We’ve added a new staff member to the 2012 OSU Archaeology Field School at Cooper’s Ferry, named Hayden Wilcox.  Hayden is an OSU undergraduate who is creating a series of informational videos about the site and our excavation activities there.  You can watch Hayden’s video creations at our new YouTube channel dedicated to the Cooper’s Ferry site: http://www.youtube.com/user/coopersferrysite?feature=results_main.  He’s already posted four short videos that focus on aspects of excavation and is preparing others for distribution in the next weeks.

In March of this year, our team published a paper entitled “A PXRF-based chemostratigraphy and provenience system for the Cooper’s Ferry site, Idaho” in the Journal of Archaeological Science (Volume 39, Issue 3, Pages 663-671).  You can download a copy of our paper here: Davis et al 2012 JAS.  In a nutshell, this paper presents the application of portable x-ray fluorescence (PXRF) technology in a new approach to characterizing the geologic layers in an archaeological site from their inherent elemental geochemistry.  Knowing the difference between a site’s geologic layers allows you to correlate objects across horizontal space (i.e., when objects are contained in the same layer) and to tell when an object is in the wrong place as a result of having been moved vertically from one layer into another.   This methodological approach, which is called chemostratigraphy, allows us to take geochemical measurements in the field to determine how artifacts and other materials are related to a site’s different sedimentary layers.  Admittedly, this sounds pretty esoteric but being able to establish the spatial relationship between artifacts and disturbed or undisturbed sediments, or what is called associative context, is a critical part of our research program.  To fully understand this topic, I’ll present a hypothetical scenario of archaeological site formation to illustrate how our quest for establishing associative context can represent a “wicked problem” at the Cooper’s Ferry site.

We begin our hypothetical scenario of site formation on a sand bar along the Salmon River.  At one point, say 10,000 years ago, foraging peoples set up camp on this sand bar and in the process of practicing their daily activities, leave behind artifacts, food remains, and activity features such as fire pits.  In this process, our hypothetical foragers create a site.  Eventually, the foragers depart camp and the stone tools, bits of bone and shell, and charcoal-filled fit pits they leave behind on the sand bar get buried beneath silt deposited by a flooding Salmon River.  At this point, our hypothetical site consists of two layers—a lower sand layer containing 10,000-year-old archaeological materials, which is overlain by an archaeologically sterile layer of silt.  Foragers return to the site after a 1000-year absence and leave behind more artifacts, faunal materials and make a new fire pit feature, all of which are incorporated into the surface of the silt layer.  This particular arrangement of sediments and the different traces of cultural occupation that they contain will stay preserved in their vertically layered stratigraphic sequence until site formation processes work to alter them.  Site formation processes are those natural and cultural actions that work to alter the original state of an archaeological sequence by moving, removing or destroying items and sedimentary layers through time.  At our hypothetical site, burrowing rodents enter our site just after 9,000 years ago and dig tunnels through its deposits.  In the process of constructing their burrow networks, the rodents displace sediments and the objects they contain and push them vertically and horizontally from their original locations.  Through this process, the burrowing rodents change parts of the site’s layered sequence, moving older deposits and objects into the younger layer and vice versa.  If we were to excavate our hypothetical archaeological site, knowing how to identify and separate the effects of the burrowing rodents would be critical to our efforts to separate the 9,000 and the 10,000 year old cultural occupations from one another.

It is imperative that we are able to identify when an object has been moved from one layer to another as a result of any site disturbance processes.  Being able to accurately determine whether an object is in association with disturbed or undisturbed sediments is a “wicked problem” that must be solved if we are to be able to accurately evaluate the archaeological record at Cooper’s Ferry.  Lacking an ability to scientifically evaluate the associative context between an object and the sediments it was found with introduces an unacceptable level of uncertainty into archaeological research.  When I say scientifically evaluate, I am speaking about the use of a method that generates empirical observations about the relationship between an artifact and its adjacent sedimentary matrix that can be subjected to statistical tests of correlation, discrimination, and significance.  Such a scientific method of evaluation is different from that typically practiced in field archaeology, where archaeologists typically use their eyes and sense of touch to make observations about whether an artifact is “in place” or “disturbed.”  In most cases, field observations are probably good enough to tell whether an artifact is in its original position or if it is within the confines of a rodent burrow or some other kind of post-depositional alteration.  At the majority of sites, correctly guessing the associative context of an artifact in most cases is good enough; however, at an extraordinary archaeological site like Cooper’s Ferry, we’ll need to do better to satisfy the critics (and ourselves, for that matter).

As in the earlier hypothetical scenario, our wicked problem is that rodents have burrowed through many parts of the Cooper’s Ferry site and if we cannot accurately and consistently discriminate between mixed sediments and unmixed sediments, we’ll never be able to understand its archaeological record.  Because the burrowing actions of rodents leave behind sedimentary signatures (e.g., infilled rodent burrows containing sediments with texture, color and geochemical attributes that contrast significantly with surrounding undisturbed sediments), they can be identified and addressed separately from undisturbed sediments.  Some kinds of sedimentary disturbance are subtler and can elude detection by the naked eye.  To avoid this problem, we’ll use our Olympus Innov-X Delta PXRF unit to measure the elemental geochemistry of sediments directly associated with all formed artifacts (e.g., bifaces, projectile points, cores), faunal materials and key samples (e.g., charcoal for radiocarbon dating).  We’ll subject the geochemical data collected by the PXRF to a set of statistical tests that will evaluate how well the elemental composition of the measured sediments compare to our previously established chemostratigraphic framework.  This approach will allow us to generate scientific assessments about the quality of associative contextual relationships between objects and sediments as we find them during the course of excavation.  Furthermore, the use of our new PXRF method provides the first quantitative assessments of associative context—an entirely new class of archaeological evidence that takes our investigation of Cooper’s Ferry to a higher level.

Aleks: What is your interest in archaeology?

Jasmine: Right now I am looking at Geoarchaeology, it seems to be a field of archaeology that is really interesting to me and I would like to work more on the subject to determine if its something I would like to further pursue. This field school offers a good opportunity for that.

Aleks: What is your grad student project while working with Dr. Loren Davis and the Cooper’s Ferry field school?

Jasmine: I got the chance to test out the magnetic susceptibility gun and looking at the lithostratigraphic levels of Unit A, specifically pit feature 1. I am interested in looking at the magnetic properties of the soil.

Aleks: How will you do this?

Jasmine: By using the magnetic susceptibility gun I was able to take magnetic readings from the layers in the soil. I pointed a small gun-like instrument at the soil and my pit partner Jamie Klotz pushed the button on a netbook and the instrument shot a magnetic pulse which then bounced back and read the magnetic composition of the soil. The information then appeared in the netbook.

Aleks: Is it safe to use the magnetic susceptibility gun?

Jasmine: Yes, it’s 100% safe.  There is no radiation and it is quiet and easy to use. You simply point and push a button, the instrument does the rest of the work.

Aleks: Can you describe the pit feature?

Jasmine: The pit is composed of eleven different layers, which is more than were established in 1997. This means by looking at the profile, or the side wall of the pit we can see different color sediments. Each layer has a different composition and so with the magnetic susceptibility we can distinguish these layers from each other due to their magnetic difference. At least, that is what we want to establish.

Aleks: How did you proceed to do this?

Jasmine: We took 25 readings from each of the layers in the pit feature and then took 50 readings from each of the lithostratigraphic level (LU), excluding LU 1.

Aleks: So what will all of the readings tell you?

Jasmine: Hopefully, after the analyses are complete, we will be able to discern the LUs from each other using their magnetic properties.

Aleks: What were the results so far?

Jasmine: We have completed the testing and have taken enough information but the results have yet to be determined. We are still working on the data and with the help of Dr. Shane MacFarlan, one of the staff members, we should have the information soon.

Aleks: How did you like using the magnetic susceptibility gun? Did you value the integrity of the procedure?

Jasmine: I really enjoyed using this procedure I was not familiar with the magnetic susceptibility gun but the procedures were very carefully explained and any questions I had Dr. Loren Davis was always at hand to help me. I think a test such as this is good because it will allow us to understand the sediment layers in a different manner, which will then either support our previous hypothesis of disprove them. Either way we will definitely discover something new.

Aleks: Did you enjoy your time in such a deep hole looking at sediments?

Jasmine: It was very dusty and I was very deep but with my pit partner, Jamie Klotz.  I like to think we had a good time. We certainly learned a lot, such as using the Munsel book to properly identify coloring of the sediments, we looked at texture and learned about texture analysis and about sediment identification.

Aleks: Any final thoughts?

Jasmine: My unit partner and I definitely learned a lot about the magnetic susceptibility procedure and it also allowed us to start thinking about archaeology in a different manner. There are many possibilities to help us understand the nature of archaeological sites and by using procedures such as the magnetic susceptibility we begin to understand that there are no limits to how we can proceed to understand archaeological sites.  I cannot wait to see the results.

First, we purchased another Nikon Total Station laser transit, which is used to double the rate at which we can record artifacts and other objects exposed in our excavations.  Last year, three-point spatial coordinates from our lone total station were in high demand and students often had to wait 30 minutes or more for their turn to obtain readings.

We have also acquired a Bartington Magnetic Susceptibility meter that we’ll use to measure the magnetic properties of sediments and artifacts alike.  This meter allows us to generate descriptive physical data about different materials that we can use to reveal patterns in the site’s geoarchaeological record.

We’ve written in the past about the portable x-ray fluorescence (PXRF) device that we use to measure the geochemistry of artifacts, sediments and other objects relevant to our research.  The PXRF device is a sophisticated piece of field technology and has tremendous potential for solving different kinds of problems.  We’re awaiting the arrival of our new Olympus Innov-X Delta PXRF device, which is currently being built and calibrated at the factory.  Anticipated arrival of our new PXRF device is in two weeks and we look forward to putting the machine through its paces until we close the site for the season.

Prior to coming out to the field, staff members Davis, Macfarlan and Henrickson submitted a manuscript to the Journal of Archaeological Science that presents a method for establishing and using a chemostratigraphic framework at the Cooper’s Ferry site.  The method described in this paper harnesses the power of the PXRF device to discriminate between different deposits of undisturbed archaeological site sediments on the basis of their geochemical attributes.  Moreover, this method can also identify the presence of disturbed sediments.  Being able to tell whether a particular artifact is in direct contact with disturbed or undisturbed sediments gives us a powerful means establishing when materials are contemporaneous with one another and also identifies datable samples that are in undisturbed contexts.  Having such a tool at hand is not only critical to our work at the Cooper’s Ferry site, but elevates archaeological debates about contextual associations between sediments and artifacts from the qualitative to the quantitative (and scientifically replicable) arena.  Here’s the abstract from our submitted paper:

A PXRF-Based Chemostratigraphy and Provenience System for the Cooper’s Ferry Site, Idaho

Loren G. Davis, Shane J. Macfarlan, and Celeste N. Henrickson

Paper in review at the Journal of Archaeological Science

Correlating archaeological finds with their associated stratigraphic context is elementary to modern excavation methods. Ascribing primary depositional position and associative context is traditionally a qualitative exercise. To improve the empirical nature of this process as part of new excavations at the Cooper’s Ferry site in western Idaho, we established a chemostratigraphic framework that enables us to quantitatively relate the elemental geochemistry of sediments associated with artifacts and other samples back to a master lithostratigraphic sequence. We subjected a total of 151 portable x-ray fluorescence (PXRF) readings from six lithostratigraphic units to multiple discriminant function analysis, which led to the identification of characteristic elements. To test the site’s chemostratigraphic framework, we collected PXRF readings from an infilled rodent burrow, which visually appeared to contain mixed sediments from multiple lithostratigraphic units. Statistical analysis could not relate the rodent burrow’s sedimentary geochemistry well to any of the known lithostratigraphic units, thus marking it as disturbed. This methodological approach allows us to make quantitative correlations between stratigraphic units across the site and most importantly, enables us to independently evaluate whether objects from any part of the site are in direct association with disturbed or undisturbed sediments.

As we await the arrival of our new PXRF device, students work to collect sediment samples from the vicinity (ca. 2 cm west, directly underneath, and ca. 2 cm east) of artifacts found in the excavation floor.  We’ll measure the elemental geochemistry of these gathered sediments taken near with artifacts in order to assess whether they indicate the presence of disturbed or undisturbed contextual association.  Once the PXRF device is in our hands, we’ll take these readings from in situ sediments near and under artifacts.

Last week, we had an unusual visit from the air.  Mary Crommett—a graduate of our field school from two years ago—and her pal Toby flew over our camp and landed at a local airstrip.  They had brought Toby’s experimental two-seater airplane from Oregon on a tour of western Idaho’s canyonlands.  Mary took several photos of our camp, the top of the canyon, and our excavation shelter at Cooper’s Ferry.

Upon arrival to the Nez Perce National Historical Park the students were given the opportunity to assemble a tepee. One by one the students all helped to place the canvas cover, the stakes and the door. The students then all gathered inside to experience what the inside of a tepee felt like.

Afterwards, the students were presented a short film that explained the Nez Perce culture, history, and how they have maintained their traditions to this day. Kevin Peters, a National Parks Service Interpretative Specialist and member of the Nez Perce Tribe, and discussed historical photographs of Nez Perce figures and was able to answer questions pertaining to the Nez Perce culture.

After this introduction to the Nez Perce culture, the students were treated to a demonstration of the dart thrower (atlatl (say “at-lat-l”)) and were given the opportunity to use the weapon on a cardboard target of Rocky and Bullwinkle. Of our group, only two were successful in hitting the target. Clearly, throwing the Atlatl takes years of training and precise technique, and had this been a real hunt we would have been pretty hungry.

Next, the students were shown how to string and use a bow and arrow system.  Although more familiar to some students than the atlatl, the results were pretty much the same: only a few were able to hit the target.  The bow was small and comparable to the same type of bow used traditionally by the Nez Perce peoples.

Once the students had their fill of trying to kill the cardboard animals, they were taken back inside to the museum portion of the park where they were given explanations of cultural materials from the Nez Perce culture.  For this part, Diane Mallicken, Nez Perce interpretative specialist explained various materials such as the basket caps woven out of hemp and sometimes cornhusks. These caps were valued by the Nez Perce women as they were worn only by women of influence. The students also heard about the importance of camas root and the Nez Perce harvesting technique, which embraced the sustainable ideal of taking only as much as one needed.

To end the tour, Jason Lyon, a Park Ranger with archaeological experience, took the students to the rest of the park, which extends along the Clearwater River, downhill from the museum. He showed and discussed various archaeological sites, including semi-subterranean house pit depressions. The park is rich with contact and pre-contact period archaeological sites and provides the public with many educational opportunities.

Students of the Cooper’s Ferry field school were given a unique and memorable adventure as well as a very informative and educational experience about the Nez Perce culture. The students were very thankful to receive such a wonderful tour and day of educational activities.  Everyone gained invaluable knowledge that they will apply to their work at the Cooper’s Ferry site.  Many thanks to the staff of the Nez Perce National Historical Park!

We set up our new excavation shade shelter (40′ x 60′) and set to work uncovering our excavation block.  Like last year, we had to re-excavate the thousands of sand bags we placed into the site, which protected our block over the winter.  There’s not getting past it: removing several thousand sand bags is hard work; however, our gang was able to empty the excavation block in about four hours.

With the excavation block opened once again, we set to work cleaning the floors and walls of loose dirt and fine roots.  We reviewed excavation procedures and how we record archaeological data in different ways.  By the end of the week, students had recorded the elevations of their excavation units and were ready to start this year’s excavations.

Today, students began excavating in their units and immediately uncovered numerous lithic flakes and fragments of bone and shell.  Everyone approached their first day of excavation at the site with care and enthusiasm.  The day passed quickly and we were forced to close up the operation just before 3:00 pm as a black cloud rolled through the canyon, bringing a short but intense thunderstorm.

In all, this has been a good week.  Everyone is settling in and cheerfully approaching this summer’s field season.  Tonight, we’ll have a lecture on the archaeology of Cooper’s Ferry and how it fits into the early prehistory of the Pacific Northwest.  Tomorrow, the crew will go to the Nez Perce National Historical Park for a tour of the facility’s collections and to learn through some hands-on activities.

Don’t you realize that you’re only digging through road fill?
In the 20th century, road construction took place in the lower Salmon River canyon in the vicinity of the Cooper’s Ferry site. To make the modern road, construction workers removed gravelly sediments and basalt bedrock deposits, cutting a notch into the toe of the canyon slope. The geological materials that they removed to create the road needed to be moved elsewhere and some of this material was pushed over the edge of the bank toward the river in the area of the Cooper’s Ferry site. Because road fill is a recent kind of deposit that will not contain intact archaeological evidence of ancient human occupation at the site, working only in these deposits would be a bad thing. So, before we spend our time and effort to carefully excavate at a potential site, we must know more about what the site contains. We can gain this advance knowledge of what’s in a site in two ways: first, we need to understand what’s already known about the site from any previous archaeological or geological excavations; second, we can dig a small hole into the site to quickly see what’s under the ground.

During several summers in the 1960s, an archaeologist named B. Robert Butler excavated a trench toward the site’s eastern end. Butler noted that they encountered thick deposits of fill dirt, likely from road construction; however, intact archaeological deposits were found toward the bottom of their excavation units. In the summer of 1997, Loren Davis directed the excavation of a single test pit (measuring 2 x 2 m or about 6 x 6 feet in surface area) on the western edge of the site to a depth of 2.5 meters (a little over 8 feet deep). This test pit gave us a window into the ground, so to speak, showing a series of different layers made of varying colors and kinds of geological materials—nearly all of which contained prehistoric artifacts. The 1997 test pit did encounter a layer of fill, which measured less than a foot thick, at the site’s surface. In addition to finding artifacts, our 1997 test pits also found the intact forms of several ancient campfire hearth and two different pits. One of these pits contained a collection of stone tools, including beautifully crafted spear points, which were placed in the ground for safekeeping. We also sent small fragments of animal bone and charcoal to scientists at a commercial laboratory called Beta Analytic (you can learn more about this lab at www.radiocarbon.com) who conducted radiocarbon analyses on our samples. The results of these radiocarbon analyses showed that organic items held in the layers at Cooper’s Ferry range in age between about 8,500 and 13,000 years old.

So, there clearly is road fill at the site, but the thickness of this deposit varies across the site. On the basis of information from prior excavations, we know that both disturbed road fill material and undisturbed archaeological deposits exist at the site and that the road fill deposits appear to be thicker on the upstream (east) end of the site’s landform. Based on our study of the site, we also understand how to tell the difference between road fill and undisturbed archaeological deposits. Unlike undisturbed deposits in the site, road fill deposits show swirled coloration (like a calico cat), lack fine sedimentary layering produced by ancient floods of the Salmon River, do not contain intact archaeological features like pits and campfire hearths, and commonly contain items from the 20th Century.

Geological cross section through the Cooper’s Ferry site from south (left) to north (right) through the site’s western (downstream) end.

This cross section model shows our expectation of what we would see if we cut a large trench through the site, based on previous archaeological and geological studies. The 1997 excavation unit is shown as the light orange rectangle and extended through deposits 3 and 5. Our recent excavations were built as an extension of the 1997 unit and have progressed through about half of the depth of the 1997 unit. The excavation units are actually oriented along an east-west line but are shown in a north-south orientation here in order to best illustrate how they relate to the site’s deposits.

For this week’s post, we’ll focus on the first step in our laboratory analysis: artifact cataloging. Before we can do any other kinds of analyses on the archaeological materials, we must account for all of the artifacts and samples collected during the previous field season. The catalog has information about each artifact recovered from our site including its catalog number, location within the site, contents, weight, basic morphological measurements, and any special notes. Building an artifact catalog requires us to examine each artifact or sample, collect new information about the item, and enter these data into a paper-based catalog. Recording these new data and other information recorded during the item’s original discovery at the site, will take several people hundreds of hours.

Student working hard on the catalog.

Although we are not certain just how many items we will have to catalog before the end of our project, we can make an educated guess about how large that number might be. As a result of the 1997 excavation of a single 2 x 2 m unit at the site, 52,025 items were grouped into 5,347 catalog entries. Our current project has opened up nine new 2 x 2 m excavation units, thus, if the new units produce the same amounts as the 1997 2 x 2 then we may ultimately need put something like 468,225 items into 48,123 catalog entries. Metaphorically, it’s like eating a whale and we’ll just have to start one bite at a time…

One page of many from the artifact catalog.

Here’s our cataloging procedure: starting with an excavation unit’s level bag, artifacts are given a gentle dry brush cleaning (it’s where old toothbrushes go to die). The artifacts may then be counted, measured and weighed depending on their type—some items, like bone or mussel shell fragments are weighed but not counted at this stage, given their fragile state (too much handling creates new fragments, which must then be counted, which makes new fragments—you get the picture). A formed stone tool, such as a projectile point, is counted and weighed; its length, width, and thickness are measured; and its rock type is determined (e.g., igneous, metamorphic, cryptocrystalline silicate).

A biface's width is measured.

Once we gather all of this information, the item is returned to its bag and placed back into the correct storage container. We’ll have completed cataloging the 2010 artifact collection before we return to Idaho for this summer’s field school session.

Plywood is placed along the walls of the unit to help prevent erosion.

Once the plywood was in place, students began to carry thousands of sandbags and placed them into the units. These sandbags could weigh up to 40 lbs.

Students begin to fill in the site with sandbags.

After only a few hours, the entire unit was mostly filled with sandbags. The large number of students greatly reduced the time it usually takes to fill in a site.

The site is filled in with sandbags.

Students stomp down the sandbags.

Next, students place a tarp over the sandbags.

In order for the excavated units to blend in with the environment, students pour the sediments from the extra sandbags and from the screening area on the surface of the sandbags.

The sediments in the extra sandbags are dumped onto the site.

The site is filled in and the tents are taken down.

After the speedy backfill and deconstruction of the site, students are able to gather around Cooper’s Ferry one last time before heading back to camp for some food and a shower.

OSU’s 2010 Field School at Cooper’s Ferry

Here is a video showing the backfilling process (no audio). The video is only 2 minutes long (we wish backfilling would have only taken 2 minutes!).