SCOTTS VALLEY (CBS SF) — A Cal Fire crew doing mop-up work and extinguishing spot fires while battling the massive CZU Lightning Complex fire near the Boulder Creek County Club made a stunning discovery Thursday night — an abandoned toolbox containing an apparent pipe bomb and other explosives.

At a Friday morning news conference, Santa Cruz County Deputy Sheriff Chris Clark said a bomb squad had safely detonated the device and explosives.

“At this point, we are investigating,” Clark said. “You hear about a pipe bomb, you hear about explosive devices. It’s concerning to the people who live up there.”

The incident began Thursday afternoon as the crews were working in neighborhoods forced to evacuate in advance of the massive fire.

“It started with firefighters doing mop-up work and putting out spot fire in the Boulder Creek Country Club area (in the 100 block of Lake Drive),” Clark said. “In doing that, they ended up noticing a toolbox that was open. They looked down and found what appeared to be a pipe bomb.”

Sensing immediate danger, the firefighters backed away to a safe distance and called the sheriff’s department. Arriving deputies quickly called in the bomb squad.

Clark said he has examined photos of the device.

“By the pictures I looked at that’s exactly what it appeared to be (a pipe bomb),” he said. “That’s exactly the impression I would have gotten had I looked down and seen it.”

A search warrant was obtained for the nearby home. Detectives searched the residence overnight, but Clark would not reveal what they found. A suspect search was also underway.

“Somebody built that, so somebody possessed it,” Clark said. “Our detectives are looking into it.”

By Friday morning, the massive fire complex still burning in the timber-rich Santa Cruz Mountains had grown to 82,540 acres, was 26 percent contained and had destroyed at least 554 homes.