Posted like sentries along U.S. Highway 24, weary spotters kept their backs to the flames of the Waldo Canyon fire and their eyes on the sky.

Their vigil paid off again and again Tuesday – as when Vaughn Robbins and Tyler Erskine saw a single ember float into the sky and chased it into the hills across the highway, where it ignited a tree stump.

“That’s our major concern,” said firefighter David Moravek. “If it goes on the other side, it’s in Woodland Park.”

In this case, however, Robbins and Erskine were ready — and they doused the flames using 5-gallon water bladders strapped to their backs.

As the Waldo Canyon fire blew up Tuesday afternoon, fire crews in less active areas were working hard to preserve their fragile gains — facing whipping winds, tinder-dry brush and a towering inferno of smoke. They provided an overview of their efforts during a brief tour of the burn areas west of Colorado Springs.

El Paso County Sheriff Terry Maketa said during a news conference Tuesday that if the fire were to spread south of Highway 24, it would create a “chimney effect” that would drive flames to the north, toward Green Mountain Falls and beyond.

Firefighter George Bennett of Colorado Springs was among those working to ensure that wouldn’t happen.

Bennett and Moravek were among a small crew posted along Pyramid Mountain Road in Cascade, watching for spot fires.

Two days earlier, however, they and a crew of approximately 20 firefighters were all that stood between homes along Pyramid Mountain Road and the encroaching flames. During 16-hour shifts, they used chainsaws to clear brush and worked with hand tools to carve out containment lines in the soil.

“We had a pine torch up about 3 feet away from us,” said Conner Barkley. “That’s when we decided we needed to leave.”

The crew said they were briefly pulled off the lines Sunday morning as the fire crawled out of neighboring Waldo Canyon and made a push along a ridge top. When they returned on Sunday, they found their lines had held — leaving them with the equally important job of patrolling for spot fires.