An earthquake of preliminary magnitude 3.0 shook Contra Costa County on Monday morning.
The United States Geological Survey detected the quake at 6:47 a.m. with an epicenter 7.4 miles southwest of central Brentwood and a depth of 10.5 miles underground.
The fault that caused the quake was not immediately known, but the epicenter was 1.9 miles northeast of Greenville fault zone (Marsh Creek-Greenville section), according to the USGS fault database…