Timing of surficial process changes down a Mojave Desert piedmont

We measured 10Be and 26Al in 29 sediment samples to infer the history and millennial-scale rates of change down a low-gradient piedmont, a common but enigmatic landform that dominates the Mojave Desert. Nuclide data suggest that a large volume of sediment was deposited on the proximal East Range Road piedmont in Fort Irwin, California, ∼ 75,500 yr ago. Since then, this material has been stable or eroding slowly. In contrast, on the distal piedmont (3.5 km from the upland source basins) soil stratigraphy suggests that there have been alternating periods of surface stability, erosion, and deposition over the last 70,000 yr. Nuclide data from samples amalgamated along cross-piedmont transects suggest that long-term average down-gradient sediment speeds range from 9 cm yr− 1 near the uplands to 22 cm yr− 1 6 km down-piedmont. These speeds are similar to 10Be-estimated sediment speeds down three other piedmonts in the Mojave Desert, suggesting that piedmont surface morphologies dominated by shallow migrating channels have similar sediment transport rates. The timing of surface process change down the East Range Road piedmont is determined by a combination of sediment available in the source basins, sediment transport rates, and the size of the piedmont.