We utilized field measurements of erosion rates and topographic analyses to constrain the timing and magnitude of landscape rejuvenation on the western flank of the Rocky Mountains in central Idaho, United States. Deeply incised canyons of the Clearwater, Salmon, and Snake Rivers dissect a broad region of roughly 8 × 10 4 km 2 . Along the Salmon River, an observable break in slope separates relict landscapes of low relief (<400 m valley depth) from high-relief landscapes (1200-1600 m valley depth) adjusting to base-level forcing. The 10 Be cosmogenic radionuclide concentrations in river sediment record basinwide erosion rates that increase from 0.05 mm/yr ± 0.008 in the low-relief topography to 0.12 mm/yr ± 0.016 in the adjusting, high-relief landscapes over the last 10 3 -10 4 yr and are consistent with longer-term estimates of erosion. Using the covariance of erosion rates and channel morphology, we calibrated a 1-dimensional river incision model to constrain the dynamics of incision along the Salmon River. More than 10 5 model runs explored uncertainty and assumptions and found that increased incision initiated roughly 9.5 ± 2 Ma and persists to the present. New constraints on the distribution of erosion processes at locations within a 400 km transect across central Idaho suggest northward surface tilting. In light of these data, we offer a new hypothesis that attributes late Miocene landscape rejuvenation of central Idaho to surface uplift driven by density changes in the mantle-lithosphere precipitated by the Yellowstone plume. We demonstrated the hypothesis through a simple model of flexure of an elastic plate subject to a buried buoyant load, and we found that density changes extending 200 km north of the Snake River Plain can reproduce the south-north distribution of uplift with reasonable values for elastic thickness and anomalous density.

In many actively eroding rivers, the dominant process of incision is thought to be driven by solid particle impacts Sklar & Dietrich, 2001;Turowski, 2012;Whipple et al., 2013) where the transport of bed load sediment imparts kinetic energy to the channel boundary through rolling, sliding, or saltating ("hopping"). Current understanding of the erosive energy delivered to the bed by sediment is based on particle saltation trajectories in experiments with planar beds or flat alluvium (

Lithology is an important control on the efficiency of bedrock incision and thus the pace of landscape evolution. Rock strength is commonly considered the limiting lithologic factor that resists erosion. Yet, rock strength is a dynamic property that oscillates during advection of rock to the channel surface as damaging processes weaken rock and erosion exposes fresh rock. We approach the problem by investigating damage on bedrock surfaces that vary by the frequency they are eroded in channels of different lithologies. Our data set includes measurements of channel slope and width to characterize channel morphology, and Schmidt hammer rebound, P wave velocity, slake durability, and porosity to characterize the mechanical properties of channel surfaces. The average damage accumulation rate of lithologies ranges over 41% of the mean. We find a range of damage patterns among the different lithologies. Local surface damage increases with erosion frequency in channels comprised of coarse‐grained bedrock but decreases with erosion frequency in channels comprised of fine‐grained bedrock. We interpret these patterns to develop from lithological influences on weathering, abrasion, and the threshold of damage to erosion. The cross‐channel damage patterns between channel floors and margins are well correlated with stream power demonstrating links between microstructural rock properties, reach‐scale morphology, and landscape‐scale processes. We conclude that the morphodynamics of bedrock channels are sensitive to the lithological influences on the direction and magnitude of feedback in the coevolution of bedform morphology and the mechanical properties of the surface.

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