Samples of sandstones and shales were analysed by instrumental neutron activation analysis for a total of 30 elements. Three irradiation and five counting periods wer employed. Solutions and National Bureau of Standards Reference Materials wer used for comparison. The samples were obtained from drill cuttings (with a few core samples) from drillings in the Salton Sea geothermal field of California. These determinations form part of a major study to elemental variation as a function of mineral variation as depth and temperature in the well vary. The overall goal is to examine mineral alteration and/or element migration under typical geothermal conditions. The techniques involve typical compromises between maximizing precision for individual element determinations and the amount of time and effort that can be expended, as it is desired to examine large numbers of samples. With the limitations imposed by the reactor flux ailable at the U. C. Irvine TRIGA reactor, the detectors available, and time factors, most precisions are acceptable for geological comparison purposes. Some additional measurements wer made by delayed-neutron counting methods to compare with uranium determinations made by conventional instrumental neutron activation analysis methods.