CLIMATIC CONTROLS EVIDENT IN THE LATE CENOZOIC RECORD OF THE EASTERN UINTA MOUNTAINS

The northeastern Uinta Mountains lie at the center of the Rocky Mountain/Colorado Plateau region and contain a relatively complete post-Laramide landscape history that has been the focus of classic geologic study. Though the middle-Cenozoic component of the post-Laramide history has been investigated, there has been little or no direct study of the prominent late Cenozoic deposits, specifically stream terraces. Previous workers widely held that late Cenozoic tectonism was the primary driving mechanism for the region’s drainage adjustments and canyon cutting, but our research suggests that climate plays a significant role in shaping this landscape.

Detailed mapping of the late Cenozoic stratigraphy extending below the glaciated high Uintas, down tributaries such as the Henrys Fork, and along the mainstem Green River is being combined with sedimentologic, geochronologic, and soil studies. The stratigraphy along the Henrys Fork drainage is characterized by direct linkages between moraines, glacial outwash, and down-valley fill terraces that converge and combine downstream. Terrace stratigraphy along the mainstem Green River is more complex than that of the Henrys Fork, involving relatively thick inset fill deposits that have several terraces developed in them. These observations suggest that the alluvial stratigraphy is dominated by aggradation and degradation cycles controlled by climate/glacial induced changes. Ongoing geochronologic, sedimentologic, and soil analyses will clarify connections between deposits and climatic events and will make the calculation of stream incision rates possible, providing further insight into the landscape evolution of this region.