Burning Man Founder's Son Busted for Shrooms at Burning Man

Talk about a bad trip ... the son of the man who created the Burning Man Festival got busted for shrooms at freakin' Burning Man.

The Pershing County Sheriff's Office in Nevada tells TMZ ... Tristan Harvey -- the son of Larry Harvey, who founded Burning Man in 1986 and died in April at 70 -- was driving with 2 friends last week into the festival when they were pulled over for not having a rear license plate.

We're told a police dog sniffed the car, honed in, and cops found Tristan was in possession of a mushroom. He was cited for possession of an illegal substance and driving with a suspended license. He was not arrested and told to go on his merry way, sans mushies.

His friend, a female passenger, also had a shroom, and she also was cited and released. Tristan's other friend wasn't so lucky. He was arrested for possession of a controlled substance, but cops aren't saying what they found.

Cops tell us over 70k attended the week-long event. They arrested 44 and cited 53.