DOVER — Two Michigan residents were arrested Friday at the Firefly Music Festival for alleged possession of a variety of drugs, including marijuana, LSD and bath salts.

According to Dover police, 31-year-old Daniel Wood and 39-year-old Dion McPherson sold what they claimed was Ecstasy to an undercover member of the Dover Police Department’s Drugs, Vice and Organized Crime Unit. Tests revealed the substance in fact contained mephedrone, also known as bath salts.

“They were selling it as MDMA or Molly, which is also a form of Ecstasy, I guess,” spokesman Cpl. Mark Hoffman said Monday. “They were selling it as that but it wasn’t that at all and it could have to led to some dangerous situations.”

Police arrested the two men at the nearby festival campsite without incident around 3:45 p.m. Friday, he said, and found 44.1 grams of mephedrone, 58.8 grams of psilocybin mushrooms, 30.5 grams of marijuana and 225 doses of LSD. Officers also seized $3,397 in suspected drug proceeds.

Mr. Wood, of Jackson, Michigan, and Mr. McPherson, of Ann Arbor, Michigan, were committed to James T. Vaughn Correctional Center near Smyrna in default of $100,000 cash bond. They were charged with possession of tier-five quantity of mephedrone, possession of tier-five quantity of psilocybin mushrooms, possession of tier-three quantity of LSD, possession with intent to deliver marijuana, delivery of mephedrone and second-degree conspiracy.

Cpl. Hoffman could not disclose how officers became aware the men were selling drugs.

In terms of scale, the bust is a large one not just for special events like Firefly but for a normal day in the city, he said.

Music festivals have a reputation for drug use, and while carrying marijuana is against the law, there are practical limitations for police.

Because Firefly and similar large-scale events like NASCAR races — and this coming weekend’s Big Barrel Country Musical Festival — draw tens of thousands of fans, Dover police cannot concentrate on every potential marijuana possession case. With 90,000 people and just a handful of police on the scene, it is “next to impossible” for officers to simply follow the scent of marijuana and pat down every person in the area, Cpl. Hoffman said.

Ultimately, while drug possession is illegal, each officer has discretion. Dover police concentrate on blatant use, drug sales or anything involving harder drugs than cannabis, Cpl. Hoffman said.

Individuals who may have overdosed on drugs and need medical attention are taken to area hospitals and treated there, he said.

While this year’s Firefly Music Festival was the largest yet, things went smoothly for the Dover Police Department.

“Any time you put 90,000 in a small area like that you’re going to have issues,” Cpl. Hoffman said, but aside from a few fights, thefts and drug crimes, he said attendees were well-behaved.

He did not know the exact number of arrests and said the statistic will likely be combined with numbers from this weekend’s Big Barrel Country Music Festival. That festival also will be in The Woodlands of Dover International Speedway and will run Friday through Sunday.