The subtle depressions known locally as "Rainwater Basins" lie scattered across the loess plain of south-central Nebraska. The majority of them lie to the south of the Platte River. Prior to European settlement, there were nearly 4,000 of these wetlands totaling up . The smaller, "pothole" depressions, which are irregular in shape and do not exhibit any orientation, range from about in size. Their bottoms generally lie less than below the surrounding land surface at their lowest point. Most of these smaller depressions have been destroyed by agricultural activities such as filling, land leveling, drainage, and sedimentation.