Measurements of apparent resistivity and phase derived from the complex surface impedance of radio waves propagating in the ground wave mode at frequencies in the radio navigational aid band (between 257 and 382 kHz) are presented. Areas encompassing between 400 and 800 km2that covered a variety of glacial sediments, land forms, and some crystalline bedrock types were surveyed. The results show that (1) loess was commonly between 20 and 40 ohm m with phases between 50° and 60°, (2) end moraines had a wide dispersion with values generally ranging between 20 and 1000 ohm m and 40° and 80°, (3) metamorphic phyllites and schists were generally between 100 and 3000 ohm m with an average near 1000 ohm m and phases usually well below 45°, and (4) granites were the most resistive at an average value of about 2000 ohm m with the lowest phases averaging 12°. The degree of dispersion in resistivity values reflects the dispersion in grain size, while the average resistivity increases with mean grain size. Dielectric properties are suggested as one cause of the low phases observed over crystalline bedrock. The combination of apparent resistivity and phase data implies that the resistivity measurements are consistent in about 50% of the areas with previous measurements of field strength attenuation performed in the AM broadcast