A 25-year-old woman and her baby were killed in a single-car rollover on Arizona 86, commonly called Ajo Highway, near Three Points on Thursday night.
The crash happened around 10:30 p.m., says a news release from the Tohono O'odham Nation.
The woman and the baby were thrown from the car and pronounced dead at the scene.
Two other people had serious but non-life-threatening injuries and were taken to a hospital by helicopter, the release said.
No other information was immediately available.