QUATERNARY MAPPING OF FLUVIAL TERRACE DEPOSITS USING HIGH RESOLUTION MAGNETIC AND SURVEYING TECHNIQUES, HUERFANO COUNTY, COLORADO

As part of GEOL425 Geomorphology class field trip to southern Colorado, students from New Mexico Highlands University (NMHU) conducted a high resolution magnetic survey across a 120m x 120m area located on an ancient fluvial terrace of the Huerfano River and a GPS survey over a 2.0 km2 extent of the terrace. Students developed proficiency with the Geometrics G-856 Proton Magnetometer, Garmin GPSmap 60CSx, and the Sokkia SET 610 Total Station as well as data reduction software. The high resolution magnetic survey attempted to identify concentrations of high susceptibility gravel- and cobble-sized materials related to paleofluvial channels within the terrace. A flagged, X-Y-Z grid network was established at a 10 meter spacing using a Sokkia total station with each site accurately located using a combination of the Garmin 60CSx and the total station; the accuracy of these two methods were critically evaluated in the laboratory. Total magnetic field measurements were collected at each flagged station, these data were recorded into a field notebook, and later transferred to an excel spread sheet for processing. Preliminary results reveal a series of very high susceptibility areas that are likely buried iron-bearing objects such as pipes and drainage culverts. Filtering of the high susceptibility signals reveals a pattern of moderate susceptibility areas that we tentatively interpret as concentrations of magnetic materials, likely point bar gravels surrounded by lower susceptibility overbank deposits. The GPS survey provided data to construct a very detailed topographic map. Students paired-up in teams and divided the survey area into four sections with several hundred data points collected by each team. Each teams data were downloaded and combined into an excel spreadsheet and imported into Surfer 8.0 to generate a series of topographic maps. Based on field mapping of the terrace deposits on the final topographic map, we recognize at least three different fluvial terraces and a decrease in slope angle of each towards the Huerfano River. This study demonstrates that field trips are an excellent forum for developing proficiency in field-based skills, observations, and integrating technology into the geological sciences curriculum at the undergraduate level.