The temblor struck at 5:44 a.m. and was centered 2 miles north of Colton, the USGS said. Its depth was measured at 9.32 miles.
ABC7 viewers reported feeling the quake in Highland, Idyllwild and Rancho Cucamonga.
Miranda Martin said the earthquake "rumbled quietly" in Fontana.
Josie Quintero said on Facebook that she "felt it in Rialto just as I jumped in the shower."
"Yup, quickest shower ever! Lol," she added.
There were no reports of injuries or damage.