Earthquake prediction research in the United States us carried out under the aegis of the National Earthquake Hazards Reduction Act of 1977. One of the objectives of the act is "the implementation in all areas of high or moderate seismic risk, of a system (including personnel and procedures) for predicting damaging earthquakes and for identifying, evaluating, and accurately characterizing seismic hazards." Among the four Federal agencies working under the 1977 act, the U.S Geological Survey (USGS) is responsible for earthquake prediction research and technological implementation. The USGS has adopted a goal that is stated quite simply; predict the time, place, and magnitude of damaging earthquakes. The Parkfield earthquake prediction experiment represents the msot concentrated and visible effor to date to test progress toward this goal.