RED HILL, NEW MEXICO MONOGENETIC VOLCANIC FIELD: VARIATIONS IN VENT MORPHOLOGY

Located in Catron County on the western border of New Mexico, the Red Hill volcanic field lies along the Jemez structural alignment between the Taylor (Arizona) Field to the west and the Bandera field to the northeast. Quaternary and Tertiary lava flows rest on Cretaceous strata. Quaternary faulting produced N 28° E-trending scarps and provided pathways for ascending gases and magmas. Quaternary volcanism produced a mix of land forms including maars, cinder cones, cinder mounds, rimless depressions, and lava flows interspersed between older basalt-capped mesas. Twenty-two vents are identified as cinder cones or cinder mounds. Fifteen vents are identified as maars or alterations of maars. Maar craters range from nearly 2.0-0.50 km in diameter. Interior relief ranges from 86-18 m. All but one are roughly circular depressions in the surface. Most craters are surrounded by raised rims composed of loosely consolidated, lithic tuffs (base surge and air fall). Some maars contain inter-crater cinder cones and cinder mounds. Two extremes of post-maar alteration are observed in the area. At one extreme, the maar craters are reduced by erosion to wide, shallow, rimless depressions. At the other extreme, an internal cone grew to such a large size as to nearly bury the maar.