Much of the western US plateau country is responding to accelerated Colorado River incision in the last few million years. The plateau landscape adjacent to the river responds by retreat of lines of cliffs made sinuous by a network of incising streams. Beyond these cliffs the landscape remains unaffected by the advancing wave of incision, preserving a relic landscape. This landscape constitutes a natural experiment in landscape evolution that will be exploited to constrain the rates of cliff retreat and plateau dissection and to explore the physics of the processes involved. The Roan Plateau of western Colorado displays particularly well all elements of plateau landscapes.
Four main tasks include: 1) Dating of Colorado River gravels to establish the most recent rate of river incision that spawned the wave of dissection of the Roan Plateau. 2) Documentation of the processes and rates of retreat of the dozens of 50 m tall waterfalls responsible for this dissection. 3) Documentation of lowering rates of the remnant landscape atop the Roan Plateau to constrain models of hillslope evolution in this low-relief landscape. 4) Measurement of the recession rate of the Book Cliffs just west of the Roan Plateau. The landscape rates, and the field observations of the physical processes, will constrain numerical models of landform evolution that will add to our quantitative understanding of these classic American landscapes.
Broader impacts: Beyond training two graduate students, the results will be broadly applicable to many landscapes that are responding to changes in rates of river incision. Cliffs dominate landscapes visited by many tourists of the American West; it is the intricate rocky staircases of the Grand Canyon, Zion, and Bryce that attract attention. Both the rates of cliff retreat and the simulations of landscape evolution will be made available to these Parks.
