Evidence of leaching below the average depth of water storage is commonly observed in Aridisols and is explained by: (i) more humid paleoclimates, and/or (ii) the influence of occasional, exceptionally large precipitation events. Examination of soil forming processes in arid zones invariably requires consideration of possible paleoclimatic influences (i.e. some features in the soil may have formed under conditions quite different from those operating at present), the periodic occurrence of large precipitation events that can punctuate the otherwise dry environment of these regions and local variation in factors that prescribe soil genesis.