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A picture of firefighters holding the fire line of the Arizona wildfire

Firefighters hold a fire line—a barrier of cleared or plowed land—in Arizona on June 7.

Photograph by Jae C. Hong, AP

Ker Than

Published June 14, 2011

Hundreds of archaeological sites are under threat from a weeks-old, still raging wildfire in eastern Arizona. (See Arizona-fire pictures.)

Since it began in late May, the so-called Wallow Fire—the biggest in Arizona's history—has burned at least 733 square miles (1,900 square kilometers), and has now crossed the state line into New Mexico (regional map), the Associated Press reported Tuesday.

Within that vast expanse are large swaths of Arizona's Apache and Sitgreaves National Forests and New Mexico's Gila National Forest, parts of which have already burned.

Both forests contain thousands of known prehistoric and historic archaeological sites, from Native American stone ruins to remnants of 19th-century mines and mills.

The majority of the threatened sites once belonged to the Mogollon culture, a Native American farming civilization that occupied the region between around the year zero and A.D. 1500, said Bob Schiowitz, the U.S. Forest Service archaeologist for the Gila National Forest.

Schiowitz estimates there could be up to a thousand known Mogollon sites that could be affected by the Wallow Fire.

However, "not all of those are incredibly significant," he said, referring to the rubble piles that make up most of the sites.

Among the more exceptional sites are areas with standing architecture as well as rock shelters and cliff dwellings with "exceptional preservation," he said. Ancient rock paintings are also at risk, he added. "If the fire's hot enough, it can cause all that stuff to chip and flake off."

When wildfires threaten, Schiowitz and colleagues "look at the records and try to figure out which ones have fire-sensitive elements or that are most important."

Firefighters will then try to save the sites that are marked as high priority by archeologists. "You can't go and look at all of the sites," Schiowitz said. "There's just no way to do that."

(Related: "Fires Can Create 'Volcanic' Thunderclouds.")

Arizona Sites Face Unprecedented Fire Risk?

Archaeologists expect many of the Mogollon sites to survive the Arizona fires.

"Most of these sites have been abandoned for at least 500 to 1,000 years, so over that time they've stabilized and have probably been burned over before," Schiowitz said.

The majority of the artifacts—mostly fragments of ceramic bowls and jars and stone tools and weapons—are also relatively fire resistant.

Even so, the sites may now be more likely than ever to be harmed by fires, in part because for decades the Forest Service made a policy of stomping out blazes before they grow out of control. This can lead to a buildup of flammable plant material—adding fuel to future fires.

"There's an unusually high buildup of fuels in some places, and that tends to make these fires a little more catastrophic than they might've been in [past centuries]," Schiowitz said.

For example, some Mogollon sites have experienced so few fires in recent decades that trees have begun to sprout from their ruins. When these trees catch fire, they can burn all the way down to their roots, baking the soil and any artifacts buried in it.

"Over the last 15 to 20 years, we've been doing a lot to reduce those fuels" around archaeological sites, Schiowitz said.

Bulldozers and Backfires

Sometimes reducing those fuels is just the problem, however, Schiowitz said.

For example, firefighters will intentionally set sections of forest aflame to deprive an approaching wildfire of kindling. These so-called backfires, or backburns, "can be just as damaging to cultural sites as a natural fire coming through," he said.

Additionally, bulldozers are sometimes used to construct barriers to wildfires, called firebreaks, which can cause unintentional damage to sites.

To steer bulldozers clear of important sites, archaeologists often go into the field with firefighters. If time permits, scientists have even been known to help plan firebreaks and backfires so they do the least damage possible, Schiowitz explained.

(Hope for the future? "Electric Wand Makes Fire Disappear.")

Fires Threaten More Recent Sites Too

In addition to prehistoric sites, the Wallow Fire could damage non-Native American historic sites from the 19th and 20th century, especially since many are wooden.

"These include ranches, cabins, old mines, and mills," Schiowitz said. "They also have historical value, and some of them we're actively trying to preserve."

Retired archaeologist Fred Kraps noted that wildfires often expose previously unknown archaeological sites by burning off concealing surface material.

This can be a silver lining for archaeologists—but only if they discover the new sites before the public does, said Kraps, who is president of the Yavapai Chapter of the Arizona Archaeological Society.

"Looters and pot hunters can follow in on the fires," he said. "That happens a lot."

See National Geographic magazine wildfire-fighting pictures >>

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