The hydrogeology of the Permian Yeso Formation within the upper Rio Hondo Basin and the eastern Mescalero Apache Indian Reservation, Lincoln and Otero Counties, New Mexico
— Maryann. Wasiolek

The Yeso Formation of late Early Permian (Leonardian) age is the principal aquifer of the western Pecos slope. Within the area of the upper Rio Hondo basin and the eastern part of the Mescalero Apache Indian Reservation the vertical thickness of the formation ranges from a few feet to nearly 1700 ft. Both the thickness and the nature of the formation were greatly affected by the continued expression of the ancient Pedernal high during the period of deposition. The upper two-thirds of the Yeso is composed mainly of interbedded limestone, dolomite, siltstone and silty sandstone, but it becomes less dominated by carbonates and more evaporitic with depth. The lower part of the formation is characterized by layers of gypsum and anhydrite interbedded with siltstone. Ground-water movement within the aquifer is eastward under water-table conditions. Flow is preferentially through fractured and dissolved limestone beds, although persistent thin beds of sandstone may also transmit ground water. In deep aquifer tests on the Mescalero Apache Indian Reservation, the hydraulic conductivity of the aquifer strata tests at 7.0 E-08 m/sec (0.02 ft/day) for unfractured siltstone and gypsum beds. The average hydraulic conductivity ranged from 2.1 E-06 to 5.3 E-06 m/sec (0.6 to 1.5 ft/day). These and other aquifer tests indicate that limestone beds with secondary permeability may be characterized by hydraulic conductivities which are several orders of magnitude higher than those of unfractured siltstone beds.