The Joys of Ground-Truthing

In past posts I have noted the importance that geophysical survey has played in our project. From the initial magnetic survey carried out in 2008 to our efforts to "ground-truth" the results by excavating where significant magnetic anomalies have been recorded, magnetic gradient survey has proven its value many times over. Its most spectacular success was the detection of the pit house, Feature 09-04, last season, but this year's work reveals how truly sensitive the instrument is, and, of course, the great proficiency of its operator and data-cruncher, Jarrod Burks.

In this post, I provide some of the results of our ground-truthing for a quite busy section of our current excavation area. The image below is a closeup view of the magnetic survey map for the western section of our bulldozer transect. The dark anomalies with feature numbers are those that mark prehistoric features. Note that every significant anomaly turned out to be a feature! No duds in the bunch. Pretty darn good and a great help to our efforts.

Probably the most indistinct feature is 09-18, a section of the oval enclosure ditch. It contained little of the oxidized soils, pottery, or fire-cracked rock that make for a strong anomaly. And it wasn't very easy to see when we dug into it! Feature 09-14 was a large but very thin lens of midden soil, charcoal and patches of burned earth. Still, the two small decorated pot sherds it contained proved very useful for placing its origin in the Late Prehistoric period. In contrast, Feature 09-26 was a large and deeper pit that contained nothing but charcoal, FCR, and a few flakes--very uninformative by comparison. Feature 09-34, shown below, was small but magnetically powerful since it was filled with fire-cracked rock.


Feature 10-13 was just opened today. It appeared as a rather indistinct, gray-brown feature stain in plan. Excavation of one half revealed a healthy amount of FCR, pottery, and charcoal-laden soil. A respectable amount of magnetic stuff but seemingly not that different from other features we have found that did not show up on the mag map. But we still have the other half to dig, so we will see.

Finally, there is what I have been calling "the big blob," a very large, somewhat irregular mag. anomaly, the north half of which lies within our transect. Now I suspected that this was more than one feature, but upon excavation it proved to be very complex. What we found were at least three overlapping pit features with some dark soil zones between them. We have spent the last several work days carving these features up in such a way as to sort them out. We are still


at it, but at least one we now know dates to the Middle Woodland period. I will have more to report on these interesting features later, but for now they reveal how complex the relationship is between the archaeological record and our high-tech methods of reading it.

Soggy Site

A series of thunderstorms from Wednesday to Thursday dumped over an inch of rain on our beloved site. We were forced to 'bug-out' on Wednesday afternoon at 2:00 pm as an impressive thunderstorm approached us rapidly from the northwest. We were so busy packing up equipment and taking down our canopies that we didn't even feel the minor earthquake that came through about that time--what a dedicated crew!

We spent part of Thursday morning bailing water out of the units. This is a vital task that must be learned by all budding archaeologists; the trick is to get as little water on yourself as possible and to avoid slipping on the slick plastic tarps.

The upside of all this is that, because all but one of our currently open units were much too wet to excavate, we were forced to open up two new 3 x 3 meter units eastward along the transect. The wet remnants of the plow zone soil shoveled off rather easily and the weather was cool. Soon the subsoil was reached, and we were met with a wealth of possible post molds and some very interesting-looking feature stains (note some of the dark stains in the image above). One unit, 508N 515E came down on several distinct pit features that had shown up as half of a huge magnetic anomaly during the geophysical survey--mag anomaly no. 79 for those of you keeping score. More on this and other new discoveries later. A muddy time was had by all.

Following the Stockade Line

Last Monday, we opened another 3 x 3 meter unit, but unlike the others, this unit was placed just to the north of our bulldozer transect at 514N 509E. This spatial deviation was designed to expose more of the eastern stockade line discovered last week. As expected, more of the distinct line of post molds were seen clearly on the floor of the unit and the line continued to the northeast. This particular segment of the line told us even more since it clearly ran across Feature 09-18, the filled ditch of the oval enclosure which was also exposed in this unit. Thus, we now know that the stockade line was erected after about 300 B.C., which is our current date for the filling of the enclosure ditch. How many years after is still uncertain.

The image below shows unit 514N 509E with the stockade post molds marked by red flagging tape. The line runs directly southwest (toward the corner where Jim and Debbie--with the fancy knee pads--are standing). You will notice that the line runs through an oval feature stain that is


partially excavated. This is Feature 10-11, a shallow pit or lens of dark soil that contained FCR and a few pot sherds. Interestingly, the post mold line disappeared at this feature, but upon excavation, the two missing post molds were exposed. As the image below shows, the post molds were 'hidden' under the pit (one is indicated by the arrow), which means that this small feature was constructed after the eastern stockade line came down. Unlike Feature 10-02, which also interrupted the post line, we recovered no good diagnostic artifacts from Feature 10-11 which could give us some chronological information. We will not chase this stockade line farther for the time being; we have much still to do in our main transect.