Abstract

Although inversion of relief is a common attribute of landscape evolution, these landforms as a class have been little reported in the terrestrial literature. The Colorado Plateau is a unique geologic setting where multiple exposures of exhumed paleochannels are preserved. Following uplift of the region in middle to late Cenozoic time, erosion by the Colorado River and its tributaries stripped away younger rock strata, revealing Late Jurassic and Early Cretaceous sediments. Fluvial sediments in these paleochannels were indurated by carbonate cements, which made them more resistant to erosion than the surrounding material. As a result of differential erosion, the former valley floors are now preserved as conglomeratic sandstone-capped ridges. The present-day arid climate over the Colorado Plateau has inhibited the development of thick soil horizons and pervasive vegetative cover, both of which would obscure these sedimentary bodies. Exhumed paleochannels expose fluvial sediments and internal sedimentary structures in three dimensions. Multiple examples of individual and superimposed exhumed paleochannel segments are found within the Jurassic Morrison and Cretaceous Cedar Mountain Formations in southeast Emery County of east-central Utah. These sites, located south and west of the town of Green River, Utah, vary in scale and represent a range of depositional environments. This paper illustrates the morphology of these landforms with aerial and ground-based images that highlight the paleochannel form and beautifully exposed sedimentary structures. In addition, we discuss the paleohydrologic conditions and paleoenvironmental factors that influenced channel development, as well as the processes responsible for their ultimate preservation within the geologic record. The morphology of these landforms is similar to comparably sized, raised curvilinear features on Mars. Further study of these terrestrial analogs holds tremendous potential for understanding the time scales and environmental conditions associated with fluvial events in Martian history.