A kayaker digging for rocks in a sandbar on a Kansas river Sunday uncovered a human skull believed to have been buried for decades, police say.

Police and firefighters responded to the scene around 4:20 p.m. at Bonner Springs and took the partial skull to the Wyandotte County Coroner’s Office on Monday, according to the Kansas City Star.

The Coroner’s Office preliminary investigation indicates it’s the skull of a middle-aged or elderly man.