SUB-SUMMIT SURFACES IN THE ROCKY MOUNTAINS: REEVALUATING PAST IDEAS WITH LANDSCAPE DIMENSIONAL ANALYSIS
We use GIS and dimensional analysis as tools to reexamine these surfaces and the questions regarding their origin, age, and subsequent modification. Our approach is to identify the low-relief flat topography within the ranges using factors including the surface derivative, variance, and fractal dimension. Flat topography is then correlated with elevation, relief, lithology, age constraints, and denudation history to test the following hypotheses: 1) the surfaces are re-exhumed disconformities, 2) the surfaces represent the lower glacial limit within the ranges, 3) the surfaces grade to the top of the late Tertiary basin fill, and 4) the surfaces are lithologically controlled.
Preliminary results indicate that there is a positive relationship between the median elevation, average relief and location of these surfaces. There is no correlation with the timing, history and underlying lithology. This suggests that the surfaces were created by either a time transgressive process or multiple processes. Ultimately, understanding the geomorphic development of these surfaces has significant implications as they have been used repeatedly as a datum for delineating the late Cenozoic elevation and erosion history of the Rocky Mountain orogenic plateau.