LAKEWOOD, Colo. (CBS4) – Explosives found at a park west of Denver were safely detonated on Friday, with the sound ricocheting around a nearby neighborhood.

Contractors for the Defense Department discovered the pre-World War II munitions at Green Mountain Park, a popular place for hikers and bikers. Authorities say five of the 10 75 millimeter shells were still live and potentially dangerous.

The safe detonation of several unexploded shells was enough of a curiosity for several Denver teenagers to show up at the park during the day.

“It was definitely better than the 4th of July,” one teen told CBS4. “I’ve seen some pretty big fireworks and it was definitely bigger than those, I think I could even see a shockwave.”

The explosives were probably fired out of a canon from old Fort George three miles away, near the National Renewable Energy Lab.

Marliyn Null of the Colorado Department of Public Health and Environment told CBS4 anyone who is hiking and comes across such ordnance should definitely report it, and be particularly careful.

“(Know) the 3 R’s: ‘Recognize’ what it might be, ‘Retreat’ — Get away from it. Don’t throw rocks at it. Don’t kick it. Don’t pick it up. And then ‘Report it’ — call 911.”

The five shells that were considered live rounds were packed with 270 lead balls that, if mishandled, could lead to disaster.

The contractor who found the shells will return to Green Mountain next month and will be examining a one acre site, but they also have another 1,000 acres to explore as they hunt for more unexploded ordnance.