Deglaciation and the Archaeology of Trapper Creek, South-Central Alaska Brian T. Wygal and Ted Goebel ➤ Keywords: Deglaciation, late Pleistocene, south-central Alaska The Trapper Creek Overlook (TCO) site occupies an esker formed by ice stagnation in the middle Susitna River valley of south-central Alaska and has yielded two Holocene archaeological components, the earliest dated between 9500 and 7800 CALYBP (Wygal 2009). A significant unanswered question regarding the prehistory and paleoecology of the middle Susitna basin be- tween Cook Inlet and Broad Pass surrounds the timing of glaciation during the late Pleistocene. Refined glacial histories are essential for understanding the paleoecology of early hunter-gatherers in the region, and for reconstruct- ing the process of human colonization of deglaciated landscapes. Ice flows from high mountain valleys mantled the Trapper Creek area sometime during the late Pleistocene (Hamilton and Thorson 1983:38); how- ever, the timing of deglaciation is not well understood (Schmoll and Yehle 1986). The OSL-dated stratigraphic record from TCO may shed light on this problem. Figure 1 represents the 12 strata at TCO beginning with basal morainal gravel (Stratum 1) capped by 95 cm of sediments including four soil complexes and a series of tephras (Wygal 2009). Optically stimulated lumines- cence (OSL) dating at TCO suggests postglacial sediment deposition occurred during the last glacial maximum (LGM). Laboratory analyses included mul- tiple aliquot regenerative dosing processes (for descriptions of method, see Jain et al. 2003; Murray and Wintle 2003) and employed infrared excitation on components dominated by feldspar and blue or green excitation on quartz particles. Because multiple methods produced statistically identical ages over- lapping at 1σ, the feldspar and quartz components of these sediments appear to be consistent geochronometers (Forman 2007). In 2006, two sediment samples were dated from Stratum 3a, a 25- to 35-cm- thick loess deposit grading from greenish gray loamy sand at its base (3a) into a yellowish brown sandy loam at its top (3b). While 3a lacks artifacts, overlying Stratum 3b contains the earliest component. The lowest OSL sample (UIC1865) produced three ages (32,540 ± 2480, 27,610 ± 2125, and 24,710 ± 1510 CALYBP). The second (UIC1935) yielded two aberrant dates (42,860 ± 3260 and 47,800 ± 3650 CALYBP) from 14 cm above basal gravel; and UIC1866 from Stratum 3b produced four ages (19,530 ± 1500, 17,685 ± 1360, 17,450 ± 1050, and 15,580 ± 980 CALYBP). Several unusually old estimates did not conform to stratigraphic superposition and were dismissed (Wygal 2009). Brian T. Wygal, Adelphi University, Department of Anthropology, 102 Blodgett Hall, 1 South Ave, Garden City, NY 11530-0701; e-mail: bwygal@adelphi.edu Ted Goebel, Center for the Study of the First Americans, 4352 Texas A&M University, College Station, TX 77843-4352; e-mail: goebel@tamu.edu 136 WYGAL/GOEBEL Geosciences