RELICT TERTIARY PEDIMENT SURFACES IN THE WICHITA MOUNTAINS, SOUTHWEST OKLAHOMA

Digital Elevation Models (DEMs) were used to identify and characterize sub-horizontal topographic surfaces found at high elevations in the Wichita Mountains, Oklahoma.  The extent and form of these topographic surfaces correlate well with the bedrock geology. In the eastern Wichita Mountains, surfaces on the medium-grain Mount Scott Granite are typically gently sloping and have an interior topographic high. Surfaces on the adjacent coarse-grain Quanah Granite are typically horizontal, cover a larger area, and lack interior topographic highs.  These surfaces are common at ~2200 ft (approaching that of the highest peaks) and are currently being dissected. To the west of the Wichita Mountains is the Southern High Plains, a pediment surface underlain by Tertiary sediments of the Ogallala Formation which extended from the Rocky Mountains to the Gulf of Mexico. NAD 27 UTM coordinates and corresponding elevations of the Southern High Plains were extracted from DEMs on 60 meter spacing. Recent topographic surfaces (e.g., sinkholes, streams) were excluded from this data set. The extracted data brackets the Wichita Mountains between the 3833970, and 3863070 northings.  The data was blocked into one kilometer wide strips and plotted on an east-west projection. Logarithmic trend lines were generated for each data set with all R² values exceeding 0.95. Projection of the logarithmic trend lines into the western Wichita Mountains reproduced the elevations of these high surfaces within 10-30 feet of actual elevations. Extension of the model to the eastern Wichita Mountains reproduced the elevations of these surfaces 20-60 feet of expected elevations.  Logarithmic slopes and intercepts from this set of equations were plotted verses the midpoint of their Y range. Then logarithmic regressions were used to combine these equations into a single equation describing the 3D Tertiary erosional surface, Z=[-108107*ln(Y)+1637269]*ln(X)+1352187*ln(Y)-20475324 (Z feet X&Y UTM coordinates).  Evaluating the equation using coordinates from the Wichita Mountains generated values within 60 feet of actual values.  The results of this study suggest sub horizontal surfaces at high elevations in the western and eastern Wichita Mountains are remnants of the paleo-erosional pediment surface developed during Tertiary time.