Cesium magnetometer surveys at a Pithouse Site near Silver City, New Mexico q Michael B. Rogers a, * , Kevin Faehndrich a , Barbara Roth b , Greg Shear a a Department of Physics, Ithaca College, 953 Danby Road, Ithaca, NY 14850, USA b Department of Anthropology & Ethnic Studies, University of Nevada-Las Vegas, USA article info Article history: Received 15 September 2009 Received in revised form 1 December 2009 Accepted 4 December 2009 Keywords: Cesium Hearth Magnetometer Pithouse American Southwest New Mexico abstract The La Gila Encantada Site is located on an isolated ridge top north of Silver City, New Mexico in an area defined culturally as the Mimbres Mogollon region. The 180 m  80 m (14400 m 2 ) sized site was origi- nally recorded as a dense scatter of ceramics, lithics, and ground stone along with a number of surface depressions that appear to represent pithouses. Cesium magnetometer surveys were conducted to identify hearths, pithouse boundaries, and activity areas outside of pithouses in support of archaeological investigations, and to test this instrument’s ability to image these features. This paper presents a char- acterization of the magnetic signature of a pithouse as a magnetic high in the center caused by the central hearth, low magnetic variability along the floor of the house, and then increased magnetic variability at the pithouse boundary. This characterization was successfully confirmed for three pithouses using cesium magnetometery and archaeological excavation. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The American Southwest provides an opportunity to study mobility, sedentism, and how people transitioned to an agricultural lifestyle. This transition caused changes in how people interacted with their environment that shows up in the archaeological record as changes in architecture, material culture, and the level of agri- cultural dependence. Several archaeological geophysical surveys in the American Southwest (Abbott et al., 1997; Bevan, 1983; Conyers and Cameron, 1998; Kvamme, 1998; Weymouth, 1986) have demonstrated the ability of these instruments to image subsurface prehistoric houses, storage pits, and a variety of activity areas, which can aid in investigating research questions concerning sed- entism, mobility, and household organization. The North American Database of Archaeological Geophysics (http://www.cast.uark.edu/ nadag/) contains overviews of additional investigations. Fig. 1 shows the location of several archaeological geophysical investi- gations in the American Southwest with most of the projects concentrated around the Four Corners region and the Rio Grande River. Our work is focused on the La Gila Encantada Site, which is located on an isolated ridge top north of Silver City, New Mexico in an area defined culturally as the Mimbres Mogollon region (Fig. 2). The 180 m  80 m sized site was originally recorded as a dense scatter of ceramics, lithics, and ground stone along with a number of surface depressions that appear to represent pithouses. Ceramics from systematic surface collections and excavations place the site occupation confidently within the Late Pithouse period (A.D. 550– 1000). Archaeological research at the site is focused on questions concerning the Late Pithouse period occupation of sites away from the Mimbres River Valley, where most Pithouse period sites have been excavated. Archaeological research at La Gila Encantada is expanding on work conducted by Roth at the Lake Roberts Vista Site in the Sapillo Valley, an upland valley northwest of the Mimbres Valley (Roth, 2007; Stokes and Roth, 1999). Work at Lake Roberts showed that groups initially moved seasonally into the Sapillo Valley during the Georgetown phase (A.D. 550–650) to hunt large game, gather pin ˜ on nuts, and farming maize, beans, and squash. This seasonal use apparently continued until the Three Circle phase (A.D. 750–1000), when groups became more sedentary and perhaps more dependent on agriculture (Stokes and Roth, 1999). However, because the pithouse component at Lake Roberts was beneath a pueblo, it was not possible to fully evaluate the degree of sedentism, nor was it possible to examine site organization and household activities, as no activity areas outside of the pithouses could be clearly assigned to the pithouse component (Roth, 2007). Unlike many other Late Pithouse period sites in this portion of New Mexico, La Gila Encantada does not have a large pueblo built over it, so it was possible to address questions raised by previous work at the Lake Roberts Vista Site concerning q Funded in part by: Ithaca College Faculty Summer Grant, Ithaca College Provost Research Grant, Ithaca College Physics Department Ford Research Fund, Ithaca College Dana Internship fund, the University of Nevada, Las Vegas Department of Anthropology & Ethnic Studies, and a UNLV Planning Initiative Award. * Corresponding author. Tel.: þ1 607 274 3963; fax: þ1 607 274 1773. E-mail address: mrogers@ithaca.edu (M.B. Rogers). Contents lists available at ScienceDirect Journal of Archaeological Science journal homepage: http://www.elsevier.com/locate/jas 0305-4403/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2009.12.010 Journal of Archaeological Science 37 (2010) 1102–1109