 When the soil swells on wetting, the former surficial material is mixed with the subsoil.Vertisolic soils develop mainly in clayey materials in semiarid to subhumid areas of the Interior Plains of Saskatchewan, Manitoba and Alberta and occupy less than 1% of the land area of Canada.The order and its 2 great groups were recognized in the Canadian system in the 1990s after extensive studies of pedons in the Great Plains.