Background to the NHPA

In the United States, archaeological sites and other cultural resources are primarily managed under the provisions of the NHPA (for more thorough reviews, see King Reference King2016, Reference King2020). The NHPA was passed in 1966 with the goal of establishing a national preservation policy to protect historical and cultural heritage, in turn creating the NRHP and requiring federal agencies to evaluate how their projects impact archaeological and historical sites. The NHPA requires federal agencies to consult with appropriate stakeholders who have vested interests in federal undertakings, which can involve SHPOs, Tribal partners, local governments, and/or the public.

Section 106 is a core component of the NHPA that requires federal agencies to consider the effects of their undertakings on historic properties, and if a project has the potential to affect buildings, structures, objects, districts, or archaeological sites that are listed or eligible for listing in the NRHP, then a thorough review will take place. Identifying archaeological properties and assessing their eligibility for listing in the NRHP thus becomes a key component of compliance archaeology in the United States. Section 110 of the NHPA works in concert with Section 106, setting out the broad historic preservation responsibilities of federal agencies and calling on these agencies to establish their own preservation programs for the identification, evaluation, and protection of historic properties.

XRF analyses of archaeological materials are often seen by CRM archaeologists as falling under the purview of Section 110; that is, research that contributes to a broader preservation program but is not directly integrated into Section 106 workflows. However, we hope that the following examples demonstrate how XRF can be effectively integrated into Section 106 decision-making processes that greatly expand the relevance of the technology in CRM archaeology and highlight how Sections 106 and 110 can work together to ensure the highest standards of quality and efficiency.

When and How Should It Be Used

This section details the ways in which XRF analysis can be practically applied to common Section 106 processes, including archaeological site characterization, NRHP evaluations, and preservation efforts.

Case Study 1: INL, Idaho

The INL Site is a complex of federal nuclear research facilities that occupies 2,305 km² of land on the Eastern Snake River Plain of eastern Idaho, within the traditional territory of the Northern Shoshone and Bannock peoples. The INL Cultural Resource Management Office (CRMO) XRF Laboratory specializes in analyzing archaeological and geological materials using XRF. Materials analyzed at the lab include obsidian and other fine-grained volcanics (FGV), ceramics, and brick. XRF equipment includes two Olympus Vanta M Series portable XRF spectrometers equipped with 4-watt X-ray tubes, rhodium anodes, and 40 mm² silicon drift detectors.

For the INL CRMO, the eastern Idaho Precontact Context (PCC) is a formal historic context document that represents an organizational framework for the identification and evaluation of precontact archaeological resources in eastern Idaho (Idaho National Laboratory Cultural Resource Management Office [INL CRMO] 2026). The PCC encompasses a study area of approximately 6 million ha, with an understanding that the significance of archaeological resources on the INL can only be understood within a broader geographic and regional context. Consultation with the Shoshone-Bannock Tribes is central to CRM at INL, and Tribal partners are regularly and actively involved in survey, site recordation, artifact analysis, and evaluation. The Tribes have been particularly receptive to XRF analyses because they are nondestructive and can be undertaken in the field without the need for artifact collection (Figure 2). The resulting data have fostered communication and become a shared touchpoint for interpretation.

Figure 2.

In-field XRF analysis at the Idaho National Laboratory (photo by Jeremias M. Pink).

Case Study 2: NAFB, Nevada

NAFB cultural resources managers are responsible for the management of lands and associated archaeological sites on the Nevada Test and Training Range (NTTR), which covers upwards of 13,000 km² of basin and range topography that includes portions of the Mojave and Great Basin Deserts, as well as the Southwestern Nevada Volcanic Field, the geologic source of many of the lithic artifacts found across the region. These sites and resources are significant to Native peoples today, testifying to their existence on these lands since time immemorial (see Stoffle et al. Reference Stoffle, Zedeño and Halmo2001).

In 2005, archaeological research sponsored by NAFB examined what was, at the time, the largest collection of obsidian artifacts (n = 2,015) across southern Nevada and adjacent areas in California and southwestern Utah (Haarklau et al. Reference Haarklau, Johnson and Wagner2005). The primary goal of this study was to understand the distribution of materials from the Obsidian Butte Volcanic Center located on the NTTR (and unrelated to the Obsidian Butte in California) with the explicit aim of developing and operationalizing research questions to study and evaluate cultural sites. The research questions driving the study included the following:

• • What obsidian sources are present on government-managed lands, and how are those sources defined geologically, spatially, and geochemically?

• • How does the distribution of obsidian, both geologically and archaeologically, align with Indigenous food procurement strategies?

• • How does obsidian exploitation change through time?

• • How does obsidian-sourcing reinforce the cultural value of prominent landscape areas, specifically those comprising the Obsidian Butte Volcanic Center?

Unfortunately, Haarklau and colleagues’ (Reference Haarklau, Johnson and Wagner2005) research, while influential, has only partially contributed to follow-up work managing cultural sites overseen by the US Air Force. This is largely because no major research or undertakings requiring data recovery have occurred since the 2005 study and because NAFB has a no-collection policy, except under special conditions. This has effectively meant that no new geochemical studies could be done unless artifact collection was warranted as part of a Historic Properties Treatment Plan (HPTP) for mitigation or some other extenuating circumstances, under the assumption that geochemical work could only be done through collection and curation (this was certainly the case in 2005). Moreover, the current ICRMP for NAFB does not have obsidian-sourcing as a research constituent. Today, portable XRF enables in-field geochemical analysis, which has the capacity to test hypotheses developed by Haarklau and colleagues (Reference Haarklau, Johnson and Wagner2005) and in turn be integrated into Section 106 site characterization efforts and NRHP eligibility recommendations.

Most precontact archaeological sites on the NTTR are surficial lithic scatters, similar to much of southern Idaho and the Great Basin, but to date, patterns of obsidian distribution and use have been based on projectile point analysis without a consideration of debitage or other tools. Thus, source exploitation is only seen through a narrow lens that overlooks the entire chaîne opératoire of regional lithic economies (Freund et al. Reference Freund, Johnson, Duke and Young2022). Sourcing analysis of all classes of lithic artifact are warranted, which can be facilitated by in-field analysis with portable XRF. For example, some ecozones in the NTTR are high-elevation pinyon-juniper forests with no local toolstone resources, and such areas represent gathering places where populations met and interacted for extended periods. In-field XRF analysis of a representative sample of artifacts—situated in social gathering places in particular—can address questions pertaining to site function, population interactions, and material exchange at a level of detail beyond what is possible from analyses of discarded tools alone. If, for example, pinyon-juniper groves are social spaces and centers of gravity, we would expect the presence of a wider diversity of obsidian sources compared with other temporary camps.

Additional metrics can also be used to assess the relative occupation span of a site, including the quantity or density of artifacts, ratios of tools to debitage, reduction intensity, and ratios of local to nonlocal materials (Barton and Riel-Salvatore Reference Barton and Riel-Salvatore2014; Grove et al. Reference Grove, Hall, Timbrell, Benton and French2023; Pink Reference Pink2025b; Surovell Reference Surovell2009). Here, provenance data become especially useful for helping determine ratios of local to nonlocal tools and materials. Since occupation span is inversely related to the frequency of residential moves (Grove Reference Grove2018; Surovell Reference Surovell2009), information on site-level source use may provide insight into the rate of residential mobility at discrete points on the landscape, contributing to an understanding of how use of those locales fits into broader patterns of seasonal mobility (Pink Reference Pink2025b).

As with the Idaho examples, XRF analysis aligns well with existing research themes outlined in the NAFB ICRMP (Nellis Air Force Base [Nellis AFB] 2025), such as “Chronology,” “Settlement/Subsistence,” and “Tool Stone Procurement, Use, Trade, and Transport.” Data requirements for addressing research questions from such themes include temporally diagnostic artifacts or materials (e.g., known projectile point types), assemblages able to be classified as one of several site types (lithic scatters, habitation, temporary camps, etc.), cultural features that may demonstrate short- to long-term (ceremonial) habitation or site use (e.g., rock circles, petroglyphs, pinyon groves), and artifacts that may inform mobility or exchange (e.g., obsidian that can be sourced). Currently, the NAFB ICRMP (Nellis AFB 2025) considers sites with more than 100 pieces of obsidian as eligible for listing in the NRHP. Recurrent and consistent in-field XRF analysis can add nuance to such arbitrary considerations and expand the range of relevant research questions that can be addressed and integrated into NRHP eligibility recommendations.

Operationalizing in-field XRF in the manner suggested above can improve managerial efficiencies for federal cultural resources programs. In the case of NAFB, previous cultural resources program managers have classified large numbers of sites as “unevaluated” for NRHP eligibility, presumably because they felt additional studies or more data were necessary to appropriately characterize or evaluate the sites. Leaving sites unevaluated creates additional work for future program managers, particularly when turnover or gaps in the administrative record lead to unfinished business falling through the cracks. Unevaluated sites must be treated as NRHP eligible for the purposes of the Section 106 process, so it behooves program managers to make a determination whenever feasible.

Discussion and Conclusions

Through two case studies, this study demonstrates how XRF can be effectively integrated into Section 106 processes through the analysis of commonly encountered archaeological materials such as lithics, ceramics, and brick. It is further shown how such analyses can make meaningful contributions to site characterization efforts, NRHP eligibility recommendations, and preservation. Two federal programs are discussed, and while they are similar, in that surface manifestations of lithic debris are the most commonly encountered precontact resources, they nonetheless highlight how the integration of XRF technology can occur within programs with different funding capacity to justify the purchase of instrumentation, personnel, and organizational goals. Moreover, these case studies occur within archaeological contexts with different histories of academic study and foundational documentation within which to situate XRF results.

The need for context documents in justifying XRF analyses is stressed because XRF results are only as powerful as the interpretive framework within which they are anchored. For compliance archaeology, context documents provide the foundation for agency decisions in the identification, evaluation, and treatment of historic properties and should be created or revised with XRF integration in mind. For CRM professionals, beyond the inherent availability of funds, the purchase of instrumentation also requires support from management, which can be demonstrated through the creation of such documents. At its core, the integration of XRF analysis with robust contextualization leads to reduced time and costs for consultation and shared understandings between an agency, SHPO, Tribes, and stakeholders.

XRF analysis can also help to minimize the ambiguity that may lead to sites with an “unevaluated” NRHP status. Furthermore, consistent implementation of XRF analysis can reveal patterns or relationships between chronology, site type, and source diversity that can feed back into the research themes and data requirements used to evaluate sites that are codified in a historic context, CRMP, or ICRMP. In this way, arbitrary thresholds—such as considering sites with 100 or more obsidian artifacts to be eligible—can be replaced with well-contextualized research questions and evaluation criteria.

Many federal agencies, including NAFB, do not own an XRF instrument or possess a database of geological obsidian. This issue can be overcome by renting an instrument as needed, or by requiring contractors to employ XRF for site characterization or data recovery. This raises important methodological questions about the prospect of sourcing obsidian in the absence of a physical database of source material or when multiple instruments and associated analytical protocols are being used. Indeed, it is accepted practice and generally best to compare artifact data directly with source materials analyzed by the same instrumentation due to inherent inconsistencies between individual XRF instruments (Glascock et al. Reference Glascock and Shackley1998). However, in certain contexts it may be possible, depending on the similarities in elemental composition of the various obsidian sources of a region. If differences in elemental readings across instruments are systematic, they can be corrected for by using regression models, machine-learning workflows, or similar statistical techniques (Drake et al. Reference Drake, Shugar, Kipnis, Drake and MacDonald2022; Hnila et al. Reference Hnila, Frahm, Gilibert and Bobokhyan2025). Further study is warranted to more clearly define the contexts where this may be possible.