10-Be Surface Exposure Ages along the Blue Cut Fault in Joshua Tree National Park, California

To better evaluate the late Pleistocene slip rate history of the Blue Cut Fault in Joshua Tree National Park, we constrain the ages of six depositional surfaces that are correlated and offset along the fault. We collect 38 Beryllium-10 surface exposure samples, using a mixture of surface clast types on each mapped surface unit, including sampling boulder tops, cobbles, and amalgamated pebble clasts. Age agreement between sample types indicates that effects of these processes are negligible, because sample types are differentially affected by inheritance/exhumation. We crush whole rock material, remove all minerals but quartz grains, digest the quartz and proceed to extract the element Beryllium in order to measure the 10-Be/9-Be ratio in the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory. Seven of our samples were processed at Arizona State University, while the rest were processed jointly at San José State University and Lawrence Livermore National Laboratory, following the procedures of Ditchburn & Whitehead (1994). 10-Be geochronological results, in combination with geomorphic mapping indicate multiple ages of offset alluvial surfaces that range from the oldest mapped Qf1a surface of >129 ka, to the youngest offset Qf3b surface of 13.2 ± 1 ka (2𝞂). In addition, we find good agreement between ages of different sample types for each surface. See Guns et al. (2022) for further information.