Yellowstone National Park, WY – Sylvan Pass in Yellowstone National Park was closed temporarily this week after a construction worker found an unexploded artillery shell used to control avalanches.
The pass was closed at around noon Monday and reopened by midmorning today (Tuesday).
A team from Malmstrom Air Force Base in Great Falls, Montana, was called to remove and detonate the shell.
Park officials believe the shell was fired into the snow from a howitzer sometime last year.
The park has used the howitzer for years to help control avalanches on Sylvan Pass, which is about six miles inside the park's East Entrance.
Park rangers say as many as 300 unexploded shells lie in the slopes around the pass. They have been experimenting with using a helicopter to drop explosives for avalanche control instead of the howitzer.