The Elk Creek basin comprises 584 square miles in Washita, Beckham, and Kiowa Counties. The basin is typical of southwestern Oklahoma with nearly level plains broken by gentle rolling hills and low escarpments, except for the extreme southern part, where seven granite and gabbroic knobs and ridges of the Wichita Mountains protrude. The alluvium averages 40 feet in thickness and is restricted to the flood plain of Elk Creek and its major tributaries. The upper part of the alluvium is predominantly silt and clay. The lower part is predominantly very fine to medium sand. The flood plain is bounded by bedrock of Permian age except in T. 5 N. where it is bounded also by sporadic knobs and ridges composed of Precambrian rocks. Recharge to the alluvium is principally through infiltration of precipitation and surface runoff from adjacent highlands, and through percolation from the Quartermaster Formation in the northern part of the basin. Discharge is principally by seepage into the creek and transpiration by vegetation. Discharge by pumpage is small, principally for domestic and stock supply.
