Steady 10Be‐derived paleoerosion rates across the Plio‐Pleistocene climate transition, Fish Creek‐Vallecito basin, California

Rates of erosion over time provide a valuable tool for gauging tectonic and climatic drivers of landscape evolution. Here, we measure 10Be archived in quartz sediment from the Fish Creek-Vallecito basin to resolve a time-series of catchment averaged erosion rates and to test the hypothesis that aridity and increased climate variation after ca. 3 Ma led to an increase in erosion rates in this semi-arid, ice-free setting. The Fish Creek-Vallecito basin, located east of the Peninsular Ranges in southern California, is an ideal setting to derive a Plio-Pleistocene paleo-erosion rate record. The basin has a rapid sediment accumulation rate, a detailed magnetostratigraphic age record, and its stratigraphy has been exposed through recent, rapid uplift and erosion. A well-defined source region of uniform lithology and low erosion rate provides a high, reproducible 10Be signal. We find that paleo-erosion rates were remarkably consistent between 1 and 4 Ma, averaging 38 ± 24 m/Myr (2σ). Modern catchment averaged erosion rates are similar to the paleo-erosion rates. The uniformity of erosion over the past 4 Myr indicates the landscape was not significantly affected by late Pliocene global climate change, nor was it affected by a local long-term increase in aridity.