A flurry of small earthquakes centered in San Ramon shook the area Monday, according to the USGS.
The USGS reports the strongest of the quakes were part of a trio of temblors to strike in a 20-minute span.
At 4:02 p.m. a magnitude-2.8 earthquake struck the area, which was followed by a pair of magnitude-2.8 and 3.5 quakes striking at 4:21 p.m.
The USGS also reported magnitude 2.9 and 2.8 quakes at 9:33 p.m.
The temblors are along the Calaveras and Pleasanton fault lines, according to the USGS.
"They're not lining up in a fault structure," USGS Seismologist Brad Aagaard said. "We know they are strike slip events, but we don't know which direction they're lining up on fault surfaces."
Monday's quakes are part of many that have struck the area in roughly the last 10 days.
The USGS said more than 200 earthquakes have been reported in the area since last Wednesday morning, including 45 temblors in the past 24 hours.
On Sunday, a 3.1-magnitude earthquake centered about a mile from San Ramon shook the Bay Area at 3:31 P.M.
A 3.4 preliminary magnitude quake centered near San Ramon struck Thursday at 6:10 a.m., USGS officials said.
Contra Costa County Sheriff's Office officials said Monday they have had no reports of damage.
The USGS notes the flurry of small quakes do not necessarily mean a large quake is imminent.
NBC Bay Area's Cheryl Hurd and Bay City News contributed to this report.