The strongest one measured 3.9 on the Richter scale, the U.S. Geological Survey reported.
While earthquakes in the 2.0 to 3.9 range are considered minor, the 3.9 quake, coming on top of damage already done Sunday morning, was enough to close a lane on Highway 29 in Napa.
"It got so bad people were calling in comparing it to a speed bump," California Highway Patrol Officer Daniel Hill told the San Jose Mercury-News.
Sunday's quake injured scores of people, including a teenager critically hurt by a falling chimney. More than 30 buildings in the city of Napa were red-tagged as uninhabitable.
The U.S.G.S., in a preliminary estimate Monday, said the earthquake caused at least $1 billion in damage. But that could be low because the area's wineries reported losing barrels and bottles of wine.
The Hess Collection on Mount Veeder in Napa County said two 20,000-gallon tanks of wine were damaged. One spilled so much that the winery's garden courtyard was covered with a lake of cabernet sauvignon.
"It looked like some giant hand just came down and crushed them and the wine came out of them," James Caudill, a spokesman, told the Santa Rosa Press-Democrat.
But other wineries said the damage was less than they feared.
"I was shocked. I was pleasantly shocked," Alison Crowe of Plata Wine Partners said.
American Canyon, at the quake's epicenter, is a center for wine distribution and for wine-making equipment.