The unauthorised event, which resulted in the police being called, took place on part of Kirkstall Valley Nature Reserve.
One resident told the YEP they had heard loud music blasting from the site from around 11pm on July 7 until 9am the following morning.
Scorched areas where fires had been lit, a pile of bin bags filled with bottles and cans, and two abandoned gazebos greeted visitors to the Yorkshire Wildlife Trust (YWT) site afterwards.
YWT regional manager Nick Simms said it encouraged everyone to enjoy its sites in a responsible and considerate way.
Weekend weather: Your round-up for Leeds“We are very concerned about the impacts such unapproved activity could have on the sensitive wildlife and its habitat at our Kirkstall Valley reserve and we thank local residents for drawing our attention to it”, he said.
“We are working with other organisations, including the police, to assess the damage and look at how these type of events and antisocial activities can be prevented in the future.”
He said the trust would work with people who wanted to organise a particular activity to ensure it was appropriate.
Leeds City Council said it had received no complaints on July 7, but police have confirmed they received a report about music and people gathering on the land off Redcote Lane.
A spokesman said: “Officers attended shortly after 2am on July 8 and spoke to those involved and advised them about noise and annoyance. No offences were disclosed.”