The Ogallala aquifer of Texas historically has been known for elevated fluoride concentration, with many areas in excess of 4 milligrams per liter. In addition, on a regional scale, silica concentrations are also somewhat elevated, with concentrations averaging in the 40 to 50 milligrams per liter range. This aquifer provides a unique geochemical and epidemiological study area because it is completely contained within the High Plains physiographic province.