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Bulletin 58—Geology of Dog Springs Quadrangle, New Mexico

By D. B. Givens, 1957, 40 pp, 1 plate, 1 index.

Dog Springs quadrangle lies within the Gallinas Mountains of west-central NM, approximately 30 mi northwest of the town of Magdalena. The oldest rocks that crop out in the quadrangle are Triassic continental Chinle shales. Above the Chinle are the following sedimentary formations: Dakota, nonmarine Upper Cretaceous sandstone; Mancos, marine Upper Cretaceous shale; Mesaverde, nonmarine and marine Upper Cretaceous sandstone; and the Baca, Eocene continental arkose. Overlying the Baca Formation are the quartz latite tuffs of the Spears Ranch member and the rhyolite tuffs of the Hells Mesa Member of the Datil Formation. Resting on the Datil Formation are the Santa Fe gravels and basalts; these in turn, are overlain by recent gravels. Intruded into the section are basalt plugs and dikes of Pleistocene age.      

Structurally the area is characterized by broad-scale northwest trending, southeast plunging folds of Eocene age, and broad-scale, northeast trending folds of Pleistocene age. Several north-trending normal faults of considerable displacement cut the sedimentary and volcanic rocks of the area. Physiographic evidence suggest that the San Augustine Plains were once a topographic high and the source of the Santa Fe gravels.

The Gallinas Mountains are an east-west trending range which passes through the lower one-third of Dog Springs quadrangle. The highest point of the range is Gallinas Peak. From this promontory almost the entire quadrangle is visible. The crest of the Gallinas forms a dividing line in the physiography of the region. To the south of the crest the rock surface slopes gently downward and passes beneath the Bolson deposits of the San Augustin Plains. The southern mountain slopes are dissected by youthful canyons. To the north the physiography takes on a wholly different aspect. The Gallinas drop abruptly from their crest, in cliffs up to 600 ft in height, into a series of sharply dissected, round-topped hills and ridges, some of which have pinnacles on their summits. These hills then descend rapidly as a series of declivities, some as much as 300 ft in height, to a gentle slope which terminates at the Rio Salado. Low sandstone cuestas extend through the gravels of the valley of the Rio Salado. The northern one-third of the quadrangle is characterized by high, basalt-capped mesas, all of which have volcanic necks at their southern tips. The highest of these necks is D Cross Mountain.

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