RAPID CITY, S.D. (AP) — A 21-year-old Rapid City man has died after a mountain biking accident in South Dakota’s Black Hills.

Pennington County Sheriff’s Sergeant Greg Foster says that the man had been riding with a friend near Rockerville Saturday afternoon. Foster says the man was going down a steep hill when he hit a small rock in the trail, lost control of his bike and hit a tree.

The man suffered a serious head injury.

Foster says the man was reported to be a very experienced rider and was wearing a helmet.

The man’s name was not released pending notification of his family.