SOILS AND GLACIAL STRATIGRAPHY OF THE POPO AGIE RIVER BASIN, SOUTHERN WIND RIVER RANGE, WYOMING

Geomorphic relations and soil characteristics of diamictons, moraines, and outwash terraces of the Popo Agie River basin support the interpretation that additional glacial advances occurred here prior to the present configuration of the canyons on the eastern slope of the Wind River Range. High elevation diamicts and moraines indicate that glacial advances were not constrained to the canyons here during the early Pleistocene, while deposits corresponding to the mid-late Pleistocene glaciations identified in the WRR (Sacagawea Ridge, Bull Lake, Pinedale) are constrained within the present canyons. Soils developed on the moraines and diamicts suggest that the pedogenic characteristics of profile depth, clay translocation, and pedogenic carbonate accumulation continue to develop on Bull Lake-age deposits, but that erosion begins to overcome pedogenic development on Sacagawea Ridge and older units.

Outwash terraces along each of the Popo Agie drainages (North Fork, Middle, and Little) are correlated to the diamicts and moraines and mimic the stratigraphic sequence suggested by these deposits. While only 4 outwash terraces are well-preserved along these streams (which appear to correlate with the Sacagawea Ridge – Bull Lake – Pinedale glacial sequence), isolated high elevation gravel-topped surfaces are present outside the canyons and suggest a connection to older pre- or early-canyon glacial activity. Where preserved, soils developed on the terrace remnants exhibit characteristics similar to those of the moraine/diamict soils.

Although deposits corresponding to only three periods of within-canyon glacial activity (Sacagawea Ridge – Bull Lake – Pinedale) presently are recognized for the Wind River Range (Hall and Jaworowski, 1999), the presence of the outside-canyon diamicts and isolated high elevation outwash remnants is evidence of pre-Sacagawea Ridge glacial advances here and that this activity occurred prior to the development of the present canyon morphology. The Popo Agie Basin glaciofluvial sequence corresponds to that reported by Hancock et al. (1999) and Sharp et al. (2003) along the Wind River and suggests that activity in the smaller drainages of southern part of the range was synchronous to that described for the range’s more heavily glaciated northern region.