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Weekly video blog updates

Posted by: | July 12, 2013 | No Comment |

Throughout this summer’s field season, we will be posting weekly blog updates on our YouTube channel available at www.youtube.com/user/CoopersFerrySite/

 

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River mussel shells are commonly found during our excavations at Cooper’s Ferry.  Mussels were eaten by the early foragers who lived in the canyon, providing a widely available source of protein.  In addition to revealing aspects of forager diets, we can submit mussel shell samples for radiocarbon dating, which reveals when the mussels were eaten at the site.  Over the past nine months, we have been collecting shell carbonate samples from mussel shells recovered from Cooper’s Ferry and other sites in the lower Salmon River canyon as part of a larger study of past climate.  Because we radiocarbon date the shells we are using for our paleoclimate study, we also learn more about the ages of the canyon’s archaeological sites.  This year, we’ve received the results of radiocarbon dating from 77 shell samples.  These shells were recovered from LU6, which is the dark brown layer we’ve been working in for the past few summers.  Normally, we wouldn’t submit so many samples for radiocarbon dating; however, our paleoclimate project relies on large numbers of directly dated shells that span the last 12,000 years and we’re fortunate that Cooper’s Ferry holds so many shells to study.  The 77 shell samples returned radiocarbon ages spanning the time period between 8030 ±37 radiocarbon years before present (RYBP; “present” being the year AD 1950), which, in calendar years, would be between 8971 cal BP to 9011 cal BP and 9138 ±38 RYBP (10234 cal BP to 10297 cal BP).  Because these 77 shells are found throughout the upper 40 cm of LU6, we’ve not yet determined the lower chronological limit of LU6; however,we expect that the lower part of LU6 will date older than 9138 RYBP.  Because the shell samples come from different excavation units that were dug into LU6, and because LU6 has some topographic variation that makes correlation between the vertical positions of radiocarbon dates more complicated than if the dates were found in a series of perfectly horizontal deposits, more work is needed to know just how finely we can divide up stratigraphic time at Cooper’s Ferry.  Suffice to say that we are confident that the upper half of LU6 dates between 8030 to 9138 RYBP (8971-10,297 cal BP). The presence of these radiocarbon dates in LU6 makes perfect sense since this layer contains both Windust and Cascade projectile point forms.  Throughout the southern Columbia River Plateau region of the interior Pacific Northwest, the transition from the Windust archaeological phase to the Cascade phase is seen to occur between 9,000-8,000 RYBP.  In the lower Snake River of eastern Washington, radiocarbon dates on river mussel shell have been viewed as unreliable because living river mussels had incorporated ancient carbon introduced into Snake River water from deep aquifers.  To check whether river mussel shells from Cooper’s Ferry would provide reliable radiocarbon ages, I submitted five shells collected from a beach along the Salmon River for radiocarbon dating.  These five shells returned ages of “modern”, showing an absence of an old carbon effect in Salmon River water.

CF Unit A isometric figure

Apart from defining the age of LU6, these new dates help us to better understand the larger chronological sequence of the Cooper’s Ferry.  In 1997, I directed the excavation of a 2 x 2 m test unit (Unit A), which contained four other sediment layers below LU6.  In a lower layer of wind-blown dust (LU3 in the figure below), we discovered a large pit that contained four stemmed projectile points.  This large pit, designated Pit Feature 2, also contained three charcoal fragments, which were submitted for dating and returned ages of 7300 ±70 RYBP, 8710 ±120 RYBP, and 11,370 ±40 RYBP; a fragment of animal bone returned an age of 12,020 ±170 RYBP.  Two radiocarbon dates came from the surface of LU3, where we also saw the upper limits of Pit Feature 2.  These two dates are: 10,050 ±180 RYBP (on bone) and 11,410 ±130 RYBP (on wood charcoal).  Because the two bone samples were not subjected to the  most rigorous pretreatments, they might not be very accurate.  These presence of the youngest two ages (7300 and 8710 RYBP) can be interpreted from different hypothetical viewpoints.  First, the younger dates might accurately clock the age of Pit Feature 2 and the older two ages (11,370 and 11,410 RYBP) could predate the creation of Pit Feature 2 and the occupation of LU3.  Second, the younger two charcoal dates might have been introduced to Pit Feature 3 (i.e., moved downward by burrowing rodents) thousands of years after the pit was created and buried at the site and the feature dates to 11,370-11,410 RYBP.  Third, it is possible that none of the available radiocarbon ages accurately date the earliest occupation and pit feature at Cooper’s Ferry and that their true age has yet to be revealed.

In my view, the 77 new radiocarbon ages from LU6 clearly show that the 7300 and 8710 RYBP dates do not accurately clock the age of Pit Feature 2.  Photographs and drawings clearly show the presence of a rock cairn on top of Pit Feature 2 at the upper limits of LU3; thus, the feature does not begin from LU6. In consideration of the available data, we can reject the first scenario as a plausible hypothesis.  Given the 77 radiocarbon dates from LU6, the deeper 7300 and 8710 RYBP ages cannot represent the age of Pit Feature 2 nor LU3 and give support to the second hypothesis that features the role of bioturbation.  The question is, do LU3 and Pit Feature 2 date to 11,370-11,410?  This question cannot be fully answered right now; however, it is important to point out that the available data do not require us to reject the hypothesis that these late Pleistocene-aged radiocarbon dates could date the early occupation of Cooper’s Ferry.

 

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We’re 41 days away from another field season at Cooper’s Ferry and I’m anticipating another summer of wonderful new discoveries. The 2013 OSU Archaeology and Geoarchaeology Field School will return to the Cooper’s Ferry site from June 17 to August 9th. We’ll continue excavating through lithostratigraphic unit 6 (LU6) and beyond into the oldest portions of the site.  We received a large batch of radiocarbon dates over the winter, that firmly establish the age of LU6. We also have big plans for integrating more digital technologies into this summer’s work, which will allow us to capture more information about the site as it’s being excavated. I’ll discuss all this and more in a series of new blog entries to come. Stay tuned!

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We completed our third week of excavations yesterday.  Overall, the project is running well.  We’ve a great group of students to work with and everyone is making excellent progress toward becoming proficient with the many facets of excavation at Cooper’s Ferry.

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.

 

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Although our blog has been silent since August 2011, we’ve been beavering away at many different projects related to Cooper’s Ferry and have much to share.  Over the next few weeks, I’ll describe some highlights from the past few months’ work and will discuss the upcoming 2012 OSU Archaeology and Geoarchaeology Field School at Cooper’s Ferry.  In this post, I’ll kick off our return to the blogosphere by discussing a recent publication that addresses a particularly wicked problem that plagues archaeological sites everywhere and how we’ve developed a solution for our own research.

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.

 

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Magnetics at Work

Posted by: | August 2, 2011 | 1 Comment |

We integrate new technological approaches to the measurement of different aspects of the Cooper’s Ferry site in hopes of resolving a pattern or finding a significant correlation between different parts of the archaeological record.  During weeks 4 and 5, students Jasmine Kidwell and Jamie Klotz worked to measure the magnetic susceptibility of Cooper’s Ferry stratigraphic units and the sedimentary contents of a pit feature exposed in excavation unit A.  Their work contributed to Jasmine’s field school graduate student project.  OSU graduate student Alejandra (Aleks) Jimenez caught up with Jasmine to discuss her use of the Bartington magnetic susceptibility meter.

 

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.

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With three weeks under their belts, the students are becoming confident in their abilities.  Nearly all of our field methods remain unchanged from last year; however, we’ve added some new techniques and equipment that augment our usual procedures.

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.

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During our second week, the staff and students of the Cooper’s Ferry field school had the opportunity to tour the Nez Perce National Historical Park, located in Spalding, about fifteen miles outside of Lewiston in Idaho. The students were given a tour of the National Park, which included many activities such as watching a video about the history of the Nez Perce people, atlatl throwing, archery, viewing the archives and collections, and receiving a walking tour of the park.

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!

 

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On June 20, OSU staff and students converged once again on the town of Cottonwood, Idaho.  In addition those of us from Oregon State University, this year’s students also come from Georgia, Texas, Michigan, Ohio, Illinois, Washington, Idaho, California, and New Mexico.  Unlike last year, we arrived to clear skies and were able to set up tents in a dry field.  The first week in the field was initially spent setting up our field camp.  We’ve made a few improvements to our field camp this year, which should make camp life a bit better.  We’re using last year’s dig shelter as this year’s kitchen shelter and have added  kitchen sinks, shelving, and new propane stoves.

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.

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Why dig at Cooper’s Ferry?

Posted by: | February 15, 2011 | 1 Comment |

People sometimes question the wisdom behind our choice to excavate at the Cooper’s Ferry site. Mainly this questioning is based on information about the recent history of the site and on things that people know about the archaeology of the Salmon River canyon. In this entry, I attempt to dispel a common misconception about the work that we’re doing at the site by addressing an important question that I’ve heard many times over the years.

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.

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