A Summary of the 2015 ENC Season

Greetings ASWT blog followers!  We realize we have done a poor job of keeping up with our blog for the past few months, but we wanted to share a few highlights from the 2015 season at Eagle Cave.

As we said at the beginning of the spring session, our focus was on the south wall of the Eagle Cave trench (see ENC Act 2).

The look of the trench changed dramatically as the season progressed - as did the crew.

The look of the trench changed dramatically as the season progressed – as did the crew.  Photo at top from February, photo at bottom from late May.

As is often the case in archaeology, our initial goals for finishing our work on the south wall were a little too ambitious, and we had to modify our plan.  While we had hoped to step and profile the entire trench face, what we did instead was focus on the upper “zone” within Eagle Cave, and intensively sample those strats (leaving the lower deposits for the 2016 season).

These are all 2D orthographic images of the trench generated from SfM.  The scale is the same for all 5 images.

These are all 2D orthographic images of the trench generated from SfM during the 2015 season. The scale and alignment is constant.

Rather than creating a tall, vertical profile across the entire shelter we “stepped” the profile as we excavated.  This gives the profile itself a very unique shape, but follows our motto of “Low Impact, High Resolution.” The stepped profiles and excavation units are more stable, and we only excavated small areas to do as little damage to the site as possible.  What was also striking was how far back the edge of the trench had eroded since the UT excavations in 1963.  Where we encountered intact deposits at the top of the trench was nearly 5 meters (~16 feet) south of the original 1963 trench edge.

All of our units were relatively small in size, and were placed to expose the intact deposits on the south side of the trench, but also do as little harm to the site as possible.

All of our units were relatively small in size, and were placed to expose the intact deposits on the south side of the trench, but also do as little harm to the site as possible.

As we were excavating we realized we had strikingly differential preservation of materials between the dripline (front) and the rear wall of the shelter.  We had expected to find more fiber and plant remains preserved towards the rear wall, but in fact we found the best preservation to be towards the dripline.  In this area we had thousands of fragments of lechuguilla, sotol, and yucca leaves along with innumerable seeds, pieces of wood and sticks, and other plant debris, whereas we encountered mainly ashy and reworked deposits toward the rear.

A nearly complete desiccated lechuguilla plant from the fiber zone in Eagle Cave.  The primary component of these fiber zones are thousands of preserved plant parts like this.

A nearly complete desiccated lechuguilla plant from the fiber zone in Eagle Cave. The primary component of these fiber zones are thousands of preserved plant parts like this.

In the fiber zones we also found some really extraordinary artifacts that archaeologists normally do not get to find: fragments of cordage, knotted fibers, sandals, a basketry fragment, and an atlatl dart foreshaft!

Perishable artifacts recovered from Eagle Cave (clockwise from top right): sandal fragment, foreshaft, cordage, and matting fragment.

Perishable artifacts recovered from Eagle Cave (clockwise from top right): sandal fragment, foreshaft, cordage, and matting fragment.

As fascinating as all the perishable artifacts are, we found something even more important: coprolites!  Emily wrote an excellent blog post on coprolites (see From the Bowels of the Lower Pecos) so I won’t go in to much detail, but we recovered hundreds of fragments of coprolites.  These artifacts will become invaluable as we begin to study how the people used Eagle Cave because they provide a direct link to what the people ate.  A pilot study of Eagle Cave coprolites is being undertaken by Texas A&M Ph.D. student Chase Beck.

Over the course of the spring we recovered hundreds of coprolites (in various sizes, shapes, and colors) from the fiber zone in Eagle Cave.

Over the course of the spring we recovered hundreds of coprolites (in various sizes, shapes, and colors) from the fiber zone in Eagle Cave.

Speaking of what people ate, we also found a variety of well-preserved faunal (animal) remains.  Although most of the bones were from small animals (like rabbits, mice, squirrels, and fish), we did find evidence of larger game like deer, bison, and antelope.

This probable antelope skull fragment was recovered during excavations.

This probable antelope skull fragment was recovered during excavations.

Throughout the spring the core crew (Koenig, Heisinger, Larsen, Pagano, and McCuistion) did an outstanding job of managing the thousands of samples, artifacts, 3D models, photographs, and countless other pieces of archaeological data.  We were fortunate to be able to share some of what we had learned in Eagle with our colleagues when we hosted an Eagle Nest Canyon Research Palaver, May 8-9th.  We had nearly 40 people come tour the site and discuss our methods and findings.

The Core Crew discusses our work in Eagle Cave with the palaver participants.

The Core Crew discusses our work in Eagle Cave with the palaver participants.

In honor of our last field day, the ENC crew dressed in 1970's garb.

In honor of our last field day, the ENC crew dressed in 1970’s garb, echoing our dry-shelter ecological predecessors, the Texas A&M excavators of Hinds Cave (see TBH exhibit.)

The January-May 2015 field season was very successful, and we will be learning more about Eagle Cave as we begin analyses.  We will be returning to Eagle Cave next winter to finish the  south wall.  In the meantime, look out for future posts, including one about the 2015 ENC Field School at Horse Trail Shelter!

From the Bowels of the Lower Pecos

By Emily McCuistion

Howdy, you may have seen mention of me on this blog and on our facebook page but this is my first official post for the ASWT project. I introduced myself at the beginning of the season, but to refresh I am one of the three interns on the Eagle Nest Canyon 2015 Expedition. My previous archaeology work has been primarily with the National Park Service and Forest Service, neither of which generally have the resources to undertake studies such as this one. This is the first in-depth archaeological excavation I have worked on and I’ve been blown away by the site itself, the other expedition members and the leadership overseeing the project, and our numerous collaborators who contribute their specialized expertise on various and sundry sub-disciplines (chemistry, botany, entomology, geology…the list goes on). It seems that there are infinite directions that project-related studies could go. I love interdisciplinary research and so I’ve been especially taken with the subject on which I am blogging. These delicate resources contain a world of information inside them- I’m glad to introduce the coprolites of Eagle Cave!

Me, poofing sediments off a coprolite.

Me, poofing sediments off a coprolite. I’m wearing a dust mask to protect my airway from the fine particles we stir up.

The study of human coprolites, also known as paleofeces, palaeofaeces, or simply dried-up old poop, was not regarded as important by the archaeological community until the mid-20th century.  Now we realize that we have a lot to learn from coprolites; they can inform us on past diets and ecosystems, the health of an individual, and the manner in which one ate and pooped. Archaeologists can look at the plant and animal macrofossils (visible undigested remains), tiny pollen grains, phytoliths (micro-structures created by plants), viruses, parasites, and even bugs found in coprolites!  Further, coprolites can be directly radiocarbon dated (so we can determine how old they are) and they preserve not only the DNA of the person who made the deposit, but also the DNA of the animals and plants that were consumed. Though perhaps less revealing, shape, color and of course location of the deposit are relevant. The study of odor, though noted by many researchers, has as yet not proved of scientific value.


FN31041 from Eagle Cave. We give each coprolite a unique specimen ID or Field Number (FN). We’ve found that one specimen can be made up of several segments representing one bowel movement.

Victoria excavating a coprolite. After documentation and careful extraction we transport the coprolites to the lab in boxes so that they are not inadvertently crushed.

Victoria excavating a coprolite. After documentation and careful extraction we transport the coprolites to the lab in boxes or by hand so that they are not inadvertently crushed in our packs.

Though I hesitate to mention paleontology- the oft confused (with archaeology) but unrelated study of dinosaurs- the study of dinosaur coprolites pre-dates the study of human. We are indebted to paleontologists for first recognizing the potential in coprolite study. The word coprolite, derived from Greek, was termed in the 1830s by an English paleontologist and translates to “dung stone.” I have yet to hear about human coprolites that have turned to stone, nonetheless the use of the word coprolite to describe human feces in an archaeological context is pervasive.

The Lower Pecos Canyonlands is famous for its coprolite studies, specifically those conducted on specimens excavated from Hinds Cave. Coprolites have been identified at other sites in the region but none have been so well studied as those from Hinds.


Profile of latrine deposit in Hinds Cave. Coprolites are in the upper right corner. Photo from texasbeyondhistory.net.


Hinds Cave is north of Eagle Cave, along the Pecos River. This photo from texasbeyondhistory.net was taken during the 1970s excavation, as evidenced by the excavation dust swirling from the rockshelter.

Even knowing that coprolites preserve well in the Lower Pecos we didn’t really expect to find them in Eagle Cave – coprolites were not found during the 2014 field season in any of the shelters investigated in Eagle Nest Canyon. Happily, during our excavations this spring we were excited to find an abundance of well preserved coprolites!  Thus far over 80 coprolite specimens have been inventoried during this field season, the vast majority of them excavated from near the front of the rockshelter and approximately a meter or two below the surface.

South Trench Profile of Eagle Cave with point-provenienced coprolites.

South Trench Profile of Eagle Cave with coprolites plotted- click on the image to enlarge.

At Eagle Cave the coprolites are mainly found in areas of discarded fire-cracked rock and plant remains (See: Between a Rock and a Heart Place for info on the fire cracked rock in Eagle). Sometimes they are found within compacted and dry-cracked sediment which we hypothesize may be evidence of urine-soaking, and of which we are taking samples. Sometimes a coprolite is found near a smooth river cobble; speculations about wiping methods ensue…

Matt "Call me John" Larsen was the first to start finding coprolites in the FCR/fiber layers near the front of the shelter.

Matt “Call me John” Larsen, pictured here saying “poop” in American Sign Language, was the first to start finding coprolites in the fiber layers near the front of the shelter.

Analysis of the coprolites is not yet underway but there are some basic observations that can be made about the Eagle Cave specimens. (We are assuming all the specimens we have collected are human; however, it should be noted that other animals have pooped in Eagle Cave over the preceding 9000 years and some of the specimens we have collected may not be human.)

Shape- It has been found that plump, shapely coprolites are often from a fiber/plant-heavy meal while the “loose” ones may be from an individual who had recently consumed a lot of meat. There are, however, many other reasons that one could have had fluid bowel movements: parasites, water containing algae-born toxins, plants with a laxative effect (sotol and lechuguilla – both baked in earth ovens – are known to have this effect on some people), even emotional states- fear has been cited- can cause diarrhea.


The “most-shapely” and largest of our specimens, and a good example of a segmented bowel movement: FN30984.

FN31296 fell a little flat.

FN31296 fell a little flat.

Size is affected by several conditions, including length of time since the last bowel movement and types of food eaten. Meals based on a single type of food can result in smaller stools, though a vegetarian diet can result in a larger stool than an omnivorous diet.

Diminutive FN31109

Diminutive FN31109. Compare it to FN30984 pictured above.

Color can be indicative of diet; the darker specimens often result from meat consumption while the lighter ones can be indicative of a vegetarian and/or carbohydrate-rich meal. When dried, however, colors change. Nonetheless, it is interesting to note color variations.

FN31048 is unusually orange in color.

FN31048 is unusually orange in color.

FN31103 is taupe.

FN31103 appears greyish, though it is important to note that our specimens still have sediment from excavation clinging to them.

FN31063 has a warm brown color, and lots of fibers.

FN31063 has a warm brown color, and lots of fibers.

Macrobotanicals, bones and fur (Macrofossils): Botanists and faunal experts can identify large plant and animal remains within coprolites. Thorough analysis requires breaking down the coprolite and separating it into constituent parts, however, macrofossils are sometimes visible on the surface. Many thanks to our faunal and botanical associates- Christopher Jurgens, Haley Rush, Kevin Hanselka, Leslie Bush, and Phil Dering- for helping to tentatively identify bones and seeds in a couple specimens (meet our zooarcheology and archeobotany heros here: “Come Visit:” A Zoooarchaeologist Is Lured Back to the Lower Pecos and here:The Archaeobotanical Team Forms).

This bone in FN30983 came from a jackrabbit-sized animal. In the words of Charles, "Ouch."

This bone in FN30983 came from a jackrabbit-sized animal. In the words of Charles, “Ouch.”

The diamond-shaped macrofossil in the center of this stool has been identified as a mesquite endocarp.

The diamond-shaped macrofossil in the center of this stool has been identified as a mesquite endocarp. The peak sticking off the backside are fibers from a plant such as lechuguilla or sotol.

FN30984 is chock full of seeds!

FN30984 is full of seeds!

FN30983 contains what looks like prickly pear seeds, the tastiest desert food I've ever eaten (unless you count Jack Johnson's mesquite snickerdoodles).

FN30983 contains what looks like prickly pear seeds, the tastiest desert food I’ve ever eaten (unless you count mesquite snickerdoodles).

Insects: We have yet to see insects in the Eagle Cave coprolites (though a fly pupal case rolled out of a bagged specimen when I removed it for this photo shoot) but we sometimes see their bore-holes. In her 1978 dissertation on Hinds Cave coprolites, Glenna Williams-Dean reported that the experimental stools (a comparative collection of modern specimens left to dry in a rockshelter near Hinds Cave) were up to 95% consumed by insects! When conditions are not suited to an insect, especially a flying insect, it quickly moves on. For this reason they are good indicators of change in climactic and other conditions. (see: Archaeoentomology? for more details)

Holey crap- I believe insects created this swiss cheese affect in FN31021.

Holey crap- I believe insects created this swiss cheese effect in FN31021.

One morning I resumed excavation of a coprolite I hadn't finished exposing the previous day. When dusting off the specimen this beetle crawled out from under it! Perhaps coprophagous (dung-eating) insects are interested in vintage as well as fresh specimens.

One morning I resumed excavation of a coprolite I hadn’t finished exposing the previous day. When dusting off the specimen this beetle crawled out from under it! Perhaps coprophagous (dung-eating) insects are interested in vintage as well as fresh specimens.

As mentioned previously, there are numerous other avenues for coprolite study (e.g., pollen, DNA/genetics, phytoliths, lipids, parasitism, general health, dietary nutrition, seasonality, medicine, food processing techniques, past environment, food trade/exchange, and food storage), but until we begin the analysis of the Eagle Cave specimens I cannot go into great detail.  However, I can provide a brief synopsis (definitely not exhaustive) of some things archaeologists have learned from conducting coprolite studies in the Lower Pecos.

Let us start at the beginning of the digestive system: the mouth. A significant malady affecting ancient Lower Pecos people was dental wear and eventual complete toothlessness by their 40s. Danielson and Reinhard (1998) studied coprolites to examine possible causes for the dental wear and tooth loss in Archaic-age Lower Pecos skeletons. They considered several hypotheses, including that the grit from food-processing stones was wearing down the tooth enamel.  Interestingly, they found no such grit in the coprolites they studied. Rather, calcium oxalate phytoliths (microscopic structures found in certain plants which pass unscathed through the digestive system) are found in abundance in Lower Pecos coprolites. They occur in the agave and cactus plant families (Agavaceae and Cactaceae respectively), and were found to be harder than tooth enamel. Not coincidentally, agave and cactus are a major part of the aboriginal diet of the Lower Pecos people. Other factors probably contributed to dental wear and loss, but a major cause was identified.

The phytoolith pictured up top is prickly pear. The lower is a sotol phytolith (texasbeyondhistory.net).

The phytolith pictured up top is prickly pear. The lower is a sotol phytolith (texasbeyondhistory.net).

So, we have a population of largely toothless people who still must eat. But, must they chew? Specimen FN30984 from Eagle Cave, and some found at other sites, indicate there was not always much chewing – what Dr. Black charmingly calls the “grab it and gulp” method of eating.

That brings us to what they were ingesting. Certainly food availability varies with the seasons and the millennia, but there is coprolite evidence people were eating many of the same foods that are available today (e.g., sotol, lechuguilla, cattail, wild onion, prickly pear, insects, fish, deer, pronghorn, rodents, reptiles, bison [the kitchen ran out of that a few years ago], and too many other foods and medicinal plants to go into at this time – check out the TBH exhibit on the Ethnobotany of the Lower Pecos Canyonlands for more information about Lower Pecos diet.  So far we have only been able to identify a few different seeds in the Eagle Cave coprolites but as we begin detailed analysis of the coprolites we will learn a great deal more.

Finally, when the meal is ready to be passed a decision has to be made on where to release the body’s effluent. I don’t know if there are enough sites in the region with mapped coprolite “deposits” to make assertions about latrine location preferences, but it was found that the latrine at Hinds Cave was at the back of the shelter. The vast majority of coprolites from Eagle Cave have been collected from near the front of the shelter at the top of the burned-rock-strewn talus slope.

Dr. Black takes a close look at the Eagle Cave coprolite collection.

Dr. Black takes a close look at the Eagle Cave coprolite collection.

For more discussion about coprolites from the Lower Pecos and Hinds Cave, check out the TBH exhibit on Hinds Cave to learn more.  So much more on coprolites could (and will) be written, but right now other doodies call!

References Cited:

Danielson, Dennis R. and Karl J. Reinhard                                                                                          1998 Human dental microwear caused by calcium oxalate phytoliths in prehistoric diet of the lower Pecos region, Texas. American Journal of Physical Anthropology 107: 297-304.

Williams-Dean, Glenna                                                                                                                         1978 Ethnobotany and cultural ecology of prehistoric man of southwest Texas. Ph.D. Dissertation, Department of Anthropology, Texas A&M University, College Station.

P.I. Eyes Eagle Progress

By Steve Black

Over Spring Break last week I spent several days at Eagle Cave eying progress. The 2015 season is the first time since the inception of the ASWT research program in 2009 that I’ve worn only one hat, that of principal investigator (P.I.). Until this season I have also been the field director, meaning I was responsible for making most of the day-to-day strategic field decisions, as well as setting the overall research agenda, organizing the endeavor, and arranging funding and logistics. And so I found myself in Eagle Cave on Thursday, March 20th looking at the ongoing investigations with field-fresh eyes.

I have learned from experience one of the most important things to have at any archaeological site is a comfy chair for the PI to sit in and enjoy the view.

I (Charles)  have learned from experience one of the most important things to have at any archaeological site is a comfy chair for the PI to sit in and enjoy the view.

Below is what I wrote in my field journal as I sat looking out from the back of the shelter in an almost comfortable camp chair. Other than minor spelling and punctuation edits and the added contextual explanations in italics, this is verbatim.

“Work continues apace in Eagle. The crew is now a well-oiled excavation machine—six different exposures—from closest to back wall: Bryan excavating Unit 50 in Strip 3, exposing Feature 8; Tory excavating Unit 49 which spans Strips 3 + 4; Emily strating PS13 in Strip 4; Kevin Hanselka strating PS12 in Strip 7; Lindsay cutting back 2nd step in Strip 8; and Larsen and Elizabeth excavating Unit 48 in Strip 9. Wow! The Strategist—field director Charles Koenig­—moves back and forth directing the symphony, making strategic decisions, keeping track of who is doing what, looking over shoulders.”

Kevin Hanselka (left) and Emily both were identifying and describing strats (individual stratigraphic layers) within PS12 and PS13, respectively.

Kevin Hanselka (left) and Emily both were identifying and describing strats (individual stratigraphic layers) within PS12 and PS13, respectively.

“Bryan now an old hand—more confident and capable—Charles assigns him tasks requiring greater independence and/or leading the interns to accomplish a given task.” [Bryan Heisinger served as an intern in 2014 and promoted to staff archaeologist this season.]

ASWT Staff Archaeologist, Bryan Heisinger, excavating Feature 8 - an earth oven central depression

ASWT Staff Archaeologist, Bryan Heisinger, excavating Feature 8 – an earth oven central depression

“Larsen also more confident and able—building on short season. [Matt Larsen was at student volunteer for final six weeks of 2014 season; he graduated from Texas State in December and this season he is a regular intern.] Today he also has field journal duty.” [The crew takes turns keeping the daily field journal.]

Larsen delicately excavates through a fiber/FCR layer.

Larsen delicately excavates through a fiber/FCR layer.


“Tory handles TDS well—she set it up at right height for level or slightly downward shots, but must get on her tip toes to shoot down to the lower units. She is primary TDS operator this session. [Victoria Pagano is a 2015 intern and has just been accepted into the graduate Anthropology program at Texas State starting in the fall. TDS = total data station, the machine set up over a datum that gives us precise 3D coordinates for any targeted spot. A different core crew member serves as the go-to TDS operator for each 3-4 week field session. ]

Tori running the TDS - "shooting" in everything from strats to matrix samples to coprolites.

Tori running the TDS – “shooting” in everything from strats to matrix samples to coprolites.


“Emily assigning FNs in tent—flurry of requests from team members, some for Strats (she went to assign her own FNs for PS13, but wound up issuing FNs for others), some for Unit Layers, Spots, and Matrix Samples.” [Emily McCuistion is the final 2015 intern. She has defined the Strats or stratigraphic units for Profile Section 13 and assigned each Strat a unique Field Number. We also assign FNs for each small Spot sample of characteristic matrix for each Strat, and all other types of samples we collect. Our documentation system requires precise book keeping and the FNs make it possible to link one kind of data to another. We have a tent set up at the back of the shelter on the downstream end where we keep the laptop used to assign FNs and various equipment we try to keep out of the dust.]

“Kevin Hanselka volunteering today—fresh eyes with archaeobot lens—he was assigned to define strats in profile section with numerous fiber lenses. He spots various new things including a dart point with its tip sticking directly out of the profile. Charles tries out ideas on Kevin—good give and take. Kevin often mentions what he learned from previous experience or from an article he has read. “Ok, so we have agave lechuguilla and …” [Kevin earned his Ph.D. at Washington University at St Louis where he studied under Gayle Fritz, one of the leading archaeobotanical scholars in North America. His dissertation research was on plant remains from the Sierra de Tamaulipas rockshelters that famed archaeologist Scotty McNeish excavated the late 1940s.]

Kevin telling the crew about different plant parts they are finding.

Kevin points to examples of different plant parts exposed in profile. TxState graduate student Amanda Castaneda looks on.

“This is why we really appreciate our visitors and volunteers—fresh eyes and questions. SLB joins a discussion of fiber production that Kevin links to a fellow Wash U grad student who based her dissertation research on ethnographic accounts from the Eastern Woodlands—weaving and basketry done in rockshelters + houses because in open the fiber dries out too quickly. Were such weaving activities also emblematic of LPC shelters? Related, the whole issue of H-G intensification—managing landscape resources such as lechuguilla fields. Lech harvested for fiber, beverage and food. Could possibly trim leafs without harvesting bulb. But wouldn’t the heavy use for food be a ready source of fiber?”

“Elizabeth and Lindsey are a bit more tentative—the latter now has some ENC experience, the former new to area, also here for Spring Break. Chas assigns both to work on outer strips where we are working to cut back to intact layers.” [Elizabeth Jaroszewski graduated from TAMU and was just accepted as a TxState graduate student beginning in the fall. Lindsey Vermillion is a TxState senior who volunteered during last six weeks of the 2014 season and has proven to be a quick learner and hard worker.]

Lindsay and Elizabeth screening sediment from their units, while the rest of the crew works in the background.

Lindsay and Elizabeth screening sediment from their units, while the rest of the crew works in the background.

“This is the balancing act the Strategist must juggle—who has the skill set for a given task—and how to keep everyone busy productively? Long trench with different steps, strips, units, and profile sections makes this possible. Core crew can now do everything so he [Charles] lets them follow through, intermittently or continuously, from strip to unit to PS, giving them a sense of ownership and taking advantage of specific experience/familiarity w/ any given area.”

[In laying out the “Strat System” in our 2013 Eagle Nest Canyon research plan I used the term “Strategist” for the position that archaeologists of my generation usually called “Field Director.”  And although in the intro to this post I claimed to have worn the hat of field director/strategist until this season, I have shared this role with my graduate students as they have taken charge of certain investigations as part of their thesis research projects.  I am sure I have intruded into their decision making rather more than was helpful at times.  But making the strategic call is one of the things I love most about being an archaeologist and I’ve sometimes found it hard to relinquish strategic control.  It does my heart good to watch my former graduate student Charles lead the charge with aplomb.]

“Sounds—conversations in various spots across EC—some of unrelated experiences, like those told at the Screening Station. Some work related—back and forth on TDS, FN assignment. Above ideas discussions. Charles explaining steps and making sure forms are filled out… ‘Larsen this evening I’d like you to …’ iPod with jazz playing softly in background…. ‘Looking.’ ‘Shooting.’ ‘Got it.’ “Next is 329 and 318….’ Footsteps, some loud some muffled….. Scrape of trowel hitting FCR….. Soft brushing sound emanates from billowing cloud of dust. Those wearing dust masks have muffled voices—I can’t understand, but crew seems to follow easily—practice and younger ears.”

Work scene on March 20, 2015. Field director Charles takes a break shoveling out disturbed matrix while keeping an eye on the crew.

Work scene on March 20, 2015. On far left field director Charles takes a break from shoveling out disturbed matrix while keeping an eye on the busy crew. On the far right Elizabeth holds a reflector board to improve the lighting on the area where Bryan is taking yet another round of SfM images.

[Added the next day] “Strategic decisions are often tough—no clear-cut best way when dealing with very complex stratigraphy—pits dug through pits, fill vs. primary thermal features, hard structure (FCR layers and concrete-like ash conglomerates) vs. soft ash and softer burrow fill, plus the many exposure faces (of strips, profiles and units).  With SfM we can adapt and change our minds, knowing that we can reassemble/stitch [the 3D models]. Still, flexibility isn’t easy.  Use of Strat System and FN essential. Record Keeping critical. ‘Tis a challenge!”

And that is the Eagle Cave 2015 progress as eyed by this P.I. I will admit that as I started to write most of the above in my field journal it dawned on me that ASWT blog readers might appreciate a look at the excavation scene at Eagle Cave. I had realized that at the moment I was superfluous – most of the crew knew what they were doing and Charles was doing a marvelous job directing the scene. I could sit back and take it in as a participant-observer.

A competent archaeological crew intelligently and diligently investigating a fascinating rockshelter in a remote corner of the natural and modern world is indeed a joyful thing for a principal investigator to behold. I’m already looking forward to my next trip.

Adventures in the Ancient Lost City of the Rodents

Larsen hard at work.

Larsen toiling away in the Mines of Mole-ia.

By Matt Larsen

Hey y’all, I’m writing today about burrows – but I’m talking packrats not pack animals. If you don’t remember me, my name is Larsen, and I am a recent graduate of Texas State, and this is the first long-term archaeological project I have worked on. One of the things that surprised me when I first started excavating out here is the large number of burrows we encounter. The burrows range from small and winding to large and cavernous. In some places it feels more like we are exploring some vast ancient underground city created by small creatures. Was it miniature Yeti, a.k.a. Littlefoot? Nope, it’s burrowing rodents.

The focus of our Eagle Cave excavations this season is the south face of the trench originally created by the Witte Museum in the 1930s and widened by the University of Texas at Austin crew in the 1960s. When we began excavating we were attempting to cut through the surface disturbed material to intact deposits. As Emily and I excavated our first unit, we had to discontinue cutting south into the trench face because we ran into an extremely large burrow, which we started calling the “Badger Burrow”.

Charles attempting to curl up in "The Badger Burrow".

Charles attempting to curl up in the “Badger Burrow”.

In this same area, I was excavating back the face of the unit and came upon a burrow with a tail sticking out of it! I was somewhat startled by this as we had been joking about cutting into a badger burrow and having an angry badger jump into someone’s face. At first I thought it was a snake, but then I realized it was a hibernating lizard. I gently removed the lizard and moved it to a place where it would be safe from animals and archaeologists.  These burrows are good examples of today’s blog topic: bioturbation.

What is Bioturbation?

Bioturbation is the term archaeologists use for any disturbance of the ground by living things. These include plants and tree roots, rodents, reptiles, insects, worms and any other organism that delves into the ground. Bioturbation is an issue all archaeologists face in some form or another. So, how does bioturbation affect archeological digs?

Bill Murray isn’t the only one concerned with burrowing animals. Archaeologists are concerned with bioturbation because it alters the archaeological context (see Where Context is Crucial). As organisms move through the earth they can affect the archaeological record in several ways. First, and most obviously, bioturbation changes the stratigraphy. Roots and especially burrows move dirt around in the earth. Dirt that was down deep is brought up, dirt that was near the surface is carried down and earth can be moved all over as animals backfill their own burrows. In a Canadian study of pocket gophers it was estimated that, if one gopher at a time lived in a 10x20m area and digging activity remained constant over 200 years, approximately 25 metric tons of earth would be moved!

A pocket gopher.

Hello, Mr. Pocket Gopher, it’s your friend Mr. Squirrel.

Burrowing animals often move artifacts up in the ground. The gophers, for example, make burrows about 6-7cm wide. Anything they come across that is less than 6-7cm, such as tools or projectile points, will be carried by the gopher out to the surface or into a side chamber of the burrow.

Bioturbation can also cause artifacts to move down farther into the ground. Burrowing by animals can undermine artifacts, even artifacts much larger than the animal (like a grinding slab for example), which allows them to sink down in the earth.

Burrowing animals also have a tendency to bring things in to their burrow, such as food or nesting materials. This means that some objects may seem to be deposited by people, but in actuality were brought into the ground by animals.

The movement of earth and artifacts through bioturbation requires archaeologists to understand that just because an artifact is found in a certain stratum does not mean it was originally deposited at the same time as that stratum. It also means care should be taken in establishing an age for a stratum or an artifact.

The destruction of a stratum or the movement of artifacts are negative aspects of bioturbation, from an archaeological standpoint.  Bioturbation can also, however, be a positive thing. Bioturbation can be a tool an archaeologist uses to study the past.

Positive Aspects of Bioturbation

The organic things brought into a burrow can tell us a lot about the past. The plant and animal remains preserved in a burrow inform us about what kinds of plants and animals lived in the area at a certain point in time. Because plants and animals like certain kinds of conditions, such as temperature and precipitation, we can extrapolate what the climate was like in the area at that time as well.

I recently learned of another positive aspect of bioturbation while listening to the radio. There was a story about two archaeologists, one in England and one in Denmark, who were using moles to gather archaeological data. Both were analyzing things brought to the surface by moles at protected sites where the archaeologists were not permitted to conduct an excavation themselves.

A mole.

A mole (happily, not present in Eagle Cave!).

In Viborg, Denmark, Jesper Hjermind studies what moles dig up at the site of a medieval fort. The moles often bring up artifacts and pieces of brick. By analyzing these objects, Hjermind is able to determine the location of buildings at the fort. If there are many objects at a molehill, then that is where a building is underground. The story can be found at: http://cphpost.dk/news/moles-digging-in-the-name-of-archaeology.12859.html .

At the site of a Roman barracks known as Epiacum in Cumbria, England, Paul Frodsham is also not allowed to excavate because the site is protected. He sifts through the tailings at molehills to find artifacts from Roman times. While this does not give him a full picture of the archaeology at the site, it allows him at least a glimpse. The story can be found here: http://www.bbc.com/news/uk-england-cumbria-22363936 .

What all this tells us is that bioturbation is a fact of life for an archaeologist and it can be either a help or a hindrance depending on how it is approached.

Bioturbation at Eagle Cave

Common bioturbators of the region.

Common bioturbators of the Lower Pecos region.

So what does bioturbation mean for us on site in Eagle Cave? How do we recognize it? How does it hinder us and how does it help us?

At the surface in Eagle Cave, the main agents of bioturbation were sheep, goats, and people. Eagle Cave was used in the early 20th century as a convenient place to pen sheep awaiting shearing in the pens atop the cliff. This means that the surface was mixed up by their milling about and is heavily disturbed. Further, people visiting the site for nearly a century have picked, plucked, and scratched at the surface (and deeper) of Eagle. We surmise the strata from the Historic through the Late Prehistoric eras – the layers at the “top” of the shelter profile – are nearly completely destroyed.

When we excavate at Eagle Cave, we first clear away the disturbed surface layer to get to the intact deposits underneath. As we dig into these intact strata, the main agents of bioturbation are burrowing animals such as rodents, lizards, and insects. The burrows we find range from very small insect burrows to extremely large mammal burrows. Most burrows are from rodents and are, on average, about 7cm (~2-3 inches) in diameter. We are able to distinguish burrows from intact material in several ways.

PS010 is a nice example of different burrow sizes and shapes. Note the excellent color contrast in the central burrows.

PS010 is a nice example of different burrow sizes and shapes. Note the excellent color contrast in the central burrows.

First, we use visual clues to identify burrows.  We often have clear layers (e.g., alternating white, black, and gray bands of ash, charred fibers and the like), and whenever there is an interruption in the strat from a burrow, the contrasting colors stand out, like in the above photo.  We also often see nesting material in the burrow matrix, grass or straw, and sometimes there are pockets of cached seeds. In modern  burrows, we often find sheep and goat dung mixed in as well.

Plan view of Emily excavating a burrow.

Plan view of Emily excavating a burrow.

In plan view (looking down on a unit from above) we can often see the burrow as a linear track extending across the unit. In profile view (looking at a vertical surface from the side) we often see burrows as either a circle of material, a hole, or as a linear disturbance extending across a profile face.

Archaeological excavation is not just dependent on visual cues, like color changes, but is also an extremely tactile endeavor. When we hit a burrow, it usually feels very different under the trowel from the rest of the stratum. Most of the time the burrow material is exceptionally loose; the trowel just sinks right in several centimeters without any pressure applied by the excavator at all.

Bryan excavates a rodent metropolis.

Bryan excavates a rodent metropolis.

The deposits at Eagle Cave often have burrows in them, and it can be extremely frustrating for an archaeologist to work with strata that are more burrow than intact. When we began excavation this season, we were excavating near the back of the shelter and we had to move a lot of earth before we found intact deposits. As we were cutting back the trench face we finally had to stop because we came upon a burrow nearly a meter across, the aforementioned “Badger Burrow”. We are no longer excavating from this area (the far right unit in the photo to the right) to the back of the shelter because it is all the backfilled trenches of the excavations in the 1930s; which just goes to show that archaeologists can be proficient bioturbators as well!

While at times frustrating, the disturbed and burrow material does not go to waste. We screen samples of these disturbed sediments on-site and use the artifacts we find for educational purposes here and at Texas State University. We often find interesting artifacts within the burrow material, including two large bison teeth this season.

Bodilly, the Bioturbation Hedgehog, promotes awareness of bioturbation amongst archaeologists.

Bodilly, the Bioturbation Hedgehog, promotes awareness of bioturbation amongst archaeologists.

So, while these artifacts have no clear archaeological context, they do clue us in as to the types of artifacts we should find. And we retain rare items (like a mussel shell pendant we found this week). They are also exciting finds that keep us motivated and in good spirits!

In summary, bioturbation is a part of nearly every archaeological excavation. It is important for researchers to understand the role bioturbation plays in the formation of an archaeological site so we can accurately interpret the data from a site. Although bioturbation is often frustrating, it can also be helpful to an archaeologist if used as another means of gathering information. We try to keep this in mind here at ASWT when we come upon an area that is more burrow than strat and makes us feel more like rodentologists than archaeologists.

Archaeology in a Whole New Dimension

By Victoria Pagano

Hello again, it’s Victoria here to tell you that I’m excited. Excited about the work we’re doing out here in Eagle Cave and with the ASWT project as a whole. Now this is not to say that I wasn’t enthusiastic when I first found I would get a chance to intern in an amazing place, with knowledgeable people, learning and doing great new things; but, I’m writing now with a little training under my belt as to the way things work and and a better understanding of how absolutely fantastic it really is.


Okay, this isn’t at Buenavista, but it is one of the sites that is worked on by the project. Mighty “El Castillo” at Xunantunich, just one example of the architecture and archaeology to be found in Belize.

Before ASWT

First, I would like to tell you a bit about my first and only field work in archaeology…just to offer a bit of perspective. I was unbelievably lucky to work in Belize. A beautiful country full of cultural and ecological diversity– not to mention the incredible historical and archaeological richness it holds as well. The project was based in the Mopan River Valley, studying the ancient Maya sites of San Lorenzo, Xunantunich, and Buenavista del Cayo. My work was focused at Buenavista, a mid-level city center with plazas and stone structures that had been reclaimed by the jungle.


That’s where I worked, Buenavista del Cayo. Just down the river from Xunantunich and many other archaeological sites.

It was in Belize that I learned basic excavation procedures:

Step 1: Find somewhere you want to excavate and establish an excavation unit. This includes (for most) establishing a permanent datum, laying out the unit, and taking starting measurements.

Step 2: Establish your excavation protocol. Are you going to follow natural breaks in the stratigraphy, or are you going to use an arbitrary measurement to create your strata, lots, layers, etc. You’ll probably want to sketch and photograph the starting and ending surfaces, too, as you work your way down.

Step 3: You find something really cool in the floor or wall of your unit… a hearth, post-hole, projectile point, a body, etc. — you decide you want to make sure this is in your notes (hopefully you are taking notes, good notes), so you need to take additional steps.

Step 4-6: You need to 4) Take photographs— with a scale and some indication of direction 5) Map it i.e. create a drawing by measuring to and from objects in your unit to an established point or points, like a sub-datum. This will yield a plan or profile map with detail as to where your find is and where everything else in your unit is in relation to your find. Detail, detail, detail!  Depending on how precise you want your map to be, if you have help, and your level of OCD, drawing a map can take anywhere from minutes to hours.  6) Take more notes of the object’s location, this may include a GPS point that you tie to your datum later, or measurements that you will use to associate the object’s location relative to the datum.

Step 7: You’re probably pretty tired from all those steps you took to draw your unit. You need a nap, but chin up, you established your unit today AND you found something! Hopefully your notes are good, you read that compass properly, and you’re mapping skills are adequate enough that your map doesn’t simply look like a box with a few misshapen circles, squiggly lines, and a triangle.

Now I have nothing against all those steps (the old fashioned paper and pen method works), but there is always room for improvement.  So why is it I am so ecstatic to work in a place where there isn’t monumental architecture, elaborate burials, mysterious mythology and codices? Structure from Motion.

What is Structure from Motion?


Here I am focused on photographing my unit for SfM.

Structure from Motion (SfM) is a surprisingly simple technique that is easy to learn, quick to do in the field, and potentially available to archaeologists wherever they work, or at least those with access to modern technology. SfM uses still-motion photography to rebuild real-world, dimensional objects. Using a digital camera you take a series of overlapping, sequential photographs of your desired target and run them through a software program, such as Agisoft Photoscan.  The software is able to match up all the different photographs and build a virtual 3D model of the target (for more info on what Structure from Motion is, see our blog post from last spring:  Structure from Motion).

For the ASWT project, we are using SfM to document and record everything from entire sites to small excavation layers.  In other words, a digital camera and a computer take the place of the traditional pencil and sketch map technique that I became familiar with in Belize.  Creating sketch maps is somewhat fallible in terms of reliability due to human error; we can only record and note what we see or notice at the site. Often, having only a single chance to record something before we move on to the next layer. Even more often when we sketch we focus on the big things, the obvious things, not necessarily because we think the rest inconsequential, but because we cannot physically draw every detail. SfM captures all of the visual detail that we can’t see or maybe don’t even think to include at the time because we’re so focused on recording our super cool projectile point or rock alignment.

When it comes down to it, many of the steps and methods are the same (we’re still completing forms and taking notes and we aren’t taking any shortcuts), but what really changes is the end product: our results. Our notes, drawings, photos, and forms are all we have left after an excavation. SfM offers us a permanent, virtual record that preserves and offers accessibility to our excavation data for years to come (and dozens more eyes). Nothing gets skipped over, nothing forgotten.

Our Work So Far

Eagle Cave South Trench Strip numbering system.

Eagle Cave South Trench Strip numbering system. Strip 4 is where I focused my work for the first session in Eagle Cave.

As I mentioned in my introductory blog post, I am interested in archaeological applications of GIS. I also mentioned that I was intrigued by the SfM technique that I myself first learned about from this blog [Eagle Nest Canyon at the Texas Archeological Society Annual Meeting]. Now I come to you one month in, with a bit more knowledge on the project and the technique to present another perspective.

I spent the January session re-exposing a profile face, PS005, that was initially exposed in 2014. This profile sits in what we now call Strip 4, almost smack dab in the center, top section of the South Trench wall of Eagle Cave.

Digital annotation of PS005 orthophoto from 2014 before profile sampling.

Digital annotation of PS005 orthophoto from 2014 before profile sampling.

PS005 with micromorph samples superimposed and georeferenced onto the profile.

PS005 with micromorph samples superimposed and georeferenced onto the profile.

At first it was a mess. After removing the backfill and geo-cloth, we discovered that the profile face had suffered damage from continued erosion and rodent burrowing since it was originally exposed. In 2014, the investigators assigned strat numbers based on their original profile exposure –i.e. each visible stratum received a unique number.  However, they then excavated a small sampling column and did their best to follow the layer seen in profile across the unit. The presence of numerous rodent burrows, especially through the ashy layers, made strat definition challenging.

I should add one more factor, at the end of the 2014 excavations the PS005 profile was sampled by the geoarchaeologists who removed micromorphology samples.  Although done carefully, the wall was no longer pristine.

PS005 profile we exposed in 2015.

PS005 profile we exposed in 2015.

This helps explain why when we re-exposed the PS005 profile we could not easily match what we were seeing in the field to the original profile illustration. So, we decided to excavate a sampling column through a portion of the jumbled profile, using the 2014 strat numbers for our layer designations . This was done with two goals in mind:

1) Cut back eroded face (profile) and re-expose the stratigraphy.

2) Collect high-resolution samples of the matrix and artifacts within the profile.

Excavating a sampling column involves collecting the matrix of each layer (along with things like Spot Samples, Geo-matrix Samples, and samples for radiocarbon dating) that can be further analyzed in a lab.  We are not only collecting samples of each strat, but using the TDS shots of each sample and the strat location, we will add them all to the SfM model. So whoever processes and analyzes the samples can have a virtually exact geospatial reference of its origin. This will help us build an assemblage of associated artifacts, radiocarbon dates, and deposition event, aiding in our understanding of the shelter and the canyon: how it was used, when it was used, what they were doing there.

Rather than draw a standard paper and pen illustration of each layer as we excavated, we instead used SfM to document the top surface of each strat. This not only gives us an idea of what we were looking at, but it allows us to use GIS to calculate volume of matrix removed.

Field annotation of the strats in PS0010: 2015, previously PS005: 2014, that Charles and I completed.

Field annotation of the strats in PS0010: 2015, previously PS005: 2014, that Charles and I completed.

Once I finished with the sampling column, attempting to follow the strats that were assigned the previous year, the profile face that was exposed was extraordinarily rich.  In other words, by cutting back the wall we found better preserved and more complex stratigraphy. The newly exposed profile exposure is called PS010.

Previously, only about 10-12 strats were identified in this area.  We have now defined 22 individual strata from the “same” exposure. I re-photographed the profile giving us three sets of 3D data: TDS shots, 3D models of all the excavation layers, and now the model of newly exposed PS010. We now have a new high resolution 3D model to overlay all of the excavation layers and samples onto – all of which can be manipulated to aid in analysis.

Where it All Comes Together

Our field lab is where all the sets of photographs are processed. Using Photoscan we align and georeference all the images for each individual layer. The photographs, GCPs, TDS, and notes are all combined to digitally rebuild the excavation. A 3-dimensional, manipulable dataset that works hand-in-hand with all of the physical data—matrix, artifacts, etc.—and the recorded data i.e. notes, photos, etc. In order to have these georeferenced for GIS or used in photogrammetry, no less than six GCPs, ground control points, are included in each excavation exposure. Ground control points are geospatial reference points that you place on your object or in your unit, shoot in with a TDS or GPS, so that photographs and models can not only be more accurately aligned with each other, but linked to a geographic grid. This becomes incredibly handy when you are working in say, a canyon with multiple sites carrying on extensive excavations that you would like to map and relate to one another. Then, not only can you reference all of your units and sites among the canyon, but you can reference and cross-analyze your work with other sites across the region or the world. Once we have our models we can then export all or parts of the model into many different formats; GeoTIFF, TIFF, JPEG, KMZ, etc. Our models are ready to imported into GIS software where we can further manipulate and analyze them.

This shows the samples that were taken in the PS005 sampling column. They are superimposed onto the 2015: PS010 orthophoto.

This shows the samples that were taken in the PS005 sampling column. They are superimposed onto the 2015: PS010 orthophoto.

Orthophoto of complete PS010 profile face.

Orthophoto of complete PS010 profile face. An orthophoto is created once the SfM modeling is completed, GCPs added into the model, and then exported into ArcGIS for more analysis.

Our Answer

A goal of the ASWT project is to not only excavate and collect, but to gather the best data we can – or best representation of that data –backing it all up with SfM and GIS.  Structure from Motion gives us the opportunity to not only georeference our units, finds, and strata, but we can literally rebuild them, at least digitally speaking. No longer are we relying upon the traditional mapping, measuring, and sketching techniques of years past that result in rather dimensionless visualizations of excavations.

SfM also easily provides a new solution to an old problem: excavation vs. preservation. The basis of archaeology is essentially destroying material history in the name of research and discovery, so that we can preserve and record it as best we can. Granted we have gotten much, much better at recording and excavating than back in the early days of the field, there is still room for improvement and innovation. In 2014, Bryan Heisinger (2014 ASWT Intern; 2015 ASWT Staff Archaeologist) presented at the Texas Archeological Society annual meeting, on the uses of SfM and GIS for not only modeling, but extrapolating volumes of material removed and creating digital elevation models (DEMs). These can be used to study stratigraphy and depositional events of floods, people, and even animals– as Emily and Larsen can attest to. Our documentation of profiles, like PS005 and PS010 helps us build a database of all the excavations and the shelters to aid in the analysis of what is to some a rather abstract concept of time. Our work becomes more dimensional, more visible. You aren’t just looking at the profile of a wall or structure or shelter. You can virtually walk around that wall, walk into that structure, and around that shelter, without ever being there. The outreach potential is exponential.

The ASWT project personnel and many of our colleagues believe that SfM is that next step in improving archaeological documentation. Incorporating SfM and GIS technology we can model excavations with millimeter level precision recording finer detail in stratigraphy and location than ever before. Physical 3-D models that can be pieced together or pulled a part. High resolution, detailed, and accurate data that can be manipulated, viewed, and analyzed virtually any way we desire. Even better we can share our results in a brand new ways: 3D printing, virtual tours, etc., we could and can literally print pieces of art, artifacts, even a scale model of the canyon if we wanted to! This project, this technique isn’t just for the archaeologists and researchers understand the shelters better, our goal is to be able to help everyone understand the shelters better because the shelters are a part of all our histories.

To elaborate on what Charles has said numerous times and will likely say many more, “50 years ago they were using completely different techniques..50 years from now they’ll be using completely different techniques…but right now we have the technology and the opportunity to set those standards for the next 50 years. We are doing something amazing here with SfM, and sure, we’re not the only people using this method, but there could be a dang lot more of us using it.”

If you haven’t already, you should click on over to our older posts on the subject, and I highly encourage you to visit the Mark Willis Blog http://palentier.blogspot.com/, where you can see some of the other extraordinary uses of SfM 3-D modeling.

Between a Rock and a Heart Place

By Bryan Heisinger

Last year during the 2014 Eagle Nest Canyon Expedition, the crew surveyed the land around the Shumla campus for a fresh spot to establish an experimental earth oven facility. As described by Jake Sullivan and Brooke Bonorden (see Searching for the Trifecta), earth ovens are a cooking technology used by the people of the Lower Pecos (and across the world) to bake plants and animals that would otherwise be inedible to humans.

The remains of earth ovens are found at thousands of archaeological sites across the Lower Pecos Canyonlands region, including Eagle Nest Canyon.  At Eagle Cave, the massive heep of earth oven cooking debris–mainly fire-cracked rock (FCR)–has accumulated from the repeated use of the site for constructing earth ovens, probably over thousands of years. Though highly recognizable and important to our understanding of the human occupation and use of Eagle Cave, the many hundreds of tons of burned rock that fill this and other rockshelters within Eagle Nest Canyon has been poorly studied and documented by archaeologists who have worked here over the past 80 years.

In reaction to this negligence towards FCR and earth oven research, the ASWT project has made it a priority to study and quantify the amount of earth oven cooking that occurred in the uplands and rockshelters in and around Eagle Nest Canyon.  As we documented in 2011-2012, similar evidence can be found along Dead Man’s Creek, a tributary of the Devils River, and across the region and beyond. When studying earth ovens, one of the best ways to become acquainted with the methods of earth oven technology  is to use experimental archaeology and actually build one!

The ASWT Experimental Earth Oven:

Back in 2014 when we were surveying the Shumla campus for a suitable spot to build earth ovens, we had three criteria to keep in mind while looking for the perfect location: 1. Soil, 2. Fuel,  and 3. Food. Not to mention, we took care to avoid establishing an oven at a known archaeological site! Soil, fuel, and food are the desirable location traits needed for a successful earth oven, because you need soil to dig an oven pit, you need wood to build a fire, and you need food (in our case sotol or lechuguilla) to cook. The crew eventually found a favorable spot near campus and cleared the surrounding brush for the ASWT Experimental Earth Oven locality.  Unfortunately, due to burn bans, lack of time, and conflicting personal schedules, the 2014 ENC expedition was never able to build an experimental earth oven

Fast forward to this year: On January 11th, three days after the new ASWT interns arrived at the Shumla campus, the weather conditions were highly favorable to finally build our long awaited experimental earth ovenAfter gathering enough firewood (fuel), lechuguilla and sotol (food), and close to 100 kilograms of limestone clasts from the immediate surroundings, the crew was ready to begin constructing the earth oven.

We began by digging a pit close to a meter and a half in diameter, and a half a meter in depth. The firewood (hand-gathered deadwood) was then stacked in a conical pyre (similar to a tepee), and the limestone rocks were strategically placed within the cone of firewood.

The crew agreed that it was best to light the fire the traditional Lower Pecos way, so Park Archaeologist Jack Johnson of Amistad National Recreation Area (US National Park Service) used the bloom stalk of a sotol plant to start a friction fire. In under 2 minutes, Jack had the fire blazing under the stars (for a time-lapse of the earth oven fire, watch this video by Jack Johnson: https://www.facebook.com/video.php?v=10152425529847134&pnref=story).


The blazing conical pyre of firewood and limestone rock in shorty after it was fired.


After the fire burned down to embers and the rocks were glowing red hot in the bottom of the pit, the crew and several student volunteers from Texas State University began lining the the pit with prickly pear pads – the pads serve as a lower layer of packing material that helps to retain the moist heat needed to bake the food at a low temperature (ca. 100 C) for an extended period of time (typically 36 -48 hours.)


Placing the first layer of packing material (prickly pear pads) ontop of the hot limestone rock.


Once the prickly pear was placed, it was time to throw in the food we collected. Lechuguilla and sotol hearts (3 each) were placed in the center of the pit on top of the prickly pear and covered again with more packing material.


Laying the food (Sotol and lechuguilla) on top of the packing material.


After the remaining packing material was thrown over the food, we began to cover and cap the pit with dirt; this cap of soil insulates and holds in the steamy heat released from the rocks and suffocates the fire allowing no combustion. Now it was time to wait for our plants to bake and hope our hard labor would deliver some tasty results!


Capping the earth oven with soil.




Charles packing down the cap of soil to ensure no heat escapes.


Dinner is Served:

On the evening of January 13th, two days after we capped and sealed our earth oven, the crew returned to taste the baked desert succulents that were slow cooked over the last 48 hours. While digging the bulbs out of the pit, we noticed how the soil was still warm from the heated rocks below. The baked lechuguilla and sotol had a turned a caramelized color and had an aroma that smelled similar to a smokey artichoke.


The baked bulbs of sotol and lechuguilla.


The palatability  of these baked plants sent mixed expressions across the faces of our crew, some of who enjoyed the flavor and some who didn’t.


Tasting our baked food for the first time. The faces say it all.


Learning from Earth Ovens:

A great variety of scientific information potentially can be obtained from the experimental construction of earth ovens.  One aspect of earth oven use ASWT is particularly interested in is understanding the rate at which limestone rock breaks down through repeated use in earth ovens. The layer of heated limestone rocks forming the bed of an earth oven serves as a thermal storage or heating element that slowly cooks the food. During the firing process, the limestone rocks begin to break apart from the intense heat that they are exposed to (over 500 C).  Through reuse, thermal cycling–from cold to hot to cold again– causes the rocks to continue to fracture into ever smaller pieces.  Solid rocks with few flaws typically last longer than naturally fractured rocks and those with thin spots. Once the rocks becomes too small to retain heat, they are no longer effective thermal storage devices and they are discarded and tossed into what will become a debris ring around the oven pit, eventually qualifying as a burned rock midden. If we can track and measure a known mass of limestone rock (e.g., 100 kilograms/220 pounds) as it continuously breaks down into smaller rocks from heat and re-used in new earth ovens, we could then to apply this experimental rock-size attribute data to the fire-cracked rock (FCR) that we find in such profusion in the archaeological ground. In other words, this experimental use of earth ovens can potentially allow us to more accurately measure the amount of earth oven cooking that took place in Eagle Cave and other rockshelters and open sites in the region.

Eagle Cave’s Feature No. 8:

Last week, Emily and Larsen uncovered what we think is an intact earth oven heating element in their excavation unit. To a trained eye, this earth oven feature was characteristically textbook in its makeup. Many of the limestone rocks were inclined at the base of the pit and the soil that surrounded these fire-cracked rocks was heavily organic, ashy, and rich with dime-size charcoal chunks. It even appeared as if there had been a different soil that was used to cap this earth oven once long ago.


3D model (plan view) of feature 8 in Eagle Cave. Notice the dense cluster of fire cracked rock and black/grey charcoal rich soil.




Plan and profile view of feature 8 in Eagle Cave.


With intact, well-preserved finds such as Feature 8, we have the ability to obtain radiocarbon dates that can help us determine when this oven was used.  Furthermore, we can sieve the collected soil from that earth oven feature and, with the help of our collaborating archaeobotanists, identify the charred plant remains that were being processed by the people who lived in Eagle Cave. What we cannot do is accurately estimate how many times this earth oven was re-used. Was Feature 8 a one-time earth oven event? Or was it the last of series of earth ovens that had been built and re-used in this very spot using the same rocks? These are some of the questions that ASWT would like to address in our ongoing research. Through these initial tests with EEO No.1 and other experimental earth ovens to follow, we believe that the data to answer these questions could come to light.

ASWT Experimental Earth Oven (EEO) No. 1

After enjoying the success of our first experimental earth oven, we returned  a week later to dig out all the rocks from EEO No. 1.  We used 11 rocks larger than 15 cm in maximum dimension in the oven (99 kg or ~220 lbs of total), and we were able to recover all the rock that was used.  Most of the rocks survived the fire, but as you can see from the photograph below, some of the rock broke into smaller fragments.


The rock size sorted fire cracked limestone, post earth oven firing.

Once all the rocks were pulled out of the oven, we divided the rocks into four size categories: <7.5 cm in maximum dimension, between 7.5-11 cm, 11-15 cm, and >15 cm in maximum dimension.  We used the same familiar size categories we use in the recording procedure we call “Rock Sort” which allows us to quantify the rocks from each excavation unit-layer.  The smallest two size classes (<7.5cm and 7.5-11cm) contain rocks that are too small to be effectively used again as rocks for the heating element.  After counting and weighing all the rocks in each size class, almost all of our rock (93 out of 99 kg) survived to be used again.


Weighing the fire cracked limestone rock.


Likely during our next session, all the useable limestone rock from ASWT EEO No. 1 will be re-used in another experimental earth oven event.  After the second firing (ASWT EEO N0. 2.) we will once again recover all the rocks, sort the rocks into different size categories, and weight all of them.  We will continue to re-use the same rocks until the rocks all become too small (<3.5 inches) to effectively retain heat anymore. The more times we “burn” the rocks, the more data we will collect to further our goal.  We anticipate great data and results to come!


ENC Act 2: Return to Eagle Cave

By Charles Koenig

Yesterday we wrapped up our first week of field work for the 2015 season, and things are off to a great start (even if the weather is a little chilly).  Last year we worked at four sites within ENC: Skiles Shelter, Horse Trail Shelter, Kelley Cave, and Eagle Cave as discussed in previous posts.  To recap, we completed our planned investigations at Skiles and Kelley, we carried out initial testing at Horse Trail, and we got started at Eagle.   Although we learned a great deal by working at four different sites, this year we will focus on one site: Eagle Cave.

The 2015 ASWT crew, assisted by student volunteers from Texas State, begin exposing intact stratigraphy in Eagle Cave.

The 2015 ASWT crew, assisted by student volunteers from Texas State, begin exposing intact stratigraphy in Eagle Cave.

As described in the blog post from last spring (see Eagle Cave: Where Context is Crucial), previous archaeological work in Eagle Cave in the 1930s and 1960s, and subsequent erosion, resulted in the massive trench spanning from the rear wall to the dripline.  Based on the work done by the Texas Archeological Salvage Project during 1963, we know that the deposits the trench bisects are between 10 and 20 feet  deep (3-6 m).  Through the decades the once-vertical trench faces gradually succumbed to the forces of gravity, wind, burrowing critters, and misplaced footsteps, leaving a sloping U-shaped depression.  We planned from the outset of the project to expose, sample, stabilize, and backfill the trench, but we needed to gain experience working in other areas of the site before taking on the daunting task of the main trench.

Plan view of Eagle Cave showing the location of the 5 Profile Sections excavated in 2014.

Plan view of Eagle Cave showing the location of the 5 Profile Sections excavated in 2014.

Last season we opened up 5 small “windows” in different areas of the site.  Profile Section (PS) 1 was on the downstream side of the site were a large badger burrow exposed surprisingly intact deposits just under the surface.  Only a few meters away, PS 2 began in the disturbed deposits along the rear wall which had been dug out long ago by the Witte, the “local boys” of Langtry, and burrowing animals. As we removed the deeply disturbed rear wall deposits and worked our way outward we encountered intact remnants there too.

Profile Sections 1 (left) and 2 (right).  Each profile was generated using Structure from Motion software.

Profile Sections 1 (left) and 2 (right). Each profile was generated using Structure from Motion software.

Profile Sections 3 and 4 were located in the UT North excavation unit in the upstream end of the site (and are the subject of Tina Nielsen’s thesis research project).

Profile Sections 3 (right) and 4 (left) were excavated in the UT North Unit.  Excavations reached bedrock over 3 meters below surface.

Profile Sections 3 (right) and 4 (left) were excavated in the UT North Unit. Excavations reached bedrock over 3 meters below surface.

The final exposure was PS 5 – located in the upper part of the south wall of the main trench, where erosion had provided glimpses of intact layering.

PS 5 was exposed on the south wall of the main trench at the end of the season.

PS 5 was exposed on the south wall of the main trench at the end of the season.

Each of these exposures (PS 1 – 5) gave us the opportunity to test, modify, and improve our excavation and sampling methods, as well as gain experience documenting the complex and fragile stratigraphy of the dry rockshelter deposits.  Yet, each exposure provided only a rather narrow (~3-4 feet) view of the deposits, and it was difficult to link stratigraphic layers between profiles.  Our 2014 experience drove home the realization that in order to gain a better understanding of the deposits, we would need more substantial stratigraphic exposures – and there is no better place to do so than in the main trench.


The focus of the 2015 field season is exposing, recording, sampling, and stabilizing the south wall of the main trench.  We want to take advantage of the slumping trench wall and expose as much intact stratigraphy as we can.  In other words, we want to frame the microstratigraphic layering seen in small windows within the context of the larger structural patterning visible across the site. We are continuing to step our profiles vertically and horizontally to maintain stability (and provide access), and we are following the same “Low Impact, High Resolution” sampling strategy (See Low Impact High Resolution).

This past week we re-exposed PS 5, which we had draped with landscape cloth and gently covered with fill at the end of the 2014 season.  And we began opening up fresh exposures at two additional locations along the trench (see the time lapse above).  As the season progresses we will step down the exposures deeper into the trench, but for now we are focused on the upper deposits.  By the end of the 2015 field season we expect that we will have documented and sampled rather spectacular stratigraphic exposures along the main trench, and we look forward to sharing what we find!