When zoo staffers spotted the woman, they urged her to get out and she did, climbing out over the fences and ditches designed to keep people away from the animals.
Witnesses said the woman was in the sanctuary with the elephants for at least five minutes.
"She went in to kind of check the elephants out," Branden Adams, who shot the video of the woman, told KTLA-TV, Los Angeles. "She comes out and she says, 'I'm going to go pet the elephants now.' And she goes and she started touching the elephants and seeing what they were doing."
Police took the woman, who has not been identified, into custody.
She was taken to a hospital so she could receive treatment for various mental illnesses, officials said.