The performance of ground-penetrating radar (GPR) is dependent upon the electrical conductivity of soils. Soils having high electrical conductivity rapidly attenuate radar energy, restrict penetration depths, and severely limit the effectiveness of GPR. Factors influencing the electrical conductivity of soils include the amount and type of salts in solution and the clay content. A thematic map of the conterminous United States showing the relative suitability of soils for GPR applications has been developed. This map is based on field experience and soil attribute data contained in the State Soil Geographic (STATSGO) database developed by the Natural Resources Conservation Service. Attribute data used to determine the suitability of soils include clay content, electrical conductivity, sodium absorption ratio, and calcium carbonate content. Attribute data were generalized from soil surveys. Each soil attribute was rated and assigned a value ranging from 1 to 10. The most limiting (maximum) indices within depths of 1.0 or 1.25 m. were selected for electrical conductivity, sodium adsorption ratio, calcium carbonate content, and total clay for each soil component. Indices were summed for each soil component and for each map unit. The dominant value was selected as the GPR suitability index for each map unit. The GPR indices are displayed in a graduated color map. This map can be used to assess the relative appropriateness of GPR for soil investigations within comparatively large areas of the conterminous United States.