Open-File Report 2009-1051
Time-domain electromagnetic (TEM) soundings were made near Great Sand Dunes National Park and Preserve in the San Luis Valley of southern Colorado to obtain subsurface information of use to hydrologic modeling. Seventeen soundings were made to the east and north of the sand dunes. Using a small loop TEM system, maximum exploration depths of about 75 to 150 m were obtained. In general, layered earth interpretations of the data found that resistivity decreases with depth. Comparison of soundings with geologic logs from nearby wells found that zones logged as having increased clay content usually corresponded with a significant resistivity decrease in the TEM determined model. This result supports the use of TEM soundings to map the location of the top of the clay unit deposited at the bottom of the ancient Lake Alamosa that filled the San Luis Valley from Pliocene to middle Pleistocene time.
First posted April 13, 2009
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Fitterman, D.V., de Sozua Filho, O.A., 2009, Transient electromagnetic soundings near Great Sand Dunes National Park and Preserve, San Luis Valley (2006 Field Season), Colorado: U.S. Geological Survey Open-File Report 2009-1051
Description of Transient Electromagnetic Soundings
Sounding Locations and Elevation
Data Quality and Averaging Procedure
Inversion of Transient Electromagnetic Measurements
Interpretation of Results
Appendix A Description of TEM Data Processing
Appendix B Voltage Units and Apparent Resistivity
Appendix C Description of TEM Data Files
Appendix D TEM Sounding Report Files
Appendix E TEM Sounding Plots and Descriptions