Assigning Context to Artifacts in Burned-Rock Middens
Author(s): Jeff D. Leach, C. Britt Bousman and David L. Nickels
Source: Journal of Field Archaeology, Summer, 2005, Vol. 30, No. 2 (Summer, 2005), pp.
201-203
.Published by: Taylor & Francis, Ltd
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201
News and Short Contributions
Assigning Context to Artifacts in
Burned-Rock Middens
JEFF D. LEACH
University of Leicester
Leicester, England
C. BRITT BOUSMAN
DAVID L. NICKELS
Texas State University-San Marcos
San Marcos, Texas
Accumulations offire- crocked rock and carbon-stained sediment in
pits mark locations ofpast cooking and heating facilities around the
world. While the specific functions of these features may vary, the use
of stones as heating elements in earth ovens is common. After repeated
use, debris in the form offire- cracked stones, charcoal, ash, sediment,
carbonized plant fragments, and other materials accumulates to form
low mounds known in the U.S. Southern Plains and the Southwest as
burned-rock middens. The middens may include artifacts, some introduced inadvertently with sediment used to form an earthen cap to seal
the pit oven. The sediment and included artifacts for this insulating
cap may be borrowed from other parts of the site. After the cooking is
complete, the earthen cap is peeled open and all materials redistrib-
uted by trampling and slope wash. Artifacts and other materials in
burned-rock middens, therefore, may not represent discrete events or
periods directly associated with use of the ovens.
Introduction
Large accumulations of fire- cracked rock known as
burned-rock middens dot the landscape in Central Texas
(Black 1997). These features appear as amorphous masses
of fire-cracked rock and carbon-stained sediment lacking
visible structure. When excavated, however, rock-lined pits
and intact central oven features surrounded by an amorphous secondary accumulation of burned rock and other
materials are revealed (Black 1997). Many of these mounds
reach several meters in height and as much as 20 to 30 m
in diameter as the result of repeated use as oven facilities
for extended periods of time.
Material recovered from burned rock middens includes
chipped stones, ground stone tools, mammal and reptile
bones, floral remains, snails, mussel shells, ornaments,
burials, ceramics, and other items. Archaeologists often rely on artifacts and other materials recovered from these
middens to answer research questions. Unfortunately, artifacts recovered from middens may not be in situ, in the
sense of being part of the activity at the midden, but were
introduced to the midden with sediment borrowed from
other parts of the site. This sediment formed a cap that
sealed the central oven feature. When the oven was opened,
the earth cap and any artifacts it might contain were spread
away from the pit oven. Repeated use further inadvertently jumbled the intrusive artifacts with the oven deposits.
Ethnographic Examples of Burned-Rock
Midden Formation
No direct observations of people in Central Texas using
earth ovens exist, but accounts of cooking in pits using
rock heating elements are available from the American
Southwest and northern Mexico. For example, Castetter,
Bell, and Grove (1938: 28-29) describe cooking agave in
pits among the Mescalero and Chiricahua Apache:
Pits in which the crowns were baked were about ten to
twelve feet in diameter and three or four feet deep, lined
with large flatrocks... Upon this, oak and juniper wood
was placed, and before the sun came up was set on fire.
By
noon the fire
had died down, and on these hot stones was
laid moist grass, such as bunch grass... The largest mescal
crown was selected. .. they threw itin and threw the other
crowns after
it... After the mescal had been covered with
the long leaves of bear grass and the whole with earth to a
depth sufficient to prevent steam from escaping.
This account illustrates the basic steps for cooking in an
earth oven. These include digging a pit, adding stones and
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202 News and Short Contributions
Figure 1. In this badly backlit 1906 photograph an Apache woman and children are sealing an agave oven
with soil. The two children in the background appear to have collected soil from some distance from the
oven. This photograph by Edward S. Curtis is reproduced through the courtesy of Northwestern Uni-
versity Library.
fuel, and setting it on fire (Bell and Castetter 1941; Boas
1930; Chestnut 1902). Once the fire has burned down and
the stones are sufficiently heated, a layer of vegetation is
used to protect the food from the hot rocks. The plant layer also provides moisture during the cooking process. The
food to be cooked is arranged on the plant layer, and a second plant layer is placed on top of the food to serve as a
thermal barrier. Finally, earth is used to seal the feature
(fig. i). Once the food is cooked, the oven is dismantled,
the food removed, and the process is repeated.
Earth Oven Experiments
The earthen cap is the last critical step in the construction of the oven and is intended to serve as a thermal seal
allowing the food to cook. The amount of earth required
to properly seal an oven is not well documented in the
ethnographic literature. Experiments (Leach et al. 1998),
however, suggest that a moderate size oven, just a meter in
diameter, requires almost half a cubic meter of material
(490 kg of sandy loam) to adequately seal the oven. The
process of borrowing earth to cover ovens has important
implications for the understanding of formation processes.
If earth was regularly used to cap ovens, it is possible that
the collection of earth would have incorporated artifacts
from elsewhere on the site that are unrelated to the oven.
If the charred and fragmented stone in a midden is the
residue from numerous firings, many earthen caps may
have been constructed to cover the feature. In the experimental oven (Leach et al. 1998), it was necessary to borrow earth to seal the oven properly for its first use; the soil
excavated to create the pit was not enough by itself. In subsequent firings, it was possible to reuse earth but each time
an earthen cap was dismantled the earth was widely scattered. The soil is dispersed over time as the result of sheet
wash. With each additional use of the oven, fresh sediment
is needed. As a consequence, there is a cycle of earth moving and subsequent dispersal that may result in the unintentional transport of artifacts from other parts of the site
to the area of the oven.
Discussion
We do not suggest that all artifacts or ecofacts recovered
from these middens are derived from earth or sediments
excavated on the sites. Determining which materials have
been introduced by the process of transporting borrowed
sediments, and which materials are properly part of the feature and inform us about its use, remains an essential goal.
As a start, we assume that the artifactual content of burnedrock middens will almost always reflect both everyday activities associated with the use of the oven, and activities
that have very little to do with preparing or cooking foods
in earth.
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Journal of'Field Archaeology/Vol. 30, 2005
203
Hot Rock Cooking on the Greater Edwards Plateau: Four
Burned Rock Midden Sites in West Central Texas. Studies in
Archeology 22. Austin: Texas Archeological Research Laboratory, The University of Texas at Austin, 140-150.
During the use-life of an oven the discarded material
around it will be trampled, scattered, and disturbed during
subsequent firings. As this deposit accumulates, its unconsolidated and poorly sorted structure is subject to erosion,
which may remove the smaller fractions of sediment, artifacts, and stones. As the midden deposit thickens, it will
constitute a stratigraphic unit with a complicated history of
formation. It will record the depositional history of the
oven, but it will also record artifact mixing through borrowed sediment, possibly reversed stratigraphy, and certainly a mixture of different components from the site, if
Boas, Franz
1930 "The Salishan Tribes of the Western Plateaus," in James A.
Annual Report of theBureau of
Teit, ed., The Forty-fifth
American Ethnology 1927-1928. Washington, D.C.: Smithsonian Institution, 23-396.
Conclusions
Chestnut, V K.
1902 "Plants Used by the Indians of Mendocino County, California," Contributions from the US. National Herbarium 7:
multiple components exist.
It is important to appreciate that burned-rock middens
may often, if not always, contain unrelated artifacts
brought in from elsewhere on the site as the result of the
construction of caps using borrowed earth. The earth is obtained from portions of the site we call the "borrow zone."
If earlier components exist at sites with burned-rock middens, artifacts may be incorporated in the midden. Thus artifacts recovered from the midden, including radiocarbon
assays from carbonized plant remains, could produce misleading results, especially if the associated artifacts are used
to date the midden. The re-use of earth from earlier components to cover earth ovens could result in yet another
problem, namely artifacts that are functionally unrelated to
these ovens. A complete understanding of these features is
not possible until the formation processes related to them
have been examined in detail.
Castetter, Edward E, W H. Bell, and A. R. Grove
1938 The Early Utilization and the Distribution of Agave in the
American Southwest. University of New Mexico Bulletin, Biological Series Vol. 5, No. 4. Albuquerque: The University of
New Mexico.
294-408.
Leach, JefFD., David Nickels, Bruce K. Moses, and Richard Jones
1998 "A Brief Comment on Estimating Rates of Burned Rock
Discard: Results from an Experimental Earth Oven," La
Tierra 25: 42-50.
JeffD. Leach is a Ph.D. candidate at Leicester University,
United Kingdom. Mailing address: School ofArchaeology and
Ancient History, University ofLeicester, University Road,
Leicester LEI 7RH, United Kingdom. E-mail:
jejf@ cookstonetechnology. com
C. Britt Bousman is assistant professor ofAnthropology and
Director of the Center for Archaeological Studies at Texas
State University-San Marcos.
David L. Nickels is a research scientist at the Center for
Archaeological Studies at Texas State University-San Marcos.
Bell, W. H., and Edward E Castetter
1941 Ethnobiological Studies in theAmerican Southwest, VII. The
Utilization of Yucca, Sotol and Beargrass bythe Aborigines in
theAmerican Southwest. Bulletin 372. Albuquerque: University of New Mexico.
Black, Stephen L.
1997 "Scenarios of Midden Accumulation," in Stephen L. Black,
Linda W. Ellis, Darrell G. Creel, and Glenn T. Goode, eds.,
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