Abstract More than a decade has passed since the earliest geologic reports relating to proposed nuclear reactor sites were completed. Then, guidelines were few, and the safety analysis was brief and general. Today, the geologic portions of Preliminary Safety Analysis Reports (PSARs) and Final Safety Analysis Reports (FSARs) are by requirement more complex. Through the cooperative efforts of the Nuclear Regulatory Commission (NRC; formerly the Atomic Energy Commission) and the American Nuclear Society, specific seismic and geologic criteria for nuclear plant sites and a standard format for the presentation of data have been developed. These standards and requirements have shifted the emphasis of power plant siting from one that considered mainly the economics of the site and its proximity to the service area, as in the case of fossil fuel plants, to one that gives important consideration to the geologic suitability of the site. Geologic studies of nuclear plant sites require a comprehensive exposition of the areal and structural geology, hydrology, and seismicity in addition to site exploration of engineering-geology and foundation characteristics, which are the major concerns in geologic studies for fossil fuel plants. For each site a design acceleration (g) value must be derived from studies of local and regional geology and seismicity. In recent years these studies have resulted in more comprehensive as well as more voluminous reports. Such an evolution has its problems. Reports commonly lack coherence and integration of subsurface and surface geology, particularly in the case of geophysical data. Cross reference is hampered when illustrations differ in scale. The geologic safety analysis should include more basic, original field investigations of the areal geology of the site and the surrounding area.