One person was seriously injured, another was rescued, after getting trapped on a rock about 100 feet above the river near Lyons.
The Boulder County Sheriff's Office said they got a call at 9:48 p.m. Tuesday that someone was stuck on a rock, yelling for help, on Longmont Dam Road.
When deputies arrived, they said they found a 28-year-old man with head injuries and a broken arm near the road.
A second person, a 21-year-old woman was still stuck on a rock over the river.
"Rocky Mountain Rescue extracted her to safety," the Boulder County Sheriff's Office said.
The woman was not injured.
In addition to deputies and Rocky Mountain Rescue, American Medical Response and the Lyons Fire Protection District was involved in the rescue.