Eight arrests have been made and £100,00 worth of sound equipment seized after a weekend rave which drew up to 2,500 people to a clifftop.
Dyfed-Powys Police said they also impounded nine cars as the event ended near Dale, Pembrokeshire, on Monday.
Police and council officials said they planned to gather information on the organisers with the intention of prosecuting them.
But a BBC correspondent at the event said it was unclear who organised it.
Party-goers had said they intended to clean the site before leaving.
However, Supt Reg Bevan, of Dyfed-Powys Police, said there was a lot of debris left as the event wound down.
He said police were also looking to make more arrests.
Earlier, one participant told BBC Wales: "People want to do it the right way.
"No-one wants to upset anyone, but at the end of the day the police are shutting down every single legal event.
"People want to have a party. No-one wants any trouble. People are here just to have a good time."
One young woman said they would make sure to clean up after themselves, adding: "I know there are other parties that don't do that, but we're not like that."
She stressed the event was not about drug use.
"Obviously we like to have a little drink, but no drugs," she said.
"We're all friends and we like to meet up and have a good time. The club scene has changed; it's very expensive, it's very difficult to get into certain clubs and we don't like that.
"We can come out here in the beautiful countryside, and the sunshine, and have a good time."
There were no facilities at the rave site, including an absence of toilets.
Local publicans were said to be unhappy about the roadblocks which had kept customers away on a sunny weekend.
However Mark Elliott, head of public protection at Pembrokeshire council, said the priority of the police and local authority had to be ensuring public safety.
The council first had intelligence about the event late on Friday.
He said following a similar event near Marloes a few years ago, the council had set up a spontaneous event protocol in conjunction with the police and national park authority, adding that "nine out of 10" attempts to hold illegal gatherings had been thwarted.
They had not succeeded this time, but said they had managed to turn away large numbers heading to the site since it had begun.
"Many laws are being broken, the main one being [the] Licensing Act 2003.
"If these organisers want to go about it correctly and ... [have] all the facilities in place, then we could work with them," he said.
Mr Elliott added that the council was gathering information on the organisers with a view to seeking a prosecution.