New Mexico Geological Society Annual Spring Meeting — Abstracts

Detailed quaternary geologic mapping of the Sandia Mountains piedmont, from Las Huertas Creek to Embudito Canyon, provides evidence on the tectonic evolution of the Albuquerque basin during the Quaternary. These results represent both a refmement and a northward extension of earlier work by Lambert (1968). The piedmont can be divided into two significantly different geomorphic regions, separated by the intersection of the Rincon, Placitas and Valley View fault segments. This intersection also forms the western margin of a right-step in the Albuquerque basin. To the north, the piedmont is dominated by laterally extensive, generally northwestward-sloping, gravel-mantled pediment surfaces and strath terraces, associated with major drainages, that originate at the mountain front. To the south, the piedmont is dominated by westward-sloping alluvial fans that interfinger with fluvial gravels of the Rio Grande.

No numerical age-control was established; however, relative age estimates of geomorphic surfaces were made on the basis of soil-profile development, landscape position and surface morphology. Pediment surfaces (up to 73 m above local base level) of the pediment-dominated region range in age from early to late Pleistocene, suggesting that this part of the basin has undergone only minor subsidence since the early Pleistocene. In contrast, alluvial fans to the south are generally much younger, with age estimates ranging from middle Pleistocene through Holocene. The depositional nature of this portion of the piedmont suggests that this area has undergone more rapid and long-term subsidence, punctuated by a maximum basin aggradation event during the middle Pleistocene. A period of pedimentation following this aggradational event implies that basin subsidence decreased. The boundary between pediment-dominated and fandominated piedmont coincides with a right step in the Albuquerque basin, suggesting basin ward, footwall transfer of strain from the Placitas and San Francisco faults during the Quaternary. Faulting observed along the base of Rincon Ridge and within the basin supports ongoing basin subsidence. The lack of Holocene faulting to the north and east of the Rincon fault segment, near del Agua Canyon, suggests that strain may be transferred to buried structures within the basin.