Earthquake epicenters recorded between June 1 and September 16 at Long Valley Caldera, California, as part of the Mammoth 97 Seismic experiment. Approximately 1,600 earthquakes are shown here; the number of smaller events not detected by the permanent seismic network at Long Valley Caldera is probably ten times more. The largest earthquake for this period was a magnitude 3.5 event on July 17.