Authorities said the little girl had an upset stomach after the incident, but is otherwise in good health. She was placed in foster care.
The father, Elijah Benbow, 28, of Seattle was booked on charges including child neglect and meth possession.
A Jackson County sheriff's deputy caught up with the man after reports Monday about suspicious behavior at a fast-food parking lot in Ashland.
When pilled over in a traffic stop along Interstate 5, Benbow was shaking badly, fidgeting, and could not stop moving.
The deputy then interviewed the little girl said, who was in the back seat of the car. She said she'd eaten what looked like a "sort of gray" rock. She identified a bag containing more than 5 grams of meth.
Spokeswoman Andrea Carlson said the girl appeared to be OK: "She just complained of a stomach ache." She was treated at a hospital and released.
Carlson said the father faces arraignment Tuesday or Wednesday.