This data set consists of digital aquifer boundaries for the Tillman terrace and alluvial aquifer in southwestern Oklahoma. The Tillman terrace aquifer encompasses the unconsolidated terrace deposits and alluvium associated with the North Fork of the Red River and the Red River in the western half of Tillman County. These sediments consist of discontinuous layers of clay, sandy clay, sand, and gravel. The aquifer extends over an area of 285 square miles and is used for irrigation and domestic purposes. Granite and the Hennessey Formation outcrop in northern parts of the aquifer where alluvial deposits are absent. These outcrops were included as part of the aquifer in a thesis that modeled the ground-water flow in the aquifer.

Most of the aquifer boundary polygons were extracted from a published digital surficial geology data set based on a scale of 1:250,000. One of the lines in the aquifer boundary data set was digitized from a figure in a thesis in which ground-water flow was modeled for the Tillman terrace and alluvial aquifer.