PLEISTOCENE GEOLOGY OF THE SOUTHWESTERN WIND RIVER MOUNTAINS, WYOMING

Abstract

Patches of Buffalo till record the earliest glaciation in the southwestern Wind River Mountains. In places, these rest in youthful valleys cut in high gravel terrace. Two other younger and lower terraces are both topographically and stratigraphically associated with Buffalo till, which may indicate that the Buffalo advance was compound. The pattern of well-preserved moraines shows that during both Bull Lake and Pine-dale time the west-central portion of the range was covered by a mountain icecap from which piedmont glaciers flowed to the floor of the Bridger Basin. In the southern part of the range the glaciers were confined to valleys. Bull Lake stage is clearly double; two large, weathered, and modified moraines are present in several valleys. Each is associated with an extensive outwash plain and valley train. The Pinedale stage is recorded by massive, fresh, slightly modified moraines behind which are many recessional moraines. Extensive outwash aprons lead outward from the massive Pinedale moraines, and a small lower terrace can be traced through the main Pinedale moraine to the recessional loops. In several upper valleys well-formed slightly weathered small moraines of the Temple Lake stage occur within 2 miles of cirque head-walls. A terrace below the younger Pinedale outwash is correlated with the Temple Lake stage. In sheltered cirques, small very fresh moraines, probably from the Little Ice Age, occur upstream from the Temple Lake moraines and a few yards from existing small glaciers. The sequence of glacial deposits in this region is typical of many ranges in the Rocky Mountain region. Outwash terraces of the Bull Lake, Pinedale, and Temple stages have been traced down the Big Sandy valley nearly to the Green River and down the Sweetwater valley to the North Platte. Thus the Green-Colorado and Platte-Missouri drainages are linked across the Continental Divide by means of traceable outwash deposits. Eolian action was pronounced in the Eden valley during Bull Lake, Pinedale, and post-Pinedale time, and in the East Fork valley during Pinedale time. Frost action features record two phases of intensity in areas formerly covered by Pinedale glaciers: an earlier phase synchronous with the Temple Lake advance, a later during the Little Ice Age. Pollen profiles in the Eden valley show a climatic change during post-Pinedale time, notably a grass maximum which was probably contemporaneous with the Temple Lake advance and the occupation of the Finley site by Early Man.