It happened late last night on Highway 59 year Highway 111 in Edna.
Jackson County Sheriff's deputies say the adult woman and a girl, who's about 10 years old, had managed to sneak on top of the cab of the truck. Deputies say the pair were surfing on the cab as the truck moved at freeway speeds, possibly as high as 75 miles per hour, and then jumped off. Both were seriously hurt.
Deputies say both the girl and woman are believed to be illegal immigrants, possibly from El Salvador. The truck driver did stop, telling police he didn't know the woman and girl were up there until right before they jumped. He was not charged.
Stay with Eyewitness News for more on this developing story.