An earthquake that felt like an "explosion" struck near the Riverside-San Bernardino County line early Saturday, jarring area residents from their sleep and sending horses scurrying but causing no damage or injuries, authorities said.

Bob Finn, a spokesman for the Caltech Seismology Lab in Pasadena, said the shaker measured 3.2 on the Richter scale.

However, Waverly Person, a geophysicist at the National Earthquake Information Center in Golden, Colo., said his readings placed the quake at 3.7.

Both Finn and Person agreed the temblor struck at 6:22 a.m. and was centered several miles east of Riverside city limits and 23 miles southeast of San Bernardino proper.