Windblown deposits form when sand, silt, or clay (loess) materials are transported by wind and deposited on the ground surface. Although windblown deposits do not normally cause disasters they are considered hazardous because they can cause damage or loss of property.
Active windblown deposits occur in many areas of Wyoming, particularly northeast of Rock Springs, north of Sinclair, northwest of Casper, and in Goshen County. Stable windblown deposits (those that have become vegetated) may become active again if they are disturbed and not properly re-vegetated or stabilized.
Prehistoric volcanic ash weathers to form bentonite, which includes an expansive clay mineral called montmorillonite. The natural weathering process of rock distributes the montmorillonite in local soils.
Changes in moisture can cause certain clay minerals to either expand or contract, often resulting in large volumetric changes in the soil. If structures or roads are built on these soils without proper mitigation procedures, the expansion or contraction of the soil can cause cracking, movement, or even failure of a structure or road.