Archaeology Update — Waterproof Excavation Unit Opened on the South Side of the Church

Kristi Nichols, Director of Archaeology, Collections and Historical Research
November 19, 2019

At the start of this week, all excavations within the Long Barrack were finished. With these excavation units cleared by the Raba Kistner archaeology crew, the historic architects will now proceed with their investigations. No other archaeological work is currently planned to occur inside the Long Barrack as part of this project.

Work continued on the sloping of the curbs in front of the Church. Archaeologists from the University of Texas at San Antonio’s (UTSA) Center for Archaeological Research (CAR) were present during the portions of the work that contained breaking and removal of concrete. The work has not occurred at a depth in which the base under the concrete or intact soils would be encountered. All work is confined to the concrete layer present below the flagstones. The goal is to have the entire area planned to be sloped finished before Thanksgiving.

Excavation unit with several round holes on the surface
Figure 1. Holes noted in the compacted surface.

In addition to the sloping of the curb in front of the Church, UTSA-CAR monitored the removal of soils associated with the redesign meant to avoid impacting a feature previously uncovered near the south gate/south wall of the compound. The feature was originally discovered over the summer and consisted of an area of compacted soils that could be related to the entry gate into the Alamo during the mission fort periods. In an effort to preserve the feature for later investigation, the location of bollards were adjusted.

The new location placed the bollards further to the east, on an area that has been built up since the early 1990s. During the excavations, archaeologists documented that there was sand to the depth of the bollard impact. No additional excavations were conducted to determine how deep the sand extended. No artifacts were noted during the excavations in the sand.

Raba Kistner focused on excavations within and outside of the Church. Currently, three units are being excavated within the Church, while one is located along the exterior of the south wall of the Church. The interior units appear to have encountered a uniform layer of soil that contains limestone rocks, mortar, gravels, ceramics, glass fragments, and metal.

The unit located inside the room referred to as the Monk’s Burial Room has encountered an interesting feature. At approximately 24 inches below datum, the archaeologists began encountering signs of a compacted surface. As they were uncovering the compacted layer, holes of varying sizes that cut through the compacted surface were discovered. The archaeologists left the compacted surface in place while excavating the soil from the various holes. The matrix removed from the holes contained the same type of soils and materials that were present above the compacted surface.

Excavation unit with golden glow created by waterproof canvas
Figure 2. Unit located on the exterior of the south side of Church. The golden glow is an effect created by the waterproof canvas.

Artifacts noted in the holes consisted of construction related materials including brick, tile, concrete, mortar and limestone fragments. The holes varied in depth below the compacted surface, with the bottoms characterized by a distinct change in compaction (the soils of the hole were very soft and loose, the base became compact). One hole was excavated to approximately 19 inches below the compacted surface, and appeared to continue. The compacted surface contains caliche and could be up to 7 inches thick in some places. Once the holes are explored, the archaeologists will document and remove the compacted caliche surface.

Excavations outside of the Church started with a unit located on the exterior of the south side. Visitors at the Alamo are likely to see an area that is covered by a very large canvas spanning from the roof of the Church to the ground. The waterproof canvas is providing protection from the rain, keeping the unit dry, and allowing for excavations to continue during wet weather. Part of the investigation includes recording the compactness and initial moisture content of the soils at the start of each level to be able to replace the soil at relatively the same conditions after the excavations. This would reduce the amount of time needed to allow the soils to return to their original states for the monitors to collect accurate readings.

The first levels of excavations within the exterior unit have encountered sand, bull rock, gravels, and utilities, revealing the amount of disturbance that has occurred in the area over the last century. The unit is placed in a location that once acted as a Police Station, and then later housed a utility vault that provided services to the Church.

Excavations are planned to continue in these units for the next few weeks.