Origin of castiles on the Gypsum Plain of Texas and New Mexico
— Douglas W. Kirkland and Robert Evans

The Gypsum Plain, an expanse of outcropping gypsum of Late Permian (Ochoan) Castile and Salado Formations, occupies an area of about 2600 km 2 in southeastern New Mexico and West Texas (fig. 1). On the west the Gypsum Plain is bounded chiefly by the Delaware Mountains and on the east by the Rustler Hills (fig. 1). The low relief of the Gypsum Plain displays features of solution and subsidence (sinks, caves and troughs) and is interrupted by prominences of limestones (fig. 2)—the castiles of Adams (1944) or the buttes of Kirkland and Evans (1976).