Identified by a local resident as reindeer moss, if you google that name you will find it may also be called caribou moss, reindeer lichen, or, Cladonia rangiferina. There is a Wikipedia page here, which claims it is indeed food for reindeer. Photos taken here in Gulf State Park on December 15, 2011, we have not seen any reindeer in the wild. There are several very large banks of it growing on the side of a hiking trail.
Closer: it is as light as air.
And, let Sony zoom: