Geomorphic analysis of scarps along the eastern border of the Valle Vidal, north-central New Mexico
Christopher M. Menges and James Walker
A complex 3- to 5-km-long zone of west-facing topographic scarps follows the base of the steep bedrock escarpment on the northeastern border of the Valle Vidal in the eastern Sangre de Cristo Mountains of north-central New Mexico. Several possible origins may be proposed for the scarps, including: ( I) surface rupture on the basin-bounding fault, (2) semi-coherent mass-wasting phenomena (e.g., earthflows or rotational slumps), or (3) relict solifluction lobes formed during earlier full-glacial climates. Several characteristics, including the general linearity of the zone, continuity across multiple drainages and topographic position in the basin, favor a tectonic origin for the scarps. The scarps occur in surficial deposits, including thin colluvial mantles on weathered bedrock and (or) steeply sloping (10 0-20°) debris fans, ranging in age from late Pleistocene to late(?) Holocene, based on soil-profile development. Topographic field profiles indicate that individual scarps vary in height from 2.9 m to 22.5 m with maximum slope angles of 21.5 0-31°. Graphical reconstructions from these profiles suggest possible vertical surface offsets of 1.9 m to 9 m, with the larger sizes probably related to composite (multiple-rupture) scarps. Linear regressions of log-scarp-height–maximum-slope-angle data suggest a middle to late Holocene age for the most recent rupture on these scarps; a similar rupture age is estimated from diffusion analysis of a small, probable single-event scarp. The age and size of these scarps indicate that significant Quaternary faulting and seismicity may be present in some of the intramontane valleys to the east of the central rift basins in northern New Mexico.
- Menges, Christopher M.; Walker, James, 1990, Geomorphic analysis of scarps along the eastern border of the Valle Vidal, north-central New Mexico, in: Tectonic development of the southern Sangre de Cristo Mountains, New Mexico, Bauer, Paul W.; Lucas, Spencer G.; Mawer, Christopher K.; McIntosh, William C., New Mexico Geological Society, Guidebook, 41st Field Conference, pp. 431-438.