GEOLOGY OF ISLETA RESERVATION, CENTRAL NEW MEXICO

The Isleta Reservation is located south of Albuquerque, New Mexico and extends from the Rio Puerco eastward to the Manzano and Manzanita Mountains. The study area comprises twelve 7.5-minute quadrangles that have been mapped at 1:24,000 scale and complied at 1:50,000 scale.

Pre-Santa Fe Group rocks include Proterozoic metamorphic and plutonic rocks, upper Paleozoic, Mesozoic, and Paleogene strata. The late Paleogene-Neogene Santa Fe Group is divided into a lower unit, the Popotosa Formation, and upper unit. The upper Santa Fe Group is divided into three major facies: western-basin fluvial lithofacies containing deposits of the ancestral Rio Puerco; central-basin fluvial lithofacies containing deposits of the ancestral Rio Grande axial-fluvial system; and eastern-basin piedmont lithofacies derived from the adjacent rift-border uplifts of the southern Sandia, Manzanita and Manzano Mountains. Six basaltic volcanic fields interfinger with upper Santa Fe Group deposits; Black Mesa (2.68 Ma), Isleta (2.73-2.79 Ma), Cat Mesa (3 Ma), El Cerro Tome (3.4 Ma), Los Lunas (1.14 and 3.91 Ma), and Wind Mesa (4 Ma).

Dominantly north-trending faults crosscut older northwest-trending faults that segmented the Santa Fe Group into multiple sub-basins. The western basin is characterized by numerous normal faults with generally down-to-the-east movement; several shorter, down-to-the west faults are antithetic to the dominant western margin faults and bound local horsts and grabens. The eastern basin is defined by numerous down-to-the-west normal faults. Results of this study do not support the presence of the inferred north-trending Rio Grande fault of Russell and Snelson (1994). We interpret an older (late Oligocene(?)-Miocene) northwest-trending fault-bounded depression between the southwestern margin of the northwest-trending Mountainview prong and the Isleta Pueblo graben that we call the Mountainview fault zone.