The Southwestern Boundary of the Southern High Plains: The Mescalero Ridge and the Red Bed Ridge

ABSTRACT The Southern High Plains are bounded on the west through the southern half of eastern New Mexico by the roughly linear Mescalero Ridge, an erosional, well-defined, westward-facing near vertical escarpment, up to 150 ft (45.7 m) in height, capped by the 10 to 40 ft (3 to 12.2 m) thick caprock caliche. As it approaches the Texas state line, it loses linearity and much of its topographic definition, developing numerous re-entrants and exhibiting significant erosional cuts and gullying. Over this section, it is either underlain by or immediately adjacent to a corresponding ridge on the buried Triassic erosional surface termed the red bed ridge, a drainage divide that existed throughout the Cenozoic. The red bed ridge and the overlying Mescalero Ridge continue eastward into Andrews County with the Mescalero Ridge as the topographic drainage divide between the Colorado and Pecos Rivers, turning south and eventually blending into the Cretaceous rocks of the Edwards Plateau in Winkler and Ector Counties. The buried red bed ridge is on the Triassic erosional surface of the upper part of the Dockum Group mudstones, the Cooper Canyon Formation. The red bed ridge appears to be at least partially of structural origin in the vicinity of the Waste Control Specialists facility just east of the New Mexico/Texas state line. A similar anticlinal structure occurs in underlying Permian units over a thickness of several thousand feet. Several commercial facilities have been developed in the state line area with the near-surface proximity of the low permeability Triassic mudstones providing isolation from potable groundwater and reliable waste containment characteristics for hazardous and radioactive wastes.