Distribution and Properties of Vesicular Horizons in the Western United States

Vesicular horizons are thin (usually <10 cm) surface or near-surface horizons characterized by the predominance of vesicular porosity. They are widespread in arid and semiarid lands, occurring on every continent and covering 156,000 km2 of the western United States. Vesicular horizons have critical implications for management due to their role in controlling surface hydrology and dust mobilization. This study evaluates the distribution and variation in expression of vesicular horizons across the western United States using the soil databases available from the USDA. A vesicular horizon index (VHI) that incorporates vesicular horizon thickness and the size and quantity of vesicular pores was developed using soil descriptions from a published chronosequence study. The VHI was applied to descriptions from the soil survey databases to evaluate vesicular horizon expression across the western United States. Vesicular horizons were better expressed (higher VHI) in the Central and Northern Basin and Range compared to the Mojave and Sonoran Basin and Range. This may be due to differences in temperature regime or to larger areas of playas in the Central and Northern Basin and Range that serve as sources of dust that forms the parent material for vesicular horizons. The median VHI was highest in the Aridisols and Mollisols compared to other soil orders. No significant relationship was found between VHI and soil textures. Vesicular horizons are widely distributed in western United States and occur across a wide range of soil types and soil-forming environments.