The victims have been identified as Dillon Akins and Jonathan Laws, both 19, and Akins' father, 47-year-old Ronnie Akins. All three men were from Weaverville, N.C., just north of Asheville.
In addition, the Campbell County Sheriff's Office said a boy was injured and airlifted to the University of Tennessee Medical Center in Knoxville. His condition was not immediately known.
The accident was reported shortly after 1 p.m. at Windrock Park, a privately-owned off-road adventure park that offers riding trails in Oliver Springs, approximately 30 miles west of Knoxville.
The sheriff's office said rescuers had to cut through thick brush and trees to reach the crash site, a process that lasted more than an hour.
Laws and Dillon Akins played football and basketball at North Buncombe High School before graduating in 2018.
"Our hearts are saddened as we mourn the loss of Johnny, Dillon and Dillon’s father," the North Buncombe men's basketball team posted on Facebook. "Johnny and Dillon were two fine young men. Our hearts and prayers are with their families. Please remember the families in prayer".
"This is such a great loss to our community," North Buncombe basketball coach Chuck Robinson told the Asheville Citizen-Times. "These two were always side-by-side at school. It's a tragedy."