SAN DIEGO (AP) — Calmer winds helped firefighters gain ground Saturday against fires that have destroyed homes and raced through nearly 20,000 acres of northern and eastern San Diego County brush land, while authorities have charged a man for adding fuel to one of the nearly dozen blazes.

A new fire at the Camp Pendleton Marine base left some evacuations in place.

Thousands of firefighters and fleets of water-dropping military and civilian helicopters planned fresh battles Saturday. Investigators, meanwhile, continued to seek the causes of the conflagrations that burned at least eight homes and an 18-unit condominium complex, emptied neighborhoods and spread fields of flame, smoke and ash that dirtied the air in neighboring Orange County and as far north as Los Angeles County.

Alberto Serrato, 57, pleaded not guilty Friday to an arson charge in connection with one of the smaller fires, a 105-acre fire in suburban Oceanside that started Wednesday and is fully contained.

Tanya Sierra, a spokeswoman for the San Diego County district attorney’s office, said witnesses saw Serrato adding dead brush onto smoldering bushes, which flamed up. He has not been connected to any other fire, Sierra said.

All together, the wildfires about 30 miles north of San Diego have caused more than $20 million in damage.

Three fires continued to burn at Pendleton: A 15,000-acre blaze that began Thursday was 40 percent contained, and a new fire Friday that quickly grew to 800 acres was 25 percent surrounded that night. A 6,500-acre fire that started Wednesday at a neighboring Navy weapons station and rolled onto the base and the city of Fallbrook was 65 percent contained.

At their peak, the fires prompted about 8,400 military personnel and their families to be sent home from various parts of the sprawling coastal base between Los Angeles and San Diego, but some housing-area evacuations were lifted, base spokesman Jeff Nyhart said.

The most destructive fires started in Carlsbad — a densely populated coastal suburb of 110,000 people where a badly burned body was found Thursday in a transient camp — and San Marcos, a neighboring suburb of 85,000 people where strip malls and large housing tracts mix with older homes whose residents cherish their large lots and country living.

The Cocos Fire, which hopscotched through San Marcos and neighboring Escondido, was 70 percent contained Saturday morning after burning 2,520 acres, the county reported.

The region had become a tinder box in recent days because of conditions not normally seen until late summer — extremely dry weather, 50-mph Santa Ana winds and temperatures in the 90s. On Friday, though, slightly cooler weather and calming winds aided the 2,600 firefighters, and thousands of people began returning home.

Eight of the San Diego County blazes popped up between late morning and sundown on Wednesday, raising suspicions that some had been set.

In Carlsbad, investigators finished examining the burn site across the street from a park and focused on interviewing people who called a hotline that was set up to report any suspicious activity.

The Bernardo fire, the first of the North County blazes to break out, burned 1,548 acres and was 95 percent contained Friday night.

A backhoe operator at a development site accidentally started the fire while digging trenches, San Diego fire officials said Friday.