Figure 41. In 1872, a wagon crosses the Arkansas River near Great Bend. Although the river was shallow, it was 200 to 300 yards, or about one to two city blocks, wide. Now at this spot, it is only about 20 feet wide. (Photo courtesy of the Kansas Historical Society).
Figure 42. The Arkansas River southwest of Great Bend is nearly dry much of the year. This photograph was taken in 1986 within a few miles of the location of the 1872 photo.
The Arkansas and the Missouri (which forms the northeast border of Kansas) are the only rivers in Kansas that begin in the Rocky Mountains. So while the river has flattened out the land, it also has deposited sand and other sediment carried in from the Rockies and other points along its path. Sand dunes, created by wind and water, can be found in many places along the river.
Most of the sand hills don't change much anymore because they are covered with grass and other vegetation. However, some dunes in southwest Kansas are still active. Active dunes have little grass growing on them so they are always changing. Wind and water create new patterns in the sand and alter the shape of the hills and dunes. Although these changes usually don't happen overnight, the sand hills are more greatly affected by the environment than hills made of solid limestone or sandstone.
This region was once crossed by many rivers. When the Rocky Mountains were forming millions of years ago, sediment such as sand and gravel was carried in by the rivers from the mountains. Some of the loose sand and gravel was naturally cemented to form a porous and permeable rock called mortarbed. Porous means it contains holes and permeable means the holes are interconnecting so that water can seep through. However, not all of the sand and gravel was compacted or cemented. Layers of tightly packed, but uncemented, sand and gravel are found in the subsurface in western Kansas. This layer of sand, gravel, and porous rock is known as the Ogallala Formation.
Most of the Ogallala Formation is underground, but in some places the porous rock crops out. Elephant Rock in Decatur County is an outcrop of the Ogallala Formation. Other good examples of Ogallala outcrops can be found in the bluff area around Scott County State Lake.
Figure 43. Elephant Rock in Decatur County was formed from an outcrop of porous rock from the Ogallala Formation.
When it rains in the High Plains, water seeps into the ground and is stored in the Ogallala Formation. Since the region doesn't get much rainfall, people in the area have to rely on this ground water for their water supply. Much of the water in eastern Kansas is taken directly from rivers, but in western Kansas it is often necessary to dig water wells. The ground water also is used by farmers to irrigate their crops.
People originally thought the water from the Ogallala Formation would last forever and pumped water out to be used by cities, industries, and crop irrigation. Geologists began monitoring wells in the area and have recorded fairly steady water-level declines in the Ogallala over the past 20 to 30 years. The sparse rain in the area hasn't replaced the water as fast as people have pumped it. Now we know that if it isn't used carefully, much of the water could be exhausted.
Kansas has no geological features that attract hordes of tourists. But the changes that have taken place in Kansas over time, and the results of those changes, are still amazing.
Geologists, paleontologists, and other scientists have studied the rocks, minerals, fossils, landforms, water, and other natural resources for many years and have made many exciting discoveries. They have found evidence of ancient seas, glaciers, giant dust storms, buried hills and valleys, giant flying and swimming reptiles, dinosaurs, camels, woolly mammoths, and much more.
New discoveries continually add to our knowledge of the Earth around and beneath us. Scientists have found that the Earth is a very complex place. After years of exploration, there is still a lot to learn. Even Kansas, with its seemingly simple flat lands and gentle rolling hills, has a wealth of hidden information.