Circular 147—Geology of Doña Ana Mountains, New Mexico

By W. R. Seager, F. E. Kottlowski, and J. W. Hawley, 1976, 35 pp., 2 tables, 13 figs., 4 appendices, 3 sheets.

Describes physiography, stratigraphy, structural geology, and economic geology of the mountains located in central Doña Ana County, a few miles north of Las Cruces. The Doña Ana Mountains are located in central Doña Ana County a few mi north of Las Cruces. The area mapped includes parts of the Las Cruces and San Diego Mountain 15-min quadrangles. Access to the mountain range is by jeep roads beginning at Doña Ana and Hill, and from the graded Jornada road that traverses the Jornada del Muerto just east of the map. One jeep road follows Wagner Canyon through the northern part of the range, while another follows Cleofas Canyon, and still another traverses the unnamed east-west canyon just south of Cleofas Canyon. The latter two roads join near Dagger Flat and continue eastward across Dagger Flat. Access to the southern front of the range is furnished by the jeep road from Doña Ana.

Physiographically, the mountain range may be divided into three sections. North of Wagner Canyon low limestone ridges, hogbacks, and cuestas are surmounted by a group of high monzonite peaks, named Summerford Mountain. The steep, narrow mountain, 1,300 ft high, rises abruptly above the desert and dominates the surrounding landscape. It and the adjacent pedimented monzonite are carved from a laccolith intrusive into the limestone ridges. The central part of the range between Wagner Canyon and the Red Hills-Dagger Flat area comprises a maze of low rounded hills containing entrenched arroyo systems. The hills are largely developed on an andesite stock and associated volcaniclastic strata of Eocene age. The southern one-third of the range is carved largely from Oligocene intrusive rocks and ash-flow tuffs that formed within a major cauldron complex, now only partly exposed and deeply eroded. Ash-flow tuffs that erupted in and filled the cauldron form low dissected hills as well as narrow, sharp, high ridges. Pyramidal peaks that surmount the lower hills and ridges are developed on monzonite porphyry and related dike rocks. The highest of these peaks, Doña Ana Peak, altitude 5,829 ft, rises about 1,500 ft above the surrounding Bolson plains, and is about 2,000 ft above the flood plain of the Rio Grande. Cliffs or steep slopes hundreds of ft high have developed locally along joint sets in the monzonite. One group of monzonite peaks and ridges nearly surrounds a topographic and structural basin named Dagger Flat. The basin appears to be the modern physiographic expression of a small cauldron nested within the larger cauldron, and the surrounding monzonite may represent the deeply eroded roots of a ring dike or cone sheet system.

Footslopes that extend away from the base of the range, especially those in the southern section of the mountains, are largely pediments 1 to 2 mi wide dissected by entrenched arroyo systems tributary to the Rio Grande; on the eastern side of the range they are nearly undissected. Variable thicknesses of Quaternary fan gravels mantle the pediment, but locally extensive areas of bedrock are exposed, even along the eastern side of the range where Rio Grande tributary drainage has not yet established itself. Few hills rise above the level of the erosion surface. The extensive development of the pediment in the Doña Ana Mountains is in contrast to other nearby ranges which show little or no pediment development, especially the Robledo, Cedar Hills, and Tonuco uplifts.