A 6.0 magnitude earthquake hit the Napa Valley early Sunday morning.
Leslie Gordon of the U.S. Geological Survey (USGS) said the South Napa Earthquake struck just before 3:30 a.m. about 10 miles northwest of American Canyon, which is about six miles southwest of Napa.
The USGS said the depth of the earthquake was just less than seven miles, and numerous small aftershocks have occurred since the initial quake. By 7:40 a.m., the USGS said there were more than 30 aftershocks, the largest was a magnitude 3.6.
From the epicenter near Napa Valley, the quake was felt in Sacramento (about 60 miles away), Stockton (about 71 miles away) and Tracy (about 82 miles away).
USGS expert Brad Aagaard said the earthquake and its aftershocks are consistent with what is expected in the region. The earthquake was within a 44-mile-wide set of major faults of the San Andreas Fault system, which forms the boundary between the Pacific and North American tectonic plates, according to the USGS's website.
The USGS's website described the faults the earthquake was near more in-depth:
"The earthquake is located between two major, largely strike-slip fault systems. The Hayward-Rodgers Creek Fault system, which is approximately 7 km (4 miles) west of the site, generated damaging earthquakes in 1868 and probably in 1898. The Concord-Green Valley Fault system, which is 12 km (7 miles) east of the site, produced a M5.5 earthquake in 1954; while it has not generated a large historical event, there is strong evidence for recent pre-historic activity."
The USGS said this the largest earthquake to shake the Bay Area since the 1989 6.9 magnitude Loma Prieta quake.