It happened Saturday at the "Monster Air 2012" show in Harrisburg, near Eugene.
Onlooker Dustin Earls was recording video of a drag race when he captured the frightening scene.
The truck driver lost control, bounced through a mud pit and over a barricade before smashing into spectators.
Three people were hit by the truck's 48-inch tires and taken to a hospital.
A sheriff's deputy says their injuries are not considered life-threatening.
The truck driver was not hurt.