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Munroe, Jeffrey S

Cosmogenic surface-exposure 10Be dating of Last Glacial Maximum (LGM) moraines indicates that glaciers in the southwestern Uinta Mountains remained at their maximum positions until ca. 16.8 � 0.7 ka, ?2 k.y. after glaciers in the neighboring Wind River Range and Colorado Rockies began to retreat. The timing of the local LGM in the southwestern Uintas overlaps with both the hydrologic maximum of Lake Bonneville and preliminary estimates of the local LGM in the western Wasatch Mountains. This broad synchroneity indicates that Lake Bonneville and glaciers in northern Utah were responding to similar climate forcing. Furthermore, equilibrium line altitudes (ELAs) for reconstructed LGM alpine glaciers increase with distance...
Recent estimates of the timing of the last glaciation in the southern and western Uinta Mountains of northeastern Utah suggest that the start of ice retreat and the climate-driven regression of pluvial Lake Bonneville both occurred at approximately 16 cal. ka. To further explore the possible climatic relationship of Uinta Mountain glaciers and the lake, and to add to the glacial chronology of the Rocky Mountains, we assembled a range-wide chronology of latest Pleistocene terminal moraines based on seventy-four cosmogenic 10Be surface-exposure ages from seven glacial valleys. New cosmogenic-exposure ages from moraines in three northern and eastern valleys of the Uinta Mountains indicate that glaciers in these parts...
Clastic and organic sediments exposed in two stream cutbanks above modern timberline in the headwaters of the Henrys Fork drainage record multiple episodes of fluvial, lacustrine and wetland deposition. The location of the upper Henrys Fork at the boundary between modern summer-wet/winter-dry and summer dry/winter-wet precipitation regimes suggests that changes in vegetation during the Holocene were due primarily to variations in growing-season temperature. A radiocarbon date of 9310 6 70 BP on a Salix fragment from the base of one exposure indicates that the upper reaches of the Henrys Fork were vegetated by riparian willows by the early Holocene. Four other dates on wood and bulk organics ranging up to 4070 6...
I replicated and analyzed six photographs taken in A.D. 1870 near the subalpine forest-alpine tundra ecotone in the northern Uinta Mountains to quantify changes in the distribution of vegetation. Three dramatic differences were noted. First, the historical photographs document a treeline 60 to 180 m (mean of 100 m) lower than at present, with greater depression on west-facing slopes. Given the modern lapse rate for mean July temperature (6.9�C km?1), this difference corresponds to a temperature depression in A.D. 1870 of 0.4 to 1.2�C (mean of 0.7�C). Second, timberline forests in A.D. 1870 were significantly (P < 0.01) less dense, with tree densities approximately half those measured in the modern photographs. Third,...
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