Wow... I didn't know all the people who died in the crash are... or will be... buried there.
Sacred Ground
As the final resting place for the passengers and crew of Flight 93, the Sacred Ground is the focus of the Field of Honor. Here is where the plane crashed and a grove of hemlock trees absorbed the impact and inferno. The public can closely view the crash site from a plaza along its edge, which breaks the continuity of the circular Field of Honor.
http://www.nps.gov/flni/parkmgmt/the-memorial-design.htm