An aquifer is a formation beneath the surface that is made of porous layers of rock. These rock layers act like sponges, holding water in spaces between grains of rock and in cracks and spaces.
Bedrock is the layer of impenetrable rock beneath the saturated layers. There is sometimes also a less permeable layer of rock above the water-bearing layers. This type of aquifer is called a confined aquifer and is harder to drill. An aquifer is unconfined when this top layer is absent.
The Ogallala Aquifer is mostly an unconfined aquifer made of saturated layers of sand, silt, clay, and gravel. In some places, especially the Texas High Plains, the aquifer contains layers of caliche rock, which is virtually impenetrable. Where these layers are present, the Ogallala is confined.
The Ogallala Aquifer generally lies from 50 to 300 feet below the land surface, varying from region to region. In some places there is actual surface discharge, and in others the depth below surface goes to 500 feet.
The water-saturated thickness of the Ogallala ranges from a few feet in parts of west Texas, to more than 1000 feet in Nebraska and other parts of the northern plains.
N. H. Darton, geologist with the U.S. Geological Survey, conducted surveys of the Great Plains. In 1898, he described the Ogallala Aquifer and named it according to where he first identified it, near Ogallala, Nebraska.
The water in the Ogallala remained largely inaccessible until technological improvements enabled farmers to extract it in the 1930s.
Explore the Ogallala Aquifer! Drag your finger across the screen to rotate the 3D model.
The middle menu provides overlay information. Select the compass icon to view a map above the aquifer showing where it sits in relation to states in the midwestern United States. The arrow icon displays a scale alongside the model with depth (in feet) data. This 3D model is scaled up vertically to more easily show depth. The model would appear nearly as thin as paper otherwise due to the massive size.
The menu on the right provides additional information about the aquifer.