Solution-subsidence troughs are straight narrow depressions ranging in width from a few hundred feet to 1mile, and in length from about half a mile to 10 miles. The troughs are formed by subsidence of near-surface earth blocks to fill voids dissolved by underground waters moving along subjacent drainage channels parallel to the troughs. Numerous solution-subsidence troughs are developed in the Castile Formation (upper Permian) of the Gypsum Plain in west Texas and southeastern New Mexico where they characteristically have broad relatively flat bottoms, which occupy about two-thirds of the width of the trough. The bottoms are bounded by gentle slopes rising 15–20 feet to narrow straight divides, which stand 2 or 3 feet above the general level of the Gypsum Plain. The troughs trend roughly parallel to the direction of the regional dip, about l°–2° eastward. Displacement and local folding in strata of the Castile formation in and near the troughs are not reflected in the Lamar limestone member of the Bell Canyon Formation (lower Permian), which conformably underlies the Castile. The trends of the underground channels are interpreted as the result of solution along eastward-trending joints parallel to the regional dip. Most of the water that causes the solution is believed to be derived by artesian flow from the mountainous area west of the Gypsum Plain.