CUSTER, S.D. — A motorcyclist has survived a violent attack by a bison in the Black Hills of South Dakota, sheriff's officials said.

A bystander's video shows several bikers had stopped while a herd of bison crossed a road in Custer State Park on Wednesday. A 54-year-old Iowa woman got off the motorcycle on which she was a passenger and approached a bison calf, the Custer County Sheriff’s Office said.

An adult bison then charged and attacked the woman. The bison cow caught the woman's belt and jeans on its horns and swung her around — violently ripping off her pants before running away, according to the park's visitor services manager Kobee Stalder.

“These are wild and dangerous animals, even though the look docile,” Stalder said. “You have to respect these animals.”

Bison can stand 6 feet (1.8 meters) tall and weigh as much as 2,000 pounds (907 kilograms), he said.

Several witnesses ran to her aid and one man took off his shirt to cover her. The woman was taken by a medical helicopter from the scene, Stalder said. She had serious pelvic area injuries, but Stalder didn't know her current condition.

Thousands of motorcycles are traveling through the Black Hills because of the ongoing Sturgis Motorcycle Rally. The sheriff's department issued a warning as the rally began Aug. 7 for people to keep their distance from bison.