HIGH RESOLUTION MAGNETIC SURVEY OF A FLUVIAL TERRACE DEPOSIT AND REGIONAL GRAVITY -MAGNETIC SURVEY ALONG HWY 69, HUERFANO COUNTY, COLORADO

As part of a class field trip to southern Colorado, students from New Mexico Highlands University (NMHU) conducted field geophysics experiments and surveying exercises. The class projects involved two parts: a high resolution magnetic survey across a 120x120m area located on an ancient fluvial terrace of the Huerfano River, and a regional gravity-magnetic survey along an 8 km section of Hwy 69. Instrumentation included a Geometrics G-856 Proton Magnetometer, Lacoste-Romberg model G gravimeter, Trimble GeoXT, and Sokkia SET 610 Total Station. The high resolution magnetic survey attempted to identify concentrations of high susceptibility materials interpreted as paleo-fluvial channels in the terrace deposits of the Huerfano River. The students established a grid network at 10 meter spacing using the Sokkia total station and each site was accurately located with the GeoXT and flagged. Each flag was assigned a station number and different crews worked in shifts to complete the grid network. Magnetic survey teams then collected total field measurements at approximately 5 meter increments. Each measurement was recorded into a field notebook and later transferred to an excel spread sheet for processing and contoured in Surfer. Preliminary results reveal a series of high susceptibility areas that are likely buried iron-bearing objects such as pipes and drainage coverts. Filtering the high susceptibility signals revealed a pattern of moderate susceptibility areas that we tentatively interpret as concentrations of magnetic materials in channel fills surrounded by low susceptibility material. The regional gravity and magnetic survey was conducted to identify subsurface anomalies related to Spanish Peak magmatism and the extent of the Sheep Mountain intrusion. Preliminary interpretation of the complete bouguer gravity data reveal a sharp decreasing gradient in the west that steadily increases to the east with low-order features superimposed on this general trend. The regional magnetic data reveal a decrease in intensity from west to east along the profile with low-intensity +/- anomalies superimposed on the regional trend. This study demonstrates that increasing undergraduate student participation in field-based projects is an excellent forum for hands on training in the geological sciences at the undergraduate level.