Quaternary fault system in the Tularosa and Hueco Basins, southern New Mexico and west Texas
— William R. Seager

Many geologists in West Texas and New Mexico are aware of the nearly continuous fault scarps of Quaternary age that border the eastern edge of the Sierra Juarez-Franklin-Organ-San Andres Uplift and western Tularosa and Hueco Basins. Less well-known is the system of comparatively minor faults breaking the surface of the two basins (figs. 1 and 2). These minor faults, which block out a somewhat jumbled array of horsts, grabens and tilted blocks in basin-fill deposits, constitute a swath about 5 to 25 km wide subparallel to the boundary fault of the adjacent uplifts. A major conclusion of this paper is that these faults formed when basin fill warped down in response to localized extension—a pull-apartbeneath the western side of the basins. Although many of the minor faults may be comparatively shallow features, some are not; all have potential for growth as long as movement on the rangeboundary fault of the Franklin-Organ-San Andres Uplift continues.

Some of the scarps were recognized years ago. Sayre and Livingston (1945) identified several scarps and depressions in northeastern El Paso and along the Carlsbad highway (U.S. 62-180) as faults, and showed them on their map. Knowles and Kennedy (1958) subsequently acknowledged the presence of scarps in the Hueco Bolson, agreeing with Sayre and Livingston that they were a product of faulting. Only recently has the extent of the fault swarm become apparent (Woodward and others, 1978). The present study has revealed a still more remarkable array of fault blocks that provide considerable topographic variety to the floors of the western Tularosa and Hueco Basins—bolson floors usually thought of as "flat."