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We use cosmogenic radionuclide (CRN) exposure ages from polished, striated bedrock to constrain numerical simulations of deglaciation in the Middle Boulder Creek Valley, Colorado Front Range, and the Animas River Valley, San Juan Mountains, Colorado. In both valleys, the cosmogenic ages suggest initiation of deglaciation ?20 ka and ongoing retreat until 12?13 ka. While the first-order trend in CRN concentrations in each valley suggests a monotonic glacial retreat, we evaluate other retreat scenarios with different implications for post-Last Glacial Maximum regional climate. We use a 2-D numerical glacier simulation with a CRN layer to investigate how CRN-based deglaciation records are affected by retreat histories...
A sediment core taken from Dome Creek Meadow located within the Bear River corridor provides proxy data for paleoenvironmental conditions on the White River Plateau. Changes in pollen stratigraphy, macrofossil abundance, and sediment stratigraphy document at least four major shifts in environmental conditions during the last 10,600 yr. The oldest levels of the core document cool-dry, near-glacial conditions followed by the establishment of a closed spruce-fir forest around the site. The middle Holocene witnessed a major change in the local forest community, probably as a result of increased temperature. The data also indicate middle Holocene conditions at the site were warmer and drier than any other time in the...
The vegetation and climatic history of subalpine forests on the Colorado Plateau is documented from Lowder Creek Bog and Alpine Pond on the Markagunt Plateau. Pollen and macrofossil data demonstrate substantial changes at sites above 3150 m elevation during the last ca. 13,000 yr. During and after Late Wisconsin deglaciation, subalpine tree species (Picea engelmannii and Abies lasiocarpa) were rare or absent near the Lowder Creek Bog site, but nonarboreal species predominated. P. engelmannii-A. lasiocarpa forest became well-established there between 11,000 and 9800 yr BP and subalpine trees dominated this elevation throughout the Holocene. By ca. 8500 yr BP, however, Picea declined somewhat, with minimal pollen...
Fossil remains of Euceratherium collinum (extinct shrub-ox) have been found throughout North America, including the Grand Canyon. Recent finds from the Escalante River Basin in southern Utah further extend the animal's range into the heart of the Colorado Plateau. E. collinum teeth and a metapodial condyle (foot bone) have been recovered in association with large distinctively shaped dung pellets, a morphology similar to a ?Hershey's Kiss? (HK), from a late Pleistocene dung layer in Bechan Cave. HK dung pellets have also been recovered from other alcoves in the Escalante River Basin including Willow and Fortymile canyons. Detailed analyses of the HK pellets confirmed them to be E. collinum and indicate a browser-type...