Strong winds and dry grass "have made it difficult to contain," officials said.
Two firefighters were injured and more than 100 homes were evacuated as a wind-whipped wildfire spread Sunday to 14,000 acres of mostly dry grassland in Northern California, officials said.
The Corral Fire is burning in San Joaquin County, close to the Lawrence Livermore National Laboratory, which is about 50 miles outside San Francisco, according to the California Department of Forestry and Fire Protection.
"Areas west of the California Aqueduct, south of Corral Hollow Creek, west to Alameda County and south to Stanislaus County should leave now," San Joaquin emergency officials said late Saturday.
Two firefighters have been injured in the blaze, Cal Fire Battalion Chief Josh Silveira said in an interview with Sacramento ABC affiliate KXTV. One had minor injuries and the other had moderate injuries, he said, adding that both were expected to survive.
The fire ignited Saturday around 2:30 p.m. PT near Interstate 580 on the western edge of Tracy and quickly spread by midnight to about 11,047 acres, with about 13% contained, officials said.
Cal Fire officials increased that figure Sunday afternoon, saying the fire had grown to 14,000 acres and was 30% contained.
"This is a reminder fire season is year-round. Despite the wet winter, the fuels are now dry. Californians should know the fire threat," Silveira told ABC News on Sunday afternoon.
Silveira said the Corral Fire was burning in a rural area covered with thick, dry grass up to 4 feet tall in some parts.
"When everything lined up yesterday with the higher temperatures, strong winds and dry fuels, it became hard for firefighters to stop," Silveira said.
Silveira said winds, which fueled the fire Saturday night, substantially died down on Sunday, enabling fire crews to make progress on containing the blaze.
About 400 firefighters, with the help of Cal Fire air tankers, were battling the blaze on Sunday afternoon, according to Cal Fire.
The westbound lanes of Interstate 580, which was closed in both directions because of the fire, were reopened Sunday afternoon, but eastbound lanes remained closed, according to the California Highway Patrol.
Silveira said one structure was burned in the fire and about 100 homes were evacuated. He said some evacuation orders are expected to be lifted later Sunday.