Authorities said the intern was attacked and killed when she entered the male African lion's enclosure at Cat Haven about 45 miles east of Fresno.
Sheriff's deputies responding to an emergency call from Cat Haven found the woman severely injured and still lying inside the enclosure with the lion nearby, Fresno County sheriff's Lt. Bob Miller said.
Another park worker couldn't lure the lion into another pen, so deputies shot and killed it to safely reach the wounded woman. But she died at the scene, Miller said.
Paul Hanson, a Seattle-area attorney, identified the victim as his daughter Dianna Hanson of Brier, Wash. He said he drove his daughter from her home on New Year's Day, arriving at Cat Haven Jan. 2.
"She was very excited," Hanson told The Associated Press late Wednesday. "It was just a dream job for her."
Hanson said she had been fascinated by big cats from an earlier age.
"She was absolutely fearless," he said. "I always had a premonition I would get a call like this one day."
California Department of Fish and Wildlife spokeswoman Janice Mackey said she was unaware if any state regulations would prohibit an employee from entering an exotic animal's enclosure.
Cat Haven founder and executive director Dale Anderson was crying as he read a one-sentence statement about the fatal mauling at the private zoo he has operated since 1993.
Investigators were trying to determine why the intern was inside the enclosure and what might have provoked the attack, sheriff's Sgt. Greg Collins said. The facility is normally closed on Wednesdays, and only one other worker was there when the mauling happened, he said.
The lion, a 4-year-old male named Cous Cous, had been raised at Cat Haven since it was a cub, said Tanya Osegueda, a spokeswoman for Project Survival, the nonprofit that operates the animal park.
Since the 100-acre facility just west of Kings Canyon National Park opened two decades ago, it has housed numerous big cats, including tigers, leopards and other exotic species. It is permitted to house exotic animals by the California Department of Fish and Wildlife and is regulated as a zoo by the U.S. Department of Agriculture.
Results of the last 13 USDA inspections show no violations dating back to March 2010. The most recent inspection was Feb. 4.
Despite state regulations requiring annual inspections, the California Department of Fish and Wildlife most recently inspected the facility in January 2011, when the inspector found it in "good condition" after checking animal health and features such as enclosures.
"We have to do the best we can with the resources we're provided," said department spokeswoman Jordan Traverso. "Regardless of whether it was inspected, that wouldn't have prevented this from happening."
Cat Haven's current "restricted species" permit, which expires in November, states the park was authorized to house 47 animals but had only 28. The animals must be used for scientific or educational purposes.
Actress Tippi Hedren, who founded the Shambala Preserve in Southern California, home to 53 seized or abandoned exotic pets, expressed dismay over the killing of the lion.
"It wasn't the lion's fault. It's the human's fault always," Hedren said.
Nicole Paquette, vice president of the Humane Society of the United States, said the victim of Wednesday's attack should never have been in the enclosure with the animal.
"These are big cats that are extremely dangerous, and they placed a volunteer in the actual cage with a wild animal," she said. "That should have never happened."
Officials at another big cat sanctuary, Big Cat Rescue in Tampa, Fla., told The Associated Press last year that at least 21 people, including five children, have been killed and 246 mauled by exotic cats in the United States since 1990. Over that period, 254 cats escaped and 143 were killed.
In 2007, a tiger at the San Francisco Zoo was killed by police after jumping out of its enclosure and fatally mauling a 17-year-old boy and injuring two other people.
Cat Haven has housed Bengal tigers, jaguars and leopards as well as bobcats native to the area. The facility's website says it promotes conservation and preservation of wild cats in their native habitats and offers visitors tours and educational outreach.
Anderson said Project Survival would investigate to see if the intern and the other worker on-site followed the group's protocols.
"We take every precaution to ensure the safety of our staff, animals and guests," he said in a statement.
The Associated Press contributed to this report.