A rural area of Northern California has experienced its strongest earthquake since 1940, but it caused only mild shaking with no immediate reports of major damage. Mendocino County authorities say some injuries have been reported but have provided no details. The U.S. Geological Survey says the epicenter of Wednesday's quake, with a preliminary magnitude of 5.6, was about 7 miles northwest of the agricultural town of Willits. The USGS says it was about 5 miles deep. Three other quakes under a 2.7 magnitude struck near the epicenter within an hour.