It happened around 2:15am on Highway 105 near Navajo.
Deputies say an aunt and uncle were in the backseat of a car and their two teenage nieces were in the front. Authorities say a man in a pickup slammed into the back of the vehicle, killing the woman in the backseat.
The driver of the pickup allegedly ran away but later showed up at the hospital with a broken arm. Charges are pending against the pickup truck driver.