Two public safety officers who were conducting an unrelated traffic stop nearby witnessed the crash that occurred at Snyder Lane and Medical Center Driver at 5:39 p.m. and rushed to the victims' aid.
The two officers immediately began administering first aid and reported the crash, which involved a 1997 Honda driven by 18-year-old Rohnert Park woman Kaitlyn Dunaway.
Although police and fire units were called to the scene, they could not save the life of the two-year-old girl. The child's mother remained in intensive care Thursday evening, according to the department.
The cause of the collision is still under investigation.