NEW YORK (CBSNewYork) – A Long Island park is closed indefinitely after investigators found suspicious material dumped there.

The illegal dump is near the site of the popular Sweet Hills horseback riding center, which was suddenly shut down by Suffolk County officials, CBS2’s Carolyn Gusoff reported.

READ MORE: Driver Killed, Passenger Hospitalized After Vehicle Overturns In Rockland County

A tip led to the discovery of the mounds of dirt spread across 15 acres of trails in West Hills County Park.

“It’s processed construction material mixed with dirt,” said Suffolk County police Commissioner Timothy Sini.

The 900-acre park is nestled in pristine woods and near pricey real estate.

Sweet Hills’ summer camp also has been forced to close down.

Steve Cilluffo stopped by the facility to feed his granddaughter’s horse, one of 100 in limbo.

“They have their horses here,” he said. “It’s going to be a disaster.”

Police and conservation officers sealed sections of the park while the dirt is tested for toxins. They suspect someone also illegally cleared trees in preparation for more extensive dumping.

READ MORE: Police Searching For Missing Bronx Teenager Amanda Perez

“It’s clear there are certain people who think they can profit by dumping on these treasures that belong to all of us in Suffolk — our children — and it’s a disgrace,” Suffolk County Executive Steve Bellone said.

Officials are vowing zero tolerance after a dumping disaster two years ago. Toxic fill still shutters Islip’s Roberto Clemente Park.

The operator of Sweet Hills leases land from the county.

A spokesman for the riding center released the following statement: “Sweet Hills Riding Center has been providing first class equestrian programs at Suffolk County’s West Hills Park since 1982. Recently, some material was dumped near a trail area without our knowledge or consent. The Center is cooperating fully with Suffolk County Parks and all of the agencies that are investigating this incident. At the County’s direction, the Center is relocating horses to other facilities while testing is performed, but looks forward to submitting a plan to remove this material as quickly as feasible in order to resume the equestrian activities the riding community has come to enjoy over the years. The safety and enjoyment of its riders and the well-being of the horses on site have always been the highest priorities of the Sweet Hills Riding Center.”

In the meantime, park goers are being turned away.

“You hate to see people being ignorant and dumping,” said park goer Pete Bechhoff.

“I take my dog to the dog park and if something were to happen to him, I would be completely heartbroken because if one of these things turns out to be poisonous, maybe not just to humans but to animals, I’d be very upset,” another resident told WCBS 880’s Sophia Hall.

MORE NEWS: De Blasio Says City Prepared For School Staffing Shortages As COVID Vaccine Deadline Approaches

Suffolk County police are asking for anyone with tips that might help in the investigation to call 800-220-TIPS.