Zone VI: Into the Eagle Cave Unknown

By Charles Koenig

Since we began excavating the main trench in Eagle Cave in 2014, we have always had some idea of what to expect thanks to the previous work by the 1963 University of Texas excavations.  In 1963, Mark Parsons and Richard Ross spent three days illustrating the north wall of the “Old Witte Trench.”

Digitized and colorized field illustration of the 1963 Eagle Cave profile drawn by Mark Parsons and Richard Ross. The deep column in the center was added several months after the upper profile was annotated. Many more lenses, layers, and levels were noted on this profile than made it into the simplified, published version below. Original scan courtesy of the Texas Archeological Research Laboratory.

Version of the profile that appeared in Ross’s 1965 Eagle Cave report. Only the major stratigraphic zones are noted.

Even though they did not record nearly as many “zones” and “lenses” as we have documented strats (units of stratification), we can correlate some of the 1963 stratigraphic zones to 2015/2016 strats because they took the time to illustrate and describe the different layers. Broadly speaking, UT recorded 6 major stratigraphic zones (1-6), in addition to many other lenses and layers within zones. In Zones 1-5, UT recovered a variety of cultural debris (chipped-stone tools, plant and animal remains, and our favorite – burned rock), and the earliest deposits in Zone 5 were dated to 6500-7000 B.C. (Ross 1965). However, they stopped excavating at the top of Zone 6 because it was considered a “sterile layer of yellowish limestone spalls and dust.”

One of the 1963 Eagle Cave crew members beginning to dig the deep test through “sterile” fill. The white sediment at the man’s feet is Zone 6. View is looking west. Image courtesy Texas Archeological Research Laboratory.

From the outset of our work in Eagle, we have been guardedly optimistic the deposits from Zone 6 and deeper might not be sterile, but simply UT did not excavate far enough to find the next layer of cultural material. In reading the site journal for the 1963 work, we realized the UT crew stopped excavating at Zone 6 not only because they interpreted it as being sterile, but also because they simply ran out of time to excavate any deeper. They did sink a deep test to bedrock at the end of their work, but this was quickly excavated, and from what we can gather, they did no detailed recording or screening of materials that came out of this test. So, as we began excavating into the top of Zone 6 at the end of our last session (the last week in March) we were excited because we knew from that point down we would be excavating into the unknown – the oldest (>9000 years), minimally explored deposits within Eagle.

South trench in Eagle Cave profile as of 4/17/2016. Top image is just of the orthophoto of the trench, and the bottom is the same image superimposed with our interpretation of UT Zones 1-6 .

First Contact

The first place we excavated into Zone 6 was towards the rear wall in the site. Several of us (Kelton, Justin, and myself) were excavating units to expose a profile section, when Justin uncovered a most surprising artifact: a thick fragment of what appeared to be bison long bone.

Justin working in Zone 6 (white/yellow in profile).

In addition to the bison bone fragment, Justin also recovered two chunky biface fragments. After the months of anticipation, wondering what we may or may not find, and then to find artifacts and bison bone in one of our first units … we were excited, to put it mildly! As most things go on an archaeological site the bison bone find occurred on almost the last day of the field session, so we had to wait two full weeks before we could investigate Zone 6 again.

The two biface fragments (top) and sizable bison bone fragment (bottom) recovered in Zone 6 towards the rear wall.

The Trench Floor

Even though we all wanted to jump right in to excavating Zone 6 and seeing what was there, the first thing we did when we got back to work was to devote several days to removing disturbed fill from the bottom of the trench. After completing this dusty, hot, exhausting job we had exposed intact stratigraphy across the entire bottom of the trench. And, by removing the disturbed fill, we exposed more or less exactly the floor of the 1963 excavations into Zone 6.

The crew removing disturbed fill from the bottom of the trench (left), and the top of Zone 6 exposed in the bottom of the trench (right).

Once we had the top of Zone 6 exposed across the trench floor, we laid out several units with the goal of excavating down in the trench floor to give us room to work as well as expose profiles on the south wall. However, after only excavating about 10 centimeters below where the UT excavations stopped our excavations slowed dramatically when we started finding bison bone fragments; lots of them.

The scatter of bison bones as originally photographed in Unit 109.

Unlike the single bone fragment Justin found in the upper Zone 6 towards the rear of the site, Emily, Spencer, and Bryan began exposing dozens of fractured bison bones scattered over a 5 meter area. We knew we had something really cool, and that Zone 6 was definitely not sterile!

The top surface of Feature 14 (fragmented bison bone scatter) as initially exposed in the Eagle Cave trench floor. The bison bones are slightly more yellow than the surrounding white/yellow rockshelter sediments.

Feature 14

As we continued to expose more and more bone, we realized these bone fragments were all related to one another and likely represent a single behavioral episode. Because of our working interpretation that the bones were fractured and strewn across the extant surface of the shelter in a single event, we gave the bone scatter the designation Feature 14 (the 14th formally designated feature recorded in Eagle Cave since 2014). The feature designation also means we wanted to take special care in how we went about recording the provenience of the bones. To do this we took a series of SfM models and shot in with the TDS many of the bones.

Intermediate map showing Units 108 and 114 with additional bison bones exposed.

Intermediate map showing Units 109 and 115 with additional bones exposed. The cluster of rock in the center of the image is Feature 15, a likely hot-rock thermal feature.

We were also very fortunate to have Art Tawater on hand that week as one of our volunteers. Art is a longtime member of the Texas Archeological Society and the Tarrant County Archeological Society, and one of his passions and areas of expertise is zooarchaeology. After the bones were mapped in (piece-plotted with TDS shots) and photographed, Art made a preliminary field ID for the various bones. This was a huge help because none of us (except Black) had any experience with excavating bison bones, let alone trying to figure out what element each bone fragment might be from!

Art (left) helping Spencer (right) ID and package up bison bone for transport out of the site.

Mapping in the bones and collecting field observations slowed down the removal process, but we wanted to collect as much data in the field as we could so that when our collaborating zooarchaeologists Chris Jurgens and Haley Rush finally get to see the bones they will be well armed for the analysis to begin!  Plus, while the bones were well preserved, they had been purposefully fragmented originally  and some were crushed and cracked by the overlying deposits and did not remain intact upon careful removal.   Our detailed photographic record and Art’s field observations will allow a more complete analysis of the butchering and processing activities that took place on this surface over 9,000 years ago.

One of the few diagnostic bones we recovered: a proximal left mandible (jaw) fragment from a juvenile bison with deep cut marks on the posterior side. This bone is visible in the Unit 109-115 image above.

Not Just Bone

In addition to the scattering of bison bone, we also found a modest amount of associated lithic debitage and stone tools. If you look closely several of the tools are visible in the above maps. It is telling that most of the chert artifacts appear to be made of only two or three cobbles judging from the matching colors and textures.  This bespeaks a short-term occupation during which only a few cobbles were knapped.

Two bifacial tools found in direct association with the bison bone of Feature 14. Some of the debitage recovered appears to be the same raw material.

And although there is not the dense concentration of fiber within Feature 14 as in other areas of Eagle, we did recover some very badly decomposing organics.

A decomposing piece of wood recovered during excavation of Feature 14.

And I also can’t forget to mention the possible hot-rock thermal feature (Feature 15) found at the east edge of the bison scatter, with bones above and below rocks that appear burned!

Chalkboard shot of Feature 15, a likely hot-rock thermal feature in direct association with the scattered bison bones.

So What Does it All Mean?

We just finished excavating the main portion of Feature 14 earlier this week, so it is really too early to even say the analysis has begun, but we can at least offer up some of our preliminary observations and working ideas. Based on the how fragmented the bones are, we hypothesize Feature 14 represents a bison butchering and processing locale/event within Eagle Cave; possibly that of a single juvenile bison (portions thereof).

The outline of all mapped bison bones (in black) superimposed onto the initial Feature 14 exposure. The most complete bone–a rib–was recovered at the boundary between Units 114 and 109. All the other bones are fragmentary.

Not only were most of the bones fragmentary, but very few had diagnostic (articular) ends left. In most cases, the field ID was either “medial rib fragment” (~90% of bones) or “long bone shaft fragment” (~8%) of the bones. The fragmented nature of the bones suggests that the people may have been trying to extract bone marrow or render grease from the bones after the meat was removed.

We also have some interesting horizontal distributions of certain artifacts and bones. The areas where we found the highest number of bones with cut marks overlaps with where most of the debitage is clustered. Bones with cut marks plus many flakes indicates this location was where people were cutting bone and/or meat and needing to resharpen their tools. It was also telling to find the relatively few burned bone fragments we found appear to have been concentrated around several thermally altered rocks and scattered charcoal!

Distribution/highest concentrations of burned bone, bones with cut marks, and debitage overlaid against the bone scatter.

We were also fortunate to recover a projectile point from the same layer as the bison bone. Although not directly associated, this dart point fragment was recovered just to the west of the majority of the bison bones and is made of a very similar dark chert material as much of the debitage.

From top left: photograph of dart point fragment in situ; both sides of the dart point in the lab; map showing the location where the dart point was recovered in relation to the bison bone.

At the moment we are not ready to officially type the point, but it is a lanceolate, contracting stem dart point fragment that shares several attributes of Angostura points.

Where to from Here?

Myself, Jack Skiles, and Steve ponder Feature 14 when it was first exposed.

The fact that we encountered Feature 14 as quickly as we did after beginning into the “sterile” deposits of Eagle Cave gives us hope for additional, older, cultural deposits below. We do not know how old the bison bones are at the moment, but we will be sending out radiocarbon samples soon. We have had a lot of fun excavating this intriguing feature, and we look forward to sharing new findings as we make them!

The location of the Feature 14 bone scatter (linear cluster of yellow dots) and the original bison long bone fragment discovered towards the rear wall. We are excited by the prospects of what we may find as we go deeper into unknown Eagle Cave!