Week 1: Part 2
On Wednesday, the students got their first taste of what its like to work in a heavily forested (and trampled) archaeological site. The students were divided into two teams: one to learn the basics of digital mapping, the other to measure and lay out our excavation areas. Today’s post will cover the progress of the first team.
Last year our field teams spent the majority of our time digitally mapping the Cliff Mine site, focusing on the industrial remains located at the base and atop the bluff that gives the mine its name. In order to do this, you use what is called a Total Station, a surveying instrument that stores distance measurement information that can be integrated with software on a computer for storage and display. It is a common site to see road crews and civil engineers using these tools to accurately site property lines and construction boundaries. We use it for very similar purposes.
The first thing you need for accurate Total Station mapping is good, consistent, ground control points from which to establish yourself when you begin your survey. Often, known survey pins (with known GPS coordinates) embedded on the sides of roads or as corner markers are available for this. In our case, last year we were able to find two of these points that we could then begin our entire project off of. From these two points we were able to accurately sitein a few dozen more control points around the site, and eventually from these control points, shot in another 4,000 plus points corresponding to artifacts, walls, and roads.
This year, we needed to re-establish those early controls in order to make sure this year’s mapping is consistent/accurate to last year’s. Unfortunately, the weather and maybe even some curiosity made for a difficult time in that re-establishment. Both of our original points were removed, one intentionally, one by the forces of nature. Many of our other control points were also removed by the same two processes over the site. Metal detectors pick up on the nail (the control point), and then people pull them up.* Simply walking around the site disturbs the nails as well, and even a few centimeters difference in their placement from one year to the next can mean an accuracy change of several meters given the size of range of elevation at Cliff.
The students were therefore tasked with creating a new grid of points off of last year’s field notes from which to build this year’s mapping. After two days of walking the site and trying to find multiple older points outlined in the field notes that were connected by line of sight, they were able to do this. It took a bit longer than expected, but allowed the team members to learn a valuable lesson, that site integrity is not easy. It is always important to have a back-up plan and accurate recording of your work so that future researchers can follow your lead and not have to start from scratch every year.
*To those of you who do metal detect at the site, I am not complaining about your practices. I may disagree with some of your methods and feel that the site’s artifacts should be left for study, not for sale or for a box in the attic, but I know that people have the right to the public lands too. And I know that many of you have valuable information I’m dying to hear about.
If you are going to metal detect or walk the site, please leave any nails or artifacts flagged with bright tape in place. These are not marking important finds, they are marking our control points we need to continue our work.