CHARACTERIZING REGOLITH THICKNESS IN THE PINALEÑO MOUNTAINS, SE ARIZONA, USING SHALLOW SEISMIC REFRACTION

The Basin and Range physiographic province characterizing southeastern Arizona is made up of isolated mountain ranges with >1500m of relief from the desert floor to steep mountain peaks, which creates a dramatic climate gradient. The Pinaleño Mountains, one of the sky islands typical of the region, are characterized by their high-elevation low-relief summit “flats” and their flanks of steep, rocky catchments. The tectonic regime is quiescent since Basin-Range extension slowed. Using shallow seismic refraction surveys on a range of soil-mantled hillslopes across the low-relief summit area, we created depth-to-bedrock soil velocity profiles. This enables us to visualize the subsurface architecture of this unique critical zone and to compare the seismically generated soil depths with field measurements along the same seismic line. Comparing the velocity profiles to soil depth field measurements validates the pairing of these two data sets and enables greater insight into our quantification of soil production rates across the region. This work helps us further understand the post-orogenic decay of the Pinaleño Mountain sky islands and is calibrated to our cosmogenic soil production rate data. Specifically, by verifying the veracity of our seismically generated soil profiles in the field we are better able to understand the distribution of soils across the gradient between summit “flats” and the steep flanks. Combining this understanding with our cosmogenic nuclide derived soil production and erosion rate measurements across the entire field area enables us to quantify how this pos-orogenic landscape is evolving.