Where in the hell am I?

January 4, 2010

Fort Hood Day 11


11.5 Measuring elevation

Originally uploaded by texasrobo

A new year, and one more week at site 41CV389 in Fort Hood. We still haven’t named the site. I suggested “That One” so people would refer to it as “That One site.” Yeah, I’m not always that funny…
The photo shows one of my co-workers demonstrating how to measure the elevation of a unit. Various data (in the plural sense of “datum”) are set up around the units, and each is assigned an elevation based off of an arbitrary height (generally called 100.00) determined using a transit, theodolite, or total station. Or, barring this, you can just set a nail in a tree, call that 100.00, tie a string to it, and set your data by comparing the string levels.
A datum and elevation are very important, because most (if not all) sites are not on perfectly uniform, level surfaces. The ground surface of one unit may be 99.88 (or 12 cm below the 100.00 datum level), while another 5 meters away may be 98.88 (or a meter deeper). Both starting levels will be Level 1, and both may be 0-8 cm below ground surface, but by using a datum it will be clearly noted that these levels are actually a meter different in height. Basically, it creates an arbitrarily determined point to which the relative height of the site deposits can be compared.More importantly, it also helps you know when you’ve excavated to the 10 cm depth of each level. You measure the elevation of a unit using string tied to the datum rod. This string has a line level on it, so that you know when the string line is perfectly level (which can be deceiving just eyeballing it). When the string line is level, you use a tape measure to measure the distance from the string line to the floor of the unit (or whatever you’re measuring). So, if your string line is set at 99.80 and your tape measure shows 71.5 cm between the line and the floor, it means that you are at 99.085 (and most likely, as often happens to me, you’ve dug too deep again).
Not sure if that’s a very good explanation, but it’s the best I’ve got.
Anyway, there’s six of us digging this week, working 10 hour days. With the load-in, drive up from Austin, uncovering of the site, end of day packing of equipment, and return trip to the hotel, this gave us around 7 hours of actual excavation. Most of this was focused on Area C, home of the money units. Once again, I was spoiled and assigned to dig the unit most likely to have something cool. And it did, another small burned rock cluster feature with a large mussel shell at the edge! Other folks dug the other (former) money unit, and the new 1.25 x 2 meter unit north of the money units. None of these had anything of particular interest, although the low recovery from the new units shows how discrete the occupation areas in the money units are.
A couple of people also worked on Area D-1 (or Area D south). This continued to be a low recovery area. The goal here is a feature exposed at the base of Trench D. They should have all six units down at that level by tomorrow.
I’m so glad that things worked out for me to be here for the last week of the dig. While I’m completely sick of surveying in East Texas, I’ll be able to resign myself to that fate much more readily knowing that I’m not missing out on a much more interesting and fun project that I’ve invested a lot of work in.

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