Holocene eolian activation as a proxy for broad-scale landscape change on the Gila River Indian Community, Arizona David K. Wright a, b, ⁎, Steven L. Forman c , Michael R. Waters d, e , John C. Ravesloot f a Department of Archaeology and Art History, College of Humanities 14-201, Seoul National University, San 56-1, Sillim-9dong, Gwanak-gu, Seoul 151-745, Republic of Korea b Cultural Resource Management Program, Gila River Indian Community, P.O. Box 2140, Sacaton, AZ 85247, USA c Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA d Center for the Study of the First Americans, Department of Anthropology,Texas A&M University, College Station, TX 77843, USA e Department of Geography, Texas A&M University, College Station, TX 77843, USA f William Self Associates, Inc., Tucson, AZ 85719, USA abstract article info Article history: Received 14 July 2010 Available online 26 May 2011 Keywords: Arizona Gila River Holocene eolian activation paleoclimates Eolian sediments are common within the middle Gila River Valley, southern Arizona, and reflect variability in eolian and fluvial processes during the late Holocene. This study focuses on deciphering the stratigraphic record of eolian deposition and associated luminescence dating of quartz extracts by single aliquot regeneration (SAR) protocols. Stratigraphic assessment coupled with luminescence ages indicates that there are four broad eolian depositional events at ca. 3145 ± 220 yr, 1950–1360 yr, 800 ± 100 yr, and 690–315 yr. This nascent chronology, correlated with regional archeological evidence and paleoclimate proxy datasets, leads to two general conclusions: (1) loess deposits, transverse-dune formation and sand-sheet deposition in the late Holocene are probably linked to flow variability of the Gila River, though the last two events are concordant with regional megadroughts; and (2) the stability of eolian landforms since the 19th century reflects the lack of eolian sediment supply during a period of fluvial incision, resulting in Entisol formation on dunes. The prime catalyst of eolian activity during the late Holocene is inferred to be sediment supply, driven by climate periodicity and variable flow within the Gila River catchment. © 2011 University of Washington. Published by Elsevier Inc. All rights reserved. Introduction Southern Arizona currently has one of the largest population centers in the United States and includes large swaths of agricultural land irrigated with diverted water from the Colorado River. The region also hosted Pre-Columbian communities who made use of perennially flowing streams and rivers draining the surrounding uplands to maintain large tracts of cultivated plots (Haury, 1976; Bayman, 2001; Fish and Fish, 2008; Ravesloot et al., 2009). The present study area is situated within the Sonoran Desert, which is characterized by low rainfall (b 25 cm/yr) and July temperatures that average 41°C. These circumstances make the study area particularly vulnerable to catastrophic droughts, which can devastate local economies and threaten livelihoods of the region's inhabitants. Understanding the geomorphic and climatic controls on broad-scale landscape change is important for potentially mitigating the effects of extreme oscillations in precarious environments such as southern Arizona. Backhoe trenches excavated in 2005 and 2006 on landforms adjacent to the middle Gila River were analyzed for evidence of late Holocene eolian activity. The study area is located within the Gila River Indian Community (GRIC) and was undertaken with sponsor- ship of the Cultural Resource Management Program (CRMP) and the Pima–Maricopa Irrigation Project (P-MIP). The research objectives were designed to assess archeological site formation processes within eolian depositional areas, which are extensive across the GRIC. A series of optically stimulated luminescence (OSL) and radiocarbon ( 14 C) ages were generated to reveal local patterns of sand-sheet accretion and dune movement. The studies performed included geomorphic and stratigraphic analysis of eolian and alluvial landforms. Specifically, we studied four trench exposures of eolian deposits, determined Optically Stimulated Luminescence (OSL) ages on quartz extracts from eolian sediments, and radiocarbon assays of cultural features at archeological site GR-893 that underlie the eolian deposits. The time series of eolian activity is compared to drought (http://www.ncdc.noaa.gov/paleo/paleo.html), river flow (Graybill et al., 2006) and fluvial geomorphic events (Waters and Ravesloot, 2001) to infer the most likely drivers of eolian deposition in the past 2000 years. Eolian activity as a proxy for landscape change The movement of sediments by wind necessitates three primary conditions: the availability of sediment suitably sized for entrainment Quaternary Research 76 (2011) 10–21 ⁎ Corresponding author at: Department of Archaeology and Art History, College of Humanities 14-201, Seoul National University, San 56-1, Sillim-9dong, Gwanak-gu, Seoul 151-745, Republic of Korea. E-mail addresses: msafiri@snu.ac.kr (D.K. Wright), slf@uic.edu (S.L. Forman), 0033-5894/$ – see front matter © 2011 University of Washington. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.yqres.2011.04.008 Contents lists available at ScienceDirect Quaternary Research journal homepage: www.elsevier.com/locate/yqres