An oak tree was still burning nearby when Margaret Hangan made her way across a wildfire-scorched landscape and spotted to her delight a set of flat-topped granite boulders that served as kitchen counters in an ancient village 2,000 years ago.

In the rocks were manmade oval depressions in which acorns were ground into flour.

"This place was happening," said Hangan, a U.S. Forest Service archaeologist. "They had water, food, grass for baskets — everything they needed."

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For all the damage they do, wildfires can be a boon to archaeologists, laying bare the traces of long-gone civilizations.

Around the country, government archaeologists often move in to see what has been exposed after the flames have burned away the underbrush; sometimes they accompany firefighters while a blaze is still raging to make sure artifacts are not damaged.

"Fires are a double-edged sword," said Richard Fitzgerald, an archaeologist for California state parks. "They can be very destructive, but after a big fire you can find new sites, even in areas that have been surveyed before."

During a gargantuan fire that burned for nearly a month this fall in the Los Padres National Forest north of Los Angeles, fire crews found an abandoned gold mining camp and an adobe homestead from the 1800s.

After a smaller fire there in June, they discovered a cave with rock art and a site with unusual beads made from freshwater shells.

David Jurney, an archaeologist in the Ozark-St. Francis National Forest in Arkansas, estimated his teams make four times as many finds during post-fire surveys than they do digging through overgrown stretches of forest.

Most finds are small, rock flakes left behind by hunters sharpening arrowheads, or piles of rich brown earth, called midden, that remain from prehistoric kitchen scraps.

In rare instances, fires unveil large structures. Archaeologists discovered fortress-like stone walls after a 2003 fire ravaged Cuyamaca State Park northeast of San Diego.

During fires, archaeologists sometimes move with firefighters to help prevent damage to already recorded sites. Bulldozers are often directed to work around settlements, and helicopter pilots are warned against dropping fire retardant on rocks with ancient drawings on them.

"The No. 1 goal is to put the fire out, but there's flexibility in how that's done," said Paul Claeyssens, a Forest Service archaeologist in Oregon.

Fire crews working near known archaeological sites can also set backfires that can burn away fuel at lower temperatures than wildfires, which can get so hot that rocks simply explode, obliterating traces of ancient settlements.

Hangan knew that there were boulders once used by the ancient Kumeyaay Indians in the Cleveland National Forest near Descanso, just outside San Diego. After a fire in the forest last summer, Hangan was relieved to find the rocks intact.

She also discovered that the collection of boulders was more extensive than she realized — indicating a settlement large enough to support as many as five extended families instead of two or three.

Because many sites contain Indian artifacts or burial grounds, trained tribe members often join professional archaeologists for post-fire hunts. For example, Frank Brown, a Kumeyaay cultural expert and firefighter, accompanied Hangan.

After fires reveal artifacts, archaeologists must protect them from looters. Pottery, arrowheads and other items have turned up for sale over the Internet after wildfires, even though removing artifacts from public property is prohibited under federal law.

Often, archaeologists recommend closing burned-over areas to the public until new grass begins to screen the exposed sites again.

"It's a delicate balance," Hangan said. "The public has a right to see what belongs to it, but we have to protect it, too."