TECTONISM AND TOPOGRAPHIC RESPONSE IN THE SACRAMENTO MOUNTAINS, SOUTH-CENTRAL NEW MEXICO

The Sacramento Mountains and adjacent Tularosa basin comprise an east-dipping tilted half-graben system that forms the easternmost exposure of the Rio Grande rift system at this latitude. While the magnitude and style of recent tectonism in the range remains unquantified, a number of topographic measures indicate recent uplift; rugged relief along the western front where elevations grade as much as 7-13% and local bedrock incision in Tularosa basin catchments.

Hypsometric mean and maximum elevation profiles were created from 10 m DEMs over an area of 140 km x 160 km. Maximum elevations vary longitudinally from over 3600 m in the north to 2500 m in the central region before increasing to 2930 m in the south. Transverse maximum elevations from west to east display steep relief along the western front (>3600 m) and steadily decline eastward to 1500 m. Longitudinal mean elevations average around 1900 m for much of the range. At 32.77° N, the mean elevation steadily decreases southward to 1600 m.

We have begun analyzing longitudinal river profiles along the western slope to evaluate how relief may be controlled by river incision. Data from the Fresnal Creek drainage, represents a non-equilibrium river profile that cuts across the strike of bedrock geology and structure. Changes in slope-drainage area and channel gradient along the Fresnal Creek longitudinal profile indicate deviations from equilibrium. This change may be due to mapped faults; alternatively, it may be correlative to changes in bedrock lithology. Ongoing regional analysis of topography, aerial photographs and field reconnaissance indicates that a number of NW- and NE-trending lineaments and fault systems occur within the range and have influenced relief and bedrock river incision. We speculate that recent uplift and eastward tilting of the range may be accommodated by these faults and that river profiles may record recent uplift where faults have yet to be mapped.