Tectonic Geomorphology of the Sierra Nacimiento: Traditional and New Techniques in Assessing Long‐Term Landscape Evolution in the Southern Rocky Mountains

Abstract

Mountain front morphology is used to assess the relative role that tectonic and/or climatic processes play in shaping topography in the Sierra Nacimiento, a Laramide uplift in northern New Mexico. Rates of fault offset (0.013 mm/yr) in the adjacent Rio Grande rift are an order of magnitude slower than locally calculated rates of fluvial incision (0.17 mm/year) and regional denudation (0.12–0.84 mm/yr). Thus, although Quaternary fault offset may be locally important in increasing relief and driving fluvial incision, it is subordinate to high rates of regional fluvial exhumation in defining the geomorphic expression of the mountain front. The geomorphic youthfulness of the Sierra Nacimiento landscape is attributed to recent and rapid erosional exhumation facilitated by fluvial processes as streams have become increasingly well adjusted to structure and rock‐type. Repeated capture events throughout the Quaternary have increased drainage basin area as stream networks have become well integrated. To test the idea that epeirogenic uplift, perhaps associated with Quaternary volcanism of the Valles caldera and the Jemez Lineament, may have driven the increase in regional denudation, large‐scale GIS‐based analysis of digital topography (DEM) was used for the Taos range, the Colorado Front Range, and the Sierra Nacimiento. The GIS analysis also allowed us to estimate the relative residence time of topographic forms in the Southern Rocky Mountain landscape. The GIS results support our conclusions that drainage integration and accelerated denudation rates in the middle to late Pleistocene have played the dominant role in defining the characteristic relief and geomorphic expression of Sierra Nacimiento and related Lara‐mide uplifts.