These thick salt deposits are mined in central Kansas, notably near Hutchinson. The sand and silt were washed down from the distant mountains and deposited along the shores of the retreating Permian sea. The red beds have some gypsum, salt, and dolomite interbedded with them. Following the Permian Period, there was a long interval of non-deposition and erosion in Kansas. There may be some Triassic rocks in Morton County, but the age of these has not been definitely determined.
Jurassic rocks are present in the subsurface of the western part of the state.
The next rocks laid down in Kansas are those of Cretaceous age. The sea again came over the region, this time leaving a succession of sands, muds, and chalks, alternating with coastal stream, swamp, and beach deposits. The well-known chalk of Kansas is of Late Cretaceous age. These sandstone layers are the source of water in many wells in the central and western part of the state. About 80 percent of the Dakota Formation, however, consists of clays of many colors.