Stratigraphy of the San Andres Mountains in south-central New Mexico
— Frank E. Kottlowski

The San Andres Mountains, in the central part of southern New Mexico, offer almost unexcelled outcrops for strati-graphic and structural studies. Sedimentary rocks from Precambrian to early Tertiary age are well exposed along the entire 85-mile north-south length of the range and in the major east-west canyons. The range forms a flat north-south arc concave toward the east (Fig. 1) terminated on the north by Mockingbird Gap (altitude 5,260 ft) and on the south side by San Agustin Pass (5,719 ft). San Andres Peak, in the south part of the range, is 8,239 ft above sea level and more than 4,000 ft above the adjoining Tularosa Basin to the east; Salinas Peak near the north end of the range, at an altitude of 8,958 ft, is the highest point. A typical profile cross-section shows an east-facing scarp overlooking the Tularosa Basin and capped by Middle Pennsylvanian limestone that form high ridges at altitudes of 7,000 to 8,000 ft; to the west of this crest of the range are a series of lower west-dipping mesas and north-south strike valleys that have been cut in Upper Pennsylvanian shalt' beds and in Hueco, Abo and Yeso strata. The west margin of the range consists of a prominent cuesta capped by San Andres Limestone, which dips westward beneath the gravel-covered surface of Jornada del Muerto.

About 14 large canyons enter the Tularosa Basin from the range but none have cut completely through to Jornada del Muerto. The drainage divide is near the west edge of the mountains reflecting the lower elevations of the Tularosa Basin as compared to Jornada del Muerto. Along parallels of latitude the lowest points of the Tularosa Basin are 400 to 500 ft below the lowest points of the Jornada. The major canyons are east-west gashes cut perpendicular to the strike, in many places along fault zones, but most of the tributary canyons are north-south strike valleys eroded in less resistant beds such as the Upper Pennsylvanian and Yeso rocks.

At present, and for the foreseeable future, the San Andres Mountains are entirely within White Sands Missile Range and are off bounds to all except federal government personnel. Short escorted trips have been allowed for scientific purposes. The only maintained road through the mountain, other than at Mockingbird Gap and over San Agustin Pass, is the extension of New Mexico Road 52 from Tularosa to Truth or Consequences by way of Rhodes Canyon, Rhodes Pass and Engle.