The woman fell 60 feet down from the Forest Hill Bridge near Sacramento, the tallest bridge in California.
One of her friends, Paul Goncharuk, was there when it happened. He was part of a group of six friends in an off-limits section of the bridge when she lost her footing.
"They were taking a picture on the bridge, and then the big bolts that are holding the beams together, she stepped on them kind of weirdly and lost balance and fell backwards," Goncharuk said.
She was knocked unconscious and suffered a deep gash to her arm and fractured some bones that will require surgery.
The bridge has become notorious as a daredevil's playground. Sheriff's deputies patrol for people treating the bridge like a jungle gym, climbing underneath and posting photos and videos of themselves online.
"That's a really nice place. It's a cool place to take pictures, but honestly, it's not worth the risk," Goncharuk said.
Report a typo to the ABC13 staff