GEOMORPHIC ANALYSIS OF TECTONIC PROVINCES BASED ON SURFICIAL GEOLOGIC MAP DATABASES, EASTERN MOJAVE DESERT

New geologic mapping of Quaternary deposits and simplified bedrock lithology in the eastern Mojave Desert provides a GIS database for analyzing geomorphic systems. We explored 1:100,000-scale data of parts of the Basin and Range, eastern Mojave, and Eastern California shear zone tectonic provinces to examine geomorphic parameters that correlate with tectonic activity. To quantify topographic variations between tectonically active and quiescent provinces, we calculated surface roughness, mountain front sinuosity, and drainage density. The tectonically active Eastern California shear zone and Basin and Range provinces have maximum surface roughness ratios (defined as the ratio of plan area to true area) 4 to 5 times greater than the tectonically inactive eastern Mojave and Las Vegas Valley. Additionally, DEM-derived slope and aspect data indicate differences among the provinces in terms of piedmont widths, symmetry, and slope. The landscape position of alluvial and groundwater deposits were quantified to demonstrate relative influences of climate and tectonics. As expected, middle Pleistocene alluvial deposits lie in proximal fan positions but their position varies among provinces.

Mountain front sinuosity assesses the influence of tectonic uplift, assuming that tectonically inactive mountain fronts will be more embayed than those of similar lithology undergoing recent tectonic uplift. Sinuosity is defined as the ratio of the length of the mountain front to the straight-line distance between the endpoints of the mountain front. Calculations for characteristic mountain fronts in each of the provinces show that tectonically active provinces have statistically lower mean sinuosity values than less tectonically active provinces. These results may be refined by addressing under-representation of mountain fronts in the mapped area, or by subdividing the mountain fronts based on lithologic character.

Drainage density (Dd, defined as length of channel per unit area, a function of climate, surface properties, and tectonics) was used to measure landscape dissection. Dd was calculated as the inverse of twice the distance to channel using DEMs. Maps of Dd indicate variations among tectonic provinces that probably reflect tectonically influenced geomorphic characteristics of dissection.