A mobile phone video appears to show three people pushing against the famed "Pillar Rock" until it collapses.
The unique outcropping, also known as the Duckbill, has long been a popular destination for tourists visiting Cape Kiwanda park on Oregon's Pacific coast.
Officials had at first believed that the coastal sandstone pedestal had naturally eroded.
But they are currently re-evaluating that assessment after being shown the video by David Kalas, a visiting beachgoer.
Mr Kalas said that up to eight people participated in toppling it a week ago, but that five had walked away when the remaining group stayed to push it over.
"We confronted them and they said it was a safety hazard," said Mr Kalas, who had gone there to film a summer holiday video with friends.
"They said one of their friends had broken a leg on it. It's like their weird revenge thing", he added.
The pedestal was roughly 10ft (3m) across, and had been a popular destination for tourists seeking photos.
Police and parks officials will meet on Tuesday to discuss possible criminal charges.
A similar incident took place at Goblin Valley State Park in the state of Utah in 2013.
Two Boy Scout leaders received probation and a fine after posting online a video of themselves knocking over a rock formation believed to be about 170 million years old.
Officials at a state park in Oregon are investigating whether a rare rock formation was deliberately toppled.