Some Gilgaied Soils in South Dakota

The addition of material to the lower part of the solum by the swelling of clay down into desiccation voids seems to be the first step in the genesis of South Dakota gilgai. The microridges of wavy gilgai are formed by ( a ) the cyclic movement of microvalley subsoil material along oblique cleavage planes into the microridge; ( b ) a slower downslope soil creep of microridges than of microvalleys; and ( c ) the upward extrusion of material from a compacted microridge subsoil as it is moistened and clays swell. Normal gilgai are formed by extrusion. Gilgaied areas have soils similar to Chestnuts, Solodized‐Solonetz, Solonchaks, or complexes of these soils.