Arkansas River Lowlands and …

drawing of outline of this region on Kansas map

Wellington-McPherson Lowlands—Introduction

drawing of outline of this region on Kansas map

Arkansas River & Wellington-McPherson Lowlands--Intro | Arkansas River & Wellington-McPherson Lowlands--Rocks and Minerals
Arkansas River & Wellington-McPherson Lowlands--Places to Visit | Other regions

Download fact sheet on the rocks and minerals of the Arkansas River & Wellington-McPherson Lowlands.

The Arkansas River Lowlands and the Wellington-McPherson Lowlands, though separated into different physiographic regions, are geologically similar. Both regions are relatively flat alluvial plains, made up of sand, silt, and gravel that was dumped by streams and rivers.

The Arkansas River Lowlands is made up of rocks deposited by the Arkansas River during the last 10 million years as the river flowed through Kansas from its source high in the Rocky Mountains. In the Rockies, the Arkansas is supplied with runoff, snowmelt, and rock debris that weathers from the mountains, but as it moves out onto the High Plains, it receives little in the way of additional water. In fact, it loses water to its sandy riverbed. As its flow decreases, the river's ability to carry sediments also diminishes and it begins to dump its sediment load. It changes from a degrading stream (one that cuts downward in its channel) to an aggrading stream (one that builds up the riverbed).

The Wellington-McPherson Lowlands of south-central Kansas is also developed on alluvial deposits. This sand, silt, and gravel was eroded from slightly older rocks in the High Plains to the north, then carried by streams flowing south into the Arkansas River between one and two million years ago, during the Pleistocene Epoch.

The Wellington-McPherson Lowlands sit on top of one of the largest salt deposits in the world. Known as the Hutchinson salt bed, this deposit underlies much of central Kansas and is as much as 400 feet thick in places.

Another important underground feature of the Wellington-McPherson Lowlands is the "Equus beds" aquifer. The Equus beds is made up of thick (more than 250 feet) deposits of silt, sand, and gravel, in many places saturated with water. This aquifer is an important source of water for Wichita, McPherson, Newton, and other communities in this region. These Pliocene- and Pleistocene-age deposits were named for fossils of Ice Age horses that were found among the unconsolidated deposits (equus is the Latin word for horse).

Sand dunes, formed by wind and water, occur in many places in both regions. Most of these dunes are covered with grass and other vegetation, which keeps the sand from shifting. Such sand dunes are considered inactive--that is, they are no longer moving in response to wind and water.

Text by Liz Brosius, Kansas Geological Survey. Unless noted otherwise, illustrations by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey.

Arkansas River & Wellington-McPherson Lowlands--Intro | Arkansas River & Wellington-McPherson Lowlands--Rocks and Minerals
Arkansas River & Wellington-McPherson Lowlands--Places to Visit | Other regions