The magnitude 4.5 temblor struck just before 1 a.m. about 4 miles northwest of Chatsworth, according to a preliminary report from the U.S. Geological Survey.
Sheriff's deputies found minor cracking and small chunks of fallen concrete in the Whites Canyon Bridge that connects to a busy state route.
Officials shut down the bridge for further inspection and traffic was rerouted, said city spokeswoman Gail Ortiz.
"We don't know if the cracks were preexisting," said sheriff's Deputy Mark Wood.
Whites Canyon Bridge, which is 300 feet long, opened about 15 years ago.
The quick jolt was felt by residents across Los Angeles County, and many reported that their houses vibrated, windows rattled and books, pictures and other items fell.
Hundreds of alarms went off in the Chatsworth area, police said.
"It was a real jerk, then a second jerk and then it just stopped," said Chris Harris, 57, of Canoga Park.
Harris, who was working at his computer when the shaking started, said a large picture fell off a wall in his home.
Chatsworth is about 30 miles northwest of downtown Los Angeles.