A favorite of zoo visitors for decades, Avila had suffered severe arthritis in her knees since 1989 and had back surgery in 2002, the Los Angeles Times reported.
In the last few days before her death Thursday, older gorillas at the zoo gathered nearby, bringing her food and offering comfort, the newspaper said.
Alvila had four offspring and assumed a maternal role among the zoo's gorillas. She adopted a baby gorilla, Imani, in the mid-1990s that had been abandoned by its mother, and enjoyed watching younger gorillas engaging in rough-and-tumble play.
"She was a good aunt, a good grandmother," gorilla keeper Michael Bates said.
Alvila's mother, Vila, remains at the zoo and at age 53 is the third-oldest gorilla at a North American zoo, the Times said.
The zoo has 11 gorillas.
They are social creatures with roles assigned by gender, age and size.
The death of a matriarch will affect the remaining animals as the social familial structure rearranges, zoo officials said.
"It's going to be huge," Bates said.