Workers at a private nearby stable said the 13-year-old animal was being cleaned when he wandered out and slipped down a steep hill behind the property.
Honor "got out of his stall and just found his way and slid down the backside into the creek," said Demi Stiegler, who trains with the horse's owner.
Capt. Marty Driscoll of the Orange County Fire Authority said he and other firefighters "made our way down to the horse who was initially upside down, so he was kind of belly-up and in a tough position."
The OCFA's urban search and rescue team was joined by OC Animal Care personnel and a veterinarian.
San Juan Capistrano- OCFA urban search and rescue members onscene assisting OC Animal Control with a stranded down a 30' embankment pic.twitter.com/eo2K6yUM7y— OCFA PIO (@OCFA_PIO) February 7, 2017
Firefighters said recent rains had made the hillside slick, complicating the rescue operation.
The creek bed was "about waist-deep at the deepest point, so that could have been a lot more challenging if there was water flowing," Driscoll said. "But this is something we train for with the USAR program."
After sedating the horse, firefighters used chainsaws to cut him loose from the thick brush.
"He kind of pinned himself up against a branch," the Stiegler said, "so as soon as they cut that away, he got out and walked away."
Honor appeared to have escaped any serious injury.
"He walked out. He wasn't limping," the fire captain said. "So as far as I can tell, those are good signs."