Whereas soils in semiarid environments have received considerable attention, specific biogenic structures produced by the plants and animals that inhabit them are less well understood. Soils in a field site in the Santa Catalina Critical Zone Observatory in the semiarid Sonoran Desert of southern Arizona were investigated to develop a model to improve the interpretation of analogous paleosols and associated soil ecosystems in the geologic record. A flat plateau of desert scrubland was divided into thirty-six 4 m2 plots for description and study. Field methods included mapping of soil surfaces, imaging with ground-penetrating radar, casting of open burrows, description of soil trenches, and soil coring. Laboratory methods included analysis of soil bulk geochemistry, clay mineralogy, and thin sections as well as detailed descriptions of burrow casts. Soils included 10–40 cm thick Entisols and Aridisols with blocky peds, pervasive, coarse (3–5 mm) to very fine (< 1 mm) roots, and were dominated by the burrows of ground squirrels and ants, as well as those of various lizards, snakes, scorpions, spiders, centipedes, termites, and insect larvae. Burrow morphologies included small (< 1 cm) to large (> 1 cm) diameter simple vertical shafts, isolated ovoid chambers, subhorizontal tunnels, subvertical to subhorizontal networks of branching tunnels, and complex branching galleries. Bioturbation was concentrated in the upper 20 cm of the soil profile, whereas roots often extended to the base of the profile. Results from this study advance our understanding of the traces produced by different soil organisms and their impact on soil development in modern settings and will be valuable for the interpretation of the paleosols from semiarid environments in the rock record.

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