Journey to the Center of Sayles

By Justin Ayers

Howdy! Justin Ayers here, excited to explain the ongoing bucket auger testing at Sayles Adobe. You may ask what exactly is an auger? The auger is a simple but effective tool for collecting/sampling sediment below the surface without opening excavation units. It is comprised of a lengthy pole with a helical bit (and cylindrical bucket) at the end, which is designed to twist through the earth easily, while the bucket simultaneously collects the sediment displaced by the twisting bit. After one and a half turns of the auger handle, the auger bucket is filled with compressed dirt, and the device is gently pulled up out of the hole and the bucket load is dumped into a screen, examined, and recorded. The process is repeated over and over up to a depth of 3 meters (about 10 feet!).

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Me and the auger.

Conducting a bucket auger survey of Sayles is important because it is allowing us to relatively quickly sample the stratigraphy across the terrace, a task that would take months to accomplish using hand excavation units. Further, by combining the different sets of auger data we are able to map out the subsurface deposits (both natural and cultural) of Sayles. These data will contribute to Tori Pagano’s ongoing thesis research (see Tales of Sayles Adobe), as she aims to define and sample the natural and cultural deposits of the terrace.

Bucket Auger Process

Tori’s plan is to build on the ground-penetrating radar (GPR) survey conducted at the site in January by Tiffany Osburn. We wanted to follow the GPR grid with our bucket augering as closely as possible so we could investigate several interesting radar anomalies seen at certain locations and depths within the terrace.  Happily, our collaborator geoarchaeologist Ken Lawrence kindly allowed us to borrow his bucket auger!

EW_WE_270profiles_arrows

East-west GPR transect (top) and west-east transect (bottom). The yellow arrows point to the same anomaly in both transects, indicated by the upside-down V-shape.  This anomaly is approximately 1 meter (~3 feet) below the ground surface. These are the types of anomalies we wanted to hit with the auger testing.

 

We wanted to use the bucket auger tests to begin to “ground-truth” the GPR anomalies (i.e., determine what the anomalies are caused by).  We also wanted to compare the sediment sampled by the auger to the exposed stratigraphy in the “Borrow Pit” excavation area.  The auger testing is showing us that the stratigraphy of Sayles Adobe is more complex (and interesting) than that seen so far in our initial excavation exposure in the Borrow Pit.

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You can see the bucket auger on the left, leaning against a tree. To the right you can see the rest of the equipment  we used during auger testing: Munsell color chart, 2mm geologic sieve, 5-gallon bucket, and lots of recording forms!

Augering Procedures

Step 1: Stake out targeted locations of auger columns.

  • Transect sampling intervals – 4 meters apart
  • Shoot in surface points with TDS (Total Data Station)
41VV2239_Units_Auger

Plan map of Sayles Adobe showing east-west bucket auger transect. The red dots are the auger tests (laid out 4 meters apart) that have been completed thus far.

Step 2: Begin sampling

  • The auger excavates a 10cm diameter hole, and each bucket full of dirt is ~8cm deep. Once a bucket of sediment is collected, the auger is pulled up to the surface.
Justin_Augering

From left to right: auger in the hole, removing the auger, the auger fully out of the ground, and finally dumping the sediment into the sieve.

Step 3: Sieve the sediment.

  • Once the bucket is pulled out of the auger hole, it is dumped into a 2mm sieve. Only the fine sand/silt mixture will pass through the screen, leaving snail shells, roots, FCR (Fire-Cracked Rock), and debitage on the screen.
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Dumping the sediment into the sieve. The bucket auger bit is clearly visible.

Step 4: Documentation

  • A metric tape (or “pocket stadia”) is used to measure the depth of the hole after each bucket auger sample was removed. This allows us to monitor our progress and make the auger data comparable from one auger column to the next.
  • The sediment texture varies from a fine sand to a compact clay-silt.
  • Color is recorded using a Musell color chart. We found that the 10YR color sheet works best for us.
  • Lastly, general notes are made of the sediment, e.g., organic materials if present, FCR, charcoal, & ped toughness (Wikipedia: ped = a unit of soil structure such as an aggregate, … block, or granule, formed by natural processes.)

Step 5: Homogenize and Sample

The sediment that falls through the screen is homogenized (stirred around) in the bucket before we collect a small representative sample. After the field season Tori, under the tutelage of geoarchaeologists Dr. Charles Frederick and Ken Lawrence, will process the samples to determine grain size and test for magnetic susceptibility (among other things). Tori plans to use the auger column data to create composite stratigraphic profiles (sections) across the terrace that will be integrated with GPR and other lines of evidence.

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A “cube” from the auger testing of Sayles Adobe awaiting further geoarchaeological analysis.

I should note that while the bucket auger does its job very well, it mixes the sediment in each bucket load together such that thin layers only a few cm thick are hard to detect.  And even though we are careful to insert and remove the auger gently, inevitably there is some admixture of sediment from the walls of the hole.  In other words, we end up with somewhat averaged samples in 8cm increments. We homogenize each sample to make sure it truly represents an average of each increment. By carrying out each auger test in exactly the same systematic way,  we can compare apples to apples with our auger samples and differentiate significant stratigraphic changes.

Luckily Sayles Adobe has very nice silty and sandy deposits (as opposed to compact clay or gravel) and testing has gone without a hitch … for the most part. Sometimes we are impeded by rocks and roots, forcing us to move our auger test column to a new location. If we encounter something hard that we can’t get through, we simply move the auger hole 30-40cm over from the original location and try again. Overall, we able to get down to the full 3-meter depth in only about 50% of our tests. In the other half we are stopped by burned rocks or other obstructions (like large mesquite roots) before reaching maximum depth.

What Are We Finding?

Based on our initial excavation in the Borrow Pit area along with the GPR survey findings, we suspected that we would hit the upper mud drape (I will explain why I say “upper” in a bit) around the same depth at multiple points on the terrace (see below profile of the Borrow Pit in Sayles).

PS01_illustrationWstrats

The east profile of the “Borrow Pit” in Sayles. The “upper” mud drape is noted as S003,  just to the left of the orange tag.

So far we have found that the mud drape is not a perfectly flat horizontal layer, it tends to follow the topography of the deposits it covers. What I mean is that in places there may have been exposed rocks or humps in the ground that the mud drape settled over during the flood event, which may be the AD 1340 flood that we documented at nearby Skiles Shelter and Kelley Cave.  Many (all?) of these rocks are FCR that were capped by the mud drape. The upper mud drape is thin and hard (clay-silt), compared to the fine sand and sandy silt that makes up the majority of the site’s deposits. In essence, the mud drape seals the cultural material that lies beneath it. 

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Bryan standing in the “Sandbox” area at Sayles looking at FCR that he is just beginning to expoose. The mud drape in this unit (denoted by yellow arrow) is very thin compared to that seen in the Borrow Pit. Several adjacent auger columns in this area were terminated by hitting rocks and we suspect that some massive FCR accumulation must be present.

Since the mud drape covers the top of the uppermost cultural layer at Sayles Adobe, when we reach the upper mud drape the cultural layer should be directly beneath it. However,  this cultural layer contains many FCR and often the bucket auger is stopped by the rocks. The auger will dig through most Sayles Adobe sediment quickly, but when you hit a sizable rock … everything stops. This is not considered a bad thing though. Usually when we hit a rock, we bring up chips of said rock that reveal if it is FCR. The FCR fragments tended to smell of sulfur when broken by the auger bit. The FCR encountered  about one meter below the surface tells us that we are hitting the upper cultural layer … jackpot!

So far we have not created schematic stratigraphic profiles for all the auger tests, but we created a preliminary illustration based on a test from the east side of the site. The stratigraphic patterns in this auger test compare well to the stratigraphy observed in the Borrow Pit and Sandbox excavation, so we are anxious to complete augering of the entire site so we can get a better map of the stratigraphy!

GRAPHIC COLUMN

Stratigraphic profile created using data collected from an auger test. This profile matches nicely with the exposed stratigraphy in both the Borrow Pit and Sandbox areas of the site.

Looking back at the GPR research done in January, the upper anomalies seen appear to have been the upper cultural layer. The FCR are in a large enough concentration to show significant feedback from the GPR. Three of our west terrace auger tests were stopped at a depth between 80cm-1m when we hit rock—usually FCR, which the auger could just not dig through.  In fact, the Sandbox excavation area was laid out as the result of our first east-west bucket auger transect.  Next week we should expose the concentrated FCR and see why so many burned rocks are piled up in one area.

Plans for the Future

Auger testing at Sayles is an ongoing process, with more sampling columns on the way. So far, only an east to west transect has been completed. We just started on our north to south transect, targeting more anomalies from the GPR survey. If additional FCR/cultural layers are encountered, it is likely that more units will be opened up for further research. The emerging picture from the bucket auger data is proving to be quite informative and tantalizing.  Hint, hint:  we have encountered deeper layers of mud drape silt and of cultural material yet to be exposed!

JustinandToriExcited

Tori and I very excited about a flake from an auger test!

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Micromorph Mania: A Microstratigraphic Approach to Evaluating Site Formation Processes at Eagle Cave

By Christina Nielsen, Charles Frederick, and Ken Lawrence

**This post is the second of several that give additional details regarding some of the different analyses that are currently being conducted with material from Eagle Nest Canyon.**

Tina standing by her poster at TAS.

Tina standing by her poster at TAS.

Eagle Cave (41VV167) is a large dry rockshelter with deeply stratified deposits spanning the Early Archaic through Late Prehistoric periods. My thesis research focuses on deposits in the northern sector of the shelter sampled during 1963 excavations by UT-Austin and again a half century later by Texas State University in 2014. My goal is to use multiple lines of evidence to evaluate the natural and cultural formation processes that resulted in the complexly stratified, culturally rich deposits present in Eagle Cave.

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.

Our ongoing analysis involves a robust geoarchaeological sampling strategy that included the collection of micromorphological (micromorph) samples from Profile Sections (PS) 3 and 4 in Eagle Cave. This poster highlights the benefits and difficulties of collecting micromorph samples from fragile rockshelter deposits and shows how the analysis of the resulting slabbed samples and thin sections can aid in evaluating site formation processes.

Profile Section 3 and 4 excavations in Eagle Cave in 2014. Photos taken after initial recordation and sampling, but prior to geoarchaeological sampling.

Profile Section 3 and 4 excavations in Eagle Cave in 2014. Photos taken after initial recordation and sampling, but prior to geoarchaeological sampling.

Methods

Field Collection

  • Section of profile cut back to expose block of matrix
  • Block carefully removed, wrapped in toilet paper, tightly wrapped in tape, and labelled with provenience information,orientation, and north arrow
  • Sample placed in plastic Tupperware or sturdy container
  • Sample impregnated with polyester resin made from polyester, styrene, and methyl ethyl ketone peroxide (MEKP)
Charles Frederick collecting micromorphological samples from PS4 in Eagle Cave in spring 2014.

Charles Frederick collecting micromorphological samples from PS4 in Eagle Cave in spring 2014.

*The micromorph samples were carefully carried out of the canyon and up to Jack Skiles’ shed located a few hundred feet from Eagle Cave. Had the impregnation happened further from the shelter, these friable samples would have been far less successfully embedded.

Dan Rodriguez impregnating micromorphological samples with MEKP in Jack Skiles’ shed.

Dan Rodriguez impregnating micromorphological samples with MEKP in Jack Skiles’ shed.

Slabbing

  • After completely solidified, sample removed from container and north orientation notched in block
  • Outer casing removed using oil-based rock saw to expose intact soil block
  • Each side of block is scanned using high resolution
  • Block is cut into 1cm slabs for thin section production, curation, and macroscopic analysis
  • 4 x 6cm sections cut from slabs to be sent to Spectrum Petrographics, Inc. to be made into thin section slide

 Sampling

The sampling strategy was fairly simple: capture as many stratigraphic layers (strats) as possible within the PS3 and PS4 profiles. As archaeological and geoarchaeological sampling had already occurred prior to the micromorph collection, some strats identified during the initial profile recordation were no longer visible in the profile.

Summary of Micromorphological Samples from PS3 and PS4 in Eagle Cave

Summary of Micromorphological Samples from PS3 and PS4 in Eagle Cave

Specific types of strats that were especially important to capture in the micromorphs included microstratigraphy such as thin lamina and lenses as well as strats that were associated with cultural features. Using this strategy, the 13 relevant micromorph samples captured approximately 27 of the 85 total stratigraphic layers identified in the field. A total of 22 thin section slides were made then from the 13 micromorph samples.

Micromorph sample MM1 from PS3A (FN 30744). This micromorph slab was cut into three 4 x 6 cm blocks to be sent off and made into thin section slides (denoted by red boxes). The three sections were numbered FN 30744-1 through 30744-3. High resolution scans of each of the resulting thins section slides are presented on the right. Thin section analysis is currently underway.

Micromorph sample MM1 from PS3A (FN 30744). This micromorph slab was cut into three 4 x 6 cm blocks to be sent off and made into thin section slides (denoted by red boxes). The three sections were numbered FN 30744-1 through 30744-3. High resolution scans of each of the resulting thins section slides are presented on the right. Thin section analysis is currently underway.

Thin section slide 30744-1 from PS3A. This thin section correlates to strat S40 and S41. S40 was initially recorded as a light gray ash deposit and S41 was characterized as a thin, white ash lens. From the micromorph block and thin section, you can see that these deposits look far different from how they appeared in profile. S40 has a fairly dense concentration of charcoal as well as fragments of shell and rock

Thin section slide 30744-1 from PS3A.
This thin section correlates to strat S40 and S41. S40 was initially recorded as a light gray ash deposit and S41 was characterized as a thin, white ash lens. From the micromorph block and thin section, you can see that these deposits look far different from how they appeared in profile. S40 has a fairly dense concentration of charcoal as well as fragments of shell and rock

Thin section slide 30744-2 from PS3A. This thin section contains the lower boundary of strat S42 and S43. S43, was also recorded as an “ashy” layer, but does not appear so in thin section. Similar to S40, numerous charcoal and rock fragments are visible in thin section.

Thin section slide 30744-2 from PS3A.
This thin section contains the lower boundary of strat S42 and S43. S43, was also recorded as an “ashy” layer, but does not appear so in thin section. Similar to S40, numerous charcoal and rock fragments are visible in thin section.

Thin section slide 30744-3 from PS3A. This thin section possibly correlates to strat S51, which was recorded as an animal burrow. In thin section, this looks very similar to S43 and may have been misidentified during micromorph collection. S51 may have been completely removed during initial sampling. Additional analysis needs to be done to identify whether post-depositional processes are present.

Thin section slide 30744-3 from PS3A.
This thin section possibly correlates to strat S51, which was recorded as an animal burrow. In thin section, this looks very similar to S43 and may have been misidentified during micromorph collection. S51 may have been completely removed during initial sampling. Additional analysis needs to be done to identify whether post-depositional processes are present.

 

 

Benefits

The deposits in Eagle Cave, like many other Lower Pecos rockshelters, are very dry and have a loose consistency. This posed many challenges during initial recordation of strats and with the subsequent geoarchaeological sampling. Profile Section walls became enveloped in a film of dust with the slightest breeze or movement. Despite efforts to clean walls prior to all documentation, observations during strat recording were somewhat hindered by the persistent dust. The collection and analysis of micromorph samples, however, allows for a clearer examination of stratigraphy and the relationships between various deposits. Characteristics that aid in deciphering formations processes, such as boundaries between strats, are especially difficult to determine when obstructed by dust. Thin sections made from the micromorph samples can provide information crucial to the study of formations processes such as the size, orientation, sorting, and mineral composition of grains, organics, and artifacts as well as post-depositional disturbances of sediments.

Challenges

Since the micromorph samples in PS3 and PS4 were collected after all other sampling had been completed, it was sometimes difficult to correlate the samples with the strats initially identified in the field. In hindsight, ideally the micromorph samples should have been collected immediately after the strats were identified and documented to allow for a more accurate correlation.

Field collection is also not always successful in loose deposits such as these and many first (and second) attempts at collection failed. Patience and perseverance are necessary qualities to have in this type of setting. The entire micromorph process, from collection to analysis, is a lengthy one but the potential information that can be obtained from this type of analysis greatly outweighs the challenges you may face along the way.

Left: Annotated SfM image of PS3A depicting stratigraphic layers identified during initial recordation; Right: Micromorph block MM1 ready to be removed from profile PS3A. MM1 collected from area where strats S40-42 and S51 were initially recorded, but as you can see, the strats do not quite look like how they did prior to sampling. Note: In situ, many of the strats look like ash deposits. However, as you can see from the MM1 block these “ashy” deposits are not in fact ash, but have a dark-colored matrix with large quantities of rock, charcoal, and other inclusions. The dusty field conditions make it difficult to characterize the strats with a high level of accuracy during initial recording.

Left: Annotated SfM image of PS3A depicting stratigraphic layers identified during initial recordation; Right: Micromorph block MM1 ready to be removed from profile PS3A. MM1 collected from area where strats S40-42 and S51 were initially recorded, but as you can see, the strats do not quite look like how they did prior to sampling.
Note: In situ, many of the strats look like ash deposits. However, as you can see from the MM1 block these “ashy” deposits are not in fact ash, but have a dark-colored matrix with large quantities of rock, charcoal, and other inclusions. The dusty field conditions make it difficult to characterize the strats with a high level of accuracy during initial recording.

Conclusion

Long inhabited limestone rockshelters with deeply stratified deposits, such as Eagle Cave, can be difficult for an archaeologist to interpret. The natural degradation of the shelter itself, combined with human modification and natural forces create often complicated stratigraphic deposits. My thesis research involves a multidisciplinary approach to evaluate the formation processes evident in PS 3 and 4. The ongoing analysis of the micromorph slabs and thin sections from this sector of the shelter will help elucidate some of these complex processes and contribute to the overall analysis of formation processes in this sector of the shelter.

**A PDF version of this poster is available here: Nielsen_Micromorphs_TAS2015_FINAL

The Canyon Transformed

June 24, 2014

By Charles Koenig and Steve Black

It has been four days since Eagle Nest Canyon went on a historic flood, perhaps unrivaled since 1954.  We were fortunate that it hit on a Friday morning, peaked mid-day, stalled out in the afternoon as water backed up from the flooding Rio Grande, and then most of it drained out of the canyon overnight.  We were able to get back to work the next morning  (Saturday) in Eagle Cave.  We knew we would have to take the high trail into the canyon, but we weren’t really prepared for what we encountered when we looked over the edge for the first time.

Massive gravel dunes now cover the floor of the canyon.

Massive gravel dunes now cover the floor of the canyon.

The canyon bottom has been completely transformed.  There are massive gravel bars and dunes extending downstream from Eagle Cave, and they have covered the previous floor of the canyon with several meters of gravel.  The old water pump the Skiles family installed in the bottom of the canyon in the 1950s is either covered up by gravel or washed down into the Rio Grande.

Bottom of Eagle Nest Canyon after a small flood in May 2014 (left) versus June 20th (right). Several hundred tons of gravel and other debris was washed down and deposited in the canyon bottom just below Eagle Cave.

Bottom of Eagle Nest Canyon after a small flood in May 2014 (left) versus how it appeared on June 20th (right). Several hundred tons of gravel and other debris was washed down and deposited in the canyon bottom just below Eagle Cave.

Before the flood the lower canyon bottom had many trees including willow, salt cedar, cottonwood, mesquite, hackberry, and walnut, but the flood was so strong that most were ripped out, snapped in half or flattened by the flood waters.  We expect to see even fewer trees upstream from Eagle Cave once we have time to venture forth and boulder hop up the canyon.

The flood waters were so strong that even the large cottonwoods that once stood tall in the bottom of the canyon were bent over and snapped

The June 20th flood waters were so strong that even the large cottonwoods that once stood tall in the bottom of the canyon were bent over and snapped

The two sites that are most affected are Skiles and Kelley — the sites are fine, but getting to them and hauling dirt, or rather mud upslope to backfill our excavation units is … challenging.  For most of the season we were able to drive very close to the sites and take a short hike up the canyon wall to the rockshelters.  Now, the flood has left behind a massive gravel flat with braided streams below the sites.

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Kelley Cave and Skiles Shelter during the small flood in May 2014 (left), and the same shelters after the flood.

Fortunately, some of the denizens of Eagle Nest enjoy the mud.  When a small crew made their way to Kelley Cave Saturday afternoon, they followed in the footsteps of wild hogs that seem to enjoy the mud, contrary to the humans who slogged after them through the sticky slick mud.

Wild hogs seemed to enjoy the new mud that was on the trail into Skiles and Kelley.

Wild hogs seemed to enjoy the new mud that was on the trail into Skiles and Kelley.

After we collected ourselves from surveying the canyon and adjusting to the new landscape, we were able to work all day Saturday and put in a full day yesterday; however, this morning Mother Nature once again had plans for Eagle Nest …

View looking upstream to Eagle Cave just as the flood waters begin to flow across the gravel-dune field in the canyon bottom.

View looking upstream to Eagle Cave just as the surging flood waters begin to flow across the gravel-dune field in the canyon bottom.

We arrived at the canyon this morning after waiting out a thunderstorm that began just after dawn and passed just north of the canyon (Jack Skiles reported only just over 1/3″ of rain in his gauge above Eagle Cave).  When we drove over the highway bridge on our way to the canyon we saw water was running over the pour-off, so we knew another flood was headed our way.  Sure enough, not 20 minutes later we watched the water come rushing down the canyon once again, its thin leading edge advancing rapidly and swelling quickly.  From our canyon edge perch we watched with fascination as the flood torrent breached sand-gravel banks 15-20 feet high or went around them, carving new channels that crisscrossed the canyon floor and competed to see which would capture the main flow.

 

6-24 Flood: Mouth of ENC

The small flood from today winds its way through the bent over trees and gravel dunes from the massive flood 4 days ago.

The canyon ran until 1 pm, and sitting in Eagle Cave mid-morning the roaring water was loud enough that we had trouble hearing the person running the Total Data Station only a few meters away.  Today’s flood paled by comparison to Friday’s (perhaps 1/20th the volume or even less), but the water encountered virgin unconsolidated territory — the gravel bars. Over the course of the day a new channel cut through the gravel “dunes” and the floor of the canyon was once again transformed, albeit less dramatically than four days hence.

We are hopeful that our colleague the archaeo-sensing wizard Mark Willis will be able to come back out re-fly the canyon soon with his UAV to document how the canyon has changed since the flood.  It is rare to be able to watch an arid landscape dramatically change before your eyes, and Eagle Nest has done that twice in four days! Even though our best-laid plans were disrupted, we felt privileged to bear witness to flash floods massive and dinky.

 

The Canyon Runs Deep

June 20, 2014

“Scattered thunderstorms” was the forecast for today.  We had shrugged and fully expected to see little if any rain as usual in Langtry, Texas.  Landowner Jack Skiles visited our digs yesterday and asked, “Have you considered moving any of the heavy stuff [equipment] out of the canyon while the road is open, they say it might rain?”   We nodded and went back to work busily trying to finish our excavations and get our final SfM photo documentation completed to make ready for the geoarchaeological sampling that was to happen today and tomorrow.   Jack had just got the road serviceable again last week — it had been washed out last month after a 1.5″ rain — but sunny windy weather had dried it out quickly.   “Scattered thunderstorms,”  no problem.

The rain began around 4 am at the Skiles’ house overlooking Eagle Nest Canyon, and in less than eight hours 11.6″ of rain fell.  The Canyon ran deep as the following sequence of photographs attest.

9 am, view up Canyon toward Eagle Cave.

9 am, view up Canyon toward Eagle Cave.

9am, Steve Black looks across to Kelley Cave and Skiles Shelter and ponders Plan B.

9am, Steve Black looks across to Kelley Cave and Skiles Shelter and ponders Plan B.

10am, view up Canyon, Eagle Cave on the left.

10am, view up Canyon, Eagle Cave on the left.

10am, Wilmuth and Jack Skiles with Eagle Cave in the background.

10am, Wilmuth and Jack Skiles with Eagle Cave in the background.

10 am, view upstream from above Eagle Cave

10 am, view upstream from above Eagle Cave

10 am, lower Canyon with Kelley Cave on the left. The Eagle Nest Canyon flow is so strong that it is pushing water up the Rio Grande (to the right in background).

10 am, lower Canyon with Kelley Cave on the left. The Eagle Nest Canyon flow is so strong that it is pushing water up the Rio Grande (to the right in background).

ENC Pour-Off 11:30 am. Around this time is when the flood peaked.

ENC Pour-Off 11:30 am. Around this time is when the flood peaked.

Eagle Nest Canyon Flooding in 2010 (left) versus 2014 (right). This flood was not the first massive flood event ASWT has experienced at Eagle Nest. In 2010, after receiving 12" of rain over a 4 day period, the canyon went on what we thought was a massive flood (photo on left). Little did we know that by 11:30 am the flow of water over the pour-off into Eagle Nest Canyon would dwarf anything we had ever seen.

Eagle Nest Canyon Flooding in 2010 (left) versus 2014 (right).
This flood was not the first massive flood event ASWT has experienced at Eagle Nest. In 2010, after receiving 12″ of rain over a 4 day period, the canyon went on what we thought was a massive flood (photo on left). Little did we know that by 11:30 am the flow of water over the pour-off into Eagle Nest Canyon would dwarf anything we had ever seen.

Noon, view downstream from Eagle Cave

Noon, view downstream from Eagle Cave

Noon, Kelley Cave and Skiles Shelter with the Rio Grande in the background.

Noon, Kelley Cave and Skiles Shelter with the Rio Grande in the background.

Noon, view down Canyon, Eagle Cave on right with watefalls.

Noon, view down Canyon, Eagle Cave on right with waterfalls.

Noon, view upstream from above Eagle Cave.

Noon, view upstream from above Eagle Cave.

 

By 12:30 the flooding had started to subside. The water level did not get up into the shelter, but the lower couple dozen feet of our trail was washed away down to bedrock.

By 12:30 the flooding had started to subside. The water level did not get up into the shelter, but the lower couple dozen feet of our trail was washed away down to bedrock.

12:15 pm, mouth of the Canyon, Skiles Shelter on the left.

12:15 pm, mouth of the Canyon, Skiles Shelter on the left.

Noon, Kelley Cave and Skiles Shelter with the Rio Grande in the background.

12:30 pm, Kelley Cave and Skiles Shelter with the Rio Grande in the background.

2:30 pm, view of the mouth of the Canyon. Most of the flow is now coming back into the Canyon from the Rio Grande.

2:30 pm, view of the mouth of the Canyon. The flow is now starting to flow back into the Canyon from the Rio Grande.

6 pm, mouth of the Canyon. The water is slack and backed up from the Rio Grande.

6 pm, mouth of the Canyon. The water is slack and backed up from the Rio Grande.

6 pm, view upstream to Eagle Cave.

6 pm, view upstream to Eagle Cave.

 

Tomorrow we will venture into Eagle Cave using the upper “Goat Trail” and continue working with Charles Frederick and Ken Lawrence while they do geoarchaeological sampling of the deposits in Eagle.  This flood event has reminded us of the power of water in the desert, and how all of the sites within Eagle Nest have been (and are being) impacted by flooding.

My Time in a Geoarch Lab

by Jake Sullivan

I recently had the chance to work with Geoarchaeologist Dr. Charles Frederick. He invited me out to his laboratory (about 90 miles southwest of Fort Worth) for a few days so we could analyze the samples taken from Eagle Nest Canyon during his most recent visit. These included micromorphology and magnetic susceptibility samples from Kelley Cave as well as sediment samples from a small rockshelter opposite Skiles.

The micromorph endgame is to create thin sections of the intact stratigraphy which can be analyzed under the microscope. The micromorph samples were impregnated with resin and left to solidify and dry for two weeks in a shed in Langtry before being transported to the lab. However, two weeks and several layers of plastic containers did little to dispel or contain the toxic fumes wafting from the samples. But, for the sake of science, I drove the entire way with the car windows rolled down and made it—thankfully—without turning into an archaeo-popsicle.

Ken Lawrence with a successful micromorph extraction.

Ken Lawrence with a successful micromorph extraction.

My role in this process was to prepare the thin section blanks. I did this by trimming the ends of the micromorph samples as well as any excess resin, thereby exposing each face of the micromorph sample, and allowing Charles to decide the best locations for thin sectioning. Many of the laboratory procedures require multiple days to complete, and micromorph sample trimming is no exception. It takes three hours to trim one sample using a mineral oil lubricated rock saw. Thanks to the saw’s automatic shut-off I was able to complete other tasks in the interim.

Articulated and dis-articulated micromorph sample.

Articulated and dis-articulated micromorph sample.

One of the other tasks was to test the magnetic susceptibility of samples taken from the various strats of the north profile of Unit A in Kelley. Magnetic susceptibility analyzes the degree of magnetization of sediment. This is of interest to archaeologists because an elevated level can be indicative of biological activity through the fermentation process as well as burn events. As interesting as the science behind this analysis is, the actual lab process is quite simple. In Charles’ own words, “this is something a monkey can do.” I weighed each sample cube and then placed them in the magnetic susceptibility meter, recording the low and high frequency readings.

Magnetic susceptibility meter and samples.

Magnetic susceptibility meter and samples.

The last thing I did before leaving for the Lower Pecos was analyze the grain size of matrix samples using a sieve and hydrometer. Sieves are used for quantifying the large fraction particle sizes and hydrometers the small. A sieve is a series of stacked screens that go from large to small with respect to the size of particles a single screen will allow to pass. We used a shaker that utilizes sonic waves to vibrate the particles through the sieve. The particles left on each screen were then weighed and recorded. The hydrometer analyzes the small particles based on measuring the rate at which particles descend and settle in a water column at a constant temperature.

Geoarchaeologist in training.

Geoarchaeologist in training.

I had a lot of fun helping Charles and am very appreciative of him showing me the ropes of a geoarch lab. I will continue assisting him in processing many more samples in the near future. And as we learn more about micromorphology we will be sure to share our results.

Geoarchs in Action: Dirt by Many Other Names

By Steve Black and Jake Sullivan

Yesterday’s blog mentioned that geoarchaeologists Charles Frederick and Ken Lawrence would be with us in the field today.  For an archaeologist it is often a humbling experience to have a geoarch look at the same dirt you have been digging through and staring at for days—the things they see that we don’t!  They have both archaeological and geological training and whereas we ‘pure’ archaeologists look for cultural layers and cultural things, they look first at the natural formation processes.  How and when did the layers form, and how were they transformed since being created by the hand of man and the myriad vectors of ‘bioturbation’?  This may seem easy enough to decipher with a simple layer-cake stratigraphic profile, but what we have in the rockshelters of Eagle Nest Canyon is anything but simple—convoluted layers chopped up and partially blended by burrowing animals, insects, and the pits, fires, and scratching around that peoples ancient and historic have done.  Let’s introduce our collaborators of the geoarchaeological persuasion.

Dr. Charles Frederick is regarded by most as the preeminent geoarchaeologist working in Texas today and arguably one of the best in the world.  He earned his Ph.D. at UT-Austin under the famed geographer Karl Butzer and he has worked all across Texas and many other places in the world.  Charles taught in the University of Sheffield in the UK, but returned to Texas where he is an independent consultant who works as a subcontractor for many different firms and organizations.  What sets him apart is his encyclopedic knowledge of geology, pedology (study of soils), and natural science in general.  That and the way he approaches any research project—with an open, critical mind and the belief that something useful can be learned if you pose the right questions and link the big picture to the nitty gritty details.  Charles is a true scientist, he forms hypotheses (trial explanations) and then he tries to test them by seeking the hard evidence that could either disprove or strengthen the notion. 

His comrade in arms on this trip is Ken Lawrence.  Ken earned his M.A. at Texas State University where he studied under geoarchaeologist Dr. Britt Bousman.  He works for SWCA an Austin environmental consulting firm.  But like Charles he is here volunteering his time to help us because he likes the challenge of working in an area where few geoarchs have ventured. The chance to do pure research unfettered by regulation and the bottom line.  Ken, too, appreciates the opportunity to be able to spend time in the field with Frederick.  Geoarchaeologists often find it a bit frustrating to work with the unwashed (archaeologists who lack geological training) because we speak different lingo and we don’t look at the dirt through the same lens.  Watching the two of them bounce ideas and observations off one another is quite educational.

Their mission for the next several days is twofold.  First and foremost is helping Dan Rodriguez, the Texas State graduate student who is studying Kelley Cave and adjacent Skiles Shelter for his Master’s thesis. Last week Dan and fellow grad students finished digging a 1-x-2m unit in Kelley, or at least he took it as deep as they could practically (and safely) go – a bit over 7 feet deep. When the digging was done, Dan carefully cleaned several of the profiles (walls) and took many overlapping detailed photographs using LED light panels to illuminate the dark confines.  This week Black cleaned up the walls a bit more and sprayed them down with a fine mist.  Dan’s dry photos show some things well, but wetting the walls makes many subtle and obvious details ‘pop out.’  So we took another round of several hundred overlapping LED-lit close-up photos and through computer magic stitched these together to form geo-referenced mosaic and 3D model using the Structure from Motion (SfM) approach pioneered by our collaborator and archaeo-geek extraordinaire Mark Willis.  But we’ll tell more about Mark and SfM in future posts.

Today Frederick, Lawrence, and Rodriguez spent all day in and out of the Kelley Cave excavation unit, carefully and minutely examining the stratigraphy (layering) and spotting details neither the photos nor our archaeological eyes had seen.  Ken and Charles took turns in the hole, each annotating the printed photomosaics with their take on the layers.  Dan watched from above and annotated his own set, asking questions and trying to put the geoarch’s observations and explanations in the context of what his excavations had encountered. And we haven’t even mentioned the sampling.

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Ken Lawrence annotating the stratigraphic layers present in the profile.

We should explain that one of us was also present and madly taking notes.  I (Jake) have been tasked by Dr. B (Steve) to make myself useful to the geoarchaeologists, now and as the project unfolds. My minor at Texas State was Geology, so I have an inkling of what they are doing. Both Charles and Ken expressed that the Kelley profile is as complicated and messy a profile as they have ever seen. Their goal is to take as many samples as possible to try and deconstruct how all the sediment came to be in the shelter. According to Charles, the sediment could be alluvium from the Rio Grande, alluvium from Mile Canyon, soil from above the shelter on the canyon rim, and possibly even from swallow and mud dauber nests.

Ken began by taking samples from within the north profile’s different stratigraphic layers. Using a trowel he dug as far into the layers as he needed to fill the quart sized sample bags. Once Ken was finished Charles took several micromorphology samples called micromorph blocks. The blocks are handled with the utmost care, wrapped in toilet paper and tape to help maintain their structure. These intact cubes of sediment can later be impregnated with plastic, and once impregnated they can be shaved into thin sections for microscopic analysis. Ken and Charles hope to piece together the jigsaw puzzle of depositional processes within the rockshelter by analyzing the dirt’s composition. Today was the first step towards that end.

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Dr. Charles Frederick packaging a micromorph block.

Above we said that the geoarchaeological mission was twofold.  Part two is the big picture: how did the deposits within Eagle Nest Canyon form and transform over time and how did the landscape itself form and weather the passage of time?   OK, threefold: Charles and Ken are also here to help us strategize how we will investigate Eagle Cave, the biggest of the canyon’s rockshelters, over the next few months.  We have formed our basic research plan, but they will help us figure out how we can maximize the amount of data we can collect as we document and sample the rockshelter’s discontinuous stratigraphic profiles.  Data that will speak to the big picture and inform us as to the nitty gritty.  Stretching before our research eyes are many forms of dirt by other names.