The incident occurred shortly before 11 a.m. on a trail ride at the popular resort in the 1800 block of Refugio Canyon Road, said fire Capt. David Sadecki.
A 14-year-old boy suffered serious injuries, Sadecki said, while a 40-year-old woman, a 23-year-old man and a child had moderate injuries. A 49-year-old woman and another child suffered minor injuries, Sadecki said.
All of the injured were treated at the scene by county firefighters, then were transported to local hospitals via AMR ambulance. Names of those injured and their conditions were not immediately available.
A stable spokesman from Circle Bar B, who declined to give his name, said the accident occurred when a girl jumped from her mount, which frightened the group of horses that were out on the trail. The riders were injured when they either jumped or fell from their horses, he said.