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Aeromagnetic Survey of Medina and Uvalde Counties, Texas

By David V. Smith, Bruce D. Smith, and Pat L. Hill

Map Information

The map shows natural variations in the Earth's magnetic field near the ground surface. Such variations, or anomalies, are caused by the uneven distribution of magnetic rocks in the subsurface, primarily from igneous sources. Broad variations generally indicate deep-seated basement rocks and igneous intrusive bodies, whereas small, distinct features indicate shallow igneous rocks, such as volcanic laccoliths and plugs. Magnetic field intensity is displayed using a color scale where shades of blue represent low values, and shades of red and lavender represent high values

The map is generated from a rectangular grid that contains data (data processing details here) collected in an aeromagnetic survey completed in 2001 by Spectra Exploration Geoscience Corporation, under contract to the USGS. The data from this survey are high resolution and high quality. An index map shows the geographic location of the survey, which is located west of San Antonio, Texas. The contractor's report (129KB PDF file here) gives detailed specifications for the aeromagnetic survey.

Acknowledgements

This aeromagnetic survey was supported by the Mineral Resource and National Cooperative Geologic Mapping Programs of the USGS, and by the San Antonio Water System (SAWS).