The story of a crucial, dwindling natural resource: an invisible ocean of fresh water under the Great Plains.The Ogallala aquifer contains enough water to fill Lake Erie not once but nine times over, and it stretches from Texas to South Dakota, from Colorado almost to Nebraska. Every year, five trillion gallons are pumped out for irrigation, and if the aquifer went dry (or, more accurately, when it goes dry), $20 billion worth of food and fiber would disappear practically overnight.In this lively, carefully researched narrative, William Ashworth tells the history of the Ogallala, from its formation after the retreat of the glaciers through to its uncertain future. The most dramatic part of that history deals with efforts to exploit the hidden waters, starting with the primitive wells of long-vanished tribes, through the invention of the center-pivot sprinkler, and on to ever more sophisticated extraction technologies. This is an account of people as well as water, with many vignettes of those living in the shadow of the Ogallala's decline and ultimate demise.