Geological and geophysical considerations applicable to radio propagation through the rock strata of the basement complex are presented. Information on electrical characteristics of rocks, based on laboratory measurements on samples, is shown to be misleading because in situ conditions are very difficult to analyze and reproduce. The complexity of the basement geology adds to the difficulty of predicting in situ rock characteristics pertinent to radio propagation. F and fracturing of the strata, variegated rock types, and the anisotropy of rock resistivity cause the actual propagation path loss to be vastly different from that predicted on the basis of a simple geological model. This conclusion is supported by the available experimental data. Deep resistivity measurements made from the surface indicate that basement strata will have resistivities of the order of 1000 to 10,000 ohm-meters over most of the United States.