LOS ANGELES (AP) -- A huge wildfire roiled along the northwestern outskirts of the city Thursday despite a significant decline in the Santa Ana winds that spread it a day earlier. At midmorning the estimated size of the blaze took a major leap to 16,975 acres, according to city fire Capt. Carlos Calvillo. The previous estimate had been 7,000 acres.
Localized evacuations were in effect as the fire burned across ridges stretching for 10 miles along the border of Los Angeles and Ventura counties. More than 1,000 firefighters were on the lines, and a major air attack was under way.
Weather remained hot and dry, but the strong north and northeast winds that blew a small brush fire into a major conflagration Wednesday afternoon did not appear to be returning.
Firefighters remained concerned about the weather.
''We are worried because there is an abundance of fuel and wind and heat,'' said city fire Capt. Mark Savage.
The cause of the blaze was not determined.
The fire burned one home and a detached structure while threatening numerous other canyon homes in the San Fernando Valley area of Los Angeles. Fire also destroyed a building at the Rocketdyne facility where rocket engines have been developed since the 1950s. Firefighters said they didn't know what was inside the structure.
The flames crested a ridge and burned toward a cluster of dwellings in a neighborhood near Thousand Oaks in Ventura County to the west.
Firefighters launched an all-out assault at daybreak using water-dropping helicopters and tanker planes The biggest concern was that wind-fanned flames would leap U.S. 101and roar toward Malibu 10 miles to the south, Savage said.
Thursday morning, a dozen police officers on motorcycles began escorting canyon residents back to their homes to retrieve their medications and pets. Residents could only stay for a few minutes, said Officer Melissa Russin.
''They don't want people up there because the situation could change quickly,'' Russin explained.
Many residents responded quickly to evacuation orders. In Box Canyon, Jeff Johns, 48, said the hurricanes in the Gulf Coast, where people died after failing to leave, figured in his decision to evacuate.
''I wasn't going to get stupid about it. There was only one way out and it was getting real hot,'' Johns said.
Andrew Jimenez, 41, fled his Woolfey Canyon home as flames neared late Wednesday. Flames could be seen from the command center where he waited nervously. Mayor Antonio Villaraigosa arrived early Thursday and asked a couple of evacuees if they wanted a status check on their homes.
The mayor told Jimenez the good news: His house was safe.
Jimenez was shocked. ''For him to show any interest, well, I was impressed,'' Jimenez said.
Evacuation shelters were opened in Los Angeles and in Ventura County.
About 45 evacuees stayed at Canoga Park High School, where the Red Cross set up cots and provided meals.
''Our house is still OK, but oh God it's not a good feeling,'' said Phil Goldenberg, 53, who waited at the high school gymnasium with his wife and son.
Trisha Higgins and her 16-year-old son, Jake, fled their Thousand Oaks area home at 2:30 a.m. after authorities cruised their street with lights flashing, ordering evacuations through loudspeakers.
''There was a ridge of flames and everyone seemed to be leaving,'' Higgins said. ''We weren't sure where to go so we wound up here.''
Another large fire had burned 1,160 acres in San Timoteo Canyon between Redlands and Moreno Valley in Riverside County, said Capt. Julie Hutchinson of the Riverside County Fire Department.
The blaze was 25 percent contained, with full containment possible Thursday night, depending on weather conditions, fire officials said.