A magnitude 6.4 earthquake shook parts of northern California early Tuesday, jolting people awake, the US Geological Survey said, and thousands were without power afterward.
No injuries were immediately reported after the earthquake, which occurred about 2.34am near Ferndale, a small community about 213 miles (343km) north-west of San Francisco.
After the earthquake, more than 55,000 customers were reported to be without power in the surrounding area, according to poweroutage.us, which tracks outages across the country.
The earthquake came just days after a small magnitude 3.6 earthquake struck the San Francisco Bay Area, waking up thousands of people at 3.39am Saturday and causing minor damage.
That earthquake was centered in El Cerrito, about a 16-mile (25km) drive to downtown San Francisco.