By Krystain Orlinski

ACTON, Calif. (Reuters) - A deadly California wildfire that has destroyed more than a dozen homes drove thousands more residents from their dwellings on Monday as flames raged for a fourth day through drought-parched canyons and foothills north of Los Angeles.

About 300 miles (480 km) to the north, another fire ravaged a hilly area near the scenic coastal city of Carmel-by-the-Sea, churning through 15,000 acres (6,070 hectares) and destroying 20 homes and two outbuildings, authorities said.

The so-called Soberanes Fire, burning in the Los Padres National Forest in Monterey County, threatened 1,650 structures by Monday afternoon and was only 5 percent contained, the U.S. Forest Service said.

Near Los Angeles, a beefed-up force of nearly 3,000 firefighters battled to outflank the blaze there, which has charred at least 50 square miles (130 square km) on the rugged northwestern fringes of the Angeles National Forest, authorities said.

The so-called Sand Fire, which erupted on Friday, remained just 10 percent contained on Monday morning, as crews backed by bulldozers labored to hack buffer lines around the blaze's perimeter.

Fed by dense brush left desiccated during five years of drought, flames were initially stoked by triple-digit heat and extremely low humidity. Slightly cooler, moister weather and diminished winds were expected to assist firefighters on Monday.

"We have very little wind, we have an increase in relative humidity, and so it's favorable for us to get out and to put out hot spots and work on line construction," Los Angeles County Fire Chief Greg Hisel said. He said calmer winds were helping to keep the fire stationary.

At least 18 dwellings were destroyed over the weekend, and authorities have reported one fatality, an unidentified man found on Saturday evening in a burned-out car parked in the driveway of a home.

Among the properties to go up in flames was the landmark Sable Ranch, a popular location for television and movie shoots.

By Monday morning, evacuation orders had been expanded to about 10,000 homes, encompassing an estimated 20,000 to 30,000 people, fire officials said. Los Angeles County Fire Inspector Joey Marron said some 200 commercial buildings were also in harm's way.

Authorities on Sunday had put the number of evacuees at 1,500.

The blaze was concentrated near the town of Acton, about 50 miles (80 km) north of Los Angeles, as it cast a pall of smoke and soot over a wide area. Much of the Los Angeles basin was dusted with a thin layer of fine white ash from the fire on Saturday and Sunday.

The Soberanes fire, burning north of California's famed Big Sur coastal region, grew by about 5,000 acres (2,020 hectares) in the 24 hours from Sunday morning to Monday morning, the Forest Service said.

Evacuations were ordered for residents of several neighborhoods, and the number of threatened structures was expected to grow above the 1,650 given by emergency officials at around noon on Monday.

The causes of the two fires were under investigation. They are among some 3,750 blazes large and small to have erupted across California since January, a higher-than-normal total, collectively scorching more than 200,000 acres (80,940 hectares), state fire officials said.

The biggest so far was last month's Erskine Fire, which consumed 48,000 acres (19,429 hectares) northeast of Bakersfield, killing two people and destroying about 250 structures.

By comparison, the 2003 Cedar Fire ranks as the biggest on record in the state. It blackened more than 273,000 acres (110,480 hectares), leveled 2,820 buildings and claimed 15 lives.

(Additional reporting by Laila Kearney and Chris Michaud in New York and Sharon Bernstein in Sacramento, Calif.; Writing and additional reporting by Steve Gorman in Los Angeles; Editing by Grant McCool and Jonathan Oatis)