At 06:34 AM PDT (13:34 GMT) a moderate earthquake (Magnitude 4.8) occurred 20 miles east of San Bernardino. The location was near Mt. San Gorgonio. The earthquake had a strike-slip mechanism with nodal planes striking N30W and N60E. Preliminary location of aftershocks suggested that the northwest plane was the fault plane. This event is located several miles north of the San Andreas fault in a region that has had a moderate level of seismicity over the last 10 years.
In the two hours following the mainshock there have been 7 small magnitude (M2) aftershocks.
The event was lightly felt across a wide area of southern California, but there has been no reported damage.