Following the Mw = 6.5 San Simeon, California, earthquake on December 22, 2003, USGS stream gauges documented two consecutive increases in streamflow in the Salinas River and Lopez Creek in the central Coast Ranges. The first increase occurred within 15 minutes after the earthquake and lasted about an hour; the second one occurred a few hours later and lasted much longer. Evidence and simulation suggest that these increases were caused by earthquake-induced rupturing of pressurized hydrothermal reservoirs.