Suffolk officials sealed part of a county park in West Hills and shut down a horse riding center Friday as they began a criminal investigation into the dumping of construction debris and other materials there.

About 15 acres of West Hills County Park was cordoned off with fencing and yellow police tape. Piles of dumped materials could be seen pushed up against trees on trails leading away from the Sweet Hills Riding Center, a 100-horse stable that the county ordered to cease operating during the investigation.

“Preliminary tests of dumping materials secured and received by Sweet Hills Riding Center . . . contain suspicious materials,” Suffolk County Executive Steve Bellone said at a news conference Friday. “We are shuttering operations here immediately.”

But a riding center spokesman said in a statement that it was not complicit in the dumping.

“Recently, some material was dumped near a trail area without our knowledge or consent,” said the spokesman, Mark Smith. “The center is cooperating fully with Suffolk County Parks and all of the agencies that are investigating this incident.”

Smith declined to comment further, citing the ongoing investigation.

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The Sweet Hills Riding Center has been located at the 855-acre park since 1982 and provides horse boarding and weeklong summer day camps, among other services. The popular park features nature trails, a dog run and playgrounds, among other amenities.

The investigation began after county parks officials on Aug. 16 noticed the debris near the riding center.

Bellone said the county contacted the state Department of Environmental Conservation to assess the debris, which appeared to be made up of “processed construction material.” Trees had been knocked down and a fence also had been damaged, according to the county.

The DEC did not respond to a request for comment Friday.

“The Suffolk County Police Department was immediately notified and the area has been sectioned off and is secured, and is being treated as an active crime scene,” Bellone said.

Robert Clifford, spokesman for Suffolk County District Attorney Thomas Spota, said his office received word about the dumping from the police department on Wednesday, and after an investigation, “We confirmed that the dumping of construction and demolition debris has occurred.”

“What’s here didn’t happen overnight,” Suffolk Chief of Detectives Gerard Gigante said. “This dumping has been occurring over a period of time, the length of which we don’t know.”

While it was unclear how much material had allegedly been dumped at the park, Bellone said it appeared that “ground was being laid and prepared for a much larger and significant dumping of material.”

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“We will prosecute to the fullest extent of the law those who were responsible for any actions that are damaging and destructive to our parks,” Bellone said.

Police Commissioner Timothy Sini said detectives from his agency’s environmental crimes unit, attached to the district attorney’s office, have begun looking into the case. He asked that anyone who might have information about the dumping call the department’s Crime Stoppers hotline at 800-220-TIPS.

“We will get to the bottom of this, and we will hold those responsible accountable for these egregious actions,” Sini said.

Testing of the material, which has not yet begun, is expected to be completed in a week to 10 days, he said.

Clifford said the results will be made public.

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“As we did in the Roberto Clemente Park case, we will advise the park-going public about the contents of the materials as soon as we receive the analytical results of the tests done on the collected samples,” he said.

Bellone said there was “no evidence or indication of any danger to anyone, but pending testing, we’re going to take every precaution that we can to make sure that people and these animals are protected.”

The dumping investigation announced Friday is reminiscent of Suffolk authorities’ probe into dumping at Roberto Clemente Park and three other locations in and around Islip Town.

Six men and four companies were indicted in December 2014 after prosecutors said thousands of tons of contaminated fill, including construction and demolition debris, was dumped at the town’s park in Brentwood, a one-acre private lot in Central Islip, a six-home development for veterans in Islandia and a state-protected wetlands area in Deer Park, on the Islip-Babylon border.

Prosecutors said that dumping was motivated by “greed,” to avoid the tipping fees to dispose of the debris legally.

Four of the men — including two former town officials — and one of the companies pleaded guilty, and one of the men was found guilty of charges in connection with that probe.

“I think we’ve all become aware because of Roberto Clemente about this sort of nefarious work that’s been happening,” Bellone said Friday. “Suffolk County is a very big place ... and it’s clear that there are certain people who think they can profit by dumping on these treasures that belong to every single one of us in Suffolk County.”

The parking lot of the riding center was bustling Friday as employees gathered outside the stable area, which was marked off with yellow police tape. Trailers laden with horses drove away from the now-shuttered stables.

Bill Leffert, 65, of Babylon, went to the center to check on his 15-year-old quarterhorse, Chocolate, after his riding instructor called to tell him about the dumping investigation.

“I didn’t think it was going to be a big deal,” Leffert said. “I didn’t think we would have to evacuate.”

He spent part of Friday searching for a new place to board Chocolate.

“He’s going to feel a little displaced for a few days,” he said. “Horses get used to a certain environment.”