The four other adults were treated at hospitals after the tree fell while the children were eating breakfast. The tree took down power lines near the campfire area and dining hall but did not damage any buildings.
Because of the nearby power lines, authorities said Pacific Gas & Electric Co. was responsible for annual inspections of the oak tree. Tuolumne County sheriff's spokesman Sgt. Jim Oliver said PG&E had inspected the tree and found nothing wrong with it, calling is a "freak accident."
PG&E spokeswoman Nicole Lieblet said there is an annual inspection process, but she didn't know whether specific records were kept for the tree that fell. She said the utility will closely cooperate with investigators.
"Everyone wants to know how this took place," Liebelt said.
The camp's executive director Ken Kramarz called Rittenberg a "beloved member of our staff."
"As our own hearts are still hurting, we send our sincerest condolences to her family and loved ones," Kramarz said in an email sent to campers' parents.
He said the children had been told only that a tree fell and some staff had been injured.
"We believe that you, their parents, are best suited to share the sad news that one of the injured staff did not survive," read the email.
Parents of the campers said it was nerve-wracking having to wait hours to receive reassurance.
"I can't shake this anxiety about my child, even though I've been assured she is safe," said Lena Brook, of San Francisco.
"Towanga is pretty remote, and that's one of the beauties of being there and sending your kid there in our crazy media, social media and technology-saturated world. That isolation clearly made the communication very difficult. It would have been much more comforting to all of us if we had heard earlier."
Other parents said they were worried about how their kids would process everything.
Rittenberg's mother, Penny Kreitzer, went through the same process without the reassuring ending, hearing about the tree through the news before she knew her daughter was involved. Kreitzer frantically called hospitals and was briefly hopeful when she couldn't find Rittenberg before learning the truth through a law enforcement official.
"I've lost a beautiful child through that tree," Kreitzer, told the Los Angeles Times. "I wish the tree had fallen on Saturday when no one was there."
Rittenberg attended UC Santa Cruz, a campus nestled among coastal redwoods that is itself often compared to an idyllic summer camp.
She was a poised, sweet woman and popular college DJ who served as world music director at the school's radio station, station manager Alec Howard told The Associated Press.
"I'm still kind of reeling back from the shock," Howard said. "Everybody here is really saddened by it."
Sheriff's officials did not release further details about the others' injuries, but camp officials said two of the four injured staffers were treated at hospitals and released, and two others were still receiving care.
There were about 300 campers and 150 staff at Camp Tawonga, which offers sessions for students in second through 12th grades. The camp is located on 160 lush acres on the Tuolumne River, just outside Yosemite National Park. It has been in operation since 1925, according to its website.
Brook said she wanted to hear her 10-year-old daughter's voice for herself but wasn't sure if it would make the situation worse.
"If I was in town right now I would seriously consider picking her up," she said. "Even though I know she is in good hands and there is an incredible bonding and community-building opportunity in going through something like this, as parent it feels like you want to hold your kid and never let them go."