Cheyenne Bottoms


A Wetland of International Importance With Disputed Origins

Stephanie Trump
Field Geomorphology
Portion of Cheyenne Bottoms owned and managed by The Nature Conservancy, taken from observation tower. Photo by Stephanie Trump, 10/9/2009.


Introduction

Cheyenne Bottoms is a large, elliptical depression located in Barton County, Kansas. It is located principally in Township 18 South and Ranges 12 and 13 West (Bayne, 1977). It is well known for being a bird-watching spot, and has been designated a Wetlands of International Importance. The origin of the name “Cheyenne Bottoms” is said to come from a battle between Native Americans, in which the Cheyenne tribe defeated the Pawnees or Kiowas in 1825. Blood Creek, one of the creeks that flow into the Bottoms, is said to also derive its name from this battle (Schwilling, 1985). Cheyenne Bottoms is approximately 41,000 acres (Schwilling, 1985). It consists of a 20,000 acre wildlife management area operated by the Kansas Department of Wildlife and Parks, and 7,300 acres is managed by the Nature Conservancy (Great, 2009). The Rest is privately owned.

Surficial Geology of Cheyenne Bottoms


Figure 1 Sand dunes near Camp Aldrich, east of Cheyenne Bottoms (Aber, 2009)

The surficial geology is fairly simple. The depression is relatively flat and featureless. On the north, south, and west sides of the basin, the walls are Cretaceous in age and rise about 100 feet about the basin floor. (Bayne, 1977). On the northeast side, sand dunes also rise to an elevation of about 100 feet above the basin floor (Figure 1). The east and southeast side of the basin are composed of alluvial sediments (Bayne, 1977). The surficial geology can be seen in figure 2. The floor of Cheyenne Bottoms is underlain by unconsolidated clay, sand, silt, and gravel that are Pleistocene to Recent in age. The gravel is mainly composed of sandstone and ironstone fragments that were derived from the Dakota formation. The thickness of these deposits range from less than 20 feet (6.1 meters) at the margins of the basin to over 100 feet (30.5 meters) in the deepest part, an old, buried channel that trends northwest-southeast through the middle of Cheyenne Bottoms, in line with Blood Creek Valley (Latta, 1950). Flowing into Cheyenne Bottoms are Deception and Blood Creeks, and Little Cheyenne Creek flows out of the basin.


Figure 2 Surficial Geology of Cheyenne Bottoms, (Bayne, 1977)

Many theories have been proposed for formation mechanism of Cheyenne Bottoms. Some proposed ideas have been a meteor impact, salt or other evaporite dissolution, eolian deflation, and more. In 1927, an anonymous author at the Kansas Forestry, Fish, and Game Commission wrote:
Geologically, the Cheyenne Bottoms, as the oval-like bowl is called, puzzles man. Some have thought that i[t] outlines the mark of an anticline, the top of which had caved in and so drilled for oil (Schwilling, 1985).

Of the proposed creation mechanisms, one of the first to be proposed was impact of a meteorite, but this has been ruled out since no meteorite fragments or other impact evidence has been discovered.

In 1897, Erasmus Haworth proposed the Bottoms were created by stream erosion (Hayworth, 1897). Johnson, in 1901, advanced the theory of salt dissolution. Bass, in 1926, created a map of salt thicknesses in western Kansas (figure 3). This map showed a thinning of the salt layer beneath Cheyenne Bottoms. He believed this confirmed Johnson’s ideas. Latta, in 1950, believed that Cheyenne Bottoms was formed by a combination of stream erosion and salt dissolution (Bayne, 1977).


Figure 3 Map of thicknesses of salt in Western Kansas, (Bass, 1926)

Erasmus Haworth, quoting one of his assistants, Benjamin Miller, states that Blood Creek and Deception Creek, probably flowed near their current paths. They believed that once these streams were able to erode past the fairly resistant Benton and Dakota formations, the softer, less resistant layers were exposed and the rate of erosion increased. Underneath these soft layers was another resistant sandstone layer. Once this layer was encountered, erosion became lateral, rather than vertical, and these creeks widened their valleys Haworth and Miller believed that the erosion of the sandstone created the deposits of sand located at the eastern and southeastern sides of the basin (Haworth, 1897). A buried stream channel, referred to by Fent as the Chase Channel, suggests that during the Pleistocene, a stream flowed across the area that is now Cheyenne Bottoms in line with Blood Creek. Then the stream exited the area following the course of the present Little Cheyenne Creek. Fent followed the course of the Chase Channel into Rice County. A narrow divide in the vicinity of present-day Ellinwood separated this channel from the ancestral Arkansas River channel. It is believed that after the ancestral Arkansas channel became choked with deposited sediments, it overflowed the divide and began flowing into the Chase Channel. This channel then became a tributary and was later obstructed with sediments (Latta, 1950).

The only evaporite layer thick enough to cause dissolution and subsidence is the Hutchinson Salt. There is a depression in the Hutchinson Salt at this point, as seen by the map (figure 3) prepared by Bass (Bass, 1926) but if this was the cause of the depression on the land surface, the layers underlying the Hutchinson Salt would not be affected, but there is also a depression in the underlying layers, so this seems to rule out salt dissolution (Bayne, 1977).

According to the pollen record, about 20,000 years before present, there were spruce and other conifers where Cheyenne Bottoms is now located, suggesting a cooler climate (Arbogast, 1998). During the Holocene, temperatures rose, and the climate became drier. The spruce began to be replaced by deciduous forest about 12,000 years BP, becoming completely replaced about 10,500 years B.P. As the climate continued to become drier and warmer, the deciduous forest was replaced by grassland about 9,000 years B.P. (Arbogast, 1998). As the Holocene continued, it is believed that strengthened zonal flow triggered the generally warm and dry conditions of the middle Holocene that lasted from about eight to five thousand years ago. At the end of this warm, dry period, conditions became cooler and wetter. This cycle of changing conditions has repeated several times, allowing for mobilization of the nearby sand dunes (Arbogast, 1998). The periods of increase of the sand dunes correspond to periods of erosion in Cheyenne Bottoms, suggesting that the Bottoms were created by erosion of sediments.


References