Officials at Theodore Roosevelt National Park say the 17-year-old girl from Colorado was on a trail Saturday and walked between two bull bison that had been fighting. One bison charged the teen. She was struck in the back, gored in the thigh and tossed about 6 feet (2 meters) into the air.
Park rangers and Billings County paramedics treated the girl at the scene until she could be taken by helicopter to a Bismarck hospital. Authorities say the teen's condition is stable.
"There was nothing that I did to aggravate him, and then all of a sudden I kind of got this feeling that something was chasing me, and then all of a sudden, he just throws me into the air," the teen said.
Park regulations require that visitors stay at least 25 yards (22.85 meters) away from large animals such as bison, elk, deer and horses.
Last week, a bison charged a 9-year-old girl in Yellowstone, throwing her into the air.
The Associated Press contributed to this report.