page_title: Rainwater Basin
section_title: Geomorphology of Rainwater Basins
hierarchical_section_title: Rainwater Basin / Geomorphology of Rainwater Basins
caption_attribution_description: English: LiDAR image of Nebraska Rainwater Basins at latitude 40.7000 and Longitude -98.4722. The large elliptical basin has a major axis of 6,110 meters and a minor axis of 3,400 meters, which corresponds to a width-to-length ratio of 0.56. The basin is located 600 meters above sea level. Español: Imagen LiDAR de las Cuencas Pluviales de Nebraska en la latitud 40.7000 y Longitud -98.4722. La gran cuenca elíptica tiene un eje mayor de 6.110 metros y un eje menor de 3.400 metros, que corresponde a una relación ancho / longitud de 0,56. La cuenca se encuentra a 600 metros sobre el nivel del mar.
context_page_description: The Rainwater Basin wetland region is a 4,200 sq mi loess plain located south of the Platte River in south-central Nebraska. It lies principally in Adams, Butler, Clay, Fillmore, Hamilton, Kearney, Phelps, Polk, Saline, Seward, and York counties and extends into adjacent areas of southeastern Hall, northern Franklin, northern Nuckolls, western Saline, northern Thayer and northwestern Webster counties. Before European settlement, this plain was covered by prairie grasslands interspersed with thousands of ephemeral playa wetlands, called Rainwater Basins. Informally and locally, individual Nebraska Rainwater Basins are referred to as rainbasins, basins, lagoons, lakes, ponds, marshes, hay marshes, and lakes marshes. To the west, a tallgrass prairie in the east once gradually transitioned into mixed grass prairie. Currently, the Rainwater Basin wetland region is covered by farms, mainly growing corn and soybeans. Several, interspersed, stream courses, of which largest is the Big Blue River and its tributaries, drain this region. Riparian woodlands and upland slopes possessing oak woodlands are associated with these streams.
context_section_description: The large semi-elliptical to elliptical Rainwater Basins are the surface expression of older elliptical depressions developed in fluvial sands and gravels that are buried by a blanket of a 2.5–8 meters (8.2–26.2 ft) thick sequence of layered loesses and associated paleosols. The loess, which overlies these features, consists of an undisturbed sequence, from bottom to top, of Middle Wisconsinan Gilman Canyon Formation (loess), a regional paleosol developed in Gilman Canyon Formation, Late Wisconsinan Peoria Loess, Brady Soil (paleosol) developed in the Peoria Loess, and Holocene Bignell Loess in which the modern soil has developed. This loess sequence lies upon a paleosol developed in the fluvial sands and gravels in which these depressions initially developed. Thus, the modern basin landscape is a direct result of the accumulation a few meters of loess that blankets an older basin landscape. These basins are palimpsest landforms created by the episodic accumulation of a blanket of loess over a prehistoric landscape with numerous basins.
  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 3–5 meters (9.8–16.4 ft) 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.
  The age of the loesses and associated paleosols that buried the original Rainwater basins and the fluvial sand in which they formed have been dated by either radiocarbon dating, optically stimulated luminescence dating, or both. The oldest loess overlying original Rainwater basins have yielded ages from about 28,000 to 36,000 BP radiocarbon years and optically stimulated luminescence up to 36,000 BP calendar years. The fluvial sands of a pleistocene Platte River, which overlain by the Gilman Canyon formation and younger loesses, yielded optically stimulated luminescence dates from about 36,000 to 50,000 BP calendar years. These dates demonstrate that the Rainwater basins were formed prior to the Middle Wisconsinan, Marine Isotope Stage 3, and the accumulation of the Gilman Canyon Formation. Thus, Rainwater basins and their associated ridges are relict, pre-Last Glacial Maximum landforms that have migrated upward in elevation as successive layers of glacial-age loess have accumulated and intercalated soils sporatically formed.
caption: LiDAR image of Nebraska Rainwater Basins at latitude 40.7000 and Longitude -98.4722.  The large elliptical basin has a major axis of 6,110 meters and a minor axis of 3,400 meters.  The basin is located 600 meters above sea level.[11]
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