A new walking trail to the Punchbowl Lookout in Onkaparinga River National Park, south of Adelaide, has been badly damaged just days before its planned opening.
The Department of Environment, Water and Natural Resources said the damage done to almost one kilometre of pathway was an act of senseless vandalism.
Rangers said it appeared a four-wheel drive had unsuccessfully tried to drive up to the lookout using the new trail.
Director of National Parks John Schutz said the repair bill would go into the thousands of dollars.
"It's horribly disappointing … such selfish behaviour," he said.
The track is believed to have been wrecked sometime on Wednesday.
"After the recent heavy rain, the damage has been significant," Mr Schutz added.
He said staff would have to wait until the area dried out before repairs could begin.
The Punchbowl Lookout track was part of a $1.7 million upgrade to the park's facilities.
New rock climbing and carpark upgrades were planned to be revealed this weekend, with campground improvements also underway.
"We don't know when [the track] will be able to be opened," Mr Schutz said.
He asked that anyone who witnessed the damage being done or had seen suspicious activity at the park to call police on 131 444.
