If you've looked out of an airplane window while flying over the central or western United States, chances are you saw lot of the "little" circles on the ground. They are center-pivot irrigation circles. In these systems, water is pumped from an well in the center of the circle from an underground aquifer and distributed through a giant sprinkler hundreds of yards long that pivots around a central point. In the past, large spray guns were used to shoot water through the air onto the crops, but nowadays more efficient low-pressure sprinklers hang from the pipes to spray water close to the ground, which is a much more efficient method that saves water. This NASA satellite photo shows crop circles in Finney County, Kansas. These irrigated plots are 800 and 1,600 meters in diameter (0.5 and 1 mile). This area utilizes irrigation water from the Ogallala aquifer, that underlies an area from Wyoming to Texas. More information on the Ogallala aquifer, which is part of the High Plains Aquifer System, may be found here:

ne.water.usgs.gov/ogw/hpwlms/physsett.html