Geologic map of the area southwest of Gilroy showing the epicenter of the May 13, 2002 magnitude 4.9 earthquake. Note that although the epicenter is closest to the Castro fault, the first focal mechanism suggests that the earthquake occurred on a fault inclined from vertical. If this is true, then the earthquake may have been caused by movement on the Sargent fault or Carlyle Hills fault. In terms of the effect on the bedrock, the Sargent fault and the Carnederos fault are more significant than either the Castro or Carlyle Hills faults. (Geologic map from USGS Open-File Report 97-710, topographic base map from USGS Chittenden 7.5' quadrangle)