A man on an LSD-fueled rampage disrupted the annual Rainbow Gathering in Superior National Forest, assaulting a woman, biting off part of a man’s finger and attacking a sheriff’s deputy, authorities said.

The tirade Saturday night lasted until other participants used duct tape to restrain 20-year-old Spencer Fredrickson before law enforcement arrived, according to the Cook County Sheriff’s Office.

Fredrickson, of Northfield, Minn., was charged Tuesday in District Court with felony first-degree assault and fourth-degree assault on a peace officer, a gross misdemeanor.

Fredrickson was under the influence of hallucinogens LSD, LSA and “morning glories,” all of them classified as illicit drugs, the Sheriff’s Office said.

Since the early 1970s, Rainbow Gathering participants have been congregating yearly in remote forests as part of the Rainbow Family of Living Light. The U.S. Forest Service describes it as “a loose-knit group of people without leadership or organization who gather in national forests to discuss political and environmental issues, pray for world peace and celebrate life. ... Members come from all walks of life and multicultural backgrounds.”

At this year’s gathering in the forest off Trout Lake Road, the Sheriff’s Office and the County Attorney’s Office said the incident started when Fredrickson groped a 40-year-old woman. When she rebuffed him, he tried to strangle her, then grabbed the bottom and top of her jaw, “pulling her face apart as hard as he could,” the criminal complaint read.

Her screams prompted others to try to free her from Fredrickson, who was “exhibiting superhuman strength,” a Sheriff’s Office statement read. During the struggle, Fredrickson bit off part of a finger of someone going by the name Satellite.

The woman’s rescuers relied on duct tape to restrain him until a sheriff’s deputy arrived. The deputy tried to keep Fredrickson from harming himself, but the man remained belligerent, digging into the deputy’s gloves with his fingernails and breaking the skin beneath.

The injured man and woman were treated at a nearby hospital and released.

Cook County District Judge Michael Cuzzo ordered Fredrickson to undergo a medical evaluation and be assessed for his competency to stand trial. He remains jailed in lieu of $200,000 bail.

Paul Walsh • 612-673-4482