Rio Blanco Undersheriff Michael Joos says a group of people, mostly teenagers, were partying about 135 miles west of Denver near the Chapman Reservoir in the Routt County National Forest.

"Several kids, we got a report up to 16, got up there for a party," said Joos.

Several in the group then moved the party to a near by oil pump. Authorities say 17-year- old Samuel Hedemark and 19-year-old Christopher Fuller climbed on top of a large, 20-foot tall oil storage tank and began to jump up and down.

The tank exploded, killing the teens and throwing their bodies 150 yards.

"Once they got up on the tank they were jumping up and down which was causing it to release vapors from the tank through a release valve on top of tank. At some point that tank exploded," said Joos.

Authorities say a cigarette lighter may have ignited the vapor.

Joos says the tank contained 160 barrels of oil.

Joos said a dog was also killed in the explosion, but no other injuries were reported. A small fire did result from the explosion but was quickly contained.

Both of the teens who were killed attended high school in Oak Creek, where grief counselors will be on hand in the coming days.

Bob Rogers, who was camping nearby with his three grandsons, says he heard the teens jumping on the oil tank and it sounded like drums and was keeping him awake, so he went out to see what was happening.

"That's when the whole thing just went up in a big ball of flame," said Rogers. "And it wasn't a big loud explosion it was just a 'whump' noise and I just knew that nobody could have lived through that."

"It was a horrific sound and everything was engulfed in flames," said Rogers. "That memory will be coming back to haunt us all the time."

When first responders got to the scene, officials say a number of party goers had left but they were able to interview those who remained.

Hedemark is from the small town of Phippsburg; Fuller is from Yampa. Both rural communities that Yampa resident Rogers expects will be hard hit by the loss.

"It will be (hard) for the families and for those who knew them," said Rogers.

Authorities say they must still clean up the oil that was spread during the explosion, but that will take time.

It is not yet known if there will be any charges filed.

(Copyright KUSA*TV, All Rights Reserved. The Associated Press contributed to this report.)