The USGS says the quake struck at 11:38 p.m. just 2 miles east-southeast of Ontario at a depth of about 8 miles.
USGS maps indicate shaking was likely felt in Los Angeles, parts of Orange County and in Redlands.
There were no immediate reports of damage.
The quake hit just a week after a 4.6 quake centered in Malibu rocked the region, with strong shaking felt over a wide swath of Southern California.
4.6 magnitude earthquake strikes Malibu area, felt throughout Southern California