Hydrogeology
The Rattlesnake Creek subbasin is covered with a veneer of loess deposits and sand dunes with the underlying Pleistocene alluvium forming the major aquifer of the area. This alluvium was deposited by the ancestral Arkansas River and a small number of local streams, and is composed of undifferentiated early Pleistocene sediments (the Meade formation, which consists of interbedded lenses of unconsolidated gravel, sand and silt; caliche is common throughout the formation) and late Pleistocene sediments (the Sanborn formation, which consist of silt, sandy silt and fine sand that locally contain lenses of coarse sand and gravel). The Pleistocene alluvium overlies Cretaceous and Permian bedrock. The lower reaches of the Rattlesnake Creek and the Quivira National Wildlife Refuge represent a natural ground-water-discharge area of both the unconsolidated Great Bend Prairie aquifer and the underlying bedrock aquifers.
Most of the Tertiary deposits that make up the Ogallala Formation were removed by erosion before Pleistocene material was deposited. The stratigraphy of the Quaternary alluvium in descending order is generally (1) sand dunes; (2) a relatively continuous near-surface silt-clay bed, probably a loess deposit; (3) alternating sequences of sandy silt-clay, and sand and gravel lenses; (4) a basal sand and gravel bed of fluvial origin; and (5) bedrock.
The alluvium in the Rattlesnake Creek valley is relatively thin, probably less than 20 feet thick everywhere. It is composed chiefly of poorly sorted sand and gravel that was derived from the Meade formation the alluvium is underlain by thick deposits of the Meade formation. Hydrogeologically the two units are in most instances indistinguishable.
The Permian bedrock subcrops along an approximately north-south trend near US-281 and constitutes a source of poor-quality (saline) water east of US-281 in northeast Stafford County and other localities. The Permian formations in the area, known as red beds, consist of reddish-brown sandstone, siltstone, shale, salt, gypsum, anhydrite and limestone. The Permian deposits, and especially the Late Permian red beds, are a source of poor-quality water that rises upward and increases the salinity of the water in the unconsolidated aquifer in the lower reaches of Rattlesnake Creek, in particular, the Quivira National Wildlife Refuge.
Rocks of Cretaceous age form the bedrock surface in the western part of the Great Bend Prairie. These rocks consist of interbedded shales, sandy, shales and fine to coarse-grained sandstones. Of the three Cretaceous units, only the lower unit (Cheyenne Sandstone) is a potential source of water to large-capacity wells, but the water is believed to be highly materialized. The Kiowa Formation is the oldest formation exposed in the Rattlesnake Creek subbasin (in the northwestern part of T. 22 S., R. 11 W., northeastern Stafford County), where it consists of dark fossiliferous shale and rusty sandstone. The overlying Dakota Formation is not exposed in the subbasin area.
The Pleistocene drainage patterns of central Kansas record the history of the northeastward migration of through-flowing streams from the Rocky Mountain area. This migration was caused by successive captures of the southern trunk of the ancestral stream by its own northern tributaries. The captures seem to have resulted from the difference in the debris load available in the headwater areas of the streams. Throughout the Pleistocene, through-flowing streams originating from the Rocky Mountains, such as the Arkansas River, filled their channels with coarse gravel and sandy alluvium derived from igneous rocks. This material built up the surface over which the streams flowed, causing stream avulsions and the consequent spreading of alluvial material over wide areas. In contrast, the sediment load obtained by downcutting in their immediate headwater areas. The silt and fine-grained sand of local origin in the northern Great Bend Prairie with its low permeability, favored runoff and consequently more erosion and downcutting to below the level of the through-flowing streams. This downcutting led to the eventual capture of the through-flowing streams. This is evident in the relative abundance of northern tributaries to the Arkansas River in central Kansas.
Source: Final Report for the Computer Model in the Rattlesnake Creek Basin
Kansas Geological Survey and Kansas State University, May 1997
