They say she was on the way to pick up her daughter from her parents' house on Wednesday, October 16.
She never made it after she was involved in a crash on Hills Valley Road and Parlier Avenue.
Video from ABC30 insider 'Danny Jimenez' shows first responders and the damaged vehicles.
Investigators say a man driving a Toyota tried to pass another car as Diaz, driving a pickup truck, approached from the other direction.
Her truck collided with the Toyota before being t-boned by another pickup truck.
She died at the scene.
Diaz leaves behind a 6-year-old daughter.
A GoFundMe page has been set up to cover Diaz's funeral services and to support her daughter.