Those are the dunes in colorado. You can tell by the view of mountains at the end of the clip. But awesome video and way to stick that crash landing ; b
They're sliding on one of those plastic sledges. The word you're looking for is "friction". I still think butt oil was used to make things even smoother, though.
In fifth grade we took a field trip to some sand dunes and we were having a blast going down them, until this girl thought it would be fun to run down them, she got hurt and we had leave early :(