses. During Pueblo II, good stone masonry replaced the pole-and-adobe architecture of Pueblo I, the surface rooms became year-round habitations, and the pithouses (now completely subterranean) probably assumed the largely ceremonial role of the pueblo kiva. It was during this period that small cliff granaries became popular. The house style known as the unit pueblo, which had its beginning during the previous period, became the universal settlement form during this period. In the unit pueblo the main house is a block of rectangular living and storage rooms located on the surface immediately north or northwest of an underground kiva; immediately southeast of this is a trash and ash dump or midden.
The redware pottery industry continued to flourish, as a fine, red-slipped ware with black designs was traded throughout much of the Colorado Plateau. During the middle-to-late Pueblo II period, however, the redware tradition ended in the country north of the San Juan River, although it blossomed in the area south of the river. Virtually all of the red or orange pottery found in San Juan County sites postdating A.D. 1000 was made south of the San Juan River around Navajo Mountain in the Kayenta Anasazi country. The reasons for this shift are unknown, and the problem is a fascinating one. Production and refinement of the black-on-white and the gray (now decorated by indented corrugation) wares continued uninterrupted in both areas, but the redware tradition migrated across what appears to have been an ethnic boundary.
The styles of stone artifacts also changed somewhat during Pueblo II. The beautiful barbed and tanged "Christmastree" style point that had been popular since late Basketmaker III times was replaced first by a corner-notched style with flaring stem and rounded base, then by a triangular style with side notches. Also, by the end of the period, the old trough-shaped metate that had been popular for half a millennium was replaced by a flat slab form with no raised sides. The change in grinding technology appears to have accompanied a change from a hard, shattering, flint type of corn to a soft, non-shattering flour corn. This permitted use of smaller metates, and thus also increased the efficient use of the floor space.
During the 1100s and 1200s the Anasazi population began once again to aggregate into large villages. This period is known as Pueblo III, and it lasted until the final abandonment of the Four Corners country by the Anasazi during the late 1200s. Numerous small unit pueblos continued to be occupied during this period, but there was a tendency for them to become more massive and to enclose the kivas within the room block. A number of very large villages developed. It was during this period that most of the cliff villages such as the famous examples at Mesa Verde National Park and Navajo National Monument were built.
During Pueblo III times the Mesa Verde Anasazi developed the thick-walled, highly polished, incredibly beautiful pottery known as Mesa Verde Black-on-White. They also continued to make corrugated gray pottery. Redwares, often with two- or three-color designs continued to be imported north of the river from the Kayenta country. Arrowheads continued in the triangular, side-notched form, but were often smaller than those of the previous period.
Starting sometime after A.D. 1250 the Anasazi moved out of San Juan County, often walking away from their settlements as though they intended to return in a few minutes - or so it looks. Why did they leave behind their beautiful cooking pots and baskets? Perhaps because they had no means to transport them. When forced to migrate a long distance, it was more efficient to leave the bulky items and replace them after they reached their destination.
We do know that they moved south. Classic late Mesa Verde-style settlements can still be recognized in New Mexico and Arizona, in high, defensible locations in areas where the local Anasazi sites look quite different. By A.D. 1400 almost all the Anasazi from throughout the Southwest had aggregated into large pueblos scattered through the drainages of the Little Colorado and Rio Grande rivers in Arizona and New Mexico. Their descendants are still there in the few surviving pueblos.
Why did they leave? It is impossible to find a single cause that can explain it, but there appear to be several that contributed. First, the climate during the Pueblo III period was somewhat unstable with erratic rainfall patterns and periods of drought. This weather problem climaxed with a thirty-year drought starting about 1270 that coincided with a cooling trend that significantly shortened the growing season. Perhaps the expanding population had pressed the limits of the land's capacity to support the people so that they were unable to survive the climatic upheavals of the thirteenth century.
Could they have been driven out by nomadic tribes, such as Utes or Navajos? There is no direct evidence that either group, or any other like them, was in the area that early. There is mounting evidence, however, that the Numic-speaking peoples, of whom the Utes and Paiutes are part, had spread northwestward out of southwestern Nevada and were in contact with the Pueblo-like peoples of western Utah by A.D. 1200. It is certainly possible that they were in San Juan County shortly after that. Ute and Paiute sites are very difficult to distinguish from Anasazi campsites, and we may not be recognizing them. Navajos were in northwestern New Mexico by 1500, but we do not know where they were before that. Perhaps the answer to the Anasazis' departure from Utah lies in a combination of the bad-climate and the arriving-nomads theories.