The dominant process in semi-arid/arid landscapes is the accumulation of soluble minerals. Gypsum and other soluble salts require a source of the appropriate ions. These can originate from the parent material, eolian/fluvial input, sea spray, weathering of sulfide minerals, volcanic gases, industrial pollution, and chemical reactions in the atmosphere. In soils whose original parent materials do not contain soluble salts, sulfate minerals accumulate in specific morphologic stages with time. Sulfate minerals initially accumulate as stage I snowballs (1-3 mm), filaments and/or thin coatings on the bottom of clasts. Stage II is defined by nodules (approx. > 1 cm), and in coarse textured soils, continuous coatings on the base of clasts (pendants).  Stage III sulfate morphology forms indurated horizons which can contain up to 99% sulfate minerals. Rarely is gypsum found alone without other salt minerals, except in areas in which the parent material is gypsum. Because these minerals are highly soluble, their type, amount, and locations within soil profiles can change very quickly in response to land use changes or climate. These changes can render previous soil taxonomic classifications incorrect. Rapid urbanization in Las Vegas Nevada has drastically changed soils in the Las Vegas Wash through the redistribution of salt minerals. Salt minerals are active geomorphic agents. Some of the most expensive urban environmental problems are caused by the mechanisms of salt weathering, salt heave, subsidence, and salt corrosion. However, salt minerals in soils can also serve as a refuge for life in the most extreme environments.