Quaternary Geology of the San Acacia Area, New Mexico

Abstract

At San Acacia the Rio Grande passes through a narrow canyon which separates the southern end of the broad Albuquerque-Belen Valley from the northern end of the Socorro Valley. Los Pinos Mountains lie to the east and the Sierra Ladron to the west. The Socorro Mountains separate the Socorro Valley from the higher Snake Ranch Flats and Magdalena Mountains to the west. Deformation in post-Santa Fe (post-Pliocene?) time produced the present basins and determined the location of the principal highlands and main drainage lines. In general, the mountain blocks are composed of relatively resistant pre-Tertiary rocks and Tertiary volcanic rocks, the lowlands of unconsolidated Tertiary basin deposits. The four pediment remnants present in the area and their projected grades above the present flood plains are: Feet Ortiz (?) pediment..................... 370-400 Tio Bartolo pediment.................. 250 Valle de Parida pediment............... 150 Canada Mariana pediment.............. 50-75 Their origin is discussed briefly. A cut-and-fill terrace at about 100 feet above the present flood plains is found in some places. The probable development by piracy in post-Ortiz time of the Rio Puerco and of the present course of the Rio Salado is discussed. Ancient and modern sand dunes and ventifacts, recent channel incision (arroyo cutting), and caliche on pediment surfaces are briefly mentioned.