Our first session of the 2015 season wrapped up on May 4 and everyone seemed to have a lot of fun. The weather was ideal. Work continued on Structure 25 which was burned and abandoned around the middle A.D. 800s. Part of our research involves the prehistoric process of decommissioning structures and features upon abandonment. This process takes several forms but burning is the most common method. In most cases, structures were 'cleaned' prior to abandonment but sometimes, a variation of this process leaves the user's tools and other possessions in place at the time of burning. Structure 25 was 'closed' by the latter and we are taking the opportunity to study the process more closely.
Winter preparations of the exposed portions of the tri-wall and Pueblo A has led to some new and interesting discoveries over the last few months. In 1988 and 1989, tests of the tri-wall revealed an unusual architectural configuration that is somewhat different than what can be gleaned from the 4 or 5 known to exist. Vivian's (1959) seminal work on these enigmatic buildings is the only published work that I know of on tri-wall's that also involved excavation. He and his associates used relatively modern excavation and recording techniques for this work. No others have been tested or excavated since. Vivian tried to rebuild the record from earlier excavations that had been performed on the Pueblo del Arroyo great house tri-wall in Chaco and the Mound F and Hubbard Mound tri-wall at Aztec with limited success. Most known tri-wall's consist of three concentric walls; the innermost being the smallest circumference and the outer, the greatest. The chambers created by the concentric walls were often further divided by cross-walls creating compartments that are generally featureless. It is likely that these chambers held perishable products however, all excavations were performed before pollen and flotation techniques were developed so at this point, no proof has been detected to confirm this. It is known however that whatever may have been stored in these chambers was gone by the time excavators had an opportunity to examine the deposits.
Vivian concluded that the innermost concentric walls of both Mound F and the Hubbard Mound at Aztec as well as the del Arroyo tri-wall contained a building similar to the kiva. Our 1988-89 studies at Mitchell Springs revealed a structure that is somewhat different than these in that the inner chamber appeared to have performed as a platform used for burning large fires. Last month, during tests inside the eastern half of this portion of the structure, evidence to suggest the existence of an inner tower was found. Unless the interior features of the 'tower' confirm the existence of a kiva, the Pueblo A structure would by definition be a tower. If a kiva is confirmed to lie within the interior chamber, this structure might be considered a tower kiva. To date, a bench coated with multiple coatings of red, white and gray layers of plaster, an adobe floor, and one large masonry lined floor vault have been documented.
We are taking a closer look at the Mitchell Springs tri-wall in an effort to add more modern data to what is currently known about these buildings. To my knowledge, all known tri-walls except the one at Mud Springs are on publicly managed lands and it is unlikely that any excavation or productive analysis will ever take place on these until at least A.D. 2275 or beyond. Over the last 3 months, many new discoveries have been made during the process of exposing the tops of the walls of Pueblo A and its appended tri-wall. We are preparing a manuscript on this work and it should be ready to submit for publication later this year.
In the ninth century the population of the Mitchell Springs Community exploded, growing to many hundreds of rooms and setting the stage for the entry of the Chaco System and the construction of new public architecture. Four great houses and two 10+ meter kivas were constructed at the village center. Within the course of less than 100 years the Chacoan System had collapsed leaving diminished population levels in the Mitchell Springs community. By 1230 or 1240 A.D. the community and large portions of the Montezuma Valley became depopulated. People consolidated into fewer and generally larger villages and defensible locations with a source of fresh water and nearby arable fields.
Structure 25 is located at the southeast corner of Pueblo A. This building contains about 30 square meters of floor space and was probably used by a larger segment of the community rather than by a few interrelated or cooperating families. Domestic activities were still conducted inside this structure although this aspect is still under investigation. On the south side of the wingwall, the grinding of food and possibly other items was performed. Although 14 manos and 6 pecking stones were stored there, only one metate was left in this part of Structure 25 when it was set ablaze. Almost no bone byproducts, bone tools, debitage or flaked lithics were recovered south of the wingwall but 3 bone awls were evidently nested together in the ceiling immediately to the north of the wingwall (see photo above left). A hafted axe hammer, a large core, 2-hand polishing stone and a small abrading stone were also stored in this area of the structure. Fragments of mats and fabric were collected from the floor just north of the ventilator opening and in the east section of space just south of the wingwall. More than 300 tree-ring samples were processed from the burned roof. At this point in the excavation, it isn't clear if the robust artifact assemblage indicates that tools were deliberately left in the building when it was burned because they were not needed or for reasons possibly related to the ceremonial closing of the building.
Thanks to Joel Brisbin and Gay Ives, the complex stratigraphic profiles exposed by the excavation units inside the Sector 11 great kiva were documented and photographed. As part of my research questions related to the construction of special buildings on top of earlier special buildings, an early great pit structure built in 758 A.D. was tested. During excavations in the south and west ends of the great kiva the Structure 6 over-sized pit structure was discovered. It contained approximately 65 square meters of floor space and was ceremonially closed by burning immediately after abandonment. Just as we see in Sector 7 Structure 25, a large assemblage of usable tools, fabric, human hair twine, mats, baskets, ceramic vessels and ornaments were left on the floor when the building was intentionally burned in the late 8th century. In the mid to late 900's, a great kiva was built over it and was subsequently rebuilt at least two other times before being abandoned in the 1130's or 40's.
In Pueblo A , an effort to emulate a construction style which had roots in Chaco is apparent in the preplanned footprint of the pueblo as well as some masonry style characteristics incorporated into some of the rooms. The front two rows of storage rooms on the south end of the pueblo and the 3 or 4 storage rooms on the east side of Pueblo A were single story rooms. In one event, the burning pueblo's southern wall fell southward and because it was still articulated, it was documented to be a little over 3 maters tall. The southern two rows of rooms were added to the original configuration of the Pueblo, after the Tri Wall structure had been appended to it. All of the remaining rooms were two stories tall. The central kiva may have been built with rectangular rooms above it so in effect, it may have been a round, masonry enclosed structure that was concealed from view because contemporaneously used rooms surrounded it on all sides, including above it. During the partial excavation of Room 11 in the early 1990's, a subfloor test indicates the likely presence of earlier rooms beneath it, and beneath the central kiva.
Another interesting item in regard to the preplanned footprint of Pueblo A is that only two of the 22 ground floor rooms were habitation rooms. They are the only square shaped rooms in the pueblo, a trait that was also found at Salmon Ruins in Bloomfield NM. The second story rooms above these two rooms were also used for domestic activities such as cooking and sleeping but were evidently not used for grinding operations. Both the upper and lower floor rooms were directly connected via roof hatchways. In the Summer of 2015 or 2016, the area on the west side of the west wall doorway in Room 18 will be tested to determine how that space was used.
Kiva A has been a fascinating bit of discovery. Some of its masonry is of a finer style than appears to be the norm at Mitchell Springs. Like Room 18, Kiva A also burned in a cataclysmic fire that ended the occupation of Pueblo A and possibly the entire Mitchell Springs Community. It has no southern recess which is not the norm for kivas built and used during this time period in the Montezuma Valley. In the space that is often reserved for a southern recess, an elaborate ventilator feature was engineered and constructed. This feature brought fresh air down into the kiva chamber from either the floor of the room above it or from atop Pueblo A. The pressure differential between the dark spaces in Kiva A in the belly of the pueblo, to the sunlit intake point 20 feet above (on the roof of Pueblo A), would have created a natural circulating cooling effect in the summer months. Regulating the airflow into the ventilator would prevent too much cold air from entering during cold nights. On one of the masonry stones that was used to create the elaborated ventilator feature (see photo below Left), an interesting petroglyph was carved.
A very thin bench was located and a test to confirm it was indeed present removed a 4-5 cm thick section of the plaster that had been applied to the bench and bench back. This revealed 20 different layers that ranged in color from bright white to red to gray. Next season the bench will be be uncovered and we should get a look at some of the Kiva A floor. It'll be a gas.
See Mitchell Springs Tab for more information on this work.......