Earthquakes in the United States for the month of November 1997. ESRI live earthquake website (http://www.esri.com/base/data/online/earthquake/index.html). Notice the concentration of earthquakes in California.

The area surrounding Mammath Lakes has been experiencing thousands of small earthquakes during the last few weeks, so we will concentrate our investigation there. Approximately three quarters of a million years ago, this area was the site of a very violent volcanic eruption, during which time the Long Valley Caldera was created.

As we zoom in closer to the Mammath Lakes region, the large number of earthquakes occurring in that region becomes apparent.

Zooming in even closer, you can see that the earthquakes are concentrated in a relatively small area.