An investigation begun in 1937 by the United States and the Oklahoma Geological Surveys, has shown that the depth to the water table in the Oklahoma Panhandle ranges from less than 25 feet in parts of major valleys to about 300 feet in parts of the uplands. In 8 upland areas the depth is between 50 and 100 feet. The thickness of the zone of saturation differs widely in these areas, the most promising of which totals about 80 square miles in northeastern Texas County. The pervious sands and gravels of the Ogallala formation, of Pliocene age, furnish most of the ground water, and one well yielding 960 gallons a minute from them has been used for irrigation since 1937. The formation ranges from less than 100 to more than 500 feet thick, the differences being due to relief on the pre-Ogallala topography and to post-Ogallala erosion. The alluvium is also an important source of water, as are the Dakota and Cheyenne sandstones, of Cretaceous age. A few wells yield water of variable quality from Jurassic and Triassic rocks, and many wells in the valleys of the eastern part of the area yield small supplies of highly mineralized water from Permian red beds.