The woman was bitten on Thursday on Long Canyon Trail in Simi Valley and taken to Los Robles Regional Medical Center, where she received anti-venom and was in stable condition.
Ventura County Fire Department said the case was the county's seventh reported snakebite since mid-March, with recent heat blamed for bringing forward higher rattlesnake activity.
Officials said bites remain rare but serious, urged people to call 911 immediately, and advised hikers to stay on marked trails, wear protective clothing and avoid dense vegetation.
As fatal rattlesnake encounters triple in California, are local hospitals prepared for this venomous surge?
With rattlesnake bites surging due to early heat, is California facing a deadly new normal for outdoor recreation?