August 7, 2004
Alison has started her own excavations in Locality B, across the river and nearer the foothills of Mt. Olorgesailie than either Site 15 or DE 89. Like Locality G, where John has been working, Locality B has exposures of the New Formation and the later Oltepesi Formation, with some Middle Stone Age and Sangoan sites.
Last year, Alison excavated a geology trench down one hill, and found many MSA stone tools, but not many bones. This year, after surveying one area, she found more obsidian flakes and some more bones, and decided to excavate there. In Locality B, it's sometimes hard to tell exactly where on the slope of a hill the artifacts are coming from. Alison spent a day walking up and down the hill slope and noted where the artifacts can be seen. The highest place on the slope where artifacts are visible is probably the layer where they come from, before they are washed out by erosion and then rolled down the hill. But it's not always clear, so Alison makes a habit of digging test trenches near, but not right on, the highest concentration of artifacts. As you can see in the photograph, a test trench is a series of steps that run down the face of the hill. They allow Alison to see clearly the strata and any artifact layers that may be in the site. They help her orient herself vertically, so that once she knows what layers to look for. She can then extend a normal archeological excavation horizontally to one side.
In the New Formation, there are two kinds of artifact concentrations. The first consists of artifacts mixed in with gravel, where the bits of gravel are about the same size as the artifacts. These are concentrations generally caused by water that flowed in an ancient river or stream. We call this "secondary context" - artifacts that were moved to a new place from the original site where hominins left them. Gravels are definitely not the best place to dig if you're interested in the actual behavior and original places where hominins lived or visited. The second kind of concentration occurs in a paleosol. A paleosol is an ancient soil layer that supported plants and was relatively stable over time (it's sort of like your yard). Artifacts on this surface generally aren't put there by water, but rather by the hominins who used them, and if they haven't been disturbed, we say the artifacts are 'in primary context.'
Paleosols are interesting to Alison not only for the tools, but also because bones are also often preserved in these soil layers. There have been some animal remains found in the New Formation in Locality B, including an ostrich eggshell, a crocodile tooth, some bovid teeth, and a turtle or tortoise shell. Alison hopes to find more, since finding animal fossils will help give us a clearer picture of how the environment had changed over the last 300,000 years or so.