Phippsburg — A night of drinking in the woods turned deadly for two South Routt teenagers Saturday when an oil storage tank exploded in the Routt National Forest.

Sam Hedemark, 17, of Phippsburg and Christopher King Fuller, 19, of Yampa were among a group of about 20 teens and young adults partying near Chapman Reservoir in northeast Rio Blanco County. The area is about 15 miles southwest of Phippsburg.

Investigators say Hedemark and Fuller were jumping on top of a 20-foot-tall oil storage tank when it exploded at about 10:15 p.m. Saturday. The bodies of the two teens were found more than 400 feet away from the blast site, investigators said.

The cause of the explosion still is unknown.

Rio Blanco County Undersheriff Michael Joos said investigators are considering several possibilities for the blast at a well site off Forest Service Road 949.

"We don't know what the source is," Joos said Monday afternoon. "It could have come from a lighter, but there was also a campfire down at the site. It could have been static electricity. All we know is that it ignited and that we don't know the ignition source at this point."

Joos said witness statements indicate that Hedemark and Fuller were jumping up and down on the oil storage tank prior to the explosion. The tank, which was half-full with about 160 barrels of oil, had a release valve on the top that allows vapors to escape when the pressure builds up. Joos said when Hedemark and Fuller jumped on the tank, it could have increased the amount of vapor escaping the release valve.

At some point, those vapors ignited. Joos said one of the teens was found with cigarettes, marijuana and a lighter.

"Initially, when it was called in as an explosion, we didn't really know what we were looking at," Joos said. "This wasn't an oil field accident with workers where something went wrong."

'Fire everywhere'

Jessica Almeida, 17, said she was at the party when the accident happened.

"A bunch of people were jumping on it," Almeida said. Everyone except Hedemark and Fuller then climbed down from the tank. She said her back was turned when it exploded.

"It was just like fire everywhere," Almeida said. "We thought there were a lot more people (hurt)."

Almeida said most of the people at the party were drinking. The group included minors and adults. After the blast, she said many of the partygoers jumped in their cars to get the cars away from the flames. Once everyone regrouped, some of them drove toward town to call for help because there is little or no cell phone reception in the area.

It was Sunday morning before Almeida knew Hedemark and Fuller were dead.

"It's very upsetting," said the Soroco High School student, who will be a senior in the fall.

Empty beer cans and bottles littered the explosion site Monday. Rio Blanco County Coroner Randall Cochran said Hedemark and Fuller had blood-alcohol levels higher than the 0.08 percent legal limit for driving. Cochran said Hedemark's blood-alcohol was 0.112 percent and Fuller's was 0.161. Both also had traces of marijuana in their systems.

Hedemark died of blunt force trauma to the head and chest, and Fuller died of blunt force trauma to the chest and abdomen, Cochran said Monday night. Cochran said he believes the teens died as a result of the initial blast.

The scene

Another teen who said he was at the party Saturday night returned to the site of the tragedy Monday to see the damage for himself.

"I had just met Chris and Sam that night," said the teen, who would not give his name. "But I was told this is what people do - come out here to have parties. Everyone said they had been here before."

Joos and Almeida confirmed that the spot is popular for South Routt teens.

The unidentified teen said he left the party at about 9 p.m. to drive to Steamboat Springs to pick up a friend to bring back to the party.

"While I was in the car coming back, I got a call at 10:15 from a friend at the party who said it blew up," he said. "We came back today just to see what it all looked like."

In a clearing just off the Forest Service Road Monday, the oil storage tank rested on its side, about 150 feet from where it exploded. The ladder that led to the top of the tank sat in a tangled mess next to the blast crater.

A second tank stood nearby, having withstood the blast. The ground surrounding the area is charred in a 100-foot diameter and is sticky with oil.

Other remnants of Saturday's party included the ashes of a bonfire that burned about 30 feet from the oil tanks. More empty beer cans sat in a nearby barrel.

A deep pool of oil collected in the crater where the exploded tank previously stood. Valves, hoses and metal were strewn across the area, and a trail of burning oil trickled down a narrow trail leading away from the site, staining the ground black.

Joos said bullet casings were found at the site, but there were no bullet holes found in the oil tank.

No word on charges

The Rio Blanco Sheriff's Office is the lead agency investigating the explosion. CBI agents are assisting with the interviews of teenagers present during the accident.

"What we are thinking is that in the interviews more kids' names are going to come out, and then more interviews will come out of that," Joos said.

There has been no decision on whether to file criminal charges, Joos said. Officials with the 9th Judicial District Attorney's Office toured the accident site Monday and won't decide on charges until the investigation is complete.

The U.S. Forest Service will be in charge of site cleanup and gauging the environmental impact of the accident.