A magnitude 4.2 earthquake rattled Sonoma and Lake counties at 3:47 a.m. Pacific time on Thursday, May 8, 2026, shaking residents awake across a wide swath of the northern San Francisco Bay Area. The U.S. Geological Survey confirmed the epicenter 4 kilometers east of Cobb, California, placing it squarely inside The Geysers, the world’s largest geothermal field and one of the most seismically active patches of ground in the state.
The quake struck at shallow depth, which means the energy had less rock to travel through before reaching the surface. That translated into sharper, more noticeable jolts for communities within about 50 kilometers of the epicenter, including Santa Rosa (roughly 39 km to the southwest), Healdsburg, Cloverdale, and the small towns ringing Clear Lake.
What the USGS data shows
The agency’s automated ShakeMap product estimated light to moderate shaking (intensity III to IV on the Modified Mercalli scale) across the felt region. At those levels, people indoors typically notice swinging fixtures and rattling dishes, but structural damage is rare. The USGS also activated its Did You Feel It? program, which collects public reports and converts them into community-level intensity estimates. Because the quake hit before dawn, early response numbers may undercount the true felt area; reports tend to climb throughout the morning as more people wake up and check the news.
Waveform recordings from the Northern California Seismic Network underpin the USGS location and magnitude calculations. Those raw seismograms allow analysts to refine the depth, origin time, and focal mechanism of the event over the hours and days that follow, so the published magnitude could shift slightly as more data is reviewed…