The woman, Brier, Washington native Dianna Hanson, died at the scene after police killed the lion -- a 4-year-old male African lion named Cous Cous -- in an attempt to save her, according to Fresno County sheriff's Lt. Bob Miller.
The victim's father, Seattle-based attorney Paul Hanson said that Dianna, an animal lover, "was very excited" to start working at the animal park at the beginning of the year, as "it was just a dream job for her."
Dianna had always loved big cats, her father said, and "was absolutely fearless" in her life.
Cat Haven has been open since 1993, and is home to exotic species such as Bengal tigers, jaguars and leopards. Cous Cous had once been used on an edition of Ellen.
Humane Society Vice President Nicole Paquette said the incident "should have never happened."
"These are big cats that are extremely dangerous," she said, "and they placed a volunteer in the actual cage with a wild animal."
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The incident is reminiscent of the 2007 Christmas Day incident at the San Francisco Zoo in which a 17-year-old boy was killed after a tiger jumped out of its' cage and mauled him.