1 For submission to GEOLOGY, 12/24/03

We used in situ-produced cosmogenic 10Be and 26Al to differentiate sediment source areas and to determine the millennial-scale sediment budget for an extremely common, long-studied, but poorly understood landform in arid and semi-arid regions, the desert piedmont. Using these nuclide data along with interpretive models, we were able to quantify long-term rates of sediment generation and transport at different locations on the piedmont and thus infer the origin and route of piedmont sediment from source to sink. The sediment budgeting approach we present is easily generalizable to other landforms in other climate zones. We intentionally chose a geomorphically complex piedmont, representative of many in the Mojave region. The Chemehuevi pediment contains multiple geomorphic surfaces including a pedimented section, the intra-piedmont Sawtooth Range, dissected alluvial surfaces, and low relief wash surfaces. Nuclide data indicate that sediment is produced more rapidly in mountain source basins than from the pediment, bedrock knobs, or the alluvial surface. Of the total sediment in long-term transport down the 12 km long piedmont, 11 % originates from the source basins, 33 % from the pediment, 3 % from the Sawtooth Range, and 53 % from the erosion of the incised alluvium. The aerial extent of source basins, pediments, and alluvium, together set the balance between sediment generated from bedrock erosion and sediment generated from the reworking of unconsolidated material.