UNDERSTANDING THE SOIL
By Emily Eichstedt Anderson & Lupe Granados
After a Memorial Day weekend we were back at work with our excavations. Everyone returned to work on Tuesday, but rain caused us to have to pack up early and we, all covered in dirt, headed to the Hoard Historical Museum in Ft. Atkinson to see their Mysteries of the Mounds exhibit. The exhibit consisted of a very informative video on the mound building cultures of the Midwest, hundreds of artifacts to view, and a diorama of a Late Woodland camp. The whole museum, and especially this exhibit, was very well done and everyone had a great time exploring. We were back to work on Wednesday and by Friday all three test pits were either at or below the base of the plow zone between 50 and 60 centimeters deep.
By the end of the week every test pit (TP) found interesting artifacts and changes in soil color and consistency. TP7 and TP8 began to see oily, dark soil mottling around 52cm-56cm. This is consistent with the features that were found immediately to the west in TP6 last summer. TP7 and TP8’s features include the possible postmolds of a palisade wall. TP9 began to see dark mottling around 49cm-50cm in depth which may indicate an old excavation unit from the 1920s. TP9 also showed plow scars that date back to the early to mid 1800s and sterile soil, soil without the evidence of human activity, both showing up around 52cm. Artifacts found throughout all pits include more pieces of pottery, bone, stone flakes, and charcoal. TP7 found a small piece of cord impressed pottery while TP9 found a small piece of animal bone.
A plow zone (PZ) is a section of soil that has been disturbed by farming and plow tools. Any artifacts found here are not in any sort of context and, while interesting, can not always tell us much about what time frame they came from or even what area of a site they came from, as plows move around large amounts of dirt. Aztalan was one of the first farmed sites in Jefferson county and had a long history of farming before it became a park and therefore has an abnormally deep PZ. Now that we have reached the end of the plow zones we are starting to see soil color changes. In the plow zone the soil was a homogenous brown color and now below the plow zone there is a large amount of mottling of lighter and darker soils, gray soils, greasy black areas, and areas with gravelly soil.
These changes in the soil must be carefully observed, noted, and mapped because they can represent things called features. A feature is something that contains evidence of human activity and can be things like hearths, post molds, wall trenches, trash pits, and house basins. Dr. Schroeder carefully examined the features in the pit floors to hypothesize what they may represent. One of the most intriguing of these features possibly represents large diameter post molds from a wall or a bastion and can be seen in TP7 and line up with the same shapes in TP8. These post molds are significant because one of the big questions of Aztalan is whether all the walls were standing at the time. These post molds intrude into other features and potentially lend evidence to the hypothesis that not all the walls at the site were standing at the same points in time. The features in TP9 possibly represent an old excavation and possible trash pits which contrast in color and texture with the sterile soil.
This week at Aztalan was very successful because the changes in soil texture and color represent features that may solve many of the questions we pose about the daily life of the Mississippian and Late Woodland culture. We are all excited to continue excavating and find a possible explanation to the uses and types of the features and the artifacts that we have found.