The CHP was notified at 7:45 a.m. about an injured dog on state Highway 128 at River Lane in Geyserville, CHP Officer Jon Sloat said.
Volunteers from the Geyserville Fire Protection District were at the scene when the CHP officer arrived, Sloat said.
When a female volunteer tried to remove the dog from the middle of the road, the dog "chomped down on her hand and wouldn't let go," Sloat said.
The volunteer suffered serious lacerations on her left hand, Sloat said.
"Based on the condition of the animal and the fact that it had caused a serious injury, the officer received permission to dispatch (shoot) it," Sloat said.
Sonoma County Animal Control removed the dog and will test it for rabies, Sloat said.