Pages 31-44 -- Jones and Munson.pmd

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Geoffrey Jones and Gene Munson Geophysical Survey

Geophysical Survey as an Approach to the EphemeralCampsite Problem: Case Studies from the Northern

Plains

Geoffrey Jones and Gene Munson

Temporary campsites and indeterminate artifact scatters are a perennial problem in archaeology.Features and artifacts are few, often scattered across an extensive area and representing considerabletime depth. Meaningful and cost-effective data recovery is difficult using conventional methods. Inte-grated with more traditional methods, geophysical methods have proven to be an effective approach onmany sites on the northwestern Great Plains. Hearths, stone rings, and other features can be detectedand mapped, allowing researchers to target areas for excavation and understand intra-site patterning.

Keywords: magnetic survey, gradiometer, campsite, geophysics, hearths

Plains Anthropologist, Vol. 50, No. 193, pp. 31-43, 2005

Geoffrey Jones, Archaeo-Physics LLC, 1313 5th Street Southeast, Minneapolis, Minnesota [email protected]

Gene Munson, GCM Services, Inc., P.O. Box 3047, Butte Montana 59702 [email protected]

Temporary campsites and indeterminate arti-fact scatters form a large percentage of prehistoricsites throughout North America, and especially onthe northwestern Great Plains, where village sitesare rare. It is obvious that our understanding of pre-historic lifeways is incomplete, if not deeply flawed,without understanding temporary campsites. Unfor-tunately, cost-effective data recovery from these sitesis problematic using conventional sampling andexcavation methods. Diagnostic artifacts and dat-able features are often present (or may be presumedto be present) but they are few and often scatteredacross an extensive area. When only a small per-centage of a site may be sampled, recovered dataare often inadequate to address meaningful researchquestions. Often these sites have distinct intra-sitepatterning and multiple components may representconsiderable time depth.

Hearths and stone rings (tipi rings) are the mosttypical features of campsites on the northern Plains(for the purposes of this article, the term hearth isbroadly used to indicate a variety of thermal fea-tures). Magnetic field gradient survey has beenproven to be highly successful at detecting thermalfeatures, and in certain conditions, stone rings, as

well. Although this article focuses on a singlemethod, there are a number of other geophysicalmethods commonly applied to archaeology. Thesecase studies are generally illustrative of a geophysi-cal approach, discussed in broader terms in a con-cluding section. As part of an integrated researchstrategy, geophysical mapping can allow research-ers to better target areas for excavation, to collect alarger sample of positive data within limited bud-gets or schedules, and to study intra-site patterningbeyond the limits of excavation.

The case studies presented in this article wereselected from the results of 55 discrete survey areasat 21 prehistoric campsites in Campbell and Westoncounties in northeastern Wyoming, and in Rose-bud and Big Horn counties in southeastern Mon-tana (Figure1). They have been selected becausethey are illustrative of issues associated with thisapproach. Most of the 55 survey areas containedanomalies thought to be caused by prehistorichearths or other archaeological features, and theyare reasonably well represented by the specific casestudies presented here. Geophysical data collectionwas performed between 2000 and 2003 by DavidMaki and Geoffrey Jones of Archaeo-Physics, LLC,

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PLAINS ANTHROPOLOGIST Vol. 50, No. 193, 2005

as part of the archaeological treatment of these sitesunder the direction of Gene Munson of GCM Ser-vices, Inc. (Munson 2002a, 2002b, 2003a, 2003b,Munson et al., 2004).

METHODSWhile an in depth discussion of magnetic

theory, survey logistics, and data processing is be-yond the scope of this article, both Clark (1996)and Gaffney and Gater (2003) provide excellentintroductions to archaeological geophysics. Surveylogistics, data processing, and technical parametersare dealt with in individual reports of investigation(Jones 2001a, 2001b, 2003). A brief non-technicalintroduction to magnetic field gradient survey ispresented in the following paragraphs.

The geophysical surveyspresented in this article wereperformed with a GeoscanFM36 magnetic gradiometer(Figure 2). This instrumentrecords local variations in theearth’s magnetic field, prima-rily caused by differences inthe magnetic properties ofsubsurface materials. The in-strument responds only whenin close proximity to discreteanomaly sources. Near-sur-face phenomena can bemapped in detail while deepor large-scale phenomena(typically geological) arelargely suppressed. The re-sults are presented graphi-cally because archaeologicalfeatures are generally recog-nized by their pattern, ratherthan by their numeric valuesalone. Typically, the result-ing map will have a back-ground value of approxi-mately zero, with local dis-tortions in the geomagneticfield appearing as negativeand positive anomalies. Val-ues are recorded innanoTeslas (nT), indicatingrelative magnetic strength.

The principal phenomenon causing detectablefeatures on these sites is thermal alteration of min-erals in soils and rock. The temperatures caused byprehistoric hearths can alter (usually increase) themagnetic susceptibility of minerals as well as causethermo-remanent magnetization (TRM). Suscepti-bility is a measurement of the ease with which thegeomagnetic field flows through a material. Thegeomagnetic field will flow preferentially throughmaterials that are of higher susceptibility than theirsurroundings and cause locally higher field strength,called induced field magnetization. Other culturalsources of induced field anomalies include organi-cally enriched deposits and disturbed soils. TRMis a permanent magnetization acquired when min-erals have heated to a critical level called the Curie

Figure 1. Regional map showing site locations.

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temperature, generally between 120 and 675 OC. Ifits source is undisturbed, a TRM field will retainthe orientation and intensity that were fixed at thetime of cooling (the basis for archaeomagnetic dat-ing).

Magnetic anomalies are often the result bothof induced field and remanent magnetization. Theobserved magnetic field strength is the result of thetotal magnetization of an object. The total magneti-zation is thus a vector sum of the induced magneti-zation and the remanent magnetization (Sharma1997). In general, induced fields appear in magneticfield gradient surveys as a positive monopole, whileremanent fields appear as bipolar anomalies, hav-ing both a positive and negative component. In prac-tice, it is not possible to quantify the different con-tributions causing an anomaly in survey data, al-though estimations may be made based on anomalystrength and appearance.

While in-situ hearths often appear as bipolaranomalies because of remanent magnetic effects,most of the suspected hearths at these sites appearwith only a very weak negative component. An ex-planation for this is that with time, bioturbation andother small-scale disturbances randomly re-orientsediment grains in the soil. The many small ran-domly oriented remanent fields of each sedimentgrain would largely cancel each other out, leavingsusceptibility effects as the dominant anomalysource. Other cultural features, such as pits,middens, and historic privies can also cause mag-netic highs. These too are due to enhanced suscep-

tibility, and may appear very similar to hearth fea-tures. In general, magnetic anomalies caused byorganic enrichment or disturbed soils alone are oflow amplitude, although additional componentssuch as metal artifacts or thermally altered miner-als may contribute as well.

The term “thermally altered rock” is used inthis article to refer to either natural or cultural ma-terials. The sedimentary bedrock in its original statedoes not display appreciable remanence (permanentmagnetization) or high susceptibility, but may bealtered by burning coal seams. Rock that had beenaltered by burning coal was found to display a strongremanence and enhanced susceptibility. Based onmagnetic survey results alone, it is not possible todistinguish between rocks that have been alteredby cultural processes from those occurring naturallyexcept by their patterning. Rocks, otherwise natu-ral, may also be culturally transported.

Near surface geology and historic cultural phe-nomena may also cause anomalies in survey data,commonly stronger and often more pervasive thanthose caused by prehistoric features. Metal, brick,and other historic materials and features can causevery strong anomalies. Fortunately, these materialsare not often pervasive on sites on the northwesternPlains. Rock formations (especially igneous) andheterogeneous sediments may also cause strong andpervasive variance that can obscure more subtleanomalies of interest.

3030 WINCHESTERThe 3030 Winchester site (48CA3030) (Fig-

ure 3) is a Late Prehistoric campsite located 31 kmsouth-southeast of Wright, Wyoming in the easternPowder River Basin. The site is on the north sideof Horse Creek in southern Campbell County justnorth of the Converse and Campbell County line.It was originally identified and evaluated by GCMServices (Munson 1997). At the time of its discov-ery, two eroding rock-filled hearths, two clusters ofthermally-altered rock, and nine lithic artifacts wereobserved on the surface. The eroded nature of theterrace on which the site is located did not inspireconfidence that additional features would be found.Gradiometer survey, completed in only a few hours,was performed over a 3900 square meter area en-compassing most of the site. The results clearlyshowed an additional seven hearth features as well

Figure 2. Magnetic survey at the Malodorous site and FM36Fluxgate gradiometer (inset).

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as an exposed but previously undetected concen-tration of thermally altered rock. An exposed hearththat had been previously recorded was detected aswell.

Excavations at 3030 Winchester consisted of12 block excavations and 15 test units measuring0.5 x 0.5 m. The block excavations were scatteredover an area measuring 105 m north to south by

Figure 3. Site plan of the 3030 Winchester site (48CA3030).

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125 m east to west. All except three of the blockexcavations were at magnetic anomalies. The testunits were placed at an arbitrary interval of fourmeters, centered on Station 3. (Figure 3). Station 3is where the majority of the cultural remains werelocated at the site. No features or intact culturalhorizons were found in the test units. A total of104.75 square meters was excavated by hand. In

addition, 102 m of backhoe trenches were dugin search for deeply buried cultural deposits(Figure 3).

The seven subsurface hearths appear inthe data plot (Figure 4) as circular magnetichighs, from 3.5 to 9.5 nT in amplitude. Theassociated negative component is diffuse andweak, but may be slightly stronger to the northof the positive component. An example of oneof the rock-filled hearth features and the asso-ciated magnetic anomaly is shown in Figure5. The single exposed hearth within the sur-vey area (B8-F1) appears as a less distinctpositive anomaly. The appearance of FeatureB4-F1, a small exposed scatter of thermally-altered rock, as a largely negative anomaly wasunexpected, and it is thought to be caused bythe coincidental orientation of the TRM fieldof the rocks. A large complex bipolar anomalywas determined to be caused by a lightningstrike (Jones and Maki 2005; Verrier et al.2002).

There is a strong relationship between thesize and composition of hearth features andthe strength and appearance of the associatedanomalies. All of the intact hearth features as-sociated with >6 nT anomalies contained sub-stantial amounts of thermally-altered rock; allof those associated with weaker anomalies con-tained none. Although negative componentswere weak, bipolar anomalies were associated

Figure 5. Planview and profile of Feature B6-F1.

Figure 4. 3030 Winchester magnetic survey results.

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Figure 6. Site plan of the Huckins site (48CA917).

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with thermally-altered rock. The two strongestanomalies were associated with the features contain-ing the greatest volume of thermally-altered rock andsoil (B8-F2 and B6-F1). Although all of the detectedfeatures were excavated, the correlation between fea-ture composition and associated anomalies demon-strates that anomaly type may be of predictive value.Experience has shown, however, that geophysicalresults should be ground truthed on every site, andthat interpretation should be made cautiously. Thecriteria posited above may be valid for this site, butcannot be extrapolated to other sites where geologicconditions, feature composition and preservation,and other factors may differ.

THE HUCKINS SITEThe Huckins site (48WE917) (Figure 6) is lo-

cated on a timbered ridge on the eastern edge of thePowder River. The site is 27 km west of New Castle,Wyoming, and is on top of the first timbered ridgewest of the Black Hills, 35 km distant. The viewthat this ridge offers across thousands of hectaresof big game habitat is thought to be a major reasonfor the habitation of the site. Mush Creek bordersthe west side of the site. Here the creek has cut asteep-sided ravine into the upper Cretaceous LanceFormation’s pale brown sandstone and gray to palebrown shale. The creek channel is some 30 m lowerin elevation than the site (Figure 6).

Based on artifacts recovered from the surface,the Huckins site appears to have been repeatedlyoccupied from at least the Late Archaic to Late Pre-historic periods. At least four distinct point typesare present. The Late Plains Archaic Period projec-tile points are Powers-Yonkee, Pelican Lake-likecorner-notched and Besant side-notched, and theLate Prehistoric and/or Plains Woodland projectilepoints are small corner-notched arrow points.

The site is spatially extensive, running over akilometer along the narrow ridge. Open air camp-sites such as Huckins are often a composite of clus-ters of features and artifacts. This type of site maycover hundreds if not thousands of square meters,but in reality there are large areas within it that arevirtually devoid of cultural remains. The geophysi-cal survey was undertaken as part of phase II evalu-ation of the site in order to identify loci that mightbe associated with different occupations and activi-ties. It is unlikely that conventional methods alone

could produce a large enough sample of positivedata for meaningful description and hypothesis test-ing on a site of this size and complexity.

The magnetic survey was conducted over foursurvey areas totaling 1.9 hectares. This sampling ofthe roughly 10-hectare site covered much of the ridgetop that was not extensively eroded and not overlyrugged, and was based on the assumption that cul-tural features would more likely occur in level, eventerrain.

The distribution of suspected thermal featuresis illustrated in Figure 6. The 61 marked anomaliesrepresent those thought to have a moderate to highprobability of associated features. Of these, 10 havebeen confirmed as thermal features. Many weakeror poorly defined anomalies that may be associatedwith features are not marked, but are similarly dis-tributed. A detail from Area 2 is shown in Figure 7,illustrating a typical range of anomalies from thissite.

Preliminary ground truthing or exposure by ero-sion has confirmed that several anomalies are asso-ciated with prehistoric hearths. All six of the testedanomalies are rock-filled thermal features. Addition-ally, four anomalies are associated with hearths vis-ible on the surface. Although systematic data recov-ery has not yet been performed at the Huckins site,it is probable that the survey results will not onlyguide the excavation of the site, but will be usefulin addressing research questions regarding culturalchronology, site function and structure, subsistence,seasonality, and social organization.

Limited electrical resistance survey was per-formed on a portion of Area 2. This method recordsdifferences in the electrical resistivity of subsurfacematerials. The instrument responds to differencesin grain size, organic content, moisture content, andchemistry. Hearths were detected as resistance lows,probably because of concentrations of rocks withinthe features.

Apparent patterning of the geophysical datasuggests additional hypotheses that may be tested,all of which have implications on the types of re-search questions mentioned above.

1. The distribution of suspected hearths is dis-tinctly clustered. Clusters of hearths may represent:

a. Single componentsb. Multiple components representing re-

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Figure 7. Detail from Area 2 of the Huckins site.

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peated (seasonal or traditional) occupations by asingle group

c. Multiple components representing re-peated exploitation of favorable locations by vari-ous groups

2. There is a very wide variation in the mag-netic strength of anomalies having the appearanceof hearth features. The amplitude of suspectedhearths ranges from nearly imperceptible to over 40nT, a far greater range than was observed at 3030Winchester. Variability in anomaly strength may bedue to:

a. Feature typeb. Differences in physical properties

within feature types (e.g., mass, degree of thermalalteration)

c. State of preservationd. Geologic environmente. Depth to featuref. Age of feature

3. Anomaly strength appears to be spatially pat-terned. For example, the strongest anomalies ap-pear in Area 2, while Area 1 is characterized by gen-erally weak anomalies. If this patterning is culturalin origin, anomaly type might be used as an indica-tor of age, cultural affiliation, or site use. Of course,this kind of reasoning must be applied very cau-tiously (if at all), and only with a preponderance ofcorroborating evidence. The small sample of diag-nostic artifacts and dates available at this time isinsufficient to generate specific hypotheses.

THE MALODOROUS SITEThe sites under consideration have generally

had little magnetic “clutter” from geologic or his-toric cultural sources. Relatively subtle anomaliesdue to prehistoric features are often readily detect-able against fairly uniform geologic backgrounds.The Malodorous site (24RB2062) (Figure 8) is anexception to this generalization, and it was chosenas a case study illustrating the use of data process-ing to overcome the technical challenge of a strongmagnetic field at a site. The survey also located bur-ied stone rings (Figure 9). No stone rings were sus-pected at the site previous to the survey.

The Malodorous site is 16 km west of Colstrip,Montana. The western edge of the site borders anorth- to south-trending ponderosa pine-coveredcanyon that is drained by the West Fork of Armells

Creek. The site lies within the Tertiary Fort UnionFormation. This formation contains thick seams ofcoal. Through erosion, many of the coal seams wereexposed and some were subsequently ignited bylightning, grass fires or, perhaps, spontaneous com-bustion. The intense heat generated by the burningcoal metamorphosed the interbedded sandstonesand shales into various grades of clinker.

Sedimentary rocks typically lack appreciableremanence and are often low in susceptibility, butmay become highly magnetic when thermally al-tered. This is, of course, the principle that makesmany features detectable, but it becomes problem-atic where thermal alteration has occurred naturally.The burning of the coal seam beneath the Malodor-ous site has resulted in very strong magnetic fieldswhose gradients are too steep to be suppressed bythe configuration of the instrument. Figure 10 showshigh amplitude variance throughout this data set(note that range of the scale is 250 nT). Althoughsome anomalies that were thought to be caused byfeatures of interest do appear, they are difficult todistinguish.

A statistical filter was designed to suppress thegeologic background and enhance small, weakanomalies. This technique, called highpass filter-ing, subtracts the local mean from each data point.The dimensions and weighting of the window usedto calculate the local mean of each point must beadapted to site-specific conditions. Processed dataplotted in Figure 11 shows small local anomaliesin greater contrast against a “flattened” geologicbackground. Unfortunately, operator/instrument in-duced defects are enhanced as well. While thesecan generally be distinguished by their rectilinearpatterning, they may obscure more subtle culturalpatterning.

When excavation results are compared to themagnetic data plot, the relationship between manyof the features and associated anomalies can be seen.This data set has a standard deviation of 3.8 nT,roughly four times that of the other sites under con-sideration. Although anomalies of interest are lessapparent in this magnetically cluttered data set thanin the other case studies presented, many of the fea-tures were accurately identified prior to excavation.While hearth features proved difficult to distinguish,all of the stone rings recorded at the site (with oneexception) were identified based on the magnetic

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Figure 8. Site plan of the Malodorous site (24RB2062).

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survey results. Five stone rings were identified bycultural patterning of naturally occurring thermally-altered rock. A sixth ring was discovered during ex-cavation that was not apparent in the geophysicalsurvey data, suggesting that it was composed mainlyof unaltered local rock.

CONCLUSIONSGeophysical methods have been most typically

employed on large, complex sites. However, theycan be an extremely effective approach to studyingmore ephemeral sites as well. The relative simplic-ity of the sites under consideration has made geo-physical interpretation unusually straightforwardwhen compared to sedentary sites where a high den-sity of features and complex stratigraphy may bepresent.

In spite of its success in these cases and manyothers like them, successful employment of any geo-physical method requires careful consideration ofmany factors in order to be successful. Soils, geol-ogy, surface conditions, vegetation and terrain, fea-ture type, size, composition, and depth, modern im-pacts, and many other factors must be consideredto determine feasibility, appropriate instrumenta-tion, and survey design. Although mathematicalmodels may be applied to survey design problems,field conditions are difficult to quantify. In spite ofongoing progress in this field, assessment is largelyqualitative and empirical. Issues related to interpre-tation are similar, and experience is critical in un-derstanding how archaeological features are ex-pressed geophysically.

On a fundamental level, archaeological featuresmust contrast sufficiently with the surroundingmatrix to be detected and recognized when appro-priate methodologies are applied. The physical com-

position, depth, and geometry of the feature mustbe considered in the context of its surrounding ma-trix. More accurate characterizations of subsurfaceconditions will lead to better feasibility assessmentand survey design. When physical samples can beobtained, laboratory testing can be invaluable. Forexample, a feature might be easily detected in a mag-netically quiet setting, but completely undetectablein the presence of metal debris or igneous cobbles.Many sedimentary rocks are essentially undetect-able, and different soils vary widely in their responseto heat. On the other hand, conditions that precludemagnetic survey may be very favorable to other geo-physical methods that measure unrelated physicalproperties.

While the specific combination of features andenvironment occurring on the sites under consider-ation has resulted single-method investigations thathave been highly successful, this should not be con-sidered typical of archaeological sites generally. Theuse of multiple methods is generally recommended,especially on more complex sites than those con-sidered here. Not only does it increase the likeli-hood of success with at least one method, but it cangreatly enhance interpretability. Because each geo-physical method responds to different properties,multiple data sets are generally complementaryrather than redundant.

INTEGRATING GEOPHYSICALMETHODS

Geophysical methods are most successful aspart of an integrated and flexible research design.Planning for geophysical survey should be consid-ered from the inception of a project, and the poten-tial information that geophysical data may offershould be anticipated. Flexibility must be designedinto every stage of the research program, as surveyresults cannot be reliably predicted, and becauseeach stage will inform subsequent stages.

Planning of a hypothetical project might an-ticipate the following stages:

• Define research goals• Site reconnaissance, sample collection• Assess feasibility• Develop appropriate survey design• Conduct survey• Develop preliminary interpretations

Figure 9. Feature B5-F5, an example of stone ring featuresfrom the Malodorous site.

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Figure 10. Malodorous site magnetic survey results.

Figure 11. Malodorous site magnetic survey data after statistical filtering.

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• Ground truthing (on-the-ground testing)• Refine interpretations• Excavation• Model site context integrating excavation, geophysical, environmental and other available data

As geophysical methods become increasinglycommon, their future use should be anticipated evenwhen they are not part of current research plans.Noting conditions that might affect geophysicalmethods and collecting small samples of soils, rock,and cultural materials may be invaluable for futureresearch. More critical, and often overlooked, is theeffect of metal artifacts left on sites by archaeolo-gists themselves. Steel pinflags, nails, datums, andother items that are deliberately or accidentally lefton sites can have a very detrimental effect on mag-netic data. Whenever possible, plastic, wood, or alu-minum substitutes should be used for these items.Steel pinflags are particularly problematic. Ubiq-uitously used, often lost, and difficult to find afterthe plastic flag has degraded or fallen off, the steelwire creates a surprisingly large magnetic anomaly.The inconvenience and expense of plastic pinflagswill be found to be well worth the benefits. It ishoped that these considerations will be reflected instandard archaeological practices in the near future.

REFERENCES CITEDClark, Anthony J.

1996 Seeing Beneath the Soil: Prospecting Methods in Ar-chaeology. B.T. Batsford Ltd., London, United Kingdom.

Gaffney, Chris, John Gater2003 Revealing the Buried Past: Geophysics for Archae-

ologists. Tempus: Stroud, United Kingdom.Jones, Geoffrey

2001a A Geophysical Investigation at 48WE917 A Late Ar-chaic Archaeological Site in Weston County, Wyoming.Archaeo-Physics Report of Investigation # 33. Archaeo-Physics LLC, Minneapolis, Minnesota. Submitted to GCMServices, Inc., Butte, Montana.

2001b A Geophysical Investigation at 48CA3030 A Prehis-toric Archaeological Site in Campbell County, Wyoming.Archaeo-Physics Report of Investigation # 34. Archaeo-Physics LLC, Minneapolis, Minnesota. Submitted to GCMServices, Inc., Butte, Montana.

2003 Geophysical Survey Of Five Archaeological Sites OnThe Western Energy Company Rosebud Mine Area C.Archaeo-Physics Report of Investigation # 64. Archaeo-Physics LLC, Minneapolis, Minnesota. Submitted to GCMServices, Inc., Butte, Montana.

Jones, Geoffrey, David L. Maki2005 Lightning Induced Anomalies on Archaeological Sites.

Archaeological Prospection, in press.Munson, Gene

1997 Class III Cultural Resource Inventory for AntelopeCoal Company’s Tract Revision, Campbell and ConverseCounties, Wyoming. GCM Services, Inc., Butte, Montana.Submitted to Antelope Coal Company, Gillette, Wyoming

2002a Excavation of Standing Water 48CA959/2914/2915Site Complex. With contributions by Dave McKee, Rich-ard Holloway, Margaret Newman, Linda Scott Cummings,Richard Hughes, Thomas Origer, Edwin Burke, David Makiand John Albanese. GCM Services, Inc., Butte, Montana.Submitted to Powder River Coal Company, Gillette, Wyo-ming.

2002b Excavation of 3030 Winchester 48CA3030. With con-tributions by Dave McKee, Richard Holloway, MargaretNewman, Linda Scott Cummings, Edwin Burke, GeofferyJones, John Albanese. GCM Services, Inc., Butte, Mon-tana. Submitted to Antelope Coal Company, Gillette, Wyo-ming.

2003a Phase II Geophysical Investigations and Data Recov-ery Plan for Huckins Site 48WE917. GCM Services, Inc.,Butte, Montana. Submitted to Powder River Coal Com-pany, Gillette, Wyoming and Thunder Basin Coal Com-pany, Wright, Wyoming.

2003b Excavation of Terrace Rings 48CA3759. With contri-butions by John Albanese, Linda Scott Cummings, Rich-ard Hughes, Richard Holloway, Ann Johnson, GeoffreyJones, William Lucius, David Maki, Dave McKee, andThomas Origer. GCM Services, Inc., Butte, Montana. Sub-mitted to Powder River Coal Company, Gillette, Wyoming.

Munson, Gene, David Ferguson, Garren Meyer2004 Excavation of Malodorous 24RB2062. With contribu-

tions by Geoffrey Jones, Richard Hughes, RichardHolloway, Dave McKee and Thomas Origer. GCM Ser-vices, Inc., Butte, Montana. Submitted to Western EnergyCompany, Colstrip, Montana.

Sharma, Prem V.1997 Environmental and Engineering Geophysics. Cam-

bridge University Press, Cambridge, United Kingdom.Verrier V., P.E. Mathe, P. Rochette, G. Jones

2002 Magnetic Anomaly Caused by Lightning on Archaeo-logical Sites. Paper prepared for the European Geophysi-cal Society XXVII General Assembly, Nice, France, April2002.

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