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Archaeology Update — Excavations on Bonham Encounter Soil That Predates Human Occupation

August 18, 2020

Archaeological work conducted by Pape Dawson resumed within Crockett and Bonham Streets as part of the Phase I of the Alamo Plan. Much of the work that occurred over the past week consisted of the excavation of a utility trench along Bonham and Crockett, as well as the excavation of the location of a utility vault on Bonham.

Much of the trench work has encountered previously disturbed soils. In certain portions of Bonham and Crockett, the layer of asphalt measured approximate one foot in thickness. Trench depths reached up to a maximum depth of 10 feet below the surface. No significant artifacts have been encountered during the current work.

During the excavation of the utility vault on Bonham, soils encountered included dark clay in the upper 6.5 feet below the surface. At approximately 6.5 feet below the surface, the soil changed to a yellowish clay, often referred to in this area as Navarro Clay. This type of soil predates human occupation, and therefore indicates that it will not contain archaeological artifacts.

Concrete sidewalk removal along Bonham Street
Figure 1. Removal of the concrete sidewalk along Bonham Street.
Dark clay beneath the concrete setting bed
Figure 2. Dark clay beneath the concrete setting bed. Lighter gravels indicate a previously installed utility line.
Navarro Clay beneath the dark clay
Figure 3. Evidence of the Navarro Clay beneath the dark clay.
Navarro Clay noted in the utility box
Figure 4. Yellow, Navarro Clay noted in the utility box.

No artifacts or features were encountered during the excavation of the utility box. The area was prepared for the installation of a 7-x-7 foot box that was placed once the terminal depth of approximately 12 feet below the surface.

Raba Kistner has continued investigations within the Alamo Church, with the exhumation of known burials and continuation of the test units to allow for the installation of the sensors for monitoring the conditions below ground. To date of this update’s publication, the archaeologists have finished exhumations and excavations in three of the four units that fall under the exhumation permit.

Archaeological investigations will continue over the next several weeks, with the archaeological excavations associated with the preservation work in the Church likely wrapping up before the end of August. The historic architects and the Alamo Conservator have been working to install the moisture monitors as well as perform the necessary boring in the historic structure’s walls to examine the mortar properties as well as place additional sensors.