The electrical resistivity of rock cores recovered from the Cajon Pass hole ranged from 5 to 46 k&OHgr;-m, as determined at pressures to 200 MPa and frequencies of 10--30,000 Hz. The resistivities of cores recovered from depths less than 1.6 km are about one-order of magnitude greater than the in situ resistivity as measured by the deep Laterolog. However, at greater depths, the laboratory resistivities and those from the deep Laterolog are in fairly good agreement. The results suggest that at these depths the fractures, whether mineralized or fluid-filled, are no longer well interconnected. ¿ American Geophysical Uion 1988