By Alex Dobuzinskis

LOS ANGELES (Reuters) - Crews battling a deadly wildfire in rugged, drought-stricken terrain north of Los Angeles made steady progress in containing the blaze on Wednesday, after a bulldozer operator helping to fight a smaller wildfire in central California died overnight when his machine overturned.

Some 3,000 firefighters battling the so-called Sand Fire in the Angeles National Forest extended containment lines around 40 percent of the 38,350-acre (15,520 hectare) blaze by Wednesday morning, according to fire information officer Sam Wu.

Lower overnight temperatures aided their efforts, he said.

The blaze has destroyed 18 homes as it tears through drought-stricken chaparral and brush, spewing out smoke that prompted the South Coast Air Quality Management District to warn residents in parts of Los Angeles County to avoid outdoor activities.

About a dozen exotic animals displaced by the blaze were set to return to an animal sanctuary in the Los Angeles suburb of Sylmar on Wednesday, officials said.

About 300 miles (480 km) to the north, a smaller blaze dubbed the Soberanes Fire continued to threaten some 2,000 properties after destroying 20 homes on Sunday in an area between Big Sur and the scenic coastal town of Carmel-by-the-Sea, officials said.

Firefighters were informed about the death of the bulldozer operator, which occurred overnight, before they headed out early on Wednesday, said fire Captain Richard Cordova, a spokesman for the team handling the blaze.

"It makes it real what this job is really about and how dangerous it is," Cordova said by phone.

Officials said the bulldozer overturned and that the operator was a private contractor. A second bulldozer also overturned while battling the flames, but that operator was uninjured, officials said.

The Soberanes Fire has scorched more than 23,500 acres (9,510 hectares) at the edge of the Los Padres National Forest since breaking out on Friday and some 3,080 firefighters had the blaze about 10 percent contained on Wednesday, officials said.

In Los Angeles County, the lone fatality in the Sand Fire was identified as Robert Bresnick, 67, whose body was found Saturday inside a burned-out car in a driveway, county officials said. The man refused to leave the area until it was too late.

Acting California Governor Tom Torlakson, filling in for Jerry Brown who is at the Democratic National Convention, declared on Tuesday a state of emergency for the counties where the fires are located.

The causes of both fires were under investigation.

(Reporting by Alex Dobuzinskis in Los Angeles and Brendan O'Brien in Milwaukee; Additional reporting by Curtis Skinner; Editing by G Crosse and James Dalgleish)