A geophysical exploration system utilizes a single conductor cable connected to a current source. This cable contains a number of earth probes coupled to it at spaced points with addressable switching units. In order to the probes inject current into the earth, the switching units are activated in sequence. At locations spaced from the probes the resistivity is measured and recorded for each injection. Resistivity measurements are compared with anomaly models to find a match of patterns, indicating the presence, size, and location of an anomaly.