Considering the fact that the Gyp Hills are a significant part of the
  landscape of Barber County, it is only fitting and proper to make some
  acknowledgement of their presence and perhaps answer the most logical
  question pertaining to their being. One wonders why and how these red
  Gypsum Hills in such unique setting are so different from their surround-
  ing terrain.
     The best answer is to look at the most generally accepted geological
  theory of their origin, which dates back two hundred and thirty million
  years ago to the Permian period of the geological time table. The red
  beds and red soil are thought to have formed in a hot, arid, and desert
  environment. The red color is due to a thin layer of hematite, a low
  content iron ore, coating the sand, clay, and silt size grains. This 
  red material was deposited in layers, that can be plainly seen as you
  look at their eroded sides, over a period of several million years by
  water of an ancient inland sea that covered a vast area of the continent
  at that time. Then came a gradual uplife of the area, leaving the land
  high and dry, 1500 to 2000 feet above sea level in the form of a moderate-
  ly flat plane. Then came periods of tremendously heavy precipitation,
  especially during the Ice Age that terminated 10,000 years ago. The
  running water gradually eroded away the softer materail, leaving the
  harder material, with the streams acting as a cutting and transporting
  agent carrying the removed material to lower areas and to the ocean. The
  hills and landscape that we see today are the result of this very gradual
  process over a period of millions of years.
     The Cap Rock acts as a buffer against erosion, preventing the material
  below it from being moved away as rapidly as the material surrounding it
  that has no Cap Rock.
     At the summit of these hills we sometimes find thick layers of gypsum
  on the surface or a few feet under the surface, such as the important
  deposit southwest of sun City where the Gyp Mine is located. These Gypsum
  beds, although a contributing factor, do not necessarily make up the total
  content of the Cap Rock.
     When viewing the hills, there is a very noticeable shale ledge several
  feet below the summit, which has no resemblance in appearance to the white
  gypsum. This shale is made up of a small percentage of gypsum and a larger
  percentage of anhydrite and clay, bonded together by the cementing properties
  of gypsum and anhydrite; it is called gypsiferous shale.
                  
     Source:Chosen Land - Barber County, Kansas,  pg. 7 
     Submitted by: Elmer Angell Jr., assisted by Professor Claude W. Shenkel,
     geologist, Kansas State University.