New Mexico Geological Society Annual Spring Meeting — Abstracts

The Abeytas Quadrangle covers the junction between the Rio Puerco and Rio Grande at the south end of the Albuquerque Basin. Rift-related Plio-Pleistocene basin fill of the Santa Fe Group exposed in the Abeytas Quadrangle came from four sources: the Rio Grande from the north, Abo Pass and Los Pinos uplift to the southeast, Rio Puerco and Rio San Jose from the northwest, and Rio Salado from the southwest. Quaternary post-basin-fill episodic entrenchment of the Rio Grande is shown by three major fluvial terraces preserved on the eastern side of the Rio Grande valley and by a correlative high terrace along the Rio Puerco. Local tributaries formed several inset levels of alluvial terraces in response to climate change and episodic downcutting and lateral planation by the Rio Grande. Thick valley fills of the Rio Grande and Rio Puerco are the hallmark of both major streams in this area. Several north-trending Quaternary faults displace deposits from less than one to more than 10 m. The Sabinal fault dies out southward in a monoclinal structure. The West Ceja fault dies out southward as the hanging wall becomes a ramp and joins the footwall at the same elevation. The newly-discovered Contreras Cemetery fault offsets the lowest Rio Grande terrace by 2 to more than 4 m and was active at the time of terrace deposition.