Abstract

Lee’s Ferry (Arizona, United States) lies at an important geologic transition between the Grand Canyon margin and the Canyonlands center of the Colorado Plateau. It marks a knickpoint along the Colorado River at the top of the steep Grand Canyon, and it is central to debate about the patterns of erosion and sources of uplift in this famous landscape. New chronostratigraphic data from the suite of fill terraces here indicate a strong fluvial response to climate drivers superimposed upon an integrated mid-to-late Pleistocene incision rate of ∼350 m/m.y. A regional compilation of well-constrained results over the same timescale reveals that this is intermediate between slower rates downstream in Grand Canyon and even faster rates in the central Colorado Plateau, which taper off again farther upstream near the plateau’s eastern edge. This bull’s-eye pattern of rapid incision in the central Colorado Plateau does not match proposed sources of uplift from mantle dynamics at the south and west flank of the plateau, nor patterns of river steepness and energy. Instead we suggest that this incision pattern is primarily driven by transient response to drainage integration and isostatic feedback from the deep exhumation of weak rocks in the central plateau.

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