The Ups and Downs of Nebraska: Recognizing Gilgai Microrelief in the State

This article details gilgai microrelief—a conspicuous pattern of repetitive small mounds or low ridges ("ups") and intervening depressions ("downs")—for the first time in Nebraska. Gilgai microrelief is a dynamic natural phenomenon that contributes to the diversity of local and regional landscapes while influencing soil processes, surface hydrology, plant communities, and land use. Scores of sites on soils atop the Pierre Shale in far northern Dawes and Sioux Counties exhibit mostly linear gilgai microrelief consisting of ridgelike microhighs and troughlike microlows that trend perpendicular to slope. Areas of linear gilgai microrelief are as large as 17.5 ha and individual ridgelike microhighs extend as long as 700 m. Linear gilgai microrelief exists chiefly on "washboard" ridges on shale, that is, parallel, elongated, strongly oriented ridges with west–northwest to north–northwest azimuths. Small areas (2.6 ha or less) of normal and lattice gilgai microrelief exist on some narrow ridge crests and summits in direct association with linear gilgai microrelief. Some wider, level summits exhibit small-scale reticulate patterning and subangular polygons (1.5 to 3.0 m in width) of uncertain origins. Our observations suggest that gilgai microrelief in the study area has been compromised by cattle tracks and soil erosion. Gilgai microrelief was likely more prominent prior to intense grazing.