In reply to balmybaldwin:
Reading through the mtb press where I originally saw this issue, there appears to be a little "explanation" as to the origin of the stakes,
It would appear they are the remains of the original jump contruction/box/dirt-enclosuure, which had become seriously damaged, and upended by some fool, not actually placed to cause harm.
There Have apparently been instances,,,,,years ago where a pit was dug and covered, resulting in a cyclist fatality,,,,,,,Apparently