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 approximately 3 Ma led to an increase in erosion rates in this semiarid, 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 paleoerosion 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 paleoerosion rates were remarkably consistent between 1 and 4 Ma, averaging 38 ± 24 m/Myr (2σ). Modern catchment‐averaged erosion rates are similar to the paleoerosion rates. The uniformity of erosion over the past 4 Myr indicates that the landscape was not significantly affected by late Pliocene global climate change, nor was it affected by a local long‐term increase in aridity.