The quake occurred at 1:35 a.m. and was centered 3 miles north of the San Bernardino County city of Fontana at a depth of 2 miles, the U.S. Geological Survey said. A series of very small aftershocks followed.
Some businesses had merchandise fall from shelves, according to TV news reports.
Off-duty county firefighter Eric Sherwin was awakened by the quake.
"At first I thought it was just a gust of wind," he told The Sun newspaper (http://bit.ly/1fzii5P). "Then I realized it was more than that."
Most residents posting to the USGS community Internet intensity map reported the quake felt light to weak. Some residents of Fontana and San Bernardino reported the shaking as moderate.