Geology of Sierra Alta quadrangle, Dona Ana County, New Mexico

Rocks exposed in the Sierra Alta quadrangle range in age from Permian to Holocene. Permian Hueco Limestone and Abo Sandstone, deformed during the Laramide, are unconformably overlain by a tripartite sequence of less deformed Tertiary volcanic and volcaniclastic strata. Basal andesitic epiclastic rocks are referred to the Palm Park Formation (late Eocene). Middle rhyolitic ash-flow tuffs and epiclastic strata of the Bell Top Formation (Oligocene) partly fill the Goodsight-Cedar Hills volcano-tectonic depression; numerous vent structures (Cedar Hills vent zone) form the eastern margin of the depression. The upper Uvas Basaltic Andesite (26 m.y.) consists of a shield-like accumulation of flows centered on the axis of the depression. The Sierra de las Uvas dome and the Sierro Kemado sag probably resulted from resurgent uplift of the central part of the volcanic pile following eruption of the basaltic andesite.The volcano-tectonic depression appears to be a precursor to Rio Grande rift structure in this area. Miocene to Pliocene faults superimposed across the depression are, in part: 1) reactivated subsidence fractures, 2) new, throughgoing faults, and 3) fractures whose pattern is governed by the geometry of the Sierra de las Uvas dome and its adjoining synclines. Bolson deposits of the lower Santa Fe Group fill Miocene basins.Fluvial (ancestral Rio Grande) and piedmont-slope deposits of the Camp Rice Formation represent latest stages in the aggradation of late Tertiary fault basins. Middle to late Quaternary evolution of the present landscape was characterized by three major episodes of valley incision by the Rio Grande and its tributaries. Each episode was followed by intervals of partial backfilling and subsequent periods of stability of valley base levels.