Like their associated Rainwater Basins, the crescent-shaped ridges (lunettes) are also blanketed by loess. Although a complete sequence of Peoria loess overlying Gilman Canyon Formation and associated paleosols cover the ridges, the overall thickness of loess is slightly thinner than the loess covering the adjacent uplands and depressions. Where they have been cored, the ridges underlying the loess consist of well-sorted sand on the order of thick. Also buried by loess beneath the surface of the Rainwater Basin wetland region are the relict channel belt of the Pleistocene Platte River and relict fields of sand dunes. The original Rainwater Basins are associated with both of these buried Pleistocene landscapes.