The late Pleistocene upland history of the Salamanca Re-entrant is characterized by repeated colluvial-erosional episodes. Thermo-luminescence age estimates and stratigraphic relations indicate that the last widespread colluviation was of late Wisconsin age and correlated with the Nissouri Stade (ca. 20,500-16,500 14C yr B.P.). This brown (10-7.5YR) medium-textured colluvium covers hillslopes and onlaps some Illinoian terrace remnants to a depth of 1 to 3 m. A thick paleosol developed in the high-terrace gravel has been truncated and is overlain by late Wisconsin brown colluvium or loess. Associated with the brown colluvium in the uplands are large debris flows. The colluvium and flow debris are considered periglacial in origin. In the Bay State Brook transect, two older colluvial units were found: (a) the red stringer colluvium (early Wisconsin?) and (b) the paleosol colluvium, which marks the removal of a Sangamon(?) paleosol from the upland. A 30- to 100-cm thickness of loess blankets the unglaciated landscape. This late Wisconsin to early Holocene loess (ca. 18.6 to 8.8 ka) is presumably derived from glaciofluvial sediment of the Allegheny River and other local trunk streams. The loess is given the informal name "Salamanca Loess."

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