First responders were dispatched to the 22900 block of Betty Road around 10 p.m.
Officials say the pit bull escaped its tether and attacked the woman in the backyard. The dog owner's son went outside and saw the family's dog attacking his grandmother, grabbed a chain connected to the dog, and pulled him off.
She was transported to Riverside County Regional Medical Center in Moreno Valley with bites to her face and arms.
The dog has been released to animal control officers to be euthanized.
His owner, identified as Edward Chavez, was cited for having the dog tethered for more than three hours, which is prohibited under state law.
CNS contributed to this report.