Napa County has been rattled by a small aftershock to the strong and damaging earthquake that hit California's wine capital over the weekend.

The US Geological Survey says the 3.9-magnitude quake struck at 5:33 a.m. Tuesday about 7 miles south of the city of Napa.

A sheriff's dispatcher says the station shook a little, but there have been no calls reporting damage or injuries.

California's wine capital is still recovering from Sunday's 6.0-magnitude earthquake, which is estimated to have caused at least $1 billion in property damage.

There have been a series of small aftershocks, mostly in the 2.0-magnitude range.

Drivers are seeing traffic delays on a Napa highway as crews inspect a bridge for possible earthquake-related damage.  

The CHP says the inspection work is causing an alternating closure of the two lanes of southbound Highway 29 at the George Butler Bridge.  

The inspection work is expected to continue for several more hours.  

The suggested alternate route is to use Highway 29 to West Imola Avenue and then to the Napa-Vallejo Highway.

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