Karen Williams was on Mile 23 of the race when she was mauled by the animal.
Chase Dekker Wild-life Images / Getty Images
The races, which also included a 10K and a half-marathon, took place along the trails of the Valles Caldera National Preserve.
In a post on Facebook, Williams wrote she was about 23.5 miles into the race when she crested a hill.
When she got to the top, she noticed the bear charging at her. Williams said she also saw a cub, leading her to believe the bear was a female protecting her young.
“Then I was on my ass and being raked with claws and bitten,” she wrote. “I cried out in pain and mama bear did not like that so she hit me with a left hook and bit my neck and started to try to shake me.”