Firefighters on the Offensive at Mesa Verde Park

Firefighters battling a 2,415-acre blaze in one of the nation’s archeological treasures took the offensive Wednesday as they began digging containment lines.

They got help from five helicopters, at least two air tankers and 30 engines. Crews were accompanied by archeologists to avoid unnecessarily damaging the sites that make Mesa Verde National Park a major tourist draw. The park remained closed.

The fire, ignited by lightning, was spreading northeast. Fire officials said cooler weather was forecast, which could help them make some progress.

“That gives us an opportunity,” said Justin Dombrowski, a fire information officer.

The top priority of firefighters was protecting a research center that holds artifacts and human remains, as well as the park’s archeological sites. After spending the previous day protecting buildings, they also began digging lines to contain the blaze.

The fire broke out Monday, forcing the evacuation of about 2,000 employees and tourists. The flames charred the mesa above a cliff dwelling, but archeological sites were not damaged because they are inside limestone cliffs.