Friday's earthquake was widely felt across Southern California, including greater Los Angeles, where shaking in some areas lasted about 40 seconds. Low-level rumbling extended as far north as the San Francisco Bay area and beyond to Reno, Nevada, and as far east as Phoenix, Arizona.
Seismologists said the initial quake on Thursday, and dozens of smaller ones that followed it, proved to be foreshocks to Friday's much larger temblor, which now ranks as Southern California's most powerful since a 7.1 quake that struck near a U.S. Marine Corps base in the Mojave Desert in 1999.
The U.S. Geological Survey said Friday's big quake was immediately followed by at least 16 aftershocks of magnitude 4 or greater and warned of a 50 percent chance of another magnitude 6 quake in the days ahead.
South of Ridgecrest, there were reports of a building collapse and gas leaks in the small town of Trona, home to about 2,000 residents, Ghilarducci said.
A rockslide closed State Road 178 in Kern County, and video footage posted on Twitter showed a stretch of road had buckled.
Luke Smith, owner of Furys Sports Bar in Ridgecrest, said in a phone interview that Friday's quake shook tiles lose from the ceiling, slightly damaging his bar and knocking down some bottles.
Southern California's Metrolink commuter rail service reported delays on several of its lines for precautionary track inspections due to Friday's earthquake.
The last major destructive quake to hit Southern California was the 6.7 magnitude Northridge quake in 1994, which struck a densely populated area of Los Angeles. It killed 57 people and caused billions of dollars in property damage.
The comparatively limited extent of damage from Friday's quake, packing greater force than the Northridge event, was a function of its location in a remote, less developed area.
Its ground motion, however, startled seismically-jaded Southern Californians over a wide region.
Pools in Los Angeles sloshed wildly, and TV cameras at major league baseball's Dodger Stadium were shaking as they filmed the night game between the Los Angeles Dodgers and San Diego Padres.
A television anchorwoman ducked under her desk in midst of a local newscast as shouts of "get under a desk" were heard in the background.
