Cultivated soils and several types of dune material were used in a study to determine what factors are responsible for the differences in wind erosiveness of a ridged and a smooth surface. A laboratory tunnel with an exposure chamber 12 ft. long and a portable field tunnel with an exposure chamber 40 ft. long were used. This study revealed several opposing factors influencing the erosiveness of the 2 surfaces, the net effect of these factors causing marked and consistent reduction in the intensity of erosion on a ridged as compared to a smooth surface.