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- Physiographic Regions
The surface of the Wellington-McPherson Lowlands region of south-central Kansas is mainly a relatively flat to rolling alluvial plain, made up of unconsolidated sand, silt, and gravel. The region is dissected by the Arkansas River Lowlands region, which encompasses the Arkansas River floodplain. Within the Wellington-McPherson Lowlands, the city of McPherson is to the north of the Arkansas River and the city of Wellington is to the south. Streams in each section flow toward the Arkansas River.
During the Pleistocene Epoch, wide-ranging streams flowing toward the Arkansas River deposited the thick layers of sand and other sediment on top of existing Permian rock layers in the region. Farming is now prevalent due to the rich soils that developed on top of the sediment, and the landscape is largely indistinguishable from that of the adjacent Arkansas River Lowlands.
The Equus Beds aquifer, which makes up the northern section of the region, is a major source of water for Wichita, Hutchinson, McPherson, and other local cities. The aquifer occurs where the deposits of sediment are up to 250 feet thick and partially saturated with groundwater. Because the Pleistocene-age deposits of the aquifer contain fossils of a type of now-extinct horse, it was named "equus," the Latin word for horse.
The eastern boundary of the Permian-age Hutchinson salt bed, one of the largest salt deposits in the world, underlies the Pleistocene-age sediment in the western portion of the Wellington-McPherson Lowlands. Thicker to the west, the salt bed is mined in Hutchinson, Lyons, and Ellsworth in adjacent regions.
On the surface, sand dunes formed by wind and water can be seen in parts of the region. Most are now inactive—covered with grasses and other vegetation that keep the sand from shifting when besieged by wind and water. Trees in the countryside grow mainly along streams.
Along the western edge of the southern section, Permian-age bedrock is exposed on the surface adjacent to the Red Hills region. However, although the division between the Arkansas River Lowlands and the Wellington-McPherson Lowlands merges nearly seamlessly, the boundary between the rugged Red Hills and flatter Wellington-McPherson Lowlands is much more pronounced and easily identified.
Streams flowing into the Arkansas River from the norther section of the region include the Little Arkansas River, and streams flowing from the southern portion include the Ninnescah and Chikaskia rivers. Lake Inman, northeast of Inman and southwest of McPherson, is the largest natural lake in Kansas. It formed after an underground layer of salt was dissolved by groundwater along the eastern edge of the Hutchinson salt bed. The land surface eventually subsided into the void where the solid salt rock had been and the irregularly shaped bowl that appeared on the surface then filled with groundwater to create the lake.
Buchanan, R., and McCauley, J. R., 2010, Roadside Kansas: A Traveler's Guide to its Geology and Landmarks: Lawrence, Kansas, University Press of Kansas, 392 p.