Eagle Cave South Trench 2015: Initial Results from Profile Section 9

By Matt Larsen

**This is the second of four blog posts showcasing a different Profile Section that was documented and sampled during the 2015 field season. Each of these Profile Sections has different sediment characteristics, artifacts, and ecofacts. Profile Section 9 is located adjacent to Profile Section 17 (see Cleaning the Kitchen at Feature 8). For a location map see 2015 Investigations at Eagle Cave.**

Matt standing next to his poster at TAS.

Matt standing next to his poster at TAS.

Profile Section 9 (PS9) is one of several profile sections along the south wall of the Eagle Cave trench. It differs from the other profile sections in that it is perpendicular to the main trench, and thereby provides a small area of different perspective. PS9, like many profile sections toward the rear of Eagle Cave, suffers from significant bioturbation.

PS9 with all strata demarcated as defined on-site. The areas marked with diagonal lines indicate the numerous krotovinas (back filled animal burrows), which complicate an already complex stratigraphy. 28 strata were defined in PS9, many of which were visible in the adjacent PS10. The strata are not numbered in order because some strata were defined originally in PS10 or PS5. In all, there were five strata description events. Areas of interest include a “striated wedge” of alternating light and dark strata in the upper right and the sudden appearance of dark charcoal rich strata in the lower half of PS9.

PS9 with all strata demarcated as defined on-site. The areas marked with diagonal lines indicate the numerous krotovinas (back filled animal burrows), which complicate an already complex stratigraphy. 28 strata were defined in PS9, many of which were visible in the adjacent PS10. The strata are not numbered in order because some strata were defined originally in PS10 or PS5. In all, there were five strata description events. Areas of interest include a “striated wedge” of alternating light and dark strata in the upper right and the sudden appearance of dark charcoal rich strata in the lower half of PS9.

 

Strat Descriptions

  • S0261 – Thick, white-gray ashy layer with small laminations.
  • S0260 – Relatively thin fiber layer with some ash, charcoal, and small (<5mm) pebbles.
  • S0259 – White-gray ashy layer with laminations.
  • S0258 – Thin horizontally bedded fiber/ash layer.
  • S0257 – Rather thin white ashy layer with possible small FCR inclusions.
  • S0256 – Light brown fiber layer with some ash and charcoal.
  • S0255 – Sloping white/gray ashy layer with some laminations.
  • S0254 – Rather faint gray white/yellowish layer of bedded fiber and ash.
  • S0253 – Thick white/gray ashy strat with FCR; slightly wedged shape in profile, thickening S->N.
  • S0252 – Horizontally bedded fiber and ash sloping down to the N.
  • S0251 – Light gray ashy compact strat sloping down slightly S->N.
  • S0060 – Dark, relatively thick organic layer; thickens as it continues N.
  • S0152 – Light ashy layer that thins as you move N across the profile.
  • Excavated Layer 1
    • S0194 – Brown organic/fiber/charcoal strat with darker layer in the middle.
    • S0195 – Thin layer of darker fiber chunks/charcoal.
    • S0196 – Compact light brown, fine-grained organics.
    • S0154 – Thin yellowish-white ash layer sandwiched; strat thickens S->N.
  • S0197 – Brownish gray fiber layer sloping down to the N.
  • S0198 – Very flaky dark, organic fibrous layer with burned plant material.
  • S0199 – Thin, compacted fiber/charcoal layer.
  • S0200 – Dark gray with chunks of charcoal. S0200 is the “pitfill” defined by the interface strat S0250.
  • S0250 – Interface strat (pit) sloping down from S->N, intruding into and originating from S0205 and filled by S0200.
  • S0205 – Thin, sloping ashy deposit whose top edge slopes sharply down to the N roughly 10 cm from S profile boundary.
  • Excavated Layer 2
    • S0206 – Thin, compact tan-grey deposit with charcoal flecks and decomposing fiber.
    • S0207 – A relatively thick layer of gray/brown ash with lots of charcoal and fiber.
  • Excavated Layer 3
    • S0208 – Thin ashy strat.
    • S0209 – Light grey-brown strat with gritty-ashy and fiber.
  • S0210 – Ashy strat with less charcoal than the overlaying “ashy” layers. S0286 – Brown charcoal and fiber rich strat with many small rocks.

 

Excavation and Sampling Strategy

Excavation Unit 58 (U58) was placed to sample all the stratigraphic units (strats) recorded in PS9. U58 was excavated strata by strata, unless individual strats were extremely thin, in which case several related strats would be combined into a layer. All artifacts and sample locations were point-plotted with a Total Data Station (TDS).

PS9 with all excavated strata defined. Several sets of strata were too small for individual excavation and excavated as a layer of related strata. All excavated strata and layers in the image are derived from SfM 3D models and projected on the profile section exactly as they were excavated with a margin of error measured in millimeters.

PS9 with all excavated strata defined. Several sets of strata were too small for individual excavation and excavated as a layer of related strata. All excavated strata and layers in the image are derived from SfM 3D models and projected on the profile section exactly as they were excavated with a margin of error measured in millimeters.

All of the sediment from U58 was collected as matrix samples. Rocks obviously larger than 2.5 cm were put aside, then weighed and counted on-site and in the field lab, then discarded once the data were collected. This data will help determine how many earth ovens were constructed in Eagle Cave.

In the field lab, each matrix sample was sifted through a ½ inch sieve, and all artifacts and ecofacts were collected and bagged by type. The remaining matrix was split into 1 liter samples, for curation and to send to various specialists for analysis.

Matt Larsen (left) and Bryan Heisinger (right) excavating Unit 5

Matt Larsen (left) and Bryan Heisinger (right) excavating Unit 5

Recovered Artifacts

Artifacts recovered from Unit 58 (lockwise from top-left): edge-modified flake, heat-shattered core, Langtry dart point, charred bone with residue.

Artifacts recovered from Unit 58 (lockwise from top-left): edge-modified flake, heat-shattered core, Langtry dart point, charred bone with residue.

Modified Flakes. Three modified flakes were collected in PS9.

Cores. Four cores were collected in PS9. Three appeared to be heat-shattered, apparently in situ.

Faunal Remains. Faunal remains in PS9 consisted of snail, various bone fragments, and two antler tine fragments. One bone tool fragment was also collected.

Projectile Points. Three points were collected in PS9: a Frio, a Langtry, and an unidentified fragment.

Debitage. Debitage was collected from ½ inch sieve and was found throughout most of U58, as can be seen in the chart below.

PS9 Debitage

Rocksort. The largest amount of rocks came from strata S0261 and S0254, as can be seen in the chart below; these were also the most voluminous strata excavated. The rocks collected in PS9 tended to be fewer and smaller than in other areas closer towards the dripline.

PS9 Rocksort

This chart shows the rocksort mass, fiber mass, and the remaining matrix mass as percentages of the mass of the entire strat or layer. This provides a clearer picture of how much burned rock was in a strat as a proportion of the whole. The only fiber was 1.65 g collected from the ½ inch sieve in the stratum S0268 matrix. This is the lowest strat in the profile and may signify the beginning of a fiber and botanical rich zone similar to that seen in PS12.

This chart shows the rocksort mass, fiber mass, and the remaining matrix mass as percentages of the mass of the entire strat or layer. This provides a clearer picture of how much burned rock was in a strat as a proportion of the whole. The only fiber was 1.65 g collected from the ½ inch sieve in the stratum S0268 matrix. This is the lowest strat in the profile and may signify the beginning of a fiber and botanical rich zone similar to that seen in PS12.

Preliminary Analysis

Intern and Archaic chef, Emily McCuistion (top) watches the fire we created to heat the rocks for an experimental earth oven and (bottom) places lechuguilla and sotol hearts on top of the prickly pear packing material in an experimental earth oven.

Intern and Archaic chef, Emily McCuistion (top) watches the fire we created to heat the rocks for an experimental earth oven and (bottom) places lechuguilla and sotol hearts on top of the prickly pear packing material in an experimental earth oven.

PS9 appears to be located in an area of Eagle Cave used for repeated earth oven events over the centuries. Only a meter to the west are the remains of a hot rock feature (Feature 8) with ash and coal directly under the rocks, as would be expected in an earth oven bed (heating element).

PS9 itself has many strata varying between fiber or charcoal rich strats and strats that have a higher volume of ash. In these “ashy” strata are also organic remains burned to white ash as well as several heat-shattered chert cores. Strat S0250 is a distinct stratigraphic interface, which appears to be a pit dug into the material beneath, and filled in with contrasting matrix.

The lack of large amounts of FCR, relative to the areas closer to the dripline, seems to indicate the area in which PS9 is located was favored for earth oven pits and cleaned out by tossing spent rocks (and fiber) out towards the dripline.

 

**A full PDF version of the poster is available here:Larsen_TAS2015_PS009_FINAL**

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Eagle Cave South Trench 2015: Cleaning the Kitchen at Feature 8

By Bryan Heisinger

**The next four blog posts will each showcase a different Profile Section that was documented and sampled during the 2015 field season. Each of these Profile Sections has different sediment characteristics, artifacts, and ecofacts. The first is Profile Section 17 and Feature 8, located closest to the rear wall. For a location map see the previous post, 2015 Investigations at Eagle Cave.**

Bryan standing next to his poster at TAS.

Bryan standing next to his poster at TAS.

During the Ancient Southwest Texas Project’s 2015 Eagle Nest Canyon Expedition, the crew uncovered and sampled Feature 8—an earth oven pit and intact heating element complex near the back of Eagle Cave (see Between a Rock and a Heart Place). The dense concentration of large fire-cracked-rocks (FCR) and charcoal within the pit are classic characteristics of earth oven baking. Further, many of the limestone rocks were large (11-15 cm) in size and inclined in a basin-shaped configuration at the base of the pit. The matrix that surrounded these fire-cracked rocks (FCR) was heavily organic, ashy, rich with dime-size charcoal chunks, and almost entirely absent of artifacts.

Plan and profile views of Feature 8 as originally exposed in Unit 25. Notice the large FCR, and how they are inclined towards the right.

Plan and profile views of Feature 8 as originally exposed in Unit 25. Notice the large FCR, and how they are inclined towards the right.

Digital Elevation Models (top) and orthographic photos (bottom) of Feature 8 during excavation of Unit 25 Layer 3. Contour interval is 2 centimeters. Elevations range from 980.138 meters (brown) down to 979.445 meters (blue).

Digital Elevation Models (top) and orthographic photos (bottom) of Feature 8 during excavation of Unit 25 Layer 3. Contour interval is 2 centimeters. Elevations range from 980.138 meters (brown) down to 979.445 meters (blue).

Methodology

After initially exposing Feature 8 in Unit 25, Units 50 and 55 were opened up as sampling units. The two units were excavated following natural stratigraphic layers, and matrix samples were collected from each layer. Back in the lab, each matrix sample was sifted through a ½ inch sieve and all artifacts and were collected and bagged by type. The remaining matrix was split into 1 liter samples for curation and further analysis by our various colleagues (archaeobotany, geoarchaeology, and entomology). All rocks greater than 2.5 cm were added to the Rocksort data. Profile Section PS17 is the east/west running profile of excavation units 50 and 55. After cleaning the profile, a 3D model was created using Structure from Motion (SfM) photography  and the stratigraphic layers (strats) were annotated on an orthophoto of the profile.

PS017 Profiles

 

PS017 Debitage

PS017 Rocksort

Preliminary Interpretations and Observations

Based on the densities of large FCR  (> 11-15 cm), organic soil, and heavy concentrations of charcoal,  PS17 appears to be located in an area of Eagle Cave that has been used for repeated earth oven events over the centuries, of which the Feature 8 pit is just the most recent iteration.

Some interesting observations:

1) Besides charcoal and other carbonized plant remains, there was no uncharred organic material in the Feature 8 complex.

2) 110 + kg of burned limestone rock from Feature 8 was counted and quantified from Units 50 and 55. Many of these rocks were >15 cm, indicative of the “pristine” rocks expected in an earth oven heating element.

3) The amount of large FCR in the PS17/ F8 area relative to the units closer to the dripline, indicate that this area was favored for earth ovens pits. The tossing of discarded rocks during cleaning episodes would have sent smaller rocks and fiber toward the dripline.

4)  A hard/cemented matrix was encountered in layer 3 of Units 55 and 50. The formation process and composition of this anomaly is awaiting further analysis.

 

**A full PDF version of the poster is available here: Heisinger_TAS2015_Feature8_FINAL

Eagle Nest Canyon Symposium at the 2015 Texas Archeological Society Annual Meeting

This past weekend (October 23-25th) the Texas Archeological Society held its 86th Annual Meeting in Houston, Texas. Our ongoing work in Eagle Nest Canyon was well represented, with a presentation by Charles Koenig on Friday detailing our use of SfM for documenting excavations, and a large poster session on Saturday. We decided the best way to share the posters with everyone who did not attend the annual meeting is to create individual blog post from each poster. So, each week through mid-December we will be adding a new blog post featuring one of the posters from TAS.  The first post is the poster by Charles and Steve that introduces our ongoing Eagle Cave work. You can also download the PDF version here: Koenig&Black_TAS2015_FINAL.

The 2015 Investigations of Eagle Cave

By Charles Koenig and Stephen Black

Charles standing next to the Eagle Cave poster.

Charles standing next to the Eagle Cave poster.

Eagle Cave (41VV167) lies within Eagle Nest Canyon, a short box-canyon tributary of the Rio Grande, just downstream from Langtry, Texas.  The canyon is owned and protected by the Jack Skiles family. Eagle Cave is one of the largest rockshelters in the Lower Pecos Canyonlands, and has been scene of archaeological investigation beginning with Sayles and Kelley in 1932, the Witte Museum in 1935-1936, UT Austin in 1963, and now Texas State University.  The legacy of the previous archaeology was a long, deep, minimally backfilled trench through the center of the shelter that continues to erode and destroy the extant intact deposits.

Eagle Cave as viewed in 2014 (left) versus 1936 (right). Image on the right courtesy the Witte Museum.

Eagle Cave as viewed in 2014 (left) versus 1936 (right). Image on the right courtesy the Witte Museum.

The large central trench, as well as a smaller unit on the upstream end of the shelter, was left mostly open.  Since the 1960s, the trench walls have slumped, collapsed, and gradually eroded by foot traffic, animal burrowing and wind, leaving a massive linear depression. In 2014 the Ancient Southwest Texas (ASWT) project returned to Eagle Cave with the ultimate conservation goal of backfilling all holes and stabilizing the site surface.

The 1930s trench begun by Sayles and Kelley and expanded upon by the Witte Museum (left) was about 6 feet wide. When the Amistad Salvage Project cleaned out the trench in 1963 (center) it was somewhat wider. Fifty years later the once vertical excavation walls have collapsed into massive depressions (right, circa 2003). Yellow arrows point to a unique spall.

The 1930s trench begun by Sayles and Kelley and expanded upon by the Witte Museum (left) was about 6 feet wide. When the Amistad Salvage Project cleaned out the trench in 1963 (center) it was somewhat wider. Fifty years later the once vertical excavation walls have collapsed into massive depressions (right, circa 2003). Yellow arrows point to a unique spall.

South Wall of the Main Trench

Based on lessons learned in 2014, in 2015 we had the ambitious goal of exposing, documenting and sampling the entire south wall of the main trench. We cut back the slumped wall and exposed the largely intact stratigraphy to frame the microstratigraphic layering within the context of the larger structural patterning visible across the site. In order to maintain stability and provide access, we stepped our profiles vertically and maintain the “Low Impact, High Resolution” sampling strategy we adopted at the outset of our work.

The 2015 field crew (from left) Emily McCuistion, Matt Larsen, Victoria Pagano, Charles Koenig, and Bryan Heisinger. This photo was taken on the last day of the 2015 field season

The 2015 field crew (from left) Emily McCuistion, Matt Larsen, Victoria Pagano, Charles Koenig, and Bryan Heisinger. This photo was taken on the last day of the 2015 field season

The 2015 Excavations

Our excavations focused on the south side of the main trench. Beginning at the top of the slumped trench wall, we removed disturbed fill and excavated small units to expose the intact stratigraphy. The cleaned profiles were given “Profile Section” designations, and the individual stratigraphic layers/interfaces, or “Strats,” were recorded for each section. Once strats were defined for each profile section, we began high-resolution sampling. We would lay out a sampling unit (e.g., 25-x-50 cm) along the profile section and excavate strat by strat, guided by the exposed stratigraphy. For every sampled strat we collected all the excavated matrix; back in the field lab we sieved this matrix through a ½” geologic sieve. The <1/2” material was split into several different samples, which will be used for future analyses (e.g., macrobotanical).  In addition to the tightly provenienced matrix, in situ artifacts were shot in with the Total Data Station and collected individually.

As the excavations continued we stepped the excavation units and profiles as we went deeper. By stepping the trench we are not only stabilizing the delicate deposits, but also preserving the intact deposits for future research.

Plan map of Eagle Cave showing the ASWT units from 2014-2015 compared to the UT units from 1963.

Plan map of Eagle Cave showing the ASWT units from 2014-2015 compared to the UT units from 1963.

South wall of the main trench in Eagle Cave at the end of the 2015 field season. The yellow outlines show the locations of only the profile sections discussed in greater detail in other posters. Overall, 16 profile sections have been defined and 11 sampled in this trench wall

South wall of the main trench in Eagle Cave at the end of the 2015 field season. The yellow outlines show the locations of only the profile sections discussed in greater detail in other posters. Overall, 16 profile sections have been defined and 11 sampled in this trench wall

Illustrated version of the south wall of the main trench in Eagle Cave. The stratigraphy is depicted as an interim interpretive graphic that does not exactly match the layers identified and described in the field.

Illustrated version of the south wall of the main trench in Eagle Cave. The stratigraphy is depicted as an interim interpretive graphic that does not exactly match the layers identified and described in the field.

Macrostratigraphic Patterns

We have recorded over 300 individual stratigraphic layers within Eagle Cave since 2014. Many of these strats are very thin (<3cm) “microstrats,” and do not extend across large areas of the site. However, as we continue to expose more of the trench profile we are able to assign many of these microstratigraphic to macrostratigraphic “zones” across the site. We have just begun the stratigraphic analysis, but at this point we have five major macrostrats: 1) upper ashy/FCR zone; 2) dense fiber/FCR zone towards the dripline; 3)  heavily mixed charcoal/fiber/ash zone; 4) zone of red/brown attrition deposit; and 5) lowest zone of yellow attrition deposits & spalls.

Each of these macrostrats represents differences in activities or discard patterns relating to intervals of site use. One activity that links the upper three zones is earth oven cooking. Much of the content is debris from earth ovens (cut leaf bases of lechuguilla and sotol and FCR).  We can follow what we infer are successive iterations of oven pit construction and use. It is only by creating large exposures that we are able to identify macrostrats and begin to understand how the hundreds of microstrats fit into the larger structural and behavioral patterns.

A variety of items recovered in situ from Eagle Cave (clockwise from top left): woven mat fragment, sandal, coprolite, dart point, painted pebble, lechuguilla central stem, two views of an antelope skull fragment, cordage, and a dart foreshaft.

A variety of items recovered in situ from Eagle Cave (clockwise from top left): woven mat fragment, sandal, coprolite, dart point, painted pebble, lechuguilla central stem, two views of an antelope skull fragment, cordage, and a dart foreshaft.

Plans for 2016

As the 2015 field season drew to a close, we knew we did not have the time to finish exposing, documenting, and sampling the entire south wall. In 2016 we will continue what we started in 2015, and finish exposing and sampling the profile. As we dig deeper, we are excavating deposits that have never been fully evaluated, and the data we will collect will be invaluable for understanding at least 9,000 years of hunter-gather use of Eagle Cave. We anticipate that our hundreds of samples will be analyzed for decades to come, much like those from the 1970s Texas A&M excavations at Hinds Cave.

 

2016 Eagle Nest Internship Call

3 Internship positions available for 2016! See the 2016 Call for Interns here:2016 Eagle Nest InternshipCall.